I'btt'lif

DEPARTMENT OF THE INTERIOR

BULLETIN

OF THE

UNITED STATES

GEOLOGICAL SURVEY

ON THE PHYSICAL CHARACTERISTICS OF THE' IRON-CARBURETS 

MORE-PARTICULARLY ON THE GALVANIC THERMO-ELECTRIC 

AND MAGNETIC PROPERTIES OF WROUGHT IRON STEEL -, 

AND CAST IRON IN DIFFERENT STATES OF HARDNESS . 

TOGETHER WITH A PHYSICAL DIAGRAM FOR 

THE CLASSIFICATION OF IRON-CARBURETS

WASHINGTON .

GOVERN^MENT PRINTING- OFFICE

 :".' -1885- . -. ,. , -

Private Library 

N. W. LORD

=~====

NO.../JL

The publications of the United States Geological Survey are issued in accordance with the statute, 

approved March 3, 1879, which declares that 

"The publications of the Geological Survey shall consist of the annual report of operations, geological 

and economic maps illustrating the resources and classification of the lands, and reports upon general 

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On July 7,1882, the following joint resolution, referring to all Government publications, was passed 

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ANNUAL REPORTS.

Of the Annual Reports there have been already published:

I. First Annual Report to the Hon. Carl Schurz, by Clarence King. 1880. 8°. 79 pp. 1 map. A 

preliminary report describing plan of organization and publications.

II. Report of the Director of the United States Geological Survey for 1880-'81, by J. W. Powoll. 

1882. 8°. lv, 588pp. 61j>I. 1 map.

III. Third Annual Report of the United States Geological Survey, 1881-'82, by J. W. Powell. 1883. 

8°. xviii, 564 pp. 67 pi. and maps.

IV. Fourth Annual Report of the United States Geological Survey, 1882-'83, by J. W. Powell. 1884., 

8°. xii, 473 pp, 85 pi. and maps. 

The Fifth Annual Report is in press.

MONOGRAPHS.

Of the Monographs, Nos. II, HI, IV, V, VI, VTI, and VIII are now published, viz:

II. Tertiary History of the Grand Canon District, with atlas, by Clarence E. Dutton, Capt., U. S. At

1882. 4°. xiv,264pp. 42 pL and atlas of 24 sheets folio. Price $10.12. 

in. Geology of the Comstock Lode and the Washoe District, with atlas, by George F. Becker.

1882. 4°. xv, 422 pp. 7 pi. and atlas of 21 sheets folio. Price $11.

IV. Comstock Mining and Miners, by Eliot Lord. 1883. 4°. xiv, 451pp. 3 pi. Price $1.50.

V. Copper-bearing Rooks of Lake Superior, by Roland D. Irving. 1883. 4°. xvi, 464 pp. 15 1, 

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VI. Contributions to the Knowledge of the Older Mesozoio Flora of Virginia, by "Wm. M. Fnntftine. 

1883. 4°. xi, 144pp. 541. 54 pi. Price $1.05.

VH. Silver-lead Deposits of Eureka, Nevada, by Joseph S. Curtis. 1884. 4°. xiii, 200 pp. 16 pi. 

Price $1.20.

Vin. Paleontology of the Eureka District, by Charles D. Walcott. 1884. 4<>. xiii, 298 pp. 24 I. 

24 pi. Price $1.10.

£230f
ADVERTISEMENT.

The following are iu press, viz:

IX. Brachiopoda and Laiuellibranchiata of the Karitan Clays and G-reensand Marls of New Jersey, 

by Robert P. Whitfield. 1885. 4°. ix. 338pp. 35 pi.

X. Dinocerata. A Monograph of an Extinct Order of Gigantic Mammals, by Othniel Charles Marsh. 

1885. 4°. , pp. 56 pi.

XI. Geological History, of Lake Lahontan, a Quaternary Lake of Northwestern Nevada, by Israel 

Cook Enssoll. 1885. 4°. , pp. 4G pi. , 

The following are in preparation, viz: 

I. The Precious Metals, by Clarence King.

Geology and Mining Industry of Leadville, with atlas, by S. F. Emmons. 

Geology of the Eureka Mining District, Nevada, with atlas, by Arnold Hague. 

Lake Bonneville, by G. K. Gilbert. 

Sanropoda, by Prof. 0. C. Marsh. 

Stegosauria, by Prof. 0. C. Marsh.

BULLETINS.

The Bulletins of the Survey will contain such papers relating to the general purpose of its work as 

do not properly come under the heads of ANNUAL REPORTS or MONOGRAPHS.

Each of these Bulletins will contain but one paper and will be complete in itself. They will, however, be numbered in a continuous series, and will in time be united into volumes of convenient size. 

To facilitate this each Bulletin will have two paginations, one proper to itself and another which belongs to it as part of the volume.

Of this series of Bulletins Nos. 1 to 14 are already published, viz^

1. On Hypersthene-Andesite and on Triclinic Pyroxene in Augitic Eocks, by Whitman Cross, with 

a Geological Sketch of Buffalo Peaks, Colorado, by S. F. Emmons. 1883. 8°. 42pp. 2 pi. Price 10 cents.

2. Gold and Silver Conversion Tables, giving the coining value of Troy ounces of fine metal, etc., by 

Albert Williams, jr. 1883. 8°. ii, 8 pp. Price 5 cents.

3. On the Fossil Faunas of the Upper Devonian, along the meridian of 76° 30', from Tompkins County, 

New York, to Bradford County, Pennsylvania, by Henry S.Williams. 1884. 8°. 36pp. Price 5 cents.

4. On Mesozoic Fossils, by Charles A. White. 1884. 8°. 36 pp. 9 pi. Price 5 cents. :

5. A Dictionary of Altitudes in the United States, compiled by Henry Gannett. 1884. 8°. 325pp. 

Price 20 cents.

6. Elevations in the Dominion of Canada, by J. W. Spencer. 1884. 8°. 43 pp. Price 5 cents.

7. Mapoteca Geologica Americana. A catalogue of geological maps of America (North and South), 

1752-1881, by Jules Marcou and John Belknap Marcou. 1884. 8°. 184pp. Price 10 cents.

8. On Secondary Enlargements of Mineral Fragments in Certain Eocks, by E. D. Irving and C. E. 

'Vanhise. 1884. 8°. 56pp. 6 pi. Price 10 cents.

9. A Eeport of work done in the Washington Laboratory during the fiscal year 1883-'84. F. W. 

Clarke, chief chemist; T. M. Chatard, assistant. 1884. 8°. 40pp. Price 5 cents.

10. On the Cambrian Faunas of North America. Preliminary studies by Charles Doolittle Walcott.

1884. 8°. 74 pp. 10 pi. Price 5 cents.

11. On the Quaternary and Recent Mollusca of the Great Basin; with Descriptions of New Forms, by 

E. Ellsworth Call; introduced by a sketch of the Quaternary Lakes of the Great Basin, -by G. K 

Gilbert. 1884. 8°. 66 pp. 6 pi. Price 5 cents'.

12. A Crystallographic Study of the Thinolite of Lake Lahontan, by Edward S. Dana. 1884. 8°. 

34 pp. 3 pi. Price 5 cents.

13. Boundaries of the United States and of the several States and Territories, by Henry Gannett. 

1885. 8°. 135 pp.. Price 10 cents.

14. The Electrical and Magnetic Properties of the Iron-Carburets, by Carl Barus and Vincent 

Strouhal. 1885. 8°. 238 pp. Price 15 cents.

Numbers 1 to 6 of the Bulletins form Volume I, and numbers 7 to 14 Volume LT. Volume HI is not 

yet complete.

The following are in press, viz:

15. On the Mesozoic and Cenozoic Paleontology of California, by Dr. C. A. White. 1885. 8°. 33 pp. 

Price 5 cents.

16. On the higher Devonian Faunas of Ontario County, New York, by J. M. Clarke. 1885. 8°.

 pp. 3 pi. Price cents.

17. On the Development of Crystallization, etc., by Arnold Hague and' J. P. Iddings. 1885. 8°. 

' pp. Price cents.

18. On Marine Eocene, Fresh-water Miocene, and other Fossil Mollusca of Western North America, 

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19. Notes on the Stratigraphy of California, by George F. Becker. 1885. 8°. pp. Price cents.

20. Contributions to the Mineralogy of the Eocky Mountains, by Whitman Cross and W. F. Hillebrand. 1885. 8°. pp. 1 pi. Price cents.

21. The Lignites of the Great Sioux Eeservation, by Bailey Willis. 1885. 8°. pp. 5 pi. Price

 cents. « ,
ADVERTISEMENT.

STATISTICAL PAPERS.

A fourth series of publications having special reference to the mineral resources of the United States 

is contemplated.

Of that series the first has been .published, viz:

Mineral Resources of the United States, by Albert "Williams, jr. 1883. 8°. xvii, 813 pp. Price 50 

cents.

The second volume of this series, Mineral Resources 1883 and 1884, is in preparation and will soon 

be put to press.

Correspondence relating to the publications of the Survey, and all remittances, which must be by 

POSTAL NOTE or HONEY OKUER, should be addressed

To THE DIRECTOR OF THE

UNITED STATES GEOLOGICAL SURVEY,

Washington, D. 0. 

WASHINGTON, B. C., April 30,1885,
DEPAKTMENT OF THE INTERIOR

BULLETIN

OF THE

UNITED STATES

GEOLOGICAL SURVEY

No. 14

WASHINGTON

GOVERNMENT FEINTING OFFICE 

1885
o

no. \

c a f >\
UNITED STATES GEOLOGICAL SURVEY

J. W. POWELL DIRECTOR

T'H E

ELECTRICAL AND MAGNETIC PROPERTIES

OP TIIK

IRCOT-CAKBUKETS

BY

GAEL BAEUS and VINCENT STEOUHAL

WASHINGTON

GOVERNMENT PRINTING OFFICE

1885
PREFACE.

Early in 1881 one of us submitted to Prof. G. F. Becker, geologist 

iu charge of the Division of the Pacific, a brief digest of the facts showing the singular adaptability of the electrical properties of the iron-carburets for the classification of these products, with the request that 

permission be given us for the extension of the work in the laboratory 

of the Geological Survey. Professor Becker at once indorsed the project 

enthusiastically, and owing to his advocacy our proposal shortly after 

received the assent of the Hon. Clarence King, then Director of the

^ Survey, given with the proviso that the electrical researches be not

\ prosecuted to such an extent as to occupy us exclusively.

1 Divers special investigations and routine duties, together with the 

labor involved in providing for the organization of a physical laboratory, 

prevented us from giving the furtherance of the proposed researches

., the attention necessary. Nevertheless, data of a varied character continually accumulated, while the scope and the conception of our general

! problem enlarged at an unexpectedly rapid rate. The publication of 

our results in some connected form, therefore, urged itself more and 

more seriously upon us.

About a year ago our plan was effectually encouraged by Prof. F. W. 

Clarke, chief chemist of the United States Geological Survey.

The experiments to be discussed in this memoir have occupied our 

available time during the last five years. Notices, more or less complete, have appeared abroad from time to time in places not readily 

accessible to the public. Some of the papers it was deemed necessary to publish in German with considerable fullness. But all English 

publication has been purposely delayed, not only because we desired to 

reduce the results originally expressed in terms of the German standards to the more current and now legal denominations of ohm, volt, etc.,1 

but principally because it seemed expedient for facility of comparison 

to refer all our data to the uniform temperature, zero centigrade. This

1 In making this reduction the legal equation, 1 ohm = 1.06 S. U., was made use of" 

in all chapters Avith the exception of III and IV, the results of which were reduced 

at an earlier date and when 1 ohm = 1.05 S. U. appeared to be nearer the truth. This, 

however, is of no serious significance, because iu these chapters the relative values 

of resistance are alone of interest. The absolute accuracy of the reduced values is of 

course immediately dependent ou the absolute accuracy of the German standards 

(Siemens) at our disposal.

(597) * 5
0 PREFACE.

premised an accurate knowledge of the relation between electrical conductivity and temperature for iron, for steel in different states of temper, and for cast iron, and required excessively tedious labor.

The results in Chapter I on the electrical temperature-coefficient of 

iron-carburets present an unexpected range of variation, and thus possess intrinsic interest.

In Chapter II we investigate and discuss the conditions of the operation of tempering. This chapter is fundamental. Such facts as essentially sustain the argument underlying the whole of the present work 

are, therefore, emphasized with a larger number of experimental data 

than would otherwise be necessary.

In Chapter III we attempt to throw new light on the laws set forth 

in Chapter II by following them into their ulterior consequences. With 

the aid of certain allied electrical properties of alloys and of malleable 

cast iron, the nature of the phenomenon of hardness as presented by 

steel is discussed from every available physical and chemical point of 

view, within the scope of the present purposes.

In Chapters IV, V, and VI, the method for the accurate definition of 

hardness, and the scheme of operations for tempering developed in 

Chapter II, are consistently applied to analogous magnetic phenomena. 

The nature of the dependence of magnetization on the three independent 

variables of cylindrical rods,'viz: carburatiori, ratio of dimensions, hardness, for given conditions of structure, is carefully discussed and In part 

graphically represented. Rules are finally given for the treatment of 

magnets, such that exceptionally great retentiveness, both as regards 

the hurtful effects of temperature and time and of shocks, may be conveniently attained with the least available sacrifice of magnetization.

We may add that a supplementary Bulletin is now iu preparation, 

in which the very remarkable annealing effect of high temperatures 

(400°.. .1000°) will be magnetically discussed, and furthermore the degree of approximate coincidence between the physical state (of the 

necessarily linear rod) characterized by the unique maximum of magnetizability and the physical state of maximum density of steel, will be 

determined. That these states must be found very nearly coincident, 

our present results permit us to predict.

Iu Chapter VII, finally, we endeavor to generalize upon the foregoing 

results, as a whole j to restate 'the fundamental laws with greater accuracy and breadth of scope than was possible in the earlier chapters; 

and, finally, to deduce from all a method for the physical definition of 

iron-carburets.

Minor discussions, the relevancy of which does not justify their immediate introduction into the chapters proper, are frequently introduced as addenda.

We desire in this place particularly to emphasize that throughout the 

present work the terms u thermo-electrically positive " and " thermo-electrically negative" are to be understood in the way defined by the original

(598)
PREFACE. 7

investigators, Seebeck,2 Becquerel,3 Hankel; 4 i. e.,with reference to the 

series arranged thus:

-Bi.... Cu... Fe.... Sb+,

an acceptation which we believe to be general on the Continent.5 In 

England the above terms are received in a sense which is precisely the 

opposite of this; that is, with reference to the thermo-electric series,6 

arranged thus:

+ BL... Cu... Fe.... Sb-.

Of the two methods of designation, the latter is obviously the more 

logical and consistent, as will readily be seen, for instance, if the galvanic and the thermo-element be analogously described. And if we 

refrained from embodying the latter acceptation in this memoir, we have 

done so merely because of the great liability to error encountered in 

changing the sense of every thermo-electric expression and diagram, as 

well as the signs of all of the many thermo-electric data. Isolated constructions are too apt to be overlooked, and this in a way completely 

to mar the drift of the context. But the English reader will find no 

difficulty in making this change of sign for himself in any set of thermoelectric data which may interest him. To avoid all misconception, moreover, we give the direction of current in each essential case.

Much of the work was done abroad in Professor F. Kohlrausch's laboratory. It is a pleasant duty which permits us to extend to Professor 

Kohlrausch, in this place, our grateful acknowledgments, not only for 

the kindly interest with which he regarded the progress of the experiments throughout their extent, but for much valuable advice by which 

the papers have materially profited.

We desire to mention, in conclusion, that work done by us conjointly, 

if published in German, is to be put under S. andB.; if in English, under 

B. and S., conformably with an original agreement.

C. BAKUS.

V. STROUHAL.

PHYSICAL LABORATORY,

UNITED STATES GEOLOGICAL SURVEY,

Washington, December 1, 1884.

2 Seebeck: Gilb. Ana., LXXIII, pp. 115 and 430,1823.

3 Becquerel: Ann..de Chim. et de Pbys., XLI, p. 353, 1829.

"Hankel: Pogg. Ann., LXII, p. 197,1844.

fi Cf. Wiedemann: Lebre v. d. Elektrieiliit, II, p. 248 et seq., 1883. Mousson: 

Physik, III, p. 381 et seq., 1875. Jarnin: Cours do Physique, 2d ed., T. Ill, p. 42,1869.

°Cf. Jenkiu: Electricity and Magnetism, p. 175 et seq., 1880. Maxwell: Electricity 

and magnetism, 2 ed., Vol. I, p. 338-9, 1881.

(599)
PREFACE.

SUPPLEMENTAL.

The principal contents of the supplementary Bulletin referred to in 

the above preface may expediently be placed on record here:

1. The inter-dependence of density, electrical conductivity, maximum 

of permanent magnetization, maximum of permanent hardness of linear 

cylindrical steel rods, under all permissible conditions of temperature. 

The location of the unique magnetic maximum.

2. The bearing of temperature and time of exposure on the tempervalue of the color of the oxide-films. *

3. The internal structure of tempered steel.

4. Certain synthetic methods of production of iron-carburets, available for the construction of the classification-diagram.

B. & S. 

WASHINGTON, March 27,1885.

(600)
CONTENTS.

Page. 

INTRODUCTION .............................~............................... 13

CHAPTER I. The relation between electrical conductivity and temperature 

in case of steel in different states of hardness, of wrought iron, and 

of cast iron ....................................................... 15

Steel .................................................................. 15

Wrought iron ......................................................... 20

Cast iron ............v.................................................. 22

Deductions .......:................................................... 24

Addendum: Statement of a resistance method for the measurement of

heat conductivity................................................. 25

CHAPTER II. The conditions which in the case of steel essentially determine 

the efficacy of the operation of tempering; the measurement of the 

state of hardness of steel.......................................... 28

Introductory remarks ...................°.............................. 28

Apparatus for imparting glass-hardness to steel........................ 29

Measurement of thermo-electric power ................................ 31

Measurement of electrical conductivity ................................ 30

The operation of sudden cooling. Glass-hardness ...................... 38

Behavior of hard steel rods annealed in hot oil baths................... 40

On the bearing of the time of exposure on the efficacy of annealing ..... 43

Behavior of hard steel annealed in vapor of boiling methyl alcohol (66°). 47 

Behavior of hard steel annealed in steam (100°) ......................... 49

Behavior of hard steel annealed in vapor of boiling aniline (185°)...... 51

Behavior of hard steel annealed in molten lead (330°).................. 53

General discussion of the results of this annealing...................... 54

The effect of higher and of lower temperatures on the temper of steel

originally annealed at a given intertnedi ate temperature............ 57

Behavior of soft steel rods ............... ^....._...............'........ fiO

The relation existing between the thermo-electric power and the specific

resistance of steel................................................. 02

Sources of error....................................................... 08

Concluding remarks................................................... 70

Addendum : On a simple method for the galvanic calibration of a wire.. 72

CHAPTER III. The nature of the phenomenon of temper, as observed in steel,

discussed from an electrical standpoint, particularly in reference to

the .analogous behavior of malleable cast iron and of alloys of silver.

Introduction.........................................................

Experiments with alloys .......... ...................................

The general phenomenon of temper regarded from the chemical and from

the mechanical standpoint ......................................... 88

The phenomenon of glass-hardness discussed from the chemical and from

^ the mechanical standpoint ........................................ 98

Experiments with malleable cast iron.................................. 100

CHAPTER IV. The thermo-electric effect of magnetization.................. 104

(601) 9
10 CONTENTS. .

Page.

CHAPTER V. The influence of hardness on the maximum of magnetization 

which thin cylindrical steel rods of different dimensions permanently 

retain ............................................................ Ill

Plan and purpose of the present experiments .......................... Ill

The material used..................................................... 115

Method of magnetization.............................................. 118

Measurement of magnetic moment..................................... 120

Determination of the degree of hardness................... ............ 121

Method of annealing ..................................................... 123

Magnetic results for rods of large dimension-ratio...................... 125

Results with rods of smaller dimensional-ratio......................... 128

Discussion.............................................................. 6 136

Conclusion........................................................... 148

Addendum: Density-effect of incipient annealing of hard steel......... 149

CHAPTER VI. The tempering of steel considered in its bearing on the power 

of magnetic retention, and on the conditions of magnetic stability of 

this material...................................................... 151

Introduction.......................................................... 151

Eetentiveness as regards variation of temperature ..................... 152

Magnetic retentiveness as regards the effects of percussion, etc.......... 166

Addendum: Results of H. Wild, of St. Petersburg, with magnets tempered and magnetized by the method proposed in this chapter...... 171

CHAPTER VII. A physical definition of steel based on the electrical behavior

of iron with gradually increasing degrees of carburation........... 173

Introduction............. ..............................................^ 173

Wrought iron......................................................... 176

Steel ....................... .......................................... 177

Cast iron ............................................................. 178""

Discussion............................................................ 184

Commercial or impure iron-carburets .................................. 188

Final .generalization .......... .................................. ...... 190

CHAPTER VIII. Brief summary of the principal data...................... 194

APPENDIX. On the relation between the thermo-electric properties, the

specific resistance, aiid the hardness of steel (1879)................. 203

Introductory remarks ................................................. 203

Apparatus for hardening thin steel wire................................ 204

Methods of measuring the hardness of steel electrically................. 205

Determination of thermo-electric hardness. Apparatus............ _. 208

Determination of specific resistance...................... .............. 210

Experimental results........ ...... .................................... 211

Hardness and thermo-electric properties of steel: deductions and supplementary experiments.............................................. 217

Hardness and specific resistance of steel: deductions................... 223

Remarks on the above considered as auxiliary to the determination of

the relation between hardness and magnetic moment............... 225

Index .................................................................... 227

(602)
ILLUSTRATIONS.

Page.

Fig. 1. Electrical conductivity and temperature-coefficient of silver-platinum alloys.................................................... 16

Fig. 2. Diagram of the relation between specific electrical resistance and 

temperature-coefficient for wrought iron, for steel, and for cast 

iron .......................................................... 23

Fig. 3. Diagram of a resistance apparatus for measuring heat conductivity.. 26 

Fig. 4. Apparatus for hardening steel rods ...............'................ 29

Fig. 5. Form of thermo-element......................................... 32

Fig. 6. Disposition of thermo-electric apparatus.......................... 33

Fig. 7. Disposition of apparatus for measuring the galvanometer-factor ... 33 

Fig. 8. Details of thermo-electric apparatus.............................. 34

Fig. 9. Hard wires annealed for six consecutive hours in steam at 100°.... 46

Fig. 10. Hard wires annealed continuously at 0°, 66°, 100°, 185°, 330°, and

1,000°,respectively............................................ 55

Fig. 11. Diagram of the relation between the thermo-electric power of steel

in different states of temper, and its specific resistance.... ..... 64

Fig. 12. Disposition of apparatus for calibration.......................... 73

Fig. 13. Specific resistance and thermo-electric constant: steel, silver-gold, 

silver-platinum, silver-zinc....................................

Fig. 14. Disposition of apparatus....................'.....................

Fig. 15. Specific magnetism of rods annealed from 0° to 1,000°.............

Fig. '16. Disposition of apparatus for resistance measurement..............

Figs. 17, 18. Relation between specific magnetism and hardness of steel for

different dimension-ratios ..................................... 141

Figs. 19, 20. Relation between specific magnetism and dimension-ratio of

steel rods, for different degrees of hardness..................... 143

Fig. 21. Diminution of specific magnetism and specific resistance produced

by continued annealing (low temperatures).................... 156

Fig. 22. Simultaneous variation of specific magnetism and Specific resistance in case of continued annealing (low temperatures)........ 162

Fig. 23. Simultaneous variation of specific magnetism and specific resistance

in case of continued annealing (high temperatures)............. 164

Fig. 24. Diagram of the mean variation of the thermo-electric hardness and 

of the specific electric resistance of iron carburets, with their 

degrees of carburation ........................................ 185

Fig. 25. Classification diagram ........................................... 192

Fig. 26. Apparatus for hardening......................................... 204

Fig. 27. Disposition of apparatus......................................... 208

Fig. 28. Original form of thermo-element................................. 209

Fig. 29. Thermo-currents evolved in a hard and thick cylinder............. 220

Fig. 30. Relation between thermo-electric power and specific resistance.... 223

Fig. 31. Diagram of Ruths' results........................................ 225

(603) 11

To avoid ambiguity and vagueness we will state here, at the outset, 

that the considerations presented in this memoir apply to that species 

of hardness Avhich can be imparted to steel by a process of tempering; *. e., by a process of sudden cooling from a given temperature 

in red heat, accompanied by a stated amount of subsequent annealing. 

Such an operation, regarded as a method in virtue of which the metal 

acted upon experiences a particular and characteristic kind of strain, 

must be accompanied by a series of physical effects peculiar to itself. 

It is true that the conditions which determine the efficacy of tempering 

will themselves have to be accurately defined. Even under favorable 

circumstances these are not thoroughly within the observer's control, 

or, at best, are attainable with extreme difficulty. All results are, therefore, distorted by a variety of anomalies. But in the great number 

of data investigated a certain normal effect clearly appears, and it is 

to this that our remarks apply. In other words, we have been led in 

an unavoidably laborious way to the results of theoretically perfect 

tempering.

With regard to the hardness of steel, we cannot as yet rigidly discriminate between the effect to be ascribed to a change in the quality of carburation and that which is due to the strain simultaneously experienced; 

i. e., the numerical value of the importance of the said effects has as yet 

remained undeterminable, though much has been done toward assigning 

to each its respective limit. But, a priori, in so far as the character of 

this strain-effect will enable us satisfactorily to interpret a majority 

if not all of the attendant physical phenomena, we are temporarily 

justified in giving the mechanical postulate preference. At all events 

it is frequently permissible to abstract from the chemical change 

altogether, and to speak of tempering a rod to glass-hardness, just as 

we do of magnetizing it to saturation, for instance. Both operations 

may be said to be such that more of a given kind of strain (hardness in 

the one case and magnetism in the other) is originally imparted to the 

rod than it is able, of itself, to maintain. A part of this disappears, while 

a residue, characteristic of the nature of the rod and of the physical circumstances under which it exists, is permanently retained. This consideration suggests some analogies between hardness and magnetism. 

Irrespective of its practical importance and from a purely physical 

point of view, tempering possesses an intrinsic interest inferior only to 

magnetization, or indeed comparable with it. Of the enormous stress 

which the former operation enables us to apply, the steel rod, in virtue of 

a peculiar internal structure, retains a phenomenal amount. This great 

intensity of available strain we may cause to disappear as gradually

(605) 13
14 INTRODUCTION.

or to reappear as often as we please. Conformably with the change 

of mechanical state, the extreme values of the electrical and magnetic 

properties of steel comprehend a similarly extended interval. We are 

thus enabled to follow these, in the case of the same material, through 

a range of variation that is enormous, and must throw new light on their 

intrinsic nature. ;

Another point deserves brief mention here. If we conceive a theoretically perfect process of tempering to glass-hardness, and suppose it 

applied to rods identical in every respect, the results must necessarily be 

identical. In other words, the type of internal structure presented by 

the first would be reproduced in all subsequent rods. Take the comparatively simple but important case of cylindrical rods : The density of 

the elementary cylindrical shells, coaxial with the respective cylinders, 

would be the same for the same radius; the distribution of density 

along similar radii would follow the same law. If now the rods be identically annealed the results must still be identical, and thus we arrive 

eventually at identical soft states. It follows, therefore, that for rods 

of the same dimensions (diameter) and composition the magnetic properties are immediately comparable as functions of hardness.

This we are no longer at liberty to assume when the (cylindrical) rods 

otherwise identical, have different diameters. For this reason alone the 

rods, though tempered alike, *. e., subjected to the same operation, are to 

be regarded as structurally dissimilar. It is in place here to present some 

concise meaning for the term " structure " as applied to hard steel rods. 

We, therefore, define it as the law of the variation of density encountered on a passage along any radius of a given (cylindrical) steel rod 

from its axis to its circumference. This premised, it is not absolutely 

impossible (however improbable) that rods of different diameters, identically tempered, may, cccteris paribus, show, identical structures. That 

such a unique condition of things cannot be postulated is obvious at 

once. Indeed, the manner of variation of the law of distribution of density, as we pass from rods of a given thickness to rods of any other 

thickness, is not even conjectural)le, and we cannot, therefore, consistently compare the magnetic intensities of rods of different diameters as 

functions of hardness. In the most favorable case we would encounter 

in our passage from rod to rod, besides the difference of hardness, something of 'the nature of a change of parameter, expressing the necessary 

difference of internal structure referred to. In other words, it will be 

shown in the sequel that with a given thickness, a characteristic family 

of magnetic curves may be obtained, referred to hardness and length of 

rod as independent variables. We infer that such a family exists for 

each thickness, and that our passage from one given diameter to another 

is expressible by a difference in the value of a parametric constant.

We have mentioned magnetic phenomena in particular, because it is 

here that the evidence derived from data illustrating the influence of 

structure is singularly cogent.

'606)
THE ELECTRICAL AND MAGNETIC PROPERTIES OF THE IRONCARBURETS.

By CARL BAIIUS and VINCENT STROUHAL.

CHAPTER I.

ON THE RELATION BETWEEN ELECTRICAL CONDUCTIVITY AND TEMPERATURE IN THE CASE OF STEEL IN DIFFERENT STATES OF HARDNESS, OJf WROUGHT IRON, AND OF CAST IRON.

STEEL.

Earlier results. The experiments made thus far ou the resistanceeft'ect of temperature7 scarcely permit us to distinguish in this particular 

between irou and steel. In fact, the data in hand for the said coefficients lie within about the same interval, 0.004 to 0.005, both for the 

one metal and the other. We will give as examples some of the best 

results of earlier observers.

According to Mousson,8 the electrical resistance st at the temperature 

t is expressible in terms of su , the corresponding quantity at zero, by 

an equation with a single constant:

*,=* (!+0.00421 x«) 

for iron;

*,=* (1+0.00406x0 to st=80 (1+0.00424x0 

for steel.

Benoit,9 who carried his researches to much higher degrees and 

through much greater intervals of temperature, finds: 

st=«0 (1+0.00452 £+0.000 005 83 - t2 ) 

in case of iron;

s(=(l+0.0049S £+0.000 007 35 t2) 

in case of soft steel.

Nevertheless we felt justified in believing that these researches in 

case of a substance which, like steel, is capable of existing in so many 

enormously different states of hardness, which presents such an incomparably wide range of values of electrical conductivity, are far from 

complete; we regarded the assertion warrantable that steel cannot, under 

all circumstances, possess a temperature-coefficient of electrical resistance so little different from that of iron. Indeed, we had reasons to

'For a very complete digest of the experimental results iu question, see G. Wiedemann, Lehre von der Elektricitiit, I, p. 502-510, 1882. 

8Mousson: G. Wiedernann, 1. c., p. 507. 

nBenoit; CPmptes. Rend., LJXJSyi, p. 342, 1873. Carl's Rep., IX, p. 55, 1873.

(607) 15
16 IEON-CARBURETS. [BULL. 14.

presume that between the resistance of a metal in any given physical 

state and the corresponding temperature-coefficient, a relation would in 

all probability be discoverable, and that an example of such a relation 

could be most satisfactorily studied with steel itself.

Analogous behavior of alloys. Some facts lending favor to this view 

may be cited. It is known that alloys of two metals vary in marked 

degree as regards their electrical conductivity with the relative quantity of a second or foreign metallic ingredient added to the original 

metal. Great numbers of valuable results on these relations have been 

gathered by Matthiessen and Vogt.10 Thus, for instance, the sdloy 

silver-platinum, according to these observers, shows the following electrical behavior: If A, be the (relative) electrical conductivity of a 

given silver-platinum alloy at £°; if volume-percents of platinum alloyed 

to silver be understood; and if the wires be supposed hard drawn j then,

Platinum, 0 per cent. A,=100 -0.38287 £+0.000 984 8 £2 ;

Platinum, .2.51 per cent. A,= 31.640-0.03936 £+0.000 036 42 £2 ;

Platinum, 5.05 per cent. A,= 18.031-0.01395 £+0.000 Oil 82 £2 ;

Platinum, 19.65 per cent. At = 6.696-0.00221 £+0.000 001 393 £2.

If we have reference to a small interval of temperature only, these 

results may be more perspicuously given by the aid of a single (mean) 

coefficient calculated from the observed conductivities. More simply,

therefore,

Platinum, 0 per cent. A,=100 (1 0.00383 £) y

Platinum, 2.5 per cent. A,= 31.6 (1-0.00124 £) j 

. Platinum, 5.1 per cent. A,= 18.0 (1-0.00077 

Platinum, 19.7 per cent. A(= 6.7 (1 0.00033 

Herefrom it is obvious that the temperature-coefficient of an alloy 

varies continuously and in a pronounced way with its electrical con-

.*) 

4001

Conductin ff 

Jg.tOO __

FIG. 1. Electrical conductivity and temperature-coefficient of silver-platinum alloys.

ductivity. This becomes all the more strikingly apparent when the 

results are represented graphically.

"~~~~ J°Matthiesseii »»cl Vogt: Pogg. Arm., CJQCIJ, p. 19, 1864. '

(608)
BAIIUB AND BTuomiAL.1 TEMPERATURE-COEFFICIENT STEEL. 17

Similar results, but less complete, and therefore superfluous here, we 

ourselves obtained with German silver. But, to give an instance: the 

specific resistance, st, of the German silver wire of C. Vogel, Berlin, was 

found to be (st given in cw/cw2 , microhm),

st=l6A (1+0.00004 *), 

whereas for that of W. Siemens, Berlin,

s£ =39.0 (1+0.000.9 t). 

Now we shall show elsewhere that the analogy between the electrical 

behavior of steel in different states of hardness, and that of alloys of 

two nietals in different proportions is, from certain points of view, very 

complete. It follows, therefore, that a relation similar to the one set 

forth is to be anticipated in case of steel, such that the variation of 

electrical resistance produced by tempering must be accompanied by a 

similarly continuous but inverse change .of the values of the temperature-coefficient of steel. Our experiments fully corroborate this.

Resistance-temperature equation. Before proceeding further, however, 

we may remark that it would be impossible iu case of steel to adhere to

the very desirable formula

st=s (1+at+bt2 ),

throughout. Consistency, therefore, induces us to assume a linear relation in all cases. The reasons are these : the relation between resistance and temperature-coefficient to be investigated necessarily and 

primarily excludes all possibility of permanent change in the material 

itself. When glass-hard steel is examined, the interval of temperature 

within which the rod -may be heated or cooled without experiencing 

perceptible annealing is very limited. The same is true of moderately 

annealed steel. We are as yet ignorant of the effects of this kind 

which may possibly also be produced by cooling below zero. Hence it 

is indispensably necessary to vary the temperature of glass-hard rods 

only so much as is just called for, if the measurements are to furnish 

satisfactorily reliable data. Should an annealing effect occur, the results would not of course be comparable. Now the available interval 

of temperature is fully large enough for the linear formula. It is insufficiently so iu the other case ; for in the quadratic formula it is possible to change the coefficieut of t to quite an appreciable' extent without 

producing marked variation in the values of st , if only an appropriate 

and compensatory change be made in the coefficient of £2, simultaneously. Hence the simple formula

has been made use of throughout, where t was permitted to vary within 

the interval 10° to 35° only.

Method of measurement. The changes of temperature, and therefore 

also those of resistance, being very slight, amounting only to a few 

huudredths ohm, it was necessary to make the electrical measurements 

with extreme accuracy. For this purpose the method of Matthiessen 

and Hockin, which we have repeatedly used, proved to be admirably 

Bull. 14 2 (609)
18 . IRON-CARBURETS. [nuu, 14.

serviceable. A few modifications had to'be introduced. In the place 

of the two needles originally employed for obtaining contacts at fixed 

distances apart, and which if submerged in water would have intro" 

duced the disturbing effects of loose contacts, two fine copper wires were 

tightly wound around the extreme parts of the steel rod under experiment, and fastened in a way that made sliding impossible. The rod 

was then alternately placed in. two vessels containing cold and warm 

water respectively, care being taken not in any way to strain the copper circuit wires. The short-circuiting through distilled water from one 

fine copper wire to the other is obviously negligible.

The temperature of the cold bath was approximately that of the room, 

and very constant; that of the warm bath varied during a single measurement not more than a few tenths of a degree. Temperature being 

read before and after the resistance measurement, the mean value 

could be regarded as a very satisfactory datum. The steel rod examined was placed first in the cold, then in the warm, and finally again in the 

cold bath. The mean of the measurements 1 and 3 was therefore to be 

combined with 2, 4 and 6 with 5, etc. The degree of approximate 

equality of the results of these distinct sets of observations, and the 

agreement between the measurements 1, 3, 4, 6j etc., give a good estimate of the accuracy of the work.

Material. Resistance-value of oxide- tints. The material used was that 

employed in all our researches, English "silver" steel in rods 0.15 cm. 

in diameter. After having been suddenly chilled in great numbers, 

certain of them were annealed by the electrical current, in this way: 

Having carefully polished the hard rod, it was introduced into the circuit of a dynamo-electric machine. As the temperature of the wire 

increased the oxide-tints appeared in a strikingly perfect manner, and 

it was only necessary to regulate the current cautiously and stop the 

operation at a given moment to obtain any oxide-tint desired almost 

uniformly over the whole length of the wire. The observations of this 

paragraph therefore give in an approximate way the temper-value of 

the oxide-tint appearing in air on a bright hard steel rod, in terms of 

electrical resistance.

Results. The following table, 1, contains a perspicuous comparison 

of the data of observation as obtained with six steel rods in different 

states of temper. For the diameter 2 p (cm) of the rod and the length 

I (cm) direct measurement showed the resistance w (ohm) at the temperature t° (C.). Also the resistance W (ohm) at 1°. This is sufficient 

for the calculation of w0 for 0° and a, the required coefficient. The 

known dimensions then enable us to deduce the specific resistance s 

(cm/cm2 0°). Finally, we give the specific gravity A of the wires, calculated for the known dimensions and the known weight. Our object in 

computing this constant was primarily that of checking the values for 

the sections of our rods as measured by the aid of the microscope. But 

they furnish a satisfactory corroboration of the general increase of dens-

(610)
BARUS AND BTBOUHAL.J TEMPERATURE-COEFFICIENT STEEL. 19

ity of steel cm passing from the hard to the soft state, conformably with 

the results of 0. Fromme:

TABLE 1. Temperature-coefficient of steel.

Kocl.

AiniGalodliglit-yollow. < 

Annealed yellow .....< 

Auiioaled blue .......< 

Aunoalod light-blue.. \ 

Soft ................<

2 p, I, A

cm. 

2 p= 0.151 

l~n. 52 

A= 7. 56 

2 p= 0. 148 

«=17. 98 

A= 7. 57 

2 p= 0. 150 

J=18. 17 

A= 7. 54 

2 p 0. 149 

fc=16. 77 

A= 7. 56 

2 p= 0. 148 

i=17. 58 

A= 7. 66 

2 P= 0.146 

J=17. 13 

A= 7. 09

w

ohm. 

0. 04523 

20 

24 

0. 03107 

06 

10 

0. 02782 

84 

81 

0. 02043 

47 

45 

0. 01948 

46 

47 

0. 01690 

91 

96

t

10.0 

10.2 

10.4 

10.2 

10.3 

10.0 

10.9 

11.0

n.o

10.0 

10.1 

10.2 

9.3 

9.5 

9.7 

9.7 

9.9 

10.0

W

oJvm. 

0. 04685 

59

0. 03297 

65

0. 02950 

22

0. 02191 

75

0. 02097 

70

0. 01850 

27

T

32.9 

29. 5

35.5 

32.2

33.2 

29.6

32.5 

29.8

31.6

27.7

32.5 

29.4

Wo

ohm. 

0. 04450

0. 03030

0. 02698

0. 01978

0. 01881

0. 01C25

a

0. 00161 

100

0. 00250 

288

0. 00278 

279

0. 00327 

332

0. 00357 

363

0. 00428 

419

s

microhm. 

45.7

28.9

26.3

20.5

18.4

15.9

If for a we take mean values, and compare these with the degrees of 

hardness of steel, characterized by s, we obtain more clearly:

TABLE 2. Oxide-tint, specific electrical resistance and electrical temperature-coefficient of

steel.

Soft.................................................................

«2ELoo 

cm2

microhm. 

45.7

99 Q

26.3

20.5

 ' 18. 4

15.9

a

0. 00161

244

280

330

300

423

The electrical temperature-coefficient of steel, therefore, decreases in proportion as its specific resistance or its degree of hardness increases, at a 

rate diminishing as we pass from soft to hard steel.

The following little table interpolated from the above values, for practical purposes, may be put on record here:

TABLE 3. Specific electrical resistance and electrical temperature-coefficient of steel.

tical table.

Prac8

C"' QO

cm2

microhm.

10

11

12

13

14

15

16

17

18

19

20

a

0. 0050

48

46

44

42

41

39

38

36

35

!J4

8

cm_

cm*

microhm.

21

22

23

24

25

26

27

28

29

30

31

a

0. 0033

32

31

29

28

27

27

26

25

24

23

8

cm 00

cm2

microhm.

32

33

34

35

36

37

38

39

40

41

42

a

0. 0022

21

21.

21

20

19

19

19

18

18

37

8

cm Oo

cm2

microhm.

43

44

45

46

47

48

49

50

60

70

8H

a

0. 0017

17

16

16

15

15

15

15

13

13

12

(611)
20 IRON-CARBUEETS. | HULL. 14.

WROUGHT IRON.

Digest of earlier results. The relation between electrical resistance 

and temperature in case of iron has been studied by a large number of 

observers, among whom Lenz, Becquerel, Arndtsen, Mousson, and 

others, are to be mentioned. But the most comprehensive and accurate 

data are unquestionably those given by Matthiessen and Vogt.11 These 

will therefore be discussed here.

Matthiessen and Vogt assume the quadratic formula

for A, the conductivity of any given metal, relatively to hard-drawn 

silver (A 0 =100). Their results for. a and &, in case of fifteen samples of 

iron, conveniently abbreviated, are contained in Table 4.

TAULE 4. Electrical temperature-coefficient and electrical conductivity of divers samples of

iron.

Description of sample.

Electrotype iron ; Nos. 2 and 4 ignited in hydrogen and I

No.

1

2 

3

4 

5. 

6

7 8' 

9 

10

11 

12 

13

14

15

a

0.512 

0.519. 

0. 514

0.509 

0.473 

0. 472

0.453 

0.463 

0.418

0.404 

0.397 

0.425

0.340

0.428

b

0.00129 

134 

132

127 

112 

112

102 

112 

109 

092

092 

091 

092

OG3

090

Ac

(10. 810) 12 

(16. 810) 12 

(1C. RIO) 1 *

.(16. 810) 12 

15.712 

15. f.40

14. 204 

12.132 

14. 723 

10.666

9.921 

9.449 

13.293

8. 568

18. 774

For the sake of facilitating a comparison of these results with our 

own, we reduced them, as nearly as possible, to absolute values of

cm s _.. 0° microhm, by accepting for u silver hard," for which Malthiesseu

cm

and Vogt put A=100,

5=1.574.

Moreover, the values have been arranged, commencing with pure 

iron, in the order of the values for resistance, the coefficient of quadratic 

t being discarded and only linear d introduced. The interpretation to 

be given to "a interpolated" will be explained presently.

11 Matthicssen and Vogt: Pogg. Ann., CXVIII,p.431,1863.

12 Probable value for pure iron, hard, deduced from the observations with impure 

metal, from an inspection of the respective temperature-coefficients.

(612)
BAUUB AND sTuouHAL.] TEMPERATURE-COEFFICIENT STEEL. 21

TABLK 5. Specific electrical resistance and electrical tentyeraturc-coefficient of different

kinds of iron.

Description of sample.

No. 5...................

No. 6...................

No. 9...................

No. 7....................

No. 15. ..................

No. 13.... ...............

No. 8...................

No. 10. ..................

No. 11. ..................

No. 12.......... .........

No. 14.... ...............

«5ELo° 

cm2

microhm. 

9.4

10.0

10.1

10.7

11.1

11.4

11.8

13.0

14.8

15. 9

10.7

18.4

15.9

a 

observed.

0. 0052

47

47

40

45

43

42

45

42

40

40

34

42

a 

iiit orpolatcd.

0. 0052

50

50

49

48

47

40

44

41

40

37

30

40.

Resistance-temperature equations of'iron and of steel The first lino of 

these data, showing the mean value of a number of observations with 

pure iron, is the most reliable. If this be added to onr results for steel 

(Table 2), the whole series of results may be compared graphically, by 

representing specific resistance, *, as abscissa temperature-coefficient, a-, 

as ordinate. The points lie satisfactorily on a locus of definite character, which in its turn may be utilized for purposes of interpolation. In 

this way the last column of the foregoing table ("a interpolated") has 

been deduced, the temperature-coefficient for each value of specific resistance for the sample of iron cited being selected. The discrepancies 

or differences between observed and calculated results are not larger 

than a combination of observations made on the great variety of material by different observers, together with the wide range of possible 

errors incident to all, would lead us to anticipate. Even the position 

of softrsteel with reference to the curve is, in every, respect, satisfactory. It is in this way, finally, that the practical results in Table 3 ' 

were derived.

Benoit finds the following relations between resistance and temperature for soft iron and soft steel, respectively:

s,=0.1272 (1+0.00452 f+0.0000058 t2), 

and

s,=0.1149 (1+0.00498 t+0.0000074 <2),

(Hg=l m | ^2 ).

These results referred to microhms and cm/cm2 are 

s=12.1 «=0.00452 

for iron, and

s=10.9 ^=0.00498

for steel. Both sets of values are in good accordance with onr graphic 

representation. We obtain by means of this:

For 0=12.1, the value #=0.00457, 

and

For s=10.9, the value «=0.00485.

13 Benoit: Comptes rend.,LXXVI, p. 342, 1873. Wiedemaim, 1. c., p. 525. The 

small value 8=10.9 obtained by Benoit for soft steel is remarkable and exceptional.

(613)
22 IRON-CARBURETS. 'PULL, k

CAST-IRON.

Anticipative results. Of particular interest in connection with this 

discussion is the behavior of the most highly carburized of commercial 

iron-products, cast-iron. Observations for pairs of the electrical magnitudes under consideration, for this material, are not in hand. Elsewhere we will describe certain experiments, made in some number, with 

reference to the thermo-electric and galvanic properties of cast-iron. 

Here we need only mention, that the specific resistance of this metal is 

very decidedly larger than the largest attainable results for glass-hard 

steel. If, therefore, a relation14 between electrical conductivity and 

electrical temperature-coefficient of the kind premised, actually exists, 

then this latter quantity must, in like manner, be smaller than the 

smallest results arrived at in case of steel.

To test this inference, three samples were selected from our supply of 

cast-iron rods, Nos. 13, 14, 15, each about 25 cm. in length, and their 

resistance in the soft or thoroughly annealed state (annealed at red heat 

and cooled very slowly) determined at different convenient temperatures. But this resistance, in view of the comparatively large section 

of the said rods (about 0'.4 cm2 ) being as small as 0.004 ohms, the 

measurement had to be made even with greater precaution than was 

necessary in the case of steel.

Method of measurement, The method of measurement was, however, 

essentially identical in the two sets of experiments, being Matthiessen 

and Hockin's. The terminal wires of copper, wherever necessary insulated by glass tubes, were wrapped around and soldered to the castiron rods; these, together with the insulated terminals and a good 

thermometer, introduced into a wide glass tube. Through the latter, 

closed at both ends by suitably perforated corks, securing tubes of influx and efflux, vapor at the boiling point of the respective liquids continually circulated. Methyl alcohol vapor, and steam were especially 

convenient. The tube itself, thickly jacketed with felt and cloth, showed 

a desirably constant temperature throughout the course of the work. 

All these precautions were necessary, for the ulterior reason of excluding possible thermo-electric action at the junctions of cast-iron and copper. Such currents are otherwise readily evoked in intensity sufficient 

utterly to vitiate the accuracy of the measurements.

Results. The following table will show that the experiments conducted with this care were satisfactorily succeessful. Here a and b 

denote the sides of the approximately rectangular section of the castiron rods; I, the effective length in the resistance measurements. From 

an inspection of the resulting errors, the linear relation assumed to exist

14A detailed discussion regarding the electrical effects of the strain accompanying 

hardness and of carburation, respectively, will be given in Chapter III.

(614)
BAUUSAKD BTBOUHAL.] TEMPERATURE-COEFFICIENT STEEL. 23

between resistance and temperature within the interval 0° 100°, will be 

found to be acceptable.

0,5

0,4-

0,3

0,2

0,1

Steel

0.0 10 30 40 70 90

FIG. 2. Diagram of the relation between specific electrical resistance and temperature-coi'ffidi'iit for 

wrought iron, for steel, and for cast iron.

The results show that the mean temperature-coefficient of cast iron 

falls very fairly on what may be considered a prolongation of the locus 

obtained for iron and steel (see figure), or that the electrical temperature-coefficients of iron-carburets, in general, may be regarded as a definite function of the respective specific resistances:

TABLE 6. Temperature-coefficient of cast-iron.

Rod 

No.

13

14

15

Constants.

cm. 

a= 0. 040

t=20. 10

a 0. 643

b 0. 042

fc=20. 10

a= 0. 646 

b 0. 647

I 20. 10

t

C.

23.8 

23.2

67.2

67.5

99.4

99.3

{

22.8 

22.8

67.8

71 9

99.5

99.5

1

20.0 

17.8

18.3

66. 0

60.0

100.0

100.0

1 100. 0

w

ohm.

0. 003749 

3738

3938

3943

409.'t

4077

3839 

3835

4041

4061

4235

4235

4095 

4095

41('8

4347

4847

4500

4490

4530

t 

mean.

23.5

67.3

99.3

22.8

69.5

99.5

18.7

66.0

100.0

w 

observed.

0. 003743

3941

4085

3837

4051

4235

4099

4347

4509

W 

calculated.

0. 003743

3941

4085

3829

40C8

42-24

 4102

4311

4513

Diff.

0

0

0

8

 17

11

 '3

6

_ 4.

0

ohm. 

0. 003637

3712

4008

.... |

a

0. 00124

138

120

8

microhm. 

70.0

70. 2

83.3

(615)
24 JRON-CAEBUEETS. .[BULL. M.

DEDUCTIONS.

Analogous behavior of alloys and of iron-carburets. The data contained 

in the above tables throw some light on the probability of an analogy 

between alloys generally aud iron carburets, inasmuch as they show, a 

certain similarity of behavior in both kinds of products. It is not impossible that we have here in hand examples of a general law; in 

other words, it may be plausibly argued that whenever the properties 

of a primary metal are altered by addition of various quantities of a 

second substance (metallic or non-metallic) alloyed thereto, that then 

the known variation of electrical resistance is invariably accompanied 

by a corresponding variation of the electrical temperature-coefficient 

in such a way that an increment of the former corresponds to a decrement of the latter in accordance with some fundamental relation. In 

the case of ordinary alloys, small quantities of a second metal are 

alloyed to the original material, producing the known electrical effect. 

In the case of steel the process of tempering is the cause of a change 

in the quality of carburation, so that in a highly tempered bar more combined or electrically active carbon is, as it were, alloyed to iron than in 

one of inferior -temper or in a soft rod. Hence the corresponding electrical effect. But it is well to waive this subject here to discuss it more 

satisfactorily in another chapter.

Temperature-coefficient and volume. We shall show elsewhere15 that for 

steel at least, and possibly ior all non-electrolyzed conductors, the specific resistance may, with some fitness, be regarded as a volume-function 

only. Probably a similar remark may also be made with reference to 

the temperature-coefficient of steel, and it would appear that with this 

metal, the most promising of the available means-for the study of the 

bearing of specific volume on specific resistance and temperature-coefficient, is furnished us. Clausius16 was the first to call attention to 

the approximate proportionality of the resistance of most pure rnetals 

with their absolute temperatures. If we accept Matbiesseirs general 

relation between resistance and temperature for pure metals:

st =s0 (l+at+6t2 ), «=0.003S24, ^=0.00000126

and put . ' " ,

dst ._! 

di =273'

we find that at about 60° C. the said proportionality is accurate. 

There would be some propriety, therefore, in considering this state of 

the metals in question as a normal state, and the corresponding specific

"Chapter III.

wClausius: Pogg. Ann., CIV, p. 650, 1858. AuerLach (Wied. Ann., VIII, p. 479, 

1879) has endeavored to explain this circumstance, aud also to interpret the exceptional value encountered in case of iron.

(61C)
BAUDS Axi) BTuouiM,.] HEAT CONDUCTIVITY STEEL. 25

resistance as their normal resistance. It may be remarked, in passing, 

that the temperature to which soft steel must be cooled in order (theoretically) to annul its resistance coincides very nearly with the absolute 

zero of temperature.

ADDENDUM.

STATEMENT OF A KESISTANCE METHOD FOR THE MEASUREMENT 

OF HEAT-CONDUCTIVITY.

The success of the above application of Matthiessen and Hockin's 

method for the accurate measurement of very small iucrements of resistance, has suggested to us the availability of the same method in determining the necessary data for the calculation of heat-conductivity.

The subject of heat-conductivity has of late been largely discussed, 

especially in German literature. In most of the cases new methods 

have been proposed and employed. Our object herewith is to offer an 

experimental modification of the well-known method due to Biot, but 

first applied by Depretz,17 which we believe has certain practical advantages.

Depretz heats the ends of a straight rod of uniform section to different 

constant temperatures Tandtf(TX). After the stationary thermal 

condition has set in. tlt t,? t3, the temperature of any three consecutive 

right sections, at the same distance I apart, respectively, are related as 

follows:

«^+e-"'=(*i+*3) = U ....... (1)

where, moreover, ^ for rods of the same section and of the same external conductivity is, under the assumption of constant Z, inversely proportional to the square root of heat- conductivity. Suppose, however, 

that instead of measuring the temperatures at three consecutive equidistant sections, we propose to determine the resistances of. three consecutive equal lengths I of the rod, after3 the thermal condition has 

become stationary. We have

where dr is the elementary resistance corresponding to the length dx, 

at the temperature <, s the specific resistance of the material, q its (uniform) section, a a given constant. In view of the steady thermal flow, 

we may write

dr.

If this equation is Integrated successively between the limits ^ and Zi, 

13 and ?2, Z4 and Z3, where ?2 Zi=Z3 Z2=Z4 Z3 =Z, we obtain jthree eqna17 Depretz: Ann. d. cliim. XXXVI, p. 422, 1827; Cf. Langberg, Pogg. Ann., LXVI, 

p. 1, 1845; Wiodemann and Franz, Pogg. Ann., LXXXIX, p. 497, 1853.

(617)
26 IRON-CARBURETS. [BULL. 14.

tions from which the constants G and may be eliminated. The following relation results:

/43 

(2)

-;'-_l

where r0 is the resistance of the length Z, at zero. Equation (2) might 

have been more elegantly derived indirectly from equation (1) above.

FIG. 3. Diagram of a resistance-apparatus for measuring heat conductivity.

Suppose, now, that in connection with this result we use Hockin and 

Matthiessen's device of two corresponding sliding contacts in the manner indicated in the annexed diagram. Let

/// //_ 7 / _ 7 7 _7 7 _7 I I 1% LI (3 13 14 <3 v

Let the points m', m", Wi....,w4 on the wire 6e correspond to I', /", 

Z: ....?4 in such a way that, if connection be made between any two of 

them with the prolonged terminals of a galvanoscope G, the needle of 

the latter will receive no additional impulse on momentarily closing the 

key K, Then we may write

m" m'~ ~T~m" m'~

-1

whence it follows that Depretz' method by application of Hockin and 

Matthiessen's device may be theoretically reduced to a simple measurement of lengths.

It is not our object here to go into any practical details. 18 But we 

may remark that hurtful thermo-currents may be reduced to a minimum by using a sliding contact at the points I of a material therm oelectrically similar to the rod to be examined. Their effect would be 

that of changing the position of equilibrium of the needle of the galvanoscope, and they would not seriously influence the impulse given 

to it by momentarily closing K. Moreover, the ends, L and M, of an 

independent, permanently closed bridge-wire may be so adjusted as 

to compensate the thermo-electric disturbance entirejy (end L}, and

18 The compendious form of Wheatstone's Bridge, invented by Kohlrauscli, suggests 

itself for these measurements.

(618)
UARUS AND OTROUHAL.] HEAT CONDUCTIVITY STEEL. 27

yet not interfere with the measurement (end M). In this case it is not 

necessary to close I' ... J4 for a short time prior to closing JK, but both 

may be closed momentarily, the latter contact a little before and a little 

after the particular one of the former, with reference to which the observation is made.

It is our intention to endeavor to apply a procedure of this kind for 

the purpose of investigating whether the abnormal diminution of electrical conductivity due to tempering (about 70 per cent.) is accompanied by a corresponding variation of heat-conductivity. The plan would 

be the same as that detailed elsewhere.19

 Strouhal and Barus, Wied. Ann., XI, p. 976, 1880; ibid., pp. 953-4, 977.

(619)
CHAPTER II.

ON THE CONDITIONS WHICH IN THE CASE OF STEEL, ESSENTIALLY 

DETERMINE THE EFFICACY OF THE OPERATION OF TEMPERING; 

THE MEASUREMENT OF THE STATE OF HARDNESS OF STEEL.

INTRODUCTORY REMARKS. .

Origin of the worlc. At the outset of the present series of experiments it was our object to subject the relation existing between the 

amount of magnetization which saturated steel rods can permanently 

retain, and their mechanical condition, particularly their state of hardness, to a new and rigid investigation. We were led to this undertaking by the results shown in a paper by Barus,20 in which it appears 

that the electrical properties of steel its thermo-electric power and 

specific resistance primarily furnish a datum of singular sensitiveness 

for the hardness of this material. It therefore lay within our scope 

and purpose to invent a method for obtaining as many well-defined degrees of hardness between the glass hard or suddenly chilled state on 

the one hand, and the soft or thoroughly annealed state on the other, 

as would be practicable.

During the progress of the work, however, the phenomena attending 

the operation of tempering, as exhibited, by the thermo-electric power 

and the specific resistances of the different stages of hardness of steel, 

began more and more to engross us, and eventually became of sufficient 

importance to occupy our attention wholly. Thus it was that a special 

research, though partaking of the nature of a digression and calling for 

a larger expenditure of time than had been allotted to this part of the 

projected series of experiments, became almost necessary. The data in 

hand throw new light on the conditions determining the temper of steel, 

and indeed enable us to discuss the whole subject perspicuously and 

from a general standpoint. These remarks will suffice to account for 

the origin, purpose,, and disposition of the parts of the present chapter.

Material used. Tne steel used in this work was of the kind known as 

"English silver-steel." 21 It came to our hands in the shape of rods, 

about 30 cm. long, varying in diameter between 0.03 cm. and 0.01 cm., 

drawn accurately cylindrical for the use of watchmakers. The rods 

were nominally identical in composition, and obtained from Cooks' 

Brothers, of Sheffield and Manchester. In view of the great complexity

20 Barus, Phil. Mag. (5), VIII, pp. 341-68, 1879 ; Wied. Ann., VII, p. 338, 1879. Cf. 

Appendix to this Bulletin, p. 203.

21 See Chapter VII.

28 (620)
BAUUB AND STltOUHAL.] APPARATUS FOE TEMPERING. 29

and vagueness associated with the term steel, it appeared necessary to 

confine the operations to the given type of this material an exceptionally favorable type, moreover, when considered with reference to 

the enormous interval of hardness comprehended between its glass-hard 

and soft states. Che.rnical analysis of this individual member of the 

infinite family of possible steels would have been more than useless, as 

will clearly appear from a perusal of the present series of papers as a 

whole. As a rule we draw our inferences from rods broken from a single longitudinally homogeneous sample only. The purely physical 

relation sought is thus investigated unaffected by secondary phenomena 

or distortions, while the material, as it were, is represented by a series 

of temporarily constant parameters. In the present chapter this 

method of research is suggested naturally by the experiments themselves, and satisfactory material is easily obtained. But in the later 

chapters on magnetism, where the necessity of using chemically and 

structurally identical rods is much more urgent, these essential conditions are often secured only with difficulty.

APPARATUS FOR IMPARTING GLASS-HARDNESS TO STEEL.

In view of the great number of steel wires to be tempered, the construction of an apparatus by the aid of whicli the operation of sudden 

cooling could be expeditiously and conveniently carried out, and which 

would impart to the wires a uniformity of hardness throughout their 

length, was an essential requisite. The following machine answered 

the purpose satisfactorily:

FlO. 4. Apparatus" for lianloiiin^ steel roils}.

(621)
30 IEON-CARBURETS. - [BULL/M.

In figure 4, A is a hollow cylinder 9 cm. long, of dense (box) wood, provided with a circular groove and slot so as to admit of its being securely 

i'astened by a sort of bayonet-joint to a substantial tripod, or again removed, conveniently. Into the lower and wider part (3K) cm. in diameter)' 

of the aperture a closely-fitting faucet communicating with the watermains by means of a hose, is inserted j into the upper opening of the same 

(1.5 cm. in diameter) there is fitted a glass tube of thin material and about 

30 cm. long. This serves primarily as a protecting envelope for the steel 

wire stretched in its axis. Besides this gradually tapering canal, the 

box-wood cylinder is provided with a second perforation at right angles 

to the axis of the latter, in which a thick steel rod B (0.5 cm. in diameter) 

fits snugly.

The wire to be hardened is drawn tensely between two clamp-screws, 

in connection with the terminals of a powerful battery, in the following 

way: The lower clamp-screw possesses a longitudinal and a cross perforation. One end of the wire is fastened in the first of these holes by a 

lateral screw and then introduced into the wooden cylinder and attached 

glass tube, A, from below, whereupon the steel rod B, passed through 

the cross perforations in both cylinder and clamp-screw, and fastened 

by the vertical screw of the latter, puts the lower end of the wire in connection with one pole of the battery. As B may be rotated around its 

own axis and at the same time moved laterally, the wire may be satisfactorily centered. JL, thus.adjusted, is now attached to the tripod as 

above described, the faucet forced tightly in from below, and the upper 

end of the steel wire, which projects slightly out of the glass tube, 

grasped by a second clamp-screw. The latter forms a part of a peculiar 

spring (7, in shape of a rhombus of very large horizontal but very short 

vertical diagonal. In this way a gentle tension, not so strong as to rupture the wire when red hot is constantly maintained, while the parts of 

the spring are thick enough to allow the passage of an intense galvanic 

current without becoming perceptibly heated. We have found that a 

wire symmetrically chilled and held tense in this way remains straight 

after the glass-hard temper has been imparted to it an important desideratum. In order to centrally adjust the upper end of the wire, or to 

regulate the tension of the spring, the latter may be moved around and 

along a horizontal arm, which in its turn is similarly adjustable around 

a vertical post screwed to the tripod. To C and B the terminals of a 

powerful battery are suitably attached.

A current of dry carbonic acid gas continually circulating through the 

tube practically obviates the annoyance of oxidation during the heating 

to redness. To introduce this gas, the faucet is doubly perforated in 

the way devised by Senguerd. The larger of the canals is intended for 

the influx of water, the smaller for carbonic acid, and they are so disposed relatively to each other that if the one is open the other is necessarily closed. To manipulate the apparatus satisfactorily a considerable 

head of water is desirable. But even when these facilities are available,

(622)
HAUUB AND STROUHAL.] THERMO-ELECTRIC POWER MEASUREMENT. 31

Hie water, on opening the faucet, is apt to enter the tube with a squirt, 

chilling1 some parts of the wire before the main column advances, and 

in this way vitiating the otherwise attainable uniformity of glass-hardness. For this reason a second faucet (not shown in the figure) belonging to the hydrant was put into use. We operated in this way: The 

former faucet was first opened, producing no other effect than the interruption of the current of carbonic acid. Then one of us rapidly opened 

the second faucet, while the other, in clue time, broke the galvanic circuit. As the glass tube was of comparatively small diameter, the water 

rushed into its interior, ascending as an unbroken column with great 

velocity and imparting to the wire the glass-hardness desired. According to Jarolimek22 this rapidity of current is of paramount importance 

when the attainment of extreme degrees of hardness is the desideratum. 

In the case of quiet water a non-conducting envelope of steam is apt to 

inclose the wire, protecting it against instantaneous chilling. Such a 

layer would effectually be torn away by a very swift current, and cold 

water and wire remain in more intimate contact. We regarded the 

hypothesis, which Jaroliinek believes to have verified by experiment, 

as plausible.

Glass tubes of thin walls were chosen, and breakage was therefore a 

rare occurrence. Of course we did not keep the wire in the red-hot 

state longer than appeared absolutely necessary.

The operation of disadjusting and drying the parts of the apparatus 

after each chilling proved to be a tedious annoyance. Nevertheless the 

efficiency of the apparatus may be said to have been demonstrated by 

the fact that after a little experience we were able to temper 50 to 60 

wires during an interval of five hours. Of the total number of hard 

wires obtained (some 180), those were selected for the measurements 

which had been operated upon during our later and more expert manipulation. The ends were broken off and discarded, and only as much of 

the central part of each wire used as would warrant the assumption of 

uniformity of hardness throughout the lengths employed. The degree 

of homogeneity, moreover, admits of being specially tested, as will be 

explained below.

The battery used consisted of 20-30 large Bunsen cells, connected in 

series or in multiple arc in a way to correspond with the external resistancei In the latter case it is necessary to keep the partial circuits as 

nearly as possible alike. Otherwise a reverse current is apt to traverse 

one of them, gradually disintegrating the carbons.

MEASUREMENT OF THERMO-ELECTRIC POWER.

Thermo-element. The thermo-electric power of our wires was deduced 

from measurements of electromotive force and temperature, obtained by

' 22Jnroliwek: Diugler's Jour., CCXXI, pp. 436, 518, 1876, "

(623)
32 - IKON-CARBURETS. [BULL. 14.

combining them therrao-electrically with the same given normal wire. 

Chemically pure silver, deposited galvanoplastically, fused, drawn, and 

softened, appeared to be the most desirable metal-of-reference for this 

purpose. Two samples of this were selected and compared. From reasons of a practical character, however, we found it expedient not to use 

these normals in the actual work.. In the. measurements, a copper wire 

of a given kind, which had frequently and very carefully been compared 

with the silver, was substituted for it, and the thermo-electric powers 

steel-copper subsequently reduced to steel-silver, by calculation. 

, After testing many modifications, we adhered to the very efficient 

form of thermo-electric apparatus diagramrnatically represented in figure 5. Si and S2 are .two doubly tubulated spherical receivers, of the

Si S2

FIG. 5. Form of tlicrmo-clcment.

capacity 1 liter approximately. These were mounted on good non-conductors in such a way as to place the axes of the tubulures A and B in 

horizontal, the other two in vertical position. The former were provided with well-fitting corks, centrally perforated, so as to admit the 

glass tube cd (diam. 1 cm.) snugly. In this way the two receivers were 

held firmly together, and at distances apart adjustable at pleasure, thus 

adapting the arrangement for examination of a long or a short wire. 

Two small suitably-perforated corks, fitting the ends of the tube cd, 

gave to the wire an axial position within it. In this way the steel rods, 

exceedingly brittle and frail when in the state of glass-hardness, were 

adequately protected. Mention is still to be made of the terminals li 

and 7c of the apparatus. These Avere specially-selected samples of covered copper wire, as stated above. They passed through the large corks 

at A and B in which they were cemented once for all to the junctions 

at the center of the respective receivers. When a new rod was to be 

introduced, this was thrust through the tube cd, and the latter duly 

closed with the small corks, in the perforations of which the rod fitted 

tightly. Then the free ends of the terminals were connected with the 

respective ends of the steel rod, either by flat brass clamp-screws, or, 

where the temper permitted it, by soldering. The tube carrying the 

large corks was now in complete adjustment, and it was only necessary 

to insert these in the tubulures A and B of the receivers. One of the 

latter was then filled with water of the temperature of the room, the 

other with hot water. A woolen jacketing appropriately surrounding 

the hot receiver reduced the loss of heat by radiation to a minimum-

(624)
BAKUB AND sTROuHAt.] THERMO-ELECTRIC POWER MEASUREMENT. 33

By the aid of two carefully calibrated thermometers, with their bulbs 

at the centers of the respective receivers, the temperature of these was 

read off. A small hole was drilled at n in the tube cd to allow for the 

expansion of the air heated by proximity to the hot water.

Method of measurement. For the measurement of the thermo-electromotive force (expressed throughout in volts) a zero method was 

adopted. If E (figure 6) be the compensating (one Daniell), e the comM M

PIG. 6. Disposition of therino- FIG. 7. Apparatus for galvanelectric apparatus. onieter-factor.

pensated element (the thermo-couple), W the resistance of AEB, w 

that of AMBj we shall have, when the current in AeB containing the 

galvanometer is zero,

\ In our experiments, in the most unfavorable cases,

* pr

*tv O

"F-ioooo"'

and hence, with sufficient accuracy for the present purpose we may put

e IP E= W'

Both w and Wwere furnished by Siemens' rheostats. The resistances 

of the connecting wires and of the Daniell are negligible. W could be 

increased to 30,000 ohms, w diminished as far as 0.1 ohm.

In order to eliminate such discrepancies as would arise from variations of the Daniell, the electromotive force of this element was measured before and after each observation. It is known that this source of 

error is by no means negligible, and that it depends on the way in 

which the Daniell has been put together, and on the time of use. For 

the purpose in question, the terminals of a Wiedemann's galvanometer 

of known .factor A could be introduced into the circuit EAMB with the 

aid of an appropriate key. If therefore the line ASB is broken, the 

resistance w excluded, we shall have a simple circuit EAMB such that 

if n be the deflection at the galvanometer

E=A Wn.

Usually W=20,000 ohms was chosen, as it was through this resistance, 

approximately, that the Daniell acted during the measurements with the 

zero method.

To determine the factor A of the galvanometer we made use of a 

tangent-compass of known factor, C. This we calculated both from the 

dimensions of the coils and from voltametric observations. Figure 7 

Bull. 14 3 (625)
34 IRON-CARBURETS. [BULL. 14.

gives the disposition of apparatus diagrararnatically, wherein E is the 

Daniell. T the tangent-compass, G the. mirror-galvanometer. Let ID be 

the resistance, i the intensity of current in the shunt A M B, IF the resistance, and I the current in A G B; then

IW=iw; 

whence

I _ w

T+i~ W+w' . 

But by measurement with the tangent compass we get

and with the galvanometer, simultaneously, I=An, whence

By a proper choice of w and W, practically convenient deflections, both 

at the tangent compass and at the galvanometer, are obtainable. The 

determination of A was frequently repeated.

Essential details. The actual arrangement of apparatus as given in 

figure 8 differs from the diagram (figure 6) described above, only in that 

serviceably-disposed commutators and keys have been introduced into 

the partial circuits.

r

FIG. 8. Details of thermo-electric apparatus.

The commutator 1, inserted immediately after the Daniell, is used, 

in the first place, in determining the value of the electromotive force of 

this element from the double deflection of the mirror of the galvanometer 

G put in circuit by the key II. In the second place, when manipulated 

in connection with another commutator, JJJ, which changes the direction of current of the thermo-element, it adds very materially to the 

attainable accuracy by enabling the observer practically to eliminate 

the discrepancies due to extraneous thermo-currents. These result 

from an irregular distribution of temperature in the connections. We 

actually measure not

where e and sr are the disturbing electromotive forces in question. 

Now £', which has its seat in the branch JEAMB, is always negligible in 

comparison with E. A similar assumption, however, by no means 

applies to e i. e., to the electromotive force which originates in the

(626)
BARUS AND sxKOUHAL.] THERMOELECTRIC POWER MEASUREMENT. 35

branch ASB. This quantity, as our experiments have shown, very frequently reaches values amounting to a considerable part of e indeed, 

when e is small, e is directly comparable with it. 

We therefore have

 }-£ W ~E~=W

If both e and £ retained the same value before and after an observation 

there would result: Before commutation,

after commutation,

e £ wl

whence

Now, although both e and f do vary during the interval of an observation, the amount is small and the change of the former so nearly linear 

with the temperature T of the warm receiver, that the. mean of the electromotive forces e may be regarded as coincident with the mean of the 

temperatures T. If the observations after commutation are rapidly 

made, which can easily be done because the approximate values of W 

and w are known from the first measurements, we may suppose e to have 

remained constant.23 A mean of the two determinations therefore will 

very nearly eliminate e. '

Finally, reference is still to be made to the form of Weber's commutator 

IV, which serves the purpose of a key of special kind. The small mercury cups are so filled that the ther mo- current is not closed until a moment after the partial current from the Baniell. When 10 and W are 

properly chosen, therefore, the needle of the galvanometer 8 remains at 

rest. An exceedingly sensitive form of apparatus with an astatic needle, 

devised by Magnus and constructed by Sauerwald, was1 used here.

While one observer made the adjustments w and W, the other read 

off the temperatures of the thermometers in the receivers at given signals.

Calculation of constants. If t and T be the temperatures of the thermoelectric junctions, e the corresponding electromotive force, we shall have 

generally 24

e=a(T-t) + l(T2 -tz) ........ (1)

Putting T t=x, T+t=u, e=y,

y=ax-\-bxu ......... (2)

Inasmuch as the number of observations was always greater than two,

23 By comrnutating again we frequently convinced ourselves that this supposition was 

quite permissible. The values otained for the first and third positions of the commutators were so nearly identical that we could sati sfac tor ily0 accept them as such.

2<Avenarius: Pogg. Ann., CXIX, p. 406, 1863 ; ibid., CXLIX, p. 374, 1873; Tait, Trans. 

R. Soc. Ediub., XXVII, 1872-73, p. 125. In this memoir the above equation is accepted merely as an empirical relation. Tait has discussed it theoretically.

(627)
36 IRON-CARBURETS. [BULL. 14.

the constants a and & were calculated by the method of least squares, 

on the basis of an equation of the form

x

We were led to choose this form not merely because the calculations are thus essentially simplified, but principally because the form 

(2) gives to the values of e, corresponding to great values of T f, 

an amount of preference which appears to us wholly unwarranted: 

for although e is much more accurately measurable in the case of large 

values of T £, the observed value of T will differ the more appreciably 

from the true temperature of the hot junction of the thermo-element, in 

proportion as T is greater than the temperature of the room in which 

the observations are made.

By aid of the well-known formulae developed by the method of least 

squares, a0 and &0, of the thermo-couple copper- silver, were calculated 

from a large number of special observations.

By the same method, moreover, we derived the constants, a1 , 6l, for 

the elements steel-copper. To reduce from these the values a, 6, which 

hold for the couples steel-silver, we made use of a set of tables calculated 

thus : If e, el, e0 correspond to a, a1 , « , we have

e=el-e0,

where el is dependent on the arguments T and t. Now e0 can be thus 

expressed:

that is, as a difference between identical functions of the same arguments T and t. A table for

is therefore calculated once for all, from which for every combination of 

T and t the quantity eot and therefore e, is easily obtained. After -all 

the observations, e, had been referred to silver, the constants a and l> 

were deduced by the thermo-electric formulae above given.

MEASUREMENT OF ELECTRICAL CONDUCTIVITY.

Method calculation. For the measurement of resistances we employed 

Kirchhoff's form of Wheatstone's bridge. The resistances w and d to 

be compared could be exchanged by the aid of a mercury commutator. 

Heavy copper plates, the resistance a. and 6 of which was such as to 

introduce a very small correction only, connected the latter with an 

interposed commutator and finally with the end points of the bridge. 

The current was advantageously furnished by Weber's magnetic inductor. Sauerwald's "sensitive apparatus, already referred to, was used 

as a galvanoscope.

(628)
BABUS AND STKOUHAL.] ELECTRICAL RESISTANCE MEASUREMENT. 37

The following is the method of calculation adopted: 

First position of commutator,

Second position of commutator. .- J.^n^. 1 7 6-\-a «2

whence

w

and therefore, if

ni n<> a 6

In the case of our bridge, at t =10°

^+f =0-00194, --^= -0-00016. jj LI

Now, in so far as HI and nz are always nearly identical, a sufficient approximation for 7c is furnished by the formula

....... .'(I)-

In this way the calculations were greatly simplified, since n could 

be immediately obtained from ') bach's25 tables. A small table of our

own contained the respective values of the term (n 1) ~ &

In a part of the measurements we obtained excellent results with 

the beautiful method due to Hockin and Matthiessen.

From this value of w, the length and the diameter 2p the latter dimension being determined microscopically the specific resistance of 

the given wire at the temperature t followed at once.

The normal resistance tf was given by a specially constructed e"talon 

of heavy German silver wire, soldered to stout terminals of copper 

properly amalgamated. We were in possession of six of these, such 

that by suitable combinations, either in series or in multiple arc, resistances as high as 0-6 ohms and as low as -fa ohm were available. We 

were thus able to keep the sliding contact near the middle of the bridge 

wire, and the value of the factor (n 1) in equation (1) was therefore invariably small.

. Resistances at points of contact. In view of the very small resistances 

(0.5 to 0.05 ohms) to be measured, great care had to be taken to reduce 

the resistances at the places where the steel wires were inserted to a 

minimum. To obtain an estimate as to the value of the discrepancies 

produced in this way we made a determination of the resistance of a 

soft steel wire for three different methods of insertion. In the first of 

these the wires were firmly held between flat clamp-sere AVS ; in the second, the ends of the wires were covered galvanoplastically with a thin 

even coat of copper, which was then amalgamated; finally, the contact 

was obtained by actually soldering the steel wires to pieces of heavy

25 E. Obach: Hiilfstafeln fiir Messungen elektrisclier Leitungswiderstande mittelst 

cler Kirchoff-Wheatstone'schen Drahtcombination, 1879.

(629)
38 IRON-CARBURETS. [BULL. 14.

copper wire. Only the last of these methods of insertion was found to be 

thoroughly satisfactory under all circumstances. In the first the error 

was quite large, while the second proved to be unsafe; for the amalgamated copper coat was apt to become insufficiently adhesive. In the 

case of glass-hard wire expeditious soldering is essential, otherwise the 

ends are annealed to an extent that will seriously affect the results. 

We avoided this at least partially by cooling the wire, immediately after 

the soldering had been effected, by a jet of water from a small washbottle. With a little practice the whole operation is finished in a few 

seconds. It is to be noted that if an error had been introduced in this 

way its effect would only have been that of giving further emphasis to 

the abnormally large results discussed in the sequel, since the values 

for specific resistance as thus actually found can only be short of the 

true values. In the later experiments all these inconveniences were 

avoided by the use of Hockin and Matthiessen's method.

Criterion for homogeneity. The method just mentioned is peculiarly 

adapted for the determination of the degrees of uniformity of hardness 

along a given length of wire, because it enables the observer to compare the resistances of different parts of the said length with facility. 

The process as actually employed will be discussed in a,nother chapter.

The method used for calibrating the essential wire of the bridge has 

been described elsewhere. (See appendix to this chapter, p. 72.)

THE OPERATION OF SUDDEN COOLING. GLASS-HARDNESS.

Effect of chemical composition. The steel rods tempered to glass-hardness in the manner described were found, on examination, to be thermo-electrically negative26 relatively to silver.

In so far as the same process had been applied to rods nominally of 

like composition, it appeared plausibly presumable that the degrees of 

hardness attained would be nearly identical; in other words, that the 

tempering would have furnished us with a set of glass-hard rods of 

nearly the same thermo-electric power. This was not the case. A 

graphic representation of the relation between thermo-electromotive 

force and temperature showed this remarkable result, that the wires 

tempered were readily referable to a few distinct groups; for the position of the different thermo-electric curves was such as to permit them 

all to be comprehended by a few narrow and well-defined sectors. This 

implies that though the maximum of, attainable hardness is different 

in the different wires, particular groups possessing nearly identical 

properties are readily discernible. We were unable to discover any 

relation between the individual members of the said groups and the

**> Cf. preface, p. 6. 

(630)
BABUB AND sTuouHAL.j THE OPERATION OF SUDDEN COOLING. 39

respective diameters of the wires. Nor did the wires hardened on any 

particular day show like thermo-electric qualities. It is conceivable, 

for instance, where currents of different intensity are employed, that 

the resulting difference in the degrees of red heat imparted to the wires 

would find its expression in a correspondingly marked difference in the 

degrees of hardness. The true cause of the difference of character observed must therefore be ascribed to chemical composition. In other 

words, the groups are distinguishable one from another by the respective amounts of carbon contained in the wires. The rods were not all 

receired at the same time. Without doubt the maximum of hardness 

attainable by sudden chilling is essentially conditioned by the degree 

of carburation of the steel rod, and to a very small degree only by the 

impurities present. In a general way we may state that the maximum 

in question is a characteristic datum for the type of steel under experiment. In Chapter YTI of the present memoir we shall have occasion 

to discuss this subject in detail.

Maximum hardness reached. The greatest hardness met with in this 

work was that possessed by two rods of.the diameters 0.056 cm. and 

0.073 cm., respectively. The thermo-electric constant a here reached 

the exceptionally small value a 2-60 (microvolts), and the specific 

resistance, at ordinary temperatures, was as large as 45 microhms, 

cm/cm2 . Unfortunately most of these very hard wires had to be discarded, because in the eailier experiments boiling water had been used 

in investigating their thermo-electric powers. We subsequently found 

that 100° produces a very pronounced annealing effect. In the later 

experiments with glass hard wires water of only 40° was employed, and 

this but for a very short period of time.

Temperature of ignition. Jarolimek and Ackermann27 in their experiments on steel arrived at the important result that the rapidity of the first 

part of the chilling of red-hot steel, say from 600° or 700° to 300° or 400°, 

is far more essential as regards the degree of hardness obtained than the 

further cooling from 300°-400° to zero. It is easily possible to harden 

a rod very perceptibly by cooling it from bright redness in a metallic 

bath (Zn, Pb) at 400°. Such a process combines in one the operations 

of chilling and of annealing. Cooling from 300° or 400°, however, produces no effect. Again, Chernoff had previously found that if the temperature from which steel is chilled be supposed to increase continuously, no observable effect will be apparent until a temperature in dark 

cherry-red heat is reached, when glass-hardness is suddenly attained.28

Our experience is in perfect accord with these results. The phenomenon was strikingly manifested both in rods of the same diameter and in

27 Jarolimek u. Ackermann, Zeitschr. fiir das chem. Grossgewerbe, 1880. Similar results, we believe, were published by the distinguished American engineer, Mr. Joshua 

Rose, but we have been unable to find them.

28 D. Cheruoff: Vortrag gehalten in der russischen Technischen Gesellschaft, im 

April u. Mai 1868.

(631)
40 IRON-CARBURETS. [BULL. 14.

those of different diameters. In the first instance we may cite our observations with comparatively thick steel rods, which the available current 

was able to.heat to dark redness only. After chilling these remained 

soft and pliable for more than one-third of their length; but at a 

particular point of the wire its mechanical condition changed suddenly 

to brittle hardness, and this despite the fact that during the heating a 

change of intensity of redness along, the parts of the wire in question 

was scarcely discernible. In the second instance we frequently noted 

that where the intensity of current used was sufficient to impart hardness readily to a given comparatively thick class of wires, this was no 

longer possible for the next larger dimension, notwithstanding the 

fact that the respective thicknesses varied as little as 0.125 cm. and 

0.145 cm. It is furthermore to be added that the sudden change in 

question is equally apparent both in the mechanical as well as in the 

electrical properties of steel.

The experiments made would certainly not warrant the forced assumption that the phenomenon in. question partakes of the nature of a true 

discontinuity. Some molecular change occurring at an extremely rapid 

rate is alone to be understood. In a general way, however, it may be 

stated that a certain critical temperature in red heat must be surpassed 

if sudden cooling is to produce glass-hardness; otherwise the steel 

remains soft.

Thermo-electric maxima and neutral points. In this place a final remark may be added. During the experiments we had frequent occasion to observe "neutral points" (occurring at the mean temperature

a

$(T-\-t)=£i- of the junctions of the thermo-element, the temperature at

which the electromotive force passes with a change of sign through zero) 

of comparatively low value. Many of the hard rods differed but 

slightly from silver as regards their thermo-electric properties. Maxima of electromotive force at low temperatures were even more frequently obtained. A number of examples of this kind will be found in 

the tables below.

BEHAVIOR OF HARD STEEL RODS ANNEALED IN HOT OIL BATHS.

Manipulation. Having thus in hand an assortment of glass-hard 

rods of excellent quality, it was our next endeavor to reduce the degrees of hardness of these consecutively by equal amounts. In other 

words, the problem was so to anneal the rods that between the glasshard and the soft states as extremes a great number of intermediate 

approximately equidistant states might be obtained. We commenced 

our operations with this end in view by heating the hard steel in a 

large bath of linseed oil very gradually to different temperatures, re-

(632)
BARUS AND STROUHAL.J STEEL ANNEALED IN HOT OIL. 41

moving samples of the series of immersed rods at different stages of 

the process. ' Inequalities of temperature in the bath were reduced to 

a minimum by constant stirring. We also adopted an inverse method 

of procedure, in which, when a desired temperature was reached, the 

hard wires selected were submerged in the oil on a false bottom of wire 

gauze, and the whole allowed to cool. After several days they were 

examined both as to their thermo-electric power and their specific 

resistance.

Results. The results of these measurements are given in the following table. It will be remembered that e (observed or calculated as 

specified) is the electromotive force in microvolts for the temperature 

T and t (centigrade) of the junctions, a and b are the thermo-electric

constants of Avenarius, s. ( .t° microhm ) the specific resistance at

Vcm / 

the temperature *, /> (cm.) finally the radius of the wires:

TABLE 7. Thermo-electrics and conductivity of steel wires, annealed.in oil batlis.

Annealed 

at 

I. 300°"..-.

II. 275<>...

m. 250°..

No.

No. 1 (2p=0. 0968)

No. 2 (2 p=0. 0900)

.

No.3(2p=0.0721)

No.4(2p=0.0568)

No. 5(2 p=0. 0345)

No.6(2p=0.0903)

No.7(2p=0.0558)

No. 8 (2 p=0. 0880)

No.9(2p=0.0720)

«^

°C.

10.3

19.3 

19.3

19.3

19.5

19.5 

19.5

19.5

19.6

19.7 

19.6

19.7

18.9

18.9 

18.9

18.9

19.7

19.7 

19.7

19.7

20.0

20.0 

20.0

20.0

20.0

20.0 

20.0

20.0

19.9

19.9 

19.9

19.9

20.0

20.0 

20.0

20.0

T

°C.

88.1

74.0 

63.3

50.1

89.5

76.2 

62.0

54.3

89.8

73.3 

59.1

50.1

87.9

70.3

57.4

48.3

86.7

72.1 

59.4

50.6

89.2

78.2 

64.9

50.9

90.1

71.9 

59.7

48.3

88.0

74.8 

61.6

51.9

80.5

65.8 

55.3

49.9

e:10* 

observed.

microvolts.

4.418

3.622 

2.982

2.125

4.619

3. 849 

2.961

2.457

4.052

3. 194 

2.406

1.893

4.497

3.468 

2.657

2.052

4.787

3.847 

2.975

2.353

3.987

3.437 

2.731

1.941

3.553

2.737 

2.141

1. 529

3.429

2.863 

2. 237

1.767

3.462

2.697 

2.124

1.827

e:10* 

calculated.

microvolts.

4.429

3.615 

2.971

2.131

4.622

3.843 

2.959

2.458

4.050

3.191 

2.414

1.888

4.503

3.462 

2.651

2. .056

4.789

3.843 

2.977

2.352

3.985

3.436 

2.733

1.940

3.562

2.729 

2.134

1.533

3.427

2.860 

2.244

1.763

3.457

2.701 

2.128

1.822

a

microvolts.

7.80

1

I 8.03

J

1

^ 6.99

J

^

I 7.78

J

^

| 8. 52

J

^

I 7.24

J

. )

I 6.15

J

^

I 6.46

J

j

I 6.96

.)

1>

microvolts.

 0. 0127

 0. 0130

 0. 0111

 0.0118

 0. 0130

 0. 0135

 0. 0097

-4.0132

~0. 0124

fft

cm t

cm2

microhm.

18.96

18.49

20.54

20.00

17.64

20.75

22.74

23.20

20.47

t

°C.

19

19

19

10

19

20

19

19

19

(633)
42 IRON-CARBURETS. [BULL. U. 

TABLE 7. Thermo-electrics and conductivity of steel wires, annealed in oil laths Cont'd.

Annealed 

at 

IV. 225°...

V. 200°. . . .

o

TL 175°...

VII. 150° .

No.

No. 10 (2 p=0. 0720)

No. 11 (2 p=0. 0565)

No. 12(2 p=0. 0548)

No. 13(2 p=0. 0337)

t

°C.

T

°C.

20. 0 ( 79. 9

20.0 

20.0

20.0

20.1

68.4 

57.3

49.0

87.1

20.1 65.9 

20.1 53.9

20.1

20.1

20.1 

20.1

20.1

20.1

i20. 1 

20.1

No. 14(2 p=0. 0900)

No. 15 (2 p=0. 0558)

No. 16 (2 p=0. 0974)

No. 17 (2 p=0. 0882)

No. 18(2 p=0. 0723)

No. 19 (2 p=0. 0560)

No. 20 (2 p=0. 0336)

No. 21 (2 p=0. 0908)

No. 22 (2 p=0. 0571)

No. 23 (2 p=0. 0335)

20.1

19.9

19.9 

19.9

19.9

20.1

20.1 

20.1

20.1.

18.9

18.9 

18.9

18.9

18.9

19.0 

18.9

19.0

19.1

19.1 

19.1

19.1

18.1

18.1 

18.1

18.2

18.3

18.3 

18.3

18.3

18.8

18.8 

18.8

18.8

18.8

18.9 

18.8

18.9

18.5

18.5 

18.5

18.5

41.8

89.4

67.9 

55.3

44.8

87.4

74.0 

62.4

52.0

89.2

75.6 

64.4

54.9

69.5

68.8 

69.1

50.1

89.8

74.3 

61.1

51.7

82.5

68.8 

59.8

51.9

78.8

68.2 

57.8

48.7

82. 0

62.8

47.8

39.8

76.8

62.3 

52.9

42.1

86.4

67.1 

53.8

43,3

87.2

72.4 

59.7

48.8

73.7

60.4 

52.1

45.4

e:102 

observed.

microvolts.

2.161

1.803 

1.335

1.144

2.663

1.948 

1.464

0.971

3.442

2.494 

1.900

3.372

3.770

3.105 

2.498

1.922

2.059

1.751 

1.434

1. 161

1.989

1.484 

1.231

0.963

2.524

2.063 

1. 631

1.294

2.056

1.681 

1.414

1.166

1.314

1.109 

0.899

0.706

1.859

1.387 

0.954

0.714

2.723

2.088 

1.680

1.177

1.828

1.366 

1. 061

0.765

1.734

1.414 

1.122

0.854

1.745

1.387 

1. 146

0. 941

calculated.

microvolts.

2.359

1. 804 ' 

1.340

1.141

2.672

1.931 

1.469

0.972

3.434

2.503 

1.902

1.369

3.769

3.107 

2.496

1.923

2.068

1.737 

1.437

1.163

1.989

1.489 

1.225

0.965

2.528

2.063 

1.626

1. 297

2. 056

1. 678 

1.417

1.165

1.312

1.112 

0,900

0.705

1.862

1.381 

0.958

0. 713

2.715

2.098 

1.677

1.176

1.809

1.388 

1.054

0.763

1.729

1.417 

1.126

0.850

1.744

1.390 

1.147

0.939

a

microvolts.

4.67

^

I 5.15

j

j

|- 6.40

)

}.

I 6.89

j

^

I 4.06

)

\

{ 3.85

J

1

i 4.67

)

^

I 4.26

)

i

I 2.79

)

,

I 3.83

J'

i

i 5. 45

j

1

i 3.76

j

i

I 3.41

J

i

I 4.24

J

b

microvolts.

 0. 0007

-0. 0109

 0. 0131

 0. 0121

 0. 0098

 0.0090

 0. 0102

 0. 0102

 0. 0060

-0. 0091

 0. 0086

-0. 0103

 0.0083

-0. 0117

«t

cm + cm*"

microhm.

25.66

24.81

22.93

20.66

27.36

28.11

26.70

27.93

31.32

28.68

24.34

29.34-

30.94

27.93

t

°c.

19

19

19

19

20

19

19

19

19

19

19

19

19

 ,

19

Digest. If-we arrange these different degrees of hardness, expressed 

both thernio-electrically and in terms of their specific resistance, with 

reference to continuous variation of the former quantity, we obtain

034)
BARUS AND 6TROUHAL. i PROLONGED INFLUENCE OF TEMPERATURE. 43

the following perspicuous tabular comparison. The table shows that 

our endeavor to reach a great number of symmetrically distributed degrees of hardness systematically, was only partially successful.

TABLE 8. Thermo-electric position and conductivity of annealed steel.

No.

5..........

2..........

1.. ........

4..........

6. .........

3..........

9..........

1 U

Q

19

7..........

20..........

a

microvolts. 

8.52

8.03 7 fin

7.78

7.24

6 00

6.96

6.89

6.46

6.40

5.45

s

microhms. 

17. 64

18.49

18.96

20.00

20.75

OA KA

20.47

20.66

23.20

22.93

99 74

24.34

Annealed at

°C. 

300

300

300

300

> 275

300

250

250

250

250

275

200

No.

11.........

36......... 10.........

17.........

23.........

14.........

15.... ....

19.........

21.........

22.........

18.........

'

a

microvolts. 

5.15

4.67

4.67

4.26

4.24

4.06

3.85

3.83

3.78

3.41

2.79

s

microhms. 

24.81

26.70

25.66

27.93

27.93

27.36

28.11

28.68

29.34

30.94

31.32

Annealed at

°G. 

250

200

200

150

225

225

200

175

175

200

ON THE BEARING OF THE TIME OF m EXPOSURE ON THE EFFICACY

OF ANNEALING.

Low annealing temperatures. In the foregoing experiments the lowest 

temperature employed was ICO0. It will be seen that the annealing 

effect thus produced is strikingly large. This observation naturally 

suggested the question as to what results are to be expected when the 

annealing is conducted even at lower temperatures. The inquiry would 

have an immediate practical bearing: It will be remembered that in the 

thermo-electric measurements it is desirable to raise one of the junctions to a high temperature relatively to the other. We are led to ask, 

therefore, how high this temperature may be chosen without destroying 

uniformity of temper and producing partial annealing at one end of the 

rod.

Results for 100°. We began the preliminary experiments with the 

two rods, Nos. 24 and 25, of nearly the same thicknesses, 0.0574 cm. 

and 0.0554 cm., respectively, bat of different degrees of glass-hardness. 

Thermo-electric measurements only were made, with results for the 

glass-hard state as follows:

TABLE 9. Thermo-electric power of glass-hard wires.

No. 24....... ................

No. 25........... ............

t

oc .

19 t\

12.5 

Us. 5

12.6

12.3

12.4 

12.4

12.4

T

°0.

go i

78.8 

58.1

44.1

89.0

80.1 

71.2

59.8

observed.

microvolt.

* O OrtQ

-2. 376 

-1. 572

-1.139

0.707

-0. 552 

-0. 415

-0. 294

e: 10* 

calculated.

microvolt.

2.793

-2. 396 

-1.567

-1.139

O CCV7

-0. 554 

-0. 428

-0. 289

a

microvolt.

-2.83

.

I +0.18

J

b

microvolt.

-0. OOP6

-0. 0103

(635)
44 1EON-CAKBURETS. [BULL. 14.

These wires were now exposed to the action of steam at 100° for a 

period of one hour, in an ordinary boiling-point apparatus. The measurement of thermo-electric position made on the following day showed

these values:

TABLE 10. Hard wires, lb at 100°.

No. 24» ...... ................

TSTn 91

t

°0.

16.9

16.9 

16.9

16.9

16.9

16.9 

16.9

16.9

T

°C.

59.4

50.7 

45.2

39.9

76.1

65.2 

54.7

46.0

e: 102 

observed.

microvolt.

-0. 069

-0. 025 

-0. 005

+0. 008

1.030

0.893 

0.750

0.599

e: 10* 

calculated.

microvolt.

-0. 069

-0. 025 

-0.005

-f 0. 008

1.029

0.890 

0.746

0.600

a

microvolt.

+0.61

1

I +2.75

'

5

microvolt.

-0. 0102

-0. 0109

'Neutralpoint: Cr+<)=-y=600.2j .-.2T=43°.3.

From a comparison of the values of a before and after annealing at 

100°, a variation of thermo-electric power, therefore also of mechanical 

state, is very'strikingly apparent; whence it follows at once that in 

the measurements of e, the use of boiling water in the hot receiver in 

the case of very hard wires is under no circumstances permissible. 

Indeed, from the magnitude of the variation in question, we infer that 

temperatures even much lower than 100° will show a tendency to produce an annealing effect seriously detrimental to a uniformity of the 

temper of the wire.

The above experiment was repeated. The rods were again annealed 

at 100° for a period of one hour, and thermo electrically examined on 

the following day.

TABLE 11. Hard loires, 2h at 100°.

No. 24'...... ................

No. 25....... ................

°C.

17.4

17.4 

17.4

17.3

17.3

17.3 

17.4

17.4

T

00.

73.8

64.7 

56.1

49.3

71.1

61.6 

53.4

46.7

e: 10*

observed.

microvolt.

0. 1'42

0.184 

0.183

0.162

1.256

1.093 

0.916

0.794

e:102

calculated.

microvolt.

0.152

0.174 

0.178

0.1G7

1.249

1.092 

0.932

0.787

microvolt.

1.26

1

I 3.64

'

b

microvolt.

-0. 0110

.

-0. 0150

* Maximum at 2?=-J-g-=57°.8 ; observed, y=18.5; calc., y=l7.S.

The results again show a smaller but nevertheless clearly pronounced 

variation of thermo-electric power, and we arrive at the important conclusion that, in addition to the temperature of the annealing bath, a second factor is essential in conditioning the resultant hardness, namely, 

the interval of time during which the annealing is prolonged, or the rod 

exposed to the given temperature.

(636)
BAEUS AND STBOUHAL.J STEEL ANNEALED IN STEAM. 45

With the object of discovering the nature of this time-effect, the ex^ 

periments were continued in the same way. The results are contained 

in the following tables:

TABLE 12. Sard wires 3h at 100°.

No. 24 ......................

No. 25 ......................

t

°0.

17.5

17.5 

17.5

17.5

17.5

17.5 

17 5

17.5

T

00.

74.1

62.0 

54.2

48.6

74.3

62.7 

53.8

-49.2

e: 10 2 

observed.

microvolt.

0. 329

0.316 

0.294

0.270

1.499

1.242 

1.033

0. 926

e:102 

calculated.

microvolt.

0.327

0.318 

0.294

0.269

1.497

1.245 

. 1. 033

0.926

a

microvolt.

0.161

1

I 3.55

'

b

microvolt.

-0.0111

-0. 0100

TABLE 13. Sard wires 4h at 100°.

No. 24......................

No. 25 ......................

t

°C.

17.7

17.7 

17.7

17.7

17.7

17.7 

17.7

17.7

T

°0.

86.4-

77.5 

G6.4

54.7

87.4

76.1 

67.7

59.5

e:10* 

observed.

microvolt.

0.484

0.480 

0.444

0.379

1.886

1.660 

1.447

1.177

e : 102 

calculated.

microvolt.

0.487

0.477 

0.445

0.379

1.887

1. 648 

1.453

1.182

a

microvolt. \

I 1. 76

J

3.77

b

microvolt.

-0.0101

-0. 0102

TABLE 14. Sard wires 5h at 100°.

TCn 9d

No. 25 ......................

t

°C.

. 17.0

17.0 

17.0

17.0

17.1

17vl 

17.1

17.1

T

°0.

71.6

58.4 

44.5

34.5

75.0

62.1 

53.6

47.0

e:102 

observed.

microvolt.

0.560

0.477 

0.326

0. 233

1. 661

1.363 

1.136

0.952

e: 102 

calculated.

microvolt.

0.562

0.468 

0. 340

0.228

1.665

1.358 

1.138

0.954

a

microvolt.

1.70

..

I 3.90

^ .

b

microvolt.

-0. 0075

-0.0111

TABLE 15. Sard wires 6h at 100°.

No. 24. .....................

No. 25. .....................

t

°0.

17.5

17.5 

17.5

17.5

17.4

17.4 

17.4

17.4

I

°0.

82.6

57.1 

40.7

33.9

72.0

48.7 

36.3

27.5

e: 102 

observed.

 microvolt.

0.637

0.483 

0.319

0.230

1.628

1.018 

0.648

0. 351

 e : 102 

calculated.

microvolt.

0 641

0.483 

0.329

0.236

i r.^9

1.019 

0.642

0.355

a

microvolt.

' 1.92

.

i 4.02

J '

b.

microvolt.

-0. 0093

-0. 0115

(637)
46 IRON-CARBURETS. [BULL. 14.

Digest. The relation between a and the time of exposure is more perspicuously apparent in the following comparison:

(24).........-....... ........................... a-

(25) ...................................... ..........aOh

-2.83

+0.13

»

+0. 61

2.75

2h

1.26

3.64

3h

1.61

3 ^

4b

1.76

3 77

5*1

1 70

3

QA

6"

1.92

4.02

From this grouping of parallel results, or, more evidently still, from a 

graphic representation (time as abscissa, thermo-electric constant as 

ordinate, mean values of Nos. 24 and 25, figure 9), it will be seen that

+ S-00

*2

+ 7-

-1-OO

"h.

Time.

FIG. 9.-Hard wires annealed for six consecutive hours in steam at 100°.

hardness varies continuously with the time of exposure of the glasshard rod to the given annealing temperature; that the amount of thermo-electric change rapidly decreases as the time increases, until finally 

a definite and superior limiting value is asymptotically reached.29 

After these introductory experiments we determined to investigate2aAmong the above results the individual values of a, 1.70 for the first and 3.77 for 

the second rod, require comment. It is obvious that from the four observations for 

each, probably affected with larger errors than usual, the method of least squares 

has not derived the constants in closest accordance with fact. This betrays itself in 

the values obtained for 6, which differ largely from the average values. The constant 6 varies but slightly (as a general mean 6=0.0100 maybe accepted). Associated with the values of a in question, however, we have 6=0.0075 (corresponding 

to the small result «=1.70) and &=0.0102 (corresponding to the large result a=3.77). 

But in view of the fact that the function of which a is the coefficient is positive, and 

that in which 6 is involved, negative, the errors of both a and 6 are partially eliminated in the sum, so that observed e and calculated e are again in satisfactory accordance.

(638)
BABU8 AND 8TROUHAL.] STEEL ANNEALED AT 66°. 47

the phenomena of annealing more rigidly, giving the effect of time of 

exposure due prominence. Besides the boiling point of water, that of 

methyl alcohol at 66°.0 and that of aniline at 185° were chosen for annealing, the wires being suspended in vapors of these substances circulating in a glass boiling-point apparatus. A still higher temperature 

(330°) was furnished by the melting point of lead. Batches of three 

wires of different diameters and different degrees of glass-hardness were 

selected to be annealed respectively at each of these temperatures. To 

trace the effects resulting, simultaneous determinations, both of thermoelectric power and conductivity, were made at as many stages of the process as appeared desirable. The data are contained in the tables 16-28*

BEHAVIOK OF HARD STEEL ANNEALED IN VAPOR OF BOILING 

METHYL ALCOHOL (66°).

The rods selected were:

No. 285 diameter (2p)=0.0827 cm., 

No. 29; diameter (2p)=0.0631 cm., 

No. 30; diameter (2p)=0.0479 cm.

After the thermo-electric power (microvolts) and specific resistance 

(microhms) for the glass-hard state had been determined, the wires were 

subjected to the annealing influence of vapor of methyl alcohol at 66° 

for three consecutive hours, and at the end of each hour examined by 

the aid of the electrical qualities in question. The results are these:

TABLE 16. Hard steel annealed at 66°. 

o. 28. 2p=0.0827.]

BemarkS;

lh in vapor of methyl alcohol, t=66°.0.

lhmorein vapor of methyl 

alcohol, t=66°.0.

lh more in vapor of methyl 

alcohol, t=66°.0.

t.

18.7

18.7 

18.7 

18.7

18.1 

18.1 

18.1 

18.1

18.3 

18.4 

18.3 

18.4

20.0 

20.0 

20.0 

20.0

T

54.8

48.9 

43.4 

35.6

58.2 

52.4 

47.9 

42.0

58.5 

49.4 

42.9 

38.7

60.6 

51.5 

46.4 

39.4

observed.

microvolt. 

-1. 003

-0. 907 

-0.721 

-0.495

-1.033 

-0.932 

-0. 792 

-0. 629

-0. 968 

-0.785 

-0. 601 

- 0. 497

-0. 956 

-0. 767 

-0. 625 

-0.453

e : 10J 

calculated.

microvolt. 

-0. 999

-0. 904 

-0. 731 

-0. 492

-1. 027 

-0.937 

-0. 798 

-0.626

-0. 964 

-0.787 

-0. 608 

-0. 492

-0. 947 

-0.774 

-0. 632 

-0. 448

a

microvolt.

j. -2. 56

\ -1.94

J -u,

> -1. 58

b

microvolt.

-0. 0064

-0.0111

-0. 0107

-0. 0122

s;

cm to

microhm.

42.64

42.55

42.45

42. 55

<

°0.

w

IS

19

18-

(639)
48 IRON-CARBURETS.

TABLE 17. Hard steel annealed at 66°. 

[KodNo. 29. 2p=0.0631.]

[BULL. 14.

Eemarks.

Glass-hard ...............

lh in vapor of methyl alcohol, t=66°.0.

lh more in vapor of methyl 

alcohol, t=66°.0.

lb more in vapor of methyl 

alcohol, t=66°.0.

t

OQ.

18.7

18.8 

18.7

18.8

18.2 

18.2 

18.2

18.2

18.5 

18.5 

18.5

18.5

19.9 

19.9 

19.9

19.9

T

°a

50.4

44.5 

38.8

34.8

57.7 

51.7 

45.8

40.4

57.2 

49.4 

43.9

40.1

61.4 

53.2 

45.3

41.1

observed.

microvolt.

-0. 696

-0.564 

-0. 429

-0. 343

-0. 704 

-0. 579 

-0. 467

-0. 378

-0.636 

-0. 487 

-0.385

-0. 324

-0. 624 

-0.469 

-0. 334

-0.280

e:10J 

calculated.

microvolt.

-0. 697

-0.559 

-0. 432

-0.342

-0. 702 

-0. 581 

-0.467

-0. 378

-0.639 

-0.486 

-0. 387

 0. 321

-0.620 

-0.471 

-0.340

-0. 275

a

microvolt.

-1.90

I -1.25

J

I -0.91

J

I -0. 70

J

b

microvolt.

-0. 0044

-0. 0076

-0. 0098

-0. 0098

st

crn

microhm.

42.08

41.70

41. 52

41.42

t

o<7.

17

18

19

19

TABLE 18. Hard steel annealed at 66°. 

[Rod No. 30. 2p=0.0479.]

Remarks.

Glass-hard ...............

lb in vapor of methyl alcohol, t=66°.0.

lk more in vapor of methyl 

alcohol, t=66°.0. '

lhmore in vapor of methyl

alcohol, fc=66°.0. 1

t

o(7.

18.7

18.7 

18.7

18.7

17.8 

20.1

19.2 

19.2

19.2

19.2

19.2

19.8

19.9 

19.8

19.9

° T

°0.

54.2

45.3 

40.2

34.4

56.9 

45.1

59.1 

54.5

49.0

42.6

38.4

54.6

49.7 

45.0

38.2

e: 102 

observed.

microvolt.

 0. 335

-0. 223 

-0. 175

-0.126

-0. 209 

-0. 117

-0. 105 

-0. 079

-0. 054

-0. 031

-0. 023

-0. 003

+0.-009 

0.015

0.018

calculated.

microvolt.

-0. 329

-0. 229 

-0. 178

-0. 124

-0. 209 

-0. 117

-0. 103 

-0. 079

-0. 055

-0. 032

-0. 021

-0.002

+0.008 

0.014

0.018

a

microvolt.

-0.42

] -o: 01

1

!> +0. 30

]

}

+0.47

b

microvolt.

-0. 0071

-0. 0070

-0. 0074

-0.0065

St

cm

microhm.

37.08

36.80

36.51

36.42

t

°C.

18

18

18

19

iNeutral point: (T-M)=-?=72.5; b

(640)
BAKU8 AND 8TKOUHAL ] STEEL ANNEALED AT 100°. 49

BEHAVIOR OF HARD STEEL ANNEALED IN STEAM (100°).

The rods selected were: .

No. 31; diameter (2p) =0.0839 cm., 

No. 32; diameter (2p)=0.0616 cm., 

No. 33; diameter (2p)=0.0491 cm.

Our earlier experiments with rods Nos. 24 and 25 had shown that the 

effect of annealing in steam is particularly marked during the first hour 

of exposure. We therefore decided to obtain intermediate stages by 

making interruptions and examinations after each of the first 10, 30, and 

60 minutes of this interval. After this the rods were annealed during 

two hours more, as above. The results for the hardness in the original 

(glass-hard) and subsequent states are fully given in the following 

tables:

TABLE 19. Hard steel annealed at 100°.

*

[Rod No. 31. 2p = 0.0839. J

Remarks.

Ulass-hard....... .......

10m in steam at 100° ......

20m more in steam at 100°.

30 more in steam at 100°.

lfc more in steam at 100° . .'

1* more in steam at 100°. .

t

°C.

22.5

22.5 

22.4

22.4

19.7

19.7 

19.7

19.7

18.5

18.5 

18. 5

18.5

18.1

18.1 

18.1

18.1

18.2

18.2 

18.3

18.3

19.2

19.3 

19.2

19.3

T

°C.

£5.2

51.3 

44.9

39.6

61.0

55.4 

48.7

42.9

76.0

65.7 

49.4

37.5

63.5

50.9 

50.0

44.5

72.4

58.8 

51.0

45.4

71.4

61.4 

55. 2

47.2

e:102 

observed.

microvolt.

-0. 621

-0. 542 

-0. 410

-0.303

-0.335

-0.266 

-0. 202

-0. 150

-0. 177

-0. 094 

-0. 009

+0. 006

+0. 122

0. 126 

0.118

0.107

0.330

0.304 

0.270

0.242

0.457

0.410 

0.371

0.314

e-.lW 

calculated.

microvolt.

-0.624

-0. 539 

-0. 409

-0. 304

-0.332

-0.269 

-0. 202

-0. 150

-0. 170

-0. 095 

-0.018

+0. 009

+0. 124

0. 125 ' 

0.118

0.107

0.329

0.304 

0.271

0.241

0. 455

0.410 

0.374

0.312

a

i

microvolt.

-1.20

j

1 -0. 08

J

1

I -|-0. 55

J

-I

I 0.86

J

1.55

^

I 1.81

J

6

microvolt.

.-0.0093

-0. 0090

-0. 0090

-0.0072

-0. 0104

-0. 0103

st

cm t

cm2

microhm.

40.47

39.05

37.64

36.33

35. 38

34.72

t

°C.

21

20

19

19

18

18

Bull. 14-

(641)
50 IRON-CARBURETS. [DOLL. 14.

TABLE 20. Hard steel annealed at 100°. 

lRodNo.32. 2p« 0.0616.]

Remarks.

Glass-hard .......... ....

10m in steam at 100° ......

20m more in steam at 10001 .

80 more in steam at 100°.

1* more in steam at 100° . .

1* more in steam at 100". .

(

°C.

20.7

20.7

20.7

1Q 9 jy. u

19.3 

19.2

19.3

18.5

18.5 

18.6

18.6

18.0

18.0 

18.0

18.0

17.7

17:7 

17.7

17.7

19.2

J9.3 

19.2

19.2

T-

°C.

50.7

46.0

41.9

56.7

53.4 

44.7

40.4

70.1

63.6 

56.0

44.8

59.1

49.6 

44.7

41.4

55.7

49.5 

41.8

36.4

67.3

58.9 

52.0

45.8

o: 10J 

observed.

microvolt.

-0. 639

-0. 545

-0.437

 0. 269

-o! 235 

-0. 168

-0. 137

0.075 0. 090- 

0.094

0.088

0.291

0. 260 

0. 225

0.201

0.519

0.451 

0.357

0.288

0.754

0.650 

0. 556

0.463

e: 103 

calculated.

microvolt.

-0. 659

-0.544

-0. 448

-0. 266

-0. 238 

-0. 168

-0. 136

0.075

0.088 

0.094

0.088

0. 294

0.253 

0.225

0.203

0 0.519

0.451 

0.359

0.287

0.754

O.C48 

0.556

0.463

a

microvolt. \

S -1. 44

)

 >

i -0. 39

J

1

t 0.80

J

^

I 1.39

J

i

I 2.01

J

 j

I 2,26

' '

b

microvolt.

-0. 0106

-0. 0042

-0. 0075

-0. 0086

-0. 0089

-0. 0080

SI

 cm t

cm2

microhm.

41. 42

39.53

38.02

36.33

35.19

34.34

t

°C.

21

20

0

19

19

18

18

'Maximum at T= j2 = 53°.l. . 

o

TABLE 21. Hard steel annealed at 100°. 

[EodNo.33. 2p = 0.0491. |

Remarks.

Glass-hard ........ ......

10m in steam at 100° ......

20m more in steam at 100°.

30m more in steam at 100°.

lk more in steam at 100°. .

lh more in steam at 100°. .

t

°C.

20.5

20.6 

20.6

20.6

19.2

19.2 

19.2

19.2

18.4

18.4 

18.4

18.4

18.0

18.1 

18.0

18.1

18.0

18.0 

18.0

18.0

19.3

19.3 

19.3

19.3

T

°C.

57.0

52.3 

45.9

41.2

of. 6

51.7 

44.4

37.8

53.2

44.7 

37.5

32.5

56.3

47.8 

41.9

32.0

66.1

58.6 

51.4

42.1

67.3

58.1 

50.2

40.8

e: 102 

observed.

microvolt.

-0. H79

-0.307 

-0. 226

-0.170

0. 15'L

0. 142. 

0.124

0.100

0.361

0. 294 

 0. 221

0.163

0.632

0.517 

0.418

0.256

0.881

0.795 

0.670

0.500

1.071

.0. 895 

0.737

0.521

e: 10* 

calculated.

microvolt.

-0.381

-0. 306 

-0. 224

-0. 171

' 0.150

0. 142 ' 

0.124

0. 100

0.364

0.290 

0.218

0.166

0. 634

0.510 

0.423

0. 257

0.893

0.783 

0. C68.

0.504

1. 070

0^897 

0.737

0.521

a

microvolt.

-0;07

 j

\ 0.97

J

^

I 1.50

j

1

I 2.25

J

1

> 2.67

J

1

> 3.00

 1

b

microvolt.

-0. 0122

-0. 0070

-0. 0062

-0. 0079

-0.0097

-0.0090

st

cm-. "cm*

microhm.

36.93

35.00

33.58

32.20

31.2:

30. 67

t

°C.

21

20

19

19

18

18

(642)
BABUS AND BTROUHAL.] STEEL ANNEALED AT 185°. 51

BEHAVIOR OF HARD STEEL ANNEALED IN VAPOR OP BOILING

ANILINE (185°).

The details of the operations in this case were the same as those described in the foregoing paragraph. The rods used were:

No. 34; diameter (2/>)=0.0835 cm., 

No. 35 : diameter (2p)=0.0627 cm,, 

No. 36; diameter (2p)=0.0481 cm.

The results obtained are the following:

TABLE 22. Hard steel annealed at 185°. ' 

[Hod NO. 34. 2p=0.0835.]

Remarks.

Glass-hard. ..............

10m in vapor of aniline at

185°.

30m more in vapor of aniline at 185°.

30m more in vapor of aniline at 185°.

lb more in vapor of aniline at 185°.

I* more in vapor of aniline at 185°.

t

°C.

22.1

22.1 

22.1

22.0

19.5

19.5 

19.5

19.5

18.7

18.7 

18.7

18.7

18.2

18.2 

18.2

18.2

18.2

18.2 

18.2

18.2

19.3

19.3 

19.3

19.3

T

°C.

59.2

51.1 

44.2

39.5

71.0

62. 8 

52.8

43.6

77.5

59/8 

'49.7

42.9

71.0

65.1 

50.9

45.9

70.9

68.2 

61.1

52.5

88.5

74.3 

65.9

58.4

e: 102 

observed.

microvolt.

-0. 573

-0. 422 

-0. 313

 0. 239

1.414

1.235 

0.981

0.722

2.694

1.321 

1.025

0.81,7

1.717

1.5C8 

1.325

0.9&6

2. 054

1.895 

1.579

1.298

2.453

2. 043 

1.782

1.526

e: 10* 

calculated.

microvolt.

-0.509

-0. 425 

-0.313

-0. 238

1. 423

1.228 

0. 975

0.726

2.700

1.312 

1. 027

0.820

1.721

1. 562 

1.327

0.986

2. 052

1.899 

1.581

1.297

2.454

2.045 

1.779

1.528

a

mvsrovolt.

 -0.83

i

I 3.59

J

^

I 4.10

J

4.33

1

I 4.61

J

}

I 4.84 

'

b

microvolt.

-0. 0087

 0. 0090

-0. 0116

-0. 0121

-0. 0118

-0. 0121

At

cm

cm2*

microhm.

39. 34

29.25

28.02

27.17

26.32

25.65

t

°C.

21

20

19

10

18

18

(643)
52 IRON-CARBURETS. [BULL. 14.

TABLE 23. Hard steel annealed at 185°.

[Rod No. 35. 2p=0.0627.]

Remarks.

Glass-hard...............

10m in vapor of aniline at

185°.

.20m more in vapor of ani-' 

line at 185°.

S0m more in vapor of aniline at 185°.

lh more in vapor of aniline at 185°.

lh more in vapor of aniline at 185°.

t

°C.

22.1

22.2 

22.1

22.1

19.8

19.9 

19.9

19.9

18.5 

18.5 

18.6

18.6

18.1 

18.1 

18.1

18.1

18.3 

18.3 

18.3

18.3

19.2 

19.3 

19.2

19.3

T

°c,

56.5

50.4 

44.4

39.1

65.0

57.0 

49.2

42.6

75.6 

66.6 

56.2

45.7

72.7 

63.2 

56.0

48.0

69.4 

62.6 

55.4

45.3

73.5 

66.2 

57.6

48.7

e: 10« 

observed.

microvolt.

 0. 847

 0. 680 

-0. 538

-0. 402

1. 531 

1.292 

1.032

0.821

2.078 

1.812 

1.453

1. 082

2.189 

1.861 

1.604

1.294

2. 226 

1.962 

1.682

1. 256

2.452 

2.155 

1.806

1. 415 .

e: 10' 

calculated.

microvolt.

 0. 846

 -0. 684 

-0.534

-0.402,

1.532

1.297 

1.038

0.819

2.081 

1.808 

1.455

' 1. 078

2.189 

1.863 

1.602

1.294

2.223 

1.964 

1.686

1.254

2.450 

2.158 

1.807

1.414

a

microvolt.

-1.97

4.22

> 4.75

J

[ 5.18

J

1

5.42

I 5.64

[

b

microvolt.

 0. 0059

-0.0097

-0. 0118

-0.0128

-0. 0122

 0. 0122

Si

cmcm**

microhm.

42.45

28.58

27.26

26.04

25.29

24. 72

t

°C.

21

20

19

19

18

18

TABLE 24. Hard steel annealed al 185°.

[Rod No. 36. 2p=0. 0481.]

Remarks.

10m in vapor of aniline at

185°.

20m more in vapor of aniline at 185°.

30 more in vapor of aniline at 185°.

lh more in vapor of ani -

line at 185°.

lh more in vapor of aniline at 185°.

t

°C.

20.3

20.4 

20.3

20.4

19.2

19.2 

19.2

19.' 2

18.5 

18.5 

18.5

18.5

17; 8

17.9 

17.9

17.9

17.9

17.9 

17.9

17.9

19.2 

19.3 

19.2

19.3

T

°C.'

51.2

46.6 

41.8

38.6

71.8

63.7 

57.4

49.4

78.5 

64.3 

54.9

45.2

78.8

65.2 

55.5

44.7

72:0

64.7 

53.8

46.5

68.3 

58.0 

52.6

44.7

e: 102 

observed.

microvolt.

-0.279

-0. 222 

 0. 171

-0.137

2.069

1.793 

1.552

1.251

2.485 

1.968 

1.609

1.207

2.605

2.115 

1.726

1.259

2.447

2.178 

1.703

1.374

2.327 

1.'880 

1.632

1.273

« e : 102 

calculated.

microvolt.

-0.279

-0. 222 

-0. 170

-0. 138

2.071

3.787 

1.555

1. 250

2.483 

1.971 

1.605

1.208

2.603

2.108 

1.720

1.262

2.461

2. 163 

1.696

1.371

2.325 

1.876 

1. 641

1.269

a

microvolt.

-0.05

i

I 4.76

J

I 5.26

J

I

I 5.50

J

1

> 5.50

J

I 5.74

>

b

microvolt.

-0. 0121

-0. 0091

 0. 0115

 0. 0125

-0. 0106

-0. 0114

«t

cm

cm2 *

microhm.

37.17

25.85

24.91

24.15

23.58

23. 12

t

°C.

2t

20

19

19

18

IS

(644)
BARUS AND STROUHAL.] STEEL ANNEALED AT 330C. 53

BEHAVIOR OF HARD STEEL ANNEALED IN MOLTEN LEAD (330°).

From an inspection of the foregoing families of curves it appeared 

probable, in view of this relatively high temperature, that annealing 

effects of great magnitude would occur during the first minutes of exposure. Conformably herewith, the rods were subjected to 330° during 

consecutive intervals of lni , 30ni , and I1 ', and examined at the end of 

each of these times. The rods selected .were :

No. 37; diameter (2p)=0.0820 cm., 

No. 38 ; diameter (2p)=0.0616 cm. . 

No. 39; diameter (2p)=0.0483. cm. 

The following results were obtained:

TABLE 25. Hard steel annealed at 330°. 

[Rod No. 37. 2p=0.0820.]

Kemarks.

Glass-hard ...............

lm in molten lead at 330° .

30m more in molten lead

at 330°.

lh more in molten lead at

330°.

t

°C.

18.7

18.8

18.8

17.8

17.8 

17.8

17.8

18.5

18.5 

18.5

18.5

18.9

18.9 

18.9.

18.9

T

°C.

56.1

52.7

51.8

77. 5'

67.5 

59.2

46.9

86.7

75.2 

02.3

50.7

69.0

57.2 

47.6

39.4

e -. 102 

observed.

microvolt.

-0. 248

-0.215

-0. 206

3.898

3.308 

2.800

2.012

4.491

3.806 

3.003

2.252

3.471

2.C67 

2.045

1.472

e : 102 

calculated.

microvolt.

-0.248

-0.215

-0.206

3.898

3.308 

2.799

2.012

4.491

3. 808 

3.005

2.251

3.458

2.685 

2.038

1.470

a '

microvolt.

 v

> 0.00

)

7.74

 v

I 7 77

j

\

!> . 7. 71

j

6

microvolt.

-0. 0089

-0. 0126

 -0. 0113

-0. 098

st >

cm

cm2 '

microhm.

36.51

18.96

18.78

18.78

(

oC.

18

18

19

19

TABLE 26. Hard steel annealed at 330°. 

[Hod No. 38. 2 p=0.0616.]

Remarks.

Glass-hard ...............

*

lm in molten lead at 330° .

30m more in molten lead

at 330°.

l h more in molten lead at

330°.

t

°C.

18.8

18.8 

18.8

18.8

17.6

17.7 

17.7.

17.6

18.8

18.9 

18.9

18.9

19.1

19.1 

19.1

19.1

T

°C.

50.2

44.8 

39.6

34.8

67.6

61.3 

53.1

42.7

87.8

73.4 

63.7

50.3

84.4

03.3 

50. 1

41.7

e : 102 

observed.

microvolt.

-0. 577

-0.459 

 0. 357

'-0. 271

4012

3.532 

2. 998

2.083

5. 470

4.413 

3. 794

2.631

5.204

3.649 

2.610

1.936

e : 10? 

calculated.

microvolt.

-0. 573

-0.461 

-0. 360

-0.269

4.015

3. 531 

2.998

2.084

5.470

4.417 

3. 784

2. 633

5.201

3.649 

2.C15

a

microvolt.

-1.19

^

I 8.96

j

^

I 9.24

J

1

i 9.39

1.93-2JJ

6

microvolt.

-0. 0093

-0. 0111

-0. 0124

-0. 0138

St

cmcm"*

microhm.

40.38

17.55

17.36

17.27

t

°C.

18

18

10

19
54 IRON-CARBURETS.

TABLE 27. Hard steel annealed at 330°. 

[Wire No. 39. 2p=0.0483.]

[BULL. 14.

Remarks.

1»> in molten leaf, at 330° .

30 more in molten lead

at 3300.

1* more in molten lead at

330e.

t

°C.

18.0

18.1

18.1

17.5

17.5 

17.5

17.5

19.1

19.1 

19.1

19.1

19.0

19.0 

19.0

19.0

T

°C.

53.8

50.7

48.1

56.6

51.7 

45.8

39.6

85.6

72.9 

61.9

50.4

82.5

66.7

57.8

49.5

e:102 

observed.

microvolt.

 0. 254

-0.221

-0. 195

2.647

2.335 

1.943

1.540

4.372

3.610 

2. 937

2.180

4. 218

3.255 

2.687

2.142

e:102 

calculated.

microvolt.

0.254

-0. 221

-0. 194

2.646

2.334 

1.948

1.537

4.372

3.615 

2.929

2.182

4.217

3.254 

2.687

2.142

a

microvolt.

 \

[ 0.08

)

7.61

7.76

1

I 7.80

'

b

microvolt.

-0.0110

-0. 0114

-0. 0113

-0. 0115

«(

cmcm2 '

microhm.

36.04

18.30

18.11

18.02

(

°C.

18

18

19

19

GENERAL DISCUSSION OF THE RESULTS OF THIS "ANNEALING.

Digest. The results thus far given adequately exhibit the general 

physical character of the process of tempering. For the sake of clearness, and with a view of partially eliminating such discrepancies as are 

. due to incidental errors, the three individual values of thermo-electric 

power and specific resistance for each of the temperatures of annealing 

will be combined and their mean chosen for discussion. We thus arrive 

at the following relations:

TABLE 28. Mean results:

I. For annealing in vapor of boiling methyl alcohol (66°). ,

Time of anuealing= 

a=

0* 

-1.62

!»> 

 1.07

2>- 

-0.80

& 

 0.60

II. For annealing in steam (100°).

Time of annealing= 

a=

0>> 

 0. 91

£h 

0.17

4" 

0.95

1» 

1.50

21" 

2.08

3h 

2.36

III. For annealing in vapor of boiling aniline (185°).

Time of annealing= 

o=

Oh 

 0.95

i" 

4.19

ih

2

4.71

lh 

5.00

2b 

5.18

3* 

5.40

IV. For annealing in molten had (330°).

Time of annealing.^ 

a=

O b 

 0.37 8*11 8.26

S b 

8.30

(646)
BABUS AND BTUOUHAL.] ANNEALING GENERAL RESULTS. 55

Deduction. If these functionalities are constructed graphically, as has 

been done in Fig. 10 (time as abscissa, thermo-electric constant as ordi9-00

8-00

7-00

5-00

S

R. 

3-00&

1-00

-1OOO '

~33O'

 WO'

Tine of ejcposwe

Fin. 10. Hard wires annealed continuously at 0°, CC°, 100°, 185°, 330°, and 1,000°, respectively.

nate), we obtain a family of typical curves, the general character of 

which is distinctly pronounced and may be thus expressed:

The degree of hardness retained by a glass-hard rod, after having 

been subjected to the operation of annealing, is dependent both on the 

temperature to which it has beeu exposed aud on the interval of time 

during which this exposure has taken place, in such a way that the 

effect of time, though of predominating importance in the case of small 

values of temperature, is more and more negligible in proportion as

(647)
56 IRON-CARBURETS [BULL.H.

these values increase. The operation is always most effective in its 

earlier stages, and this efficiency decreases very slowly where the temperatures are low very rapidly, indeed almost suddenly, where they are 

high. If the action of any temperature be indefinitely prolonged^ the 

rod under its influence ultimately reaches an inferior and limiting degree of hardness characteristic both of the temperature chosen and the 

type of steel under experiment. In other words: the annealing effect 

of any temperature increases gradually at a rate diminishing continuously through infinite time, very slowly in case of low temperature 

(<100°), with extreme rapidity in case of high temperature (>200°), 

so that the highest of the inferior states of hardness possible at any 

given temperature is approached asymptotically. The effect of the intensity of glass-hardness (strain) of the originally hard rod is not readily 

discernible.

The considerations set forth readily suggest the terminology: "maximum of permanent hardness for the temperature t" an expression which 

will be used throughout the sequel to designate the highest of the inferior states of hardness, persistent at the said temperature, t.

The relatively large effect produced by low temperatures (<100°), 

when a glass-hard rod is subjected to their influence for a long period 

of time, is deserving of special mention. It follows that a perceptible 

annealing effect must be attainable with temperatures much lower than 

the lowest above employed; indeed that the only inferior limit in this 

respect is probably the' temperature of the water in which the rod was 

originally chilled, while even the chilled, rod, though kept at constant 

temperature, cannot be regarded as existing in a state of thorough 

molecular equilibrium until the lapse of a considerable interval of time 

after the hardening has taken place. Herefrom it appears that in the 

thermo-electric experiments the danger of destroying the uniformity Of 

temper Of a glass-hard rod by overheating the hot junction is greatly 

to be apprehended. Quick work and low temperatures are, therefore, to 

be preferred at an unavoidable sacrifice of accuracy. Nor is soldering 

of the ends permissible, except with the most extreme and intelligent 

caution. We desire to advert, in conclusion, to the important bearing 

of this unlooked-for sensitiveness of hard steel, even to low temperatures, 

on all other physical properties depending on the temper of this material permanent magnetism for instance. It is obvious that the nature 

of a purely magnetic phenomenon can only be satisfactorily investigated 

when the material carrying the magnetic quality, throughout the course 

of the experiments undergoes no permanent change, otherwise we virtually commence our investigation with one rod and finish it with, 

another, obtaining data which are not immediately, if at all, comparable.

(648)
BAUUS AND STROUHAL.] SUCCESSIVE ANNEALING. 57

ON THE EFFECT OF HIGHER AND OF LOWER TEMPERATURES ON 

THE TEMPER OF STEEL ORIGINALLY ANNEALED AT A GIVEN 

INTERMEDIATE TEMPERATURE.

' Effect of lower temperatures. The marked tendency of glass-hard 

rods to suffer diminution of hardness, even when exposed to temperatures but slightly above mean atmospheric temperature, naturally led 

to another important inquiry almost the converse of the preceding. 

We refer to the behavior of a rod annealed at a given temperature 

to the prolonged effect of lower temperatures subsequently applied.

For the purpose of obtaining experimental data a steel wire (No. 26, 

2/3=0.085), which had on a former occasion been annealed'in an oil bath 

at 250°, was exposed to steam at 100° for one hour." The results of the 

thermo-electric measurements made before and after this final exposure 

were these:

TABLE 29. Steel annealed at /2C exposed to t\°, t2 ^> h

Before.

' t

16.1

16.1

16.2

16.2

16.2

16.2

T

89.1

80.7

68.1

54.6

44.5

37.9

c:102

4 05

3.62

2.9&

2.29

1.72

1.34

After.

t

16.9

16.9

16.9

17.0

T

73.2

63.2

56.5

50.2

e: 10s

3.17

2.69

2.32

1.98

e:lff>

(3. 22)

(2. 72)

(2. 35)

(1. 99)

The temperatures t in both series are approximately identical. The 

electromotive force e may therefore be regarded as dependent on the 

difference of temperature T t only,50 and with this presumption graphically represented. If, with the object of interpolating graphically, the 

two curves be carefully constructed, and the values of e for the temperatures of the one set of observations be derived from the curve for 

the other, then a comparison of corresponding values of e shows clearly 

that no annealing due to 100° is appreciable. In the table (29) the interpolated electromotive forces are distinguished by parentheses.

3°For e=a(T t)+lt (212 *S )=(T 0 (a+6 [T 1]+2 &«)=/ ( T~0 if * is constant.

(649)
58 IRON-CARBURETS. [BULL. 14..

This result was corroborated by a second experiment made in the 

same way with rod No. 27 (2p=O.OS5), which had been annealed in oil 

at 200°. The thermo-electric data obtained before and after the final 

annealing at 100° were:

TABLE 30. Steel annealed at U° exposed to <i°,

Before.

t

16.3

16.4

16.4

16.4

16.4

16.4

T

88.5

80.8

70.0

61.6

53.1

46.4

e:102

2.62

2.38

2.06

1.77

1.48

1.22

After.

t

17.0

17.0

17.1

17.2

T

84.2

71.7

62.3

43.4

e: 102

2.45

2.08

1.76

1.09

e: 102

(2. 45)

(2. 08)

a. 77)

(1. 09)

Plainly these results admit of the following generalized interpretation: A steel rod, annealed at a given temperature, will remain themore nearly passive as regards the effect of an inferior temperature, the 

lower its value and the shorter its time of application on the one hand, 

and the nearer the mechanical state of the rod to the limit of hardness 

for the said temperature on the other. Where the limit in question has 

been fully reached the rod is unaffected by the action of lower temperature, however prolonged.

Effect of higher temperatures. There is'another question of a similarly 

important bearing on the nature of the phenomena of annealing. In 

the above we drew the general inference that in the case of a given rod 

possessing a given degree of glass-hardness, the mechanical state resulting after annealing is dependent on the temperature and the time 

of exposure only; that when the latter is indefinitely prolonged, a particular and characteristic limit of hardness is reached for each temperature of the annealing bath. If this be the case, then it must be immaterial, iu so far as the identity of the final states is concerned, whetherj. 

for instance, a rod is first annealed in steam at 100° and then in aniline 

vapor at 185° to a limit, or whether it is annealed to a limit in aniline 

vapor at once. In other words, the maximum, reduction of hardness 

attainable by the action of any given temperature on glass-hard steel 

is independent of the manner of variation of hardness (the path as itwere) by which this final state is reached. On this point the following 

experiments were made:

Three steel wires of different thicknesses (Eos. 40, 41, 42), carefully 

tested for longitudinal homogeneity, were first examined in the glasshard state. They were then broken in two, and one of the halves of 

each was annealed directly in aniline vapor at 185° for 10 minuses; the 

others, however, were first exposed in steam at 100° for 40 minutes, and 

after this, as in the former case, for 1.0 minutes in aniline. Hereupon 

the six rods were tested for hardness, with the following results. It

(650)
BAEUS AND 6TUOUBAL.] SUCCESSIVE ANNEALING.

was expedient to make measurements of resistance only, Hockin and 

Matthiessen's method being employed:

In steam and in aniline vapor.

Rod If o. 40 (2p-0. 085) .................... |

Rod No. 41 (2p-0. 064) .................... j

Rod No. 42 (2p-0. 049) .................... |

Mean .................................... j

Glass-hard. 8=41.3

Glass-hard. 8=43.0

Glass-hard. 8=36.4

Glass-hard. 8=40.2

In aniline vapor only.

8=40.6

8=42. 9

o. to. o

8=36.5

8=20.0 

8=40.0

8=28. 8

(<=14°)-

(«=140)

(t=14°)

«=14°)

A second experiment was made with three other wires (Nos. 43, 44, 

45). After the hardness for^the glass-hard state had been obtained,, 

the rods were again broken in two; one of the halves of each was annealed for 40 minutes ia ethylic alcohol vapor at 78°, and then for 6 

hours in steam; the others in steam only during the same interval. 

The results obtained are these:

In vapor of alcohol and in steam.

RodNo.43 (2p-0. 085) ................... -^

Rod No. 44 (2p-0. 006) .................... j

RodNo. 45 (2p-0. 049)..... ....... :.......|

Mean ..................................... J

Glass-hard .

Glass-hard .

Glass-hard

Glass-hard .

.8=40.2

. O l>.l *)

.8=40.6

.s=35. 5

.8=i!8.7

. a itf. o

In steam only.

8=40.6

O = O 1 . O

«=41.2

8=35. 8

8=39.2

b L\y. I

(t=10°)

(«=10°)

(t=10°)

(£=10°)

Both of these series of experiments are in perfect accord, and we 

therefore infer: The specific effect of a given temperature of annealing 

on the state of hardness of steel is independent of the possibly preexisting, effects of a lower temperature, to the extent that the result of the 

influence of the latter is the more fully annulled the greater the period 

of action of the former.

Anomalous feature. This result is remarkable, inasmuch as by a sudden exposure of a glass-hard rod to (high) temperature, a very large 

amount of potential energy is instantaneously released. If, therefore, 

two identical glass-hard wires be annealed, the one by raisiug'the temperature very gradually as far as £°, the other by being suddenly exposed to i°, we would infer, ceterisparibus, that a difference of hardness 

must result. For, in view of the sudden conversion of the available 

mechanical energy into heat in the latter case, we anticipate an equivalent increase in the temperature of the rod. Virtually, therefore, this 

steel is annealed at a temperature somewhat above that of the annealing bath, or above that of the other rod. So far as our experiments 

 went this was not detected; but the test made is not exhaustive. Our 

attention was centered on other matters at the time. Possibly, however, the anomalous distribution of hardness obtained by annealing in 

oil may be partially accounted for in this way.

(651)
60 IRON-CARBUEETS. [BULL. 14.

BEHAVIOR OF SOFT ST^JEL RODS.

Object of the measurement. The above values for thermo-electric power 

all refer to elements in which steel is thermo-electrically combined with 

pure soft silver; but the latter metal, though chosen expediently, is 

otherwise arbitrary and without inherent bearing on the subject in 

hand. We will undoubtedly obtain data more in harmony with the

 purpose of the present investigation, and far more readily intelligible, 

by eliminating this foreign metal from our considerations entirely. It 

is to be our endeavor throughout the following paragraphs not only to 

add to the perspicuity of our data, but also to give them, possibly immediate theoretical significance, by referring all measurements to a 

particular and normal state of steel. The soft state would appear to 

suggest itself in so far as it occupies an extreme and inferior position 

in the scale. If, however, this is to be chosen as a point of departure, 

the rods in this state should possess normal and fixed thermo-electric 

qualities, even for different kinds of steel. This is by no means the 

case, as the special experiments presently to be detailed will show. 

Indeed, even in the case of soft rods nominally of the same material, at 

all events nearly of identical composition, the difference of thermoelectric power is often very marked.

Method of softening. With the object of reaching extreme values of 

the soft state, the rods were embedded in artificial powdered ferro-ferric 

oxide, as it falls from the anvil, and surrounded.by a closed gas-pipe; 

the latter in turn enveloped in a thick coating of fire-clay, protected 

externally with thin sheet-iron. The whole was heated to intense redness, and then allowed to cool very slowly in the ashes of the smoldering 

fire31 . The non-conducting envelopes insured a very gradual subsidence

 of temperature.

Data for soft steel and for soft iron. As examples the results obtained with rods Nos. 46, 47, and 48 will be given:

TABLE 31. Uchavior of soft sleel rods.

Remarks.

No. 46. 2p-*0. 0843 ......

No. 47. 2p=0.0625......

.No. 48. 2p=0.0485......

' 

°G.

18.7

18.7 

13.7

18.7

23.0

22.7 

22.6

22.4

19.0

19.0 

19.0

19.0

T

°C.

87.7

67.3 

54.2

45.5

85.7

63.1 

51.7

40.6

84.0

64.3 

50.8

37.9

e 

observed.

microvolt.

486. 3

354.8 

264.0

202.8

. 543.5

406.9 

266.9

169.0

474.7

338.4 

242.6

148.9

e 

calculated.

microvolt.

486.2

354 5 

264.6

202.6

544.8

405.5 

266.4

169.3

472.5

340. 1 

243. 9

148.0

a

microvolt.

1

I 8.33

)

^

> 10. 17

]

1

I 8.52

J

&

microvolt.

-0.0121

-0.0137

-0.0121

st

cm

cm"**

microhm.

17.08

15.09

16.41

t

°C.

19

19

19

31 With regard to the decarbonization possible/or incident to this operation see 

 Chapter III.

(652)
BARUS AND STKOUHAL.] BEHAVIOR OF SOFT WIRE. 61

For the sake of comparison iron wires of different kinds were treated 

in the same way and subsequently examined. The results obtained 

with Nos. I, II, and III will be cited as examples:

TABLE 32. Behavior of soft iron wire.

Remarks.

No. I. 2 p=0.0966 .......

No. II. 2 p 0.0630......

No. III. 2p=0.0312.....

t

°C.

18.7

18.8 

18.7,

18.8

18.6

18.6 

18.6

18.6

18.5

18.5 

18.5

18,5

T

°C.

79.6

66.3 

64.3

44.9

78.0

64.2 

53.4

43.4

86.9

68.1 

54.3

40.1

e 

observed.

microvolt.

581.3

465.4 

356.3

£64. 7

550.2

430.1 

332.6

241. 6'

500. 2

418.0 

310.3

190.7

e 

calculated.

microvolt.

582.0

464.9 

355.8

265.0

549.5

430.3 

333.6

241.1

560.0

419.1 

309. 3

190. 9

a

microvolt. ~\

^ 11.25

J

10.56

'

^

1 9.66

[

b

microvolt.

-0.0174

-0. 0135

 0. 0140

fie

cm

cm2 '

microhm.

13.02

12.74

13.87

t

°C.

19

19

19

Impurities in steel and iron. Now, there is reason to suppose that in 

the case of iron carburets generally the electrical effect of foreign impurities is partially masked by the phenomenally great effect of combined carbon.32 Conformably with the usually accepted views, therefore, 

the shifting of thermo-electric position due to the presence in iron of 

materials (.8., P., Si., etc.) other than carbon will be particularly marked 

for the soft states. For it is here that the quantity of combined carbon 

contained is at a minimum, while the steel itself is in a natural homogeneous state. We have analogies in.the case of alloys. For instance, 

on alloys of gold and silver small additional quantities of foreign admixtures are relatively without marked electrical effect, whereas if pure 

goldorpure silver be adulterated with the same quantities of the same material the result is pronounced. If we compare the values of a and s for 

soft iron with those obtained for soft steel the specific effect of carbon 

is strikingly obscure. We a.re induced to refer'the comparatively small 

differences apparent to the effect of foreign impurities in the iron. At 

least, in contrast with the phenomenal electrical interval between the 

glass-hard and the soft states of steel, the electrical effect of carbon i? 

here wholly masked by that of the incidental ingredients. But it is 

herewith fully demonstrated that the steel rod possessing the qualities 

of a normal must be sought for elsewhere than in the soft state.

32 Directly or indirectly. It will be shown in the sequel that the electrical variation 

discussed in this chapter is probably due to the strain accompanying hardness, but 

this in its turn is conditioned by the presence of carbon in iron.

(.653)
IRON-CARBURETS. [BULL. 14.

THE RELATION EXISTING BETWEEN THE THERMO-ELECTRIC POWER 

AND THE SPECIFIC RESISTANCE OF STEEL.

Reduction of data. In the above experiments we have thus far met 

with 86 pairs of correlative values of specific resistance and thermoelectric constant. We will supplement these results by values obtained 

wich four rods subjected to six hours of annealing in steam. They are 

as follows:

' Eod.

No. 49.....

No. 50.....

No. 51.....

No. 52.....

2P

0. 0574

0. 0554

0. 0531

0.0344

« 

a

1.90

4.08

4.06

3.90

««

35.75

29.34

27.08

28.68

t

,19

19

19

19

In all, therefore, we are in possession of 90. pairs of values. These 

amply suffice to decide in how far an intrinsic relation between thermoelectric power and specific resistance, in case of one and the same metal 

^steel), in different states of temper, demonstrably exists. Now we have

f I ______ de \i a. 

\ At T +\ ] )

\U ( J. t) / T=t

thence it appears that the thermo electric constant a primarily refers to 

the temperature zero, centigrade. It is, therefore, consistent to reduce 

the observed values of specific resistance (18° 21°) to the same temperature (zero). This is at best a laborious piece of work, and moreover presupposes a knowledge of the .relation of resistance and temperature (the coefficients vary within the large range of 0.1 per cent, 

nearly to above 0.4 per cent.) for each or' the 90 degrees of hardness 

encountered. But with the aid of the results contained in Chapter I 

of the present memoir this reduction may be satisfactorily made. The 

results are given in the following table, where s< =«(l-f-at):

(654)
BAUDS AND BTIIOUHAL.] FUNDAMENTAL CONSTANTS. ' 63

TABLE 33. Specific resistance (cm/cm* 0° microhm') of steel.

No.

1

2

3

4

5

6

7

8

9

10

11

12

13

14

. 15

16

17

18

19

20

21

22

23

.28

:28 28

:28

29 29

29

««

18. 96

18.49

20.54

20.00

17.64

20.75

22.74

23.20

20.47

25.67

24.81

22.93

20.66

27.36

28.11

20.70

27.93

31.32

28.68

24.34

29.34

30.94=

27.93

42.64

42.55

42.45

42.55

42.08

41.70

41.52

t'

19

19

19

19

19

20

19

19

19

19

19

19

19

20

19

19

19

19

19

19

19

19

19

18

18

19

19

17

18

19

aXlO3

3.4

3.5

3.1

3.3

3.6

3.2

2.9

2.9

3.2

2.6

2.7

2.9

3.2

2.5

2.4

2.5

2.4

2.2

2.4

2.8

2.3

2.2

2.4

1.6

1.6

1.6

1.6

1.6

1.6

1.7

8

17. 81

17.34

19.40

18.22

16.51

19.51

21.55

21.99

19.30

24.46

23.60

21.73

19.48

26.06

28.88

25.49

26.71

30.06

27.43

23.11

28.11

29.70

26.71

41.45

41.36

41.20

41.30

40.95

40.53"

40. 12

No.

29

30

30

30

30

31

31

31

31

31

31

32

32

32

32

32

32

33

33

33

33

33

33

34

343'1

34

34

34

35

«t

41.32

37.08

36.80

36.51

36. 42

40.47

39.05

37.64

36.33

35.38

34.72

41.42

39.53

38.02

36. 33

35.19

34.34

36.98

35.00

33.58

32.26

31.22

30.67

39.34

29.25

28.02

27.17

26 32

25.85

42.45

t

19

18

18

18

19

21

20

19

19

18

18

21

20

19

19

18

18

21

20

19

19

18

18

21

20

19

19

18

18

21

oXlO3

1.7

1.8

1.9

1.9

1.9

1.7

1.8

1.8

1.9

1.9

2.0

1.7

1.7

1.8

1.9

1.9

2.0

1.8

1.9

2.0

2.1

2.2

2.2

1.7

2.3

2.4

2.5

2.6

2.6

1.6

8

40.03

35.92

35.58

35.30

35.15

39.08

37.70

36.40

35.06

34. 21

33.50

39.99

38.23

36.76

35.06

34.03

33.14

35.64

33.72

32.35

31.02

30. 03

29.49

37.98

27.96

26.80

25.94

25.14

24.69

41.07

No.

35

35

35

35

35

36

36

36

36

36

36

37

37

37

37

38

38

38

38

89

39

39

39

46

47

48

49

50

51

52

«e

28.58

27.26

26.04

25.29

24.72

37.17

25.85

24.91

24.15

23.58

25.12

36.51

18.96

18.78

18.78

40.38

17.55

17.36

17. 25

36.04

18.30

18.11

18.02

17.08

15.09

10.41

35.75

29.34

27. 08

28.68

t

20

19

19

18

18

21

20

19

19

18

18

18

18

19

19

18

18

19

19

18

18

19

19

19

19

19

19

19

1919-

aXlO*

2.4

2.5

2.6

2.7

2.7

1.8

2.6

2.7

2.8

2.9

2.9

1.9

3.4

3.4

3.4

1.7

3.6

3.6

3.6

1.9

3.5

3.5

3.5

3.6

3.9

3.7

1.9

2.3

2.5

2.4

8

27.27

26.03

24.81

24.11

23.57

35.82

24.58

23. 69

22.93

22. 41

21 97

35.30

17.87

17.64

17.64

39.17

16 48

16.25

Hi. 16

34.85

17.22

16.98

16.89

15.98

14.05

15.34

34.51

28.11

25.85

27.43

Fundamental constants. For the sake of greater clearness in designation, let a be replaced by ;?/', so by x. Parallel variations of y' and x we 

have had frequent occasion to notice. But we have now the data in 

hand for a complete discussion of the nature of their mutual dependence, and this will manifest itself perspicuously and at once in a graphic 

representation with x as abscissa, y' as ordinate. Figure 11 contains 

the 90 points in question. They lie within a band or pathway which, 

as a rule, is narrow, especially so near its middle, but widens somewhat 

as we approach the lower extremity, where y'=0. Nevertheless, the 

character of the functionality involved within the given range of possible variation appears with due prominence. It is unquestionably linear.

We may, therefore, with great probability premise that between y' 

and x a relation of the form

y'=m nx ....... (1)

exists. If we make this equation the basis of a calculation in which the 

fundamental constants m and n are to be determined by the method of 

least squares we arrive at the values

w=15.176 w=0.4123 

:by solving the normal equations

P=mA-nB Q=mB-nC 

where

A = 2X° = 90 

B=2X =2536.55 

C=2X2 = 773.21 

P=2yl = 319.91 

=6612.1.

(655)
mON-CAKBUEETS. [HULL. 14. '

New thermo-electric data. Of these constants, m commands only secondary interest, in so far as it depends on the metal (silver in our case)

10-00

9-OO

S 00

7- 00

6-OO

5-OO

3- Of)

2-00

-1-00

Specific Resistance mzcrot rn.

-4-00

-z-on

FIG. 11. Diagram of the relation between the thermo-electric power of steel in different states of temper, and

its specific resistance.

arbitrarily chosen to fix a datum or point of departure for thermo-electric 

measurements. . This, however, is not true of m y', a quantity wholly

(656) '
BAUDS AND 8TROUHAL.1 THERMO-ELECTRIC HARDNESS. 65

independent of the arbitrary element in question. It therefore appears 

expedient to select m y'=h as a new thermo-electric variable, in which 

case (1) reduces to the simpler form h=nx. The new thermo-electric 

data (h, nx) thus obtained are exclusively dependent on qualities inherent in steel. They have no reference to metals (silver) foreign to 

the present purpose. From a mathematical standpoint m is the experimental constant by which a specially selected set of co-ordinates is 

determined. From a physical standpoint m would represent the thermoelectric constant of a couple, one member of which is silver, the other 

the imaginary steel rod, whose specific resistance, supposed diminishable 

indefinitely in accordance with the above law, is zero. It is this initial 

state of hardness (h o) at which the new variable h originates.

Thermo-electric hardness defined. The new thermo-electric variable, h, 

will, throughout the present memoir, be designated by the term thermoelectric hardness. The introduction of this quantity was Suggested to US 

by considerations similar to those which led to the conception of absolute temperature. To the absolute zero of temperature, however, Thomson has been able to give a concrete physical interpretation ; whereas 

the zero of thermo-electric hardness, so far as the results of the present 

chapter go, furnishes no more than a point of departure, at once convenient and free from arbitrary assumptions. It is hardly necessary to 

cite as a second example the hypothesis defining the modulus of elasticity, for instance.

The following is a brief summary of the advantages immediately derived from the introduction of thermo-electric hardness:

1. Hardness in the case of steel is expressed for the soft as well as 

for the hard rod in significant and at the same time convenient figures, 

which increase as this quality increases. The scale is, therefore, adapted 

to circumstances.

2. A change of signs is avoided, the current invariably flowing from 

the given specimen through hot to the normal. In other words, the 

normal is thermo-electrically positive to the whole family of iron-carburets, iron, steel and cast iron, no matter what be their mechanical state.

3. The results are independent of the shiftings of thermo-electric position common to all metals, due to small amounts^f impurity or difference of mechanical state.

4. By the aid of the coefficients discussed in chapter I and for the sake 

of concreteness of conception only, we may state that, theoretically, the 

normal condition of steel, to which thermo-electric hardness refers, would 

nearly be given by soft steel cooled down as far as the absolute zero of 

temperature. (See Chapter III.)

Tabular comparisons. A complete table follows, showing the differences between observed (h=m y') and calculated (nx) values of thermoBULL. 14 5 (657)
66 IRON-CARBUEETS. [BULL. 14.

electric hardness. As has been stated, the results are deduced by the 

method of least squares :

TABLE31 34. Comparison of the values of the thermo-electric hardness and specific resistance.

No.

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

28

28

28

28

29

29

29

h

7.38

7.15

8.19

7.40

6.66

7.94

9.03

8.72

8.22

10 51

10.03

8.78

8.29

11.12

11.33

10.51

10.92

12.39

11.35

9.73

11.42

11.77

10.94

17.74

17.12

16.99

16.76

17.08

16.43

16.09

nx

7.34

7.15

8.00

7.76

6.81

8.04

8.88

9.07

7.96

10.08

9.73

8.96

8.03

10; 74

11.08

10.51

11.01

12.39

11.31

9.53

11.59

12.25

11.01

17.09

17.05

16.99

17.03

16.89

16.71

16.54

Diff.

0.04

0.00

0.19

 0.36

 0.15

 0.10

0.15

 0.35

0.26

0.43

0.30

 0.18

0.26

0.38

0.25

0.00

 0. 09

0.00

0.04

0.20

 0.17

 0.48

 0.07

0.65

0.07

0.00

 0.27

0.19

 0.28

 0.45

No.

29

30

30

30

30

31

31

31

31

31

31

32

32

32

32

32

32

33

33

33

33

33

33

34

34

.34

34

34

34

35

h

15.88

15. 60

15.19

14.88

14.71

16.38

15.26

14.63

14.32

13.63

13.37

16.62

15.57

14. 38

13.79

13.17

12.92

15.25

14.21

13.68

12.93

12.51

12.18

16.01

11.59

11.08

10.85

10.57

10.34

17.15

nx.

16.50

14.81

14.67

14.56

14.49

16.11

15.54

15.01

14.45

14.10

13.82

16.49

15.76

15.16

14.45

14.03

13.66

14.69

13.90

13.34

12. 79

]2. 38

12.16

15.66

11.53

11.05

10.69

10. 37

10.18

16.93

Diff.

 0.62

0.79

0.52

0.32 .

0.22

0.27

 0. 28 ,

 0.38

-0.13

 0.47

 0.45

0.13

 0.19

0.78

 0. 66 |

 0.86

 0.74

0.56

0.31

0.34

0.14

0.13

0.02

0.35

0.06

0.03

0.16

0.20

0.16

0.22

No.

35

35

35

35

35

36

36

36

36

36

36

37

37

37

37

38

38

38

38

39

39

39

39

46

47

48

49

50

51

52

h

10.96

10.43

10.00

9.76

9.54

15.23

10.42

9.92

9.68

9.68

9.44

 15. 18

7.4-t

7.41

7.47

16.37

6.22

5.94

5.79

15.10

7.57

7.42

7.38

6.85

5.01

6.66

13.28

11.10

11.12

11.28

nx

11.24

10.73

10.23

9.94

9.72

14.77

10.13

9.77

9.45

9.24

9.06

14.56

7.37

7.27

7.27

16.15

6.79

6.70

6.66

14.37

7.10

7.00

. 6.97

6.59

5.79

6.32

14.23

11.59

10.66

11.31

Diff.

 0.28

 0.30

 0.23

-0.18

-0.18

0.46

0.29

0.15

0.23

0.44

0.38

0.62

0.07

0.14

0.20

0.22

 0.57

 0.76

 0.87

0.73

0.47

0.42

0.41

0.26

 0.78

0.34

 0.95

 0.49

0.46

 0.03

31 The second decimal place (h, nx, diff.) serves only, of course, to give greater accuracy to the first and might perhaps have been advantageously suppressed.

Distribution of errors. If this series of results is examined critically, 

that is with especial reference to magnitude and location of the errors, 

relatively large discrepancies encountered at the beginning of the table, 

in the case of very soft rods, are conspicuous. It is not, therefore, to 

be considered as finally decided whether the relation li=f(x) may not 

for small values of a? be other than linear; such, however, as rapidly to 

approximate to the latter form of function as x increases. The other 

'errors in general are as liable to assume positive as negative values; 

they lie within sufficiently narrow limits, and do not, with one exception, exhibit any characteristic progress for consecutive states. In the 

case of wires annealM in methyl alcohol a uniform succession of errors 

is,however, apparent. For continually decreasing values of h we have:

No. 28.....

No. 29.....

No. 30.....

7

2

8

1

 3

5

0

 5

3

 3

 6

2

In other words, with continually augmenting time of exposure, the 

temperature, 66°, produces an annealing effect such that the linear relation between thermo-electric hardness and specific resistance is not 

rigidly maintained. Here we have unquestionably the evidences of a

(658)
BAHUB ANB BTuouHAL.] THERMO-ELECTRIC POWER AND RESISTANCE. 67

structural phenomenon. The inference is plausible that the annealing 

influence of this comparatively low temperature is largely confined to 

those parts of the rod where the strain is most intense. This is probably the case with the superficial layers ; for, according to Fromrae's datum 

the density of these has been increased enormously. Now, it would 

seem that it is upon the surface layers of a rod that thermo-electric 

power is principally dependent, whereas specific resistance varies with 

the mean hardness of rod taken as a whole. The discrepancy in question is repeated with such uniformity in each of the three wires, that it 

is obvious we have in hand more than a mere error of observation. 

Furthermore, the similar variation which occurs in the case of wires 

annealed at 100° shows that the anomaly exists in steel itself, and is 

deserving of special inquiry.

Consequences of an elementary law, h=ns. A. more detailed analysis 

of the thermo-electric effects of structure does not substantiate the stated 

inference that the thermo-electric data are influenced to a greater extent 

by the condition of the surface layers of steel than the resistance data. 

From the very general evidence obtained in Table 34 in favor of the 

law 7i=ws, we are justified in giving it fundamental or elementary importance. In other words, the supposition is warranted that, for each 

of the coaxial necessarily homogeneous elementary shells of which we 

may suppose the rod to be made up, the relation

k=ns .......... (1)

applies. Suppose, now, we take into consideration any two such shells. 

Let «i, s2, AI, 7i2, 2i, % be their specific resistances, their thermo-electric 

hardness, and their right sections, respectively.

Let 812, 7i12> qi2=2i-f<fe, be the specific resistance, thermo-electric hardness, and right sections, respectively, of a single shell, which is capable 

galvanically and thermo-electrically to replace the two original shells 

(they are actually combined in multiple arc) in every respect. Then

and

£l «2

q\ <fc 

%= SA ^ ^ ' ' (3)

«i + <h 

It therefore follows, in view of equation (1), that

hn= (qi+q2 ) su=n slz

<?12

and in the same way generally

M

7i1? 2, 3 . . . =- ^ (#k) Si, 2, 3 =n8ij 2, 3 

<?1»2, 3 

That is, if the law h ns be true for the elementary (necessarily homo-

(659)
68 IRON-CARBURETS. [BULL. 14.

geneous) layers of the rod, then must it be true also for the rod taken 

as a whole, however complicated its structure may be, and whatever be 

the difference in the variation of the density of successive layers while 

annealing is in progress. The converse of this does not follow so readily.

The superficial layers of the steel, being the ones directly and Immediately operated upon in sudden cooling, will probably be the ones experiencing greatest intensity of strain. It may be plausibly argued, therefore, that the effect of incipient annealing is confined to these, or at least 

that the said layers expand at a far more rapid rate than the rod as a 

whole contracts. The law h=.ns may therefore be considered to apply 

with good approximation, both in the case of volume expansion and of 

volume contraction.

We may account for the progressive errors encountered in the case of 

hard wires annealed at low temperatures (<100°) from two points of 

view: Either the elementary law h=ns is not rigidly true throughout 

the phenomenal variation of density which the individual layers experience on tempering (probably from 7 to 10); in other words, 1i=f(s) is 

no longer rigidly linear when we approach the enormous condensation 

near the surface, for instance. Or, the discrepancy may be due to the 

facts observed by Caron32 that a hard-steel rod during the annealing 

contracts aeolotropically; i. e., not in like ratio both in the direction of 

its longitudinal and its radial axes. In such a case the law h=ns, conceded rigidly to hold good for isotropic strains, need no longer do so 

in the case in hand. This discussion will be advantageously resumed, 

in the light gained from further relevant data, in chapter III.33

SOURCES OF ERROR.

The difference between the observed and the calculated results of 

thermo-electric hardness, as exhibited in the last paragraph, pertinently 

suggest an especial inquiry in regard to how far they are referable to 

errors of observation. This involves an examination into the possible 

descrepancies incident to the various methods of measurement used.

Thermo-electric measurement. If we commence with the thermo-electric measurement we at once encounter a series of obvious sources of 

error which may be thus classified : Variation of the factor of reduction 

of the galvanometer, to be referred in part to fluctuations in the intensity of terrestrial magnetism, in part to the immediate influences due 

to changes of atmospheric temperature; the inconstancy of the electromotive force of the Daniell between the observations made for the 

determinations of the same; the effect of extraneous therino-currents in

32 Caron : Comptes rendus, LVI, p. 211, 1863.

33 Chapter III, p. 88.

(660)
BAUUS AND sTiiouHAL.] UNAVOIDABLE ERRORS. 69

the galvanic connections; and, finally, the difficulties surrounding an 

accurate measurement of the temperatures of the thermo-electric junctions, especially when they are high. The first two of these may be 

satisfactorily avoided by frequent repetitions of a series of systematic 

and corroborative measurements. The devices34 by which we endeavored 

to eliminate the third have already been fully described; nevertheless 

the distortion due to this cause is not thoroughly eliminable, and its 

effect will be most apparent in the case of small values of thermo-electric 

force. Steel wires lying very near pure silver in the thermo-electric 

scale are therefore apt to be seriously influenced. Conformably herewith, the column of "differences" in the foregoing table (34) shows large 

values when y' is approximately zero. But there is another reason for 

these relatively large discrepancies, which deserves mention as being 

even of more importance than the one just referred to. The thermoelectromotive force is expressed by the aid of two constants, thus 

e=a (T-t)+b (T -t2)

whence it follows that the accuracy of the constant a, resulting from 

the calculation, is conditioned to some extent by the accuracy of &; for, 

although the latter is usually small relatively to the former, it enters 

the equation

e=[a+b(T+t)](T-t)

as a co-efficient of the sum of the temperatures T and t. Now, an accurate measurement of & presupposes a large range of variation of the 

difference of temperatures T and t; and it is just here that in the case of 

glass-hard rods we encounter an unavoidable difficulty. Large values 

of T are inadmissible, because they change the temper of the exposed 

junction of the rod. It is equally inexpedient to cool t below zero. At 

least our attempts in this direction served only to convince us that the 

errors encountered in consequence of insufficient constancy of t more 

than counterbalance the advantages gained, to say nothing of annoyances of a practical kind. An inspection of some of the earlier tables 

will show that wherever the value of a is larger or smaller than was 

with good reason to be anticipated, this discrepancy is compensated by 

a similar error of &. Indeed the calculations from which the constants 

of the 90 series of experiments given above were derived, clearly show 

that a number of observations greater than four for each value of a is 

indispensable for an advantageous application of the method of least 

squares. This did not urgently appeal to us until the measurements 

were well in progress, and we were equally undesirous both of changing 

the routine adopted and of encountering additional labor in the calculations. Four observations, however, will not suffice where an accuracy of a within one per cent, is demanded. We also observed that

34 Cf. pp. 34-35. 

(661)
70 IRON-CARBURETS. [BULL. 14.

the correlative values of a and b were materially different, according 

as the equation

y 

or

z-= 

so

was assumed for the application of the method of least squares.

Resistance measurement. The values for specific resistance are liable 

to two sources of error. The first of these, which is due to variations of 

temperature, the results contained in Chapter 1 have enabled us largely 

to eliminate. The second error is of a more serious kind, and embraces 

the difficulties encountered in endeavoring to obtain values for the sections of (thin) rods. As the average thickness of our wires was only 

about 0.05 centimeter, it would have been necessary to measure the mean 

diameter to 4 010 0- centimeter in order to arrive at a mean section correct to within one per cent. This is not feasible, except with extreme 

precautions, either by the use of microscopic or gravimetric methods. 

In the case of thinner wires the difficulty is proportionately increased. 

Such errors as are due to imperfections of contact at the places of insertion of steel wires, etc., have been already touched upon.35 They were 

wholly avoided eventually by a change of method.

Other errors. In addition to the sources of errors just mentioned, 

such as are more intrinsically connected with the subject discussed, deserve consideration. It has been stated that the inference is warranted 

that the rods used were not quite identical as regards chemical composition, and that the electrical behavior of these, though alike in kind, 

may differ in degree.

CONCLUDING REMARKS.

A brief review of the general tenor of the results discussed in the 

above, in so far as they have a bearing on certain important consequences which we desire now to touch upon, will be in place here. We 

purposely avoid all remote theoretical speculations and confine ourselves 

to inferences immediately deducible from the facts.

Tempering. The physics of the process of tempering have thus far 

been but slightly understood; and it is therefore to the new light 

which the present chapter throws upon the essential features and results of this operation that we desire first to advert. Only cursory 

attention36 has hitherto been given to the phenomenal difference between

35 Cf. pp. 37-38.

36 In certain thermo-electric measurements incidentally made by Joule (Phil. Trans., 

1859,1, pp. 95-97). The results for variation of specific resistance of all earlier observers (Mousson, Chwolson) are erroneously small.

. (662)
IJAKUS AND-STEOUHAL.] SCHEME FOR ALLIED RESEARCHES. 71

the extremes of mechanical state: the glass hard and the soft. The 

largest thermo-electric interval observed in the"present work is 10.17 

( 2.60)=12.8; and the maximum ratio of the respective values of specific resistance, ff=3.0. It is this enormous range of variation of the 

electrical properties, together with the facility with which absolute data 

dependent merely on qualities essentially inherent in steel are obtainable, that would seem emphatically to recommend the scale of hardness 

here introduced to the attention of physicists. Furthermore, the 

method of annealing adopted enables the observer to carry the temper 

from any given initial state to any desirable final state within the range 

of possible variation in a safe and systematic way. Of the two factors 

which condition the degree of hardness reached the temperature of 

the annealing bath and the time of exposure of the hard steel rod 

the latter if sufficiently prolonged is particularly effective for very small 

values of the former. If annealing be continued through infinite time, 1 

the ultimate states (measured as thermo-electric hardness), would appear to decrease continuously as the temperature increases, though there 

is reason to predict the existence of a minimum between 400° and 600°. 

We had commenced a special investigation of this functionality, but 

the work was forcibly interrupted. It is still to be noted that the maximum annealing effect of a temperature t' is independent of the possibly 

pre-existing effects of a temperature t, and is not in any way influenced 

by subsequent applications of the latter, provided t'>t.

Scheme for magnetic and other allied researches. The results above 

detailed .open up a large field for further research in directions differing 

from those of the present chapter. Indeed, wherever we have to. deal 

with those properties which depend essentially on the hardness of steel, 

the experiments discussed in the above formally prescribe, as it were, a 

method of procedure at once expedient and safe.

From a physical point of view, steel possesses a special and peculiar 

interest in virtue of its pronounced magnetic properties. The importance of the influence of hardness on the intensity of permanent magnetization has long been known. But the confusion and discordance in 

the results of all observers bear witness to the difficulties encountered, 

not only from the vagueness which attaches to the term steel, but principally out of the want of a method by which identical mechanical 

states can be rigidly defined. As a consequence the data of many 

laborious researches do not readily admit of direct comparison, and are 

therefore nearly valueless. Indeed, we may add that even in the case of 

one and the same type of steel each rod must be regarded as an individual.

It follows, therefore, that a plan of research in which a given steel rod 

is carried, by annealing, from an initial hard to a final soft state, through 

all intermediate states, is alone adapted to the class of experiments under discussion. And here again the peculiar mechanical condition

(663)
72 IRON-CARBURETS. [DULL. 14,

which we have above characterized as the limit of hardness for a given 

temperature of the annealing bath will appear saliently important. 

The reasons for this preference are obvious. We have in hand the 

highest of the inferior states of hardness permanently unaffected by the 

given circumstances of exposure; the maximum of permanent hardness, 

in other words. We are justified in ascribing to it greater uniformity of 

temper and greater definiteness of internal structure than is possessed 

by steel tempered in any other way whatsoever. Thus it will be possible, independently of the degree of carburation of steel, or of its chemiical composition in general, independently, moreover, of the geometrical 

figure of a given sample, to investigate the magnetic variation due to the 

the change of a single variable hardness alone. With this as a point 

of departure, the inquiry leads to the effect of form or dimensions, and 

ultimately to that of carburation.

ADDENDUM: ON A SIMPLE METHOD FOR THE GALVANIC CALIBRATION OF A WIRE.

The methods in vogue for the calibration of an electrical measuring 

wire, one, for instance, to be used in the Wheatstone-Kirchhoff bridge, 

are without doubt inconvenient in so far as they presuppose a set of 

resistance coils of known simple ratios. In other words, they call for 

the preliminary work of comparing with great care the said auxiliary 

coils. The accuracy of the result immediately sought is thus dependent 

on the accuracy of the earlier measurement, and the anticipative caliber errors of the wire are obscured by the errors possible in the accepted 

ratios of the coils themselves particularly so where, as is generally 

the case, the discrepancies primarily in question are small. In view of 

the importance of the very accurate and convenient method of determining resistances by means of the sliding-contact bridge, the endeavor 

to overcome the obstacles mentioned as completely as possible is therefore at once justifiable. A method moreover which can accomplish this 

will be all the more acceptable in proportion as the auxiliary devices to 

be adopted are simple and readily available. We believe the following 

plan partakes of these advantages.

The method now to be described, and which we have profitably employed in determining the sectional errors of an electrical measuring 

wire, is a complete analogon of the procedure usually employed for the 

calibration of thermometers. The immediate principles and the point 

of departure are the same as those utilized in the well-known Matthiessen-Hockin method of resistance measurement. In the annexed figure, 

in which the ordinary bridge adjustment is diagrammatically given, let 

A NB and A MB be the two branches terminating at A and jB, where

(664)
BAHUS AND sTuouiiAL.] GALVANIC CALIBRATION. 73

A MB is the wire to be calibrated, A N B a series of resistances, whose 

sum in any given case remains constant. 

Now, if Mi and N^ Mz and N2 are, respectively, pairs of points of like

E

FIG. 12. Disposition of apparatus for calibration.

potential, and if the resistance of N} N2 be Y, and the length of the 

part MI M2 be a?, then

where G is a constant (sensitiveness) dependent only on the sum of the 

resistances A N B. Indeed, if W be this sum, and L the total length of 

wire A MB, then

W=CL.

Furthermore, let the interval of calibration a be so chosen that n, ' a 7

where n is an integer.

Suppose, now, that n approximately equal resistances are either 

specially constructed or at the observer's disposal. In our case a 

number of tenths of Siemens mercury units, which had been made for 

the purpose of serving as normals for resistance comparisons, were 

available. But in general it is wholly sufficient to select a german silver wire of appropriate length and thickness, to cut it into n approximately equal parts, and then to solder the ends of each of these to 

terminals of thick copper, the free ends of which, in their turn, are to be 

amalgamated so that mercury contacts may be used at JVa, N2. ..., JV6 ... 

throughout. . Further knowledge of the resistance ratio of these auxiliary wires is quite unnecessary.

These n approximately equal resistances T, TT, TTT . . . are joined 

in series by mercury cups, as shown in the diagram. To have a concrete case, let n=5, for which assumption the figure applies. The extreme points A and B of the measuring wire are connected by pieces of 

thick copper with the extreme mercury cups. The calibration is then 

effected as follows:

One of the prolonged terminals of a sensitive galvanoscope is con-

(665)
74 IRON-CARBURETS. (BULL. 14.

nected consecutively with the points NI, N2 ; and by means of the other 

terminal the corresponding positions of the sliding contact on the wire 

A MB, viz, MI, M2 , respectively, determined.

Then J and II are exchanged, so that the resistance wire Jnow 

occupies the former position of II, and vice versa; and while v one of the 

terminals of the galvanoscope is connected consecutively with the 

mercury cups N2 and N3 , the other enables us to determine the corresponding positions of the sliding contact on the wire A MB, viz, M2' 

and Ms, respectively.

After this, I and III are exchanged. The contacts of one galvanoscope terminal at JV3 and JV4 fix the positions of the sliding contact at 

M3f and M4, respectively. And so on until I has passed consecutively 

from its original first position to the final portion among the whole 

series of resistances A NB. In this way we obtain on the wire A MB 

the nearly consecutive parts MI M2, M2' M3 , M3' M^ ... of like resistance.

Herewith it is obvious that this method of galvanic calibration is 

strikingly analogous to the method adopted in thermometer calibration. In the latter case a mercury thread of a given constant convenient volume and the approximate length a= is moved from place

7i

to place in the tube, and its length for each of these positions determined in terms of the thermometer scale lengths which under assumption of a constancy of caliber would be proportional to the volume 

of the thread, and hence identical. In the former electrical measurement, a wire of constant resistance is moved from place to place, and 

its value, as it were, determined in terms of lengths of the measuring 

wire, which again under conditions of constant sections would be proportional to the said moving resistance, and therefore identical. In

both cases, finally, the sectional error of the tube or wire is shown by 

the discrepancies or differences in the observed lengths of mercury 

thread or wire-part, respectively. In thermometry, the two fixed points, 

with reference to which the calibration is completed, are the freezing 

and the boiling points of water. On the bridge the corresponding 

points coincide with the extremities A and B of the wire.

Let Oi, #2 , «3 ,.... be the equivalent wire parts of A M B, determined 

by direct observation. Then will the mean length of these, which 

under assumption of a mean section of the calibrated wire corresponds 

to the calibration resistance, be

+ 03+ ...-« 

But as % «2) 03 differ but slightly from the calibration interval a= ? 

it is practically convenient not to introduce into the calculation the

(666)
BABUS AND BTBOUHAL.] GALVANIC CALIBEATION. 75

whole Ungths av . . . an, but merely their (positive or negative) 

differences from a. Therefore let

and similarly

n 

Then, more simply, there follows

and therefore for the table of calibration of the wire,

from 0 to a .......... a 6\

from ato2a .......... a 6*

from2ato3a .......... a #3, etc.

Therefore by summation :

At a, correction = a $i

At 2a, correction = 2 a di 6Z ' 

At 3#, correction =3a #! tf2 #3 , etc.

As the main feature of the present method, we desire again to advert 

to the simple means by which the calibration is effected. The only 

error to be guarded against is the possibility of variation of temperature during the course of the consecutive adjustments of the calibration resistance. But the work can be accomplished rapidly all the 

more as the approximate positions of M are readily predeterminable 

with considerable accuracy. If a fairly sensitive galvanoscope be employed the errors of adjustment are of the same order as the errors of 

observation. In case of our special bridge 2£ meters long, very ordinary 

means enabled us to secure an accuracy of adjustment within 0.1 millimeter.

By means of the principle here enunciated any of the other methods 

of thermometer-calibration would be equally applicable. The convenient one given, however, is sufficient for all practical purposes.

(667)
CHAPTER III.

THE NATTTBE OF THE PHENOMENON OF TEMPEB AS OBSEBVED IN 

STEEL DISCUSSED FBOM AN ELECTBICAL STANDPOINT PABTICULABLY IN BEFEBENCE TO THE ANALOGOUS BEHAVIOB OF MALLEABLE CAST-IBON AND OF ALLOYS OF SILVEB.

INTRODUCTION.

General inferences deducible from the cast-irons. If we abstract from 

grossly impure material, details and ulterior complications, the different kinds of cast-iron may be conveniently classed with reference to 

two well-known types the gray cast-iron and the white cast-iron 

which are thoroughly distinct and well marked, as regards both their 

chemical and their mechanical properties. Keasons for this classification, it is believed, are not far to seek, and they are such as depend on 

the manner in which the carbon contained is combined with the iron. 

White cast-iron is known to contain carbon in the chemically combined 

state only. In gray cast-iron, however, the uncombined or mechanically admixed forms of carbon are present in much the greater proportion. Furthermore, it is known that a given specimen of molten iron 

may be changed into either the gray or the white type, respectively, according as the cooling, after casting, is permitted to take place very 

gradually or very rapidly.37 In this respect an experiment of Karsten's38 

is peculiarly instructive. Karsten poured molten iron into a thick iron 

mold. The outer layers of the cold mass, which in this way had cooled 

at a comparatively rapid rate, were found to contain combined carbon 

only. In the inner and axial layers, however, where cooling took place 

gradually, only about one-sixth of the total carbon occurred in the combined form.39 Suppose we compare the process of fast and slow cooling 

in the case of cast iron, with sudden chilling and very gradual cooling 

in case of steel, respectively; suppose, furthermore, we contrast the 

very high degree of hardness possessed both by white cast iron and 

chilled steel with the readiness with which gray cast-iron and slowly

37 The remarks here made present the facts under consideration only in a brief and 

introductory way. For full and exhaustive discussions the reader is referred to PercyWedding, Eisenhttttenkunde, Bd. II of the German Percy, pp. 130-186, Braunschweig, 

1864. Cf. particularly critical remarks, pp. 165-167.

ssKarsten: Eisenhiittenkunde, Bd. I, 3 Aufl., 1841, p. 581 ff.

39The results of Karsten's analysis are these:

Before melting (iron homogenous): C combined, 0.8 per cent.; C uncombined, 3.2 

per cent.

After melting (outer layers): C combined, 5.1 per cent.; C uncombined, 0.0 per 

cent. Inner layers: C combined, 0.6 per cent.; C uncombined, 3.2 per cent. (668) 76
BABUS AND 6TBOUHAL.] TEMPER CHEMICALLY INTERPEETED. 77

cooled or thoroughly annealed steel yield even to an ordinary file; then 

the inference is apparently unavoidable that the hardness which may 

be imparted to steel by a process of tempering is to be referred to the 

transfer of carbon from the uncombiued to the combined state.40

Data corroborating this analogy. If, however, what may be called the 

chemical method of accounting for the hardness in steel were alone dependent on analogies of the kind just sketched, we would not be inclined to accept it immediately and with full confidence. In glass-hard 

steel we encounter strains of a peculiar character and of enormous intensity. It is upon such observations that a purely physical explanation of the hardness in question might be based an explanation much 

better adapted for the prediction of certain physical phenomena to be 

mentioned below than the chemical view under consideration. At the 

very .outset we come upon difficulties, Suppose, for instance, we 

attempt to draw further inferences from Karsten's experiment. We 

find that the glass-hard external layers of his cylinder, consisting 

wholly of white cast iron, possess the specific gravity 7.55, whereas the 

specific gravity of the gray nucleus was only 7.18. The effect of sudden 

chilling in case of steel,41 however, is a very marked diminution of density 

of the rod, as a whole. Even if we pursue our inference further, and 

endeavor to compare the external and internal layers of a glass-hard 

steel rod with the corresponding parts of Karsten's chilled iron cylinder, respectively, we fail to arrive at satisfactory results; for the 

density of the external layer of a steel bar (about 10) is incommensurately large when compared with the above datum for white cast-iron. 

The chemical explanation, however, at once becomes of iucontestible 

importance when it is found that in addition to the given analogies 

we'have in hand a number of data which go to prove that carbon exists 

differently, as regards its mode of occurrence, in hard and in soft steel. 

The data are derived from the chemical behavior of sofb and hard steel 

toward acids. In this place the extensive experiments of Caron42 need 

alone be mentioned. The results of this observer with steel in the commercial, the hammered, and the glass-hard states, respectively, furnish 

striking evidence of the fact that the mode of occurrence of carbon in

«Cf. Karsten: Karsten u. v. Dechen's Archiv., XXV. p. 223,1853. Cf., also, p. 103 

of the present paper.

/ o

41 Karsten: op. cit.,Bd. I, p. 193-4, experiments of Hausmann and Karsten. Cf. also 

ibid., p. 184, ff. For a table for Swedish Bessemer steel, see " Steel, its history, etc.," 

J. S. Jeans, Sec. Br. Iron and Steel Inst., London, Spoil, 1880; Cf. ibid., p. 612-615. 

On the mean specific gravity of iron-carburets, cf. Karsten, op. cit., p. 183.

42 Caron: Comptes rend., LVI, p. 43, 1863. The residues in the cases referred to, 

viz., 1.62 per cent., 1.24 per cent., 0.24 per cent., were found to contain 0.83 per cent., 

0.56 per cent., 0.00 per cent, of carbon, respectively. The following remark of 

Caron's moreover, is of especial importance here: "Aiusi do 1'acier treinp6 ayante"t6 

recuit pendant un temps variant entre quelques heures et piasters jours a donne" 

apres dissolution des quantite"s de carbon libre qui ont augment^ en rnetne temps 

que la dure"e et 1'intensite" des chauffes." pp. 45-46.

(669)
78 IRON-CARBURETS. [BULL. 14.

soft steel is thoroughly different from the chemical condition of this 

element in hard steel. In so far, then, as it is necessary to associate with 

this difference of chemical state of the carbon in steel some corresponding difference in the mechanical properties of this material, the validity 

of the chemical explanation of tempering may be said to have received 

its first important vindication.

Results at variance with chemical hypotheses. Of late many facts have 

been adduced by various observers and in different ways against the 

hypothesis that the union of carbon and iron is ever of a thoroughly 

chemical character. Singularly clear in this respect are the views of 

Matthiessen,43 who supposes that iron-carburets are to be regarded either 

as solidified solutions of carbon in iron, or as solutions containing carbon 

mechanically admixed. To these new opinions Matthiessen is led by 

a study of the electrical conductivity of these materials. With this 

general hypothesis the results of the calorimetric researches of Troost 

and Hautefeuille44 are in strict accordance. These observers find that 

not only carbon but silicon show such thermo-chemical relations toward 

iron as call for a classification of iron-carburets with the category of 

solutions. Forquignon,45 finally, who has lately been occupied with similar researches, gives to this view his unqualified assent.

Ulterior consequences of the chemical theory in case of steel. In connection with our researches on the hardness of steel a careful consideration 

of the subject in hand appeared necessary. Our attention was not, however, attracted to the questions just developed, viz., whether a chemical or mechanical explanation for the mode of occurrence of carbon in 

steel is more in coincidence with facts. The subject-matter of importance to us is sketched in all its essential points in the earlier sections. 

It is our endeavor to investigate whether a given change in the state of 

hardness of a steel rod is to be ascribed to a corresponding change in

the mode of occurrence of-the carbon in this material, or whether the 

presence of carbon imparts to iron certain 'distinct and unique properties 

(" steel") in such a way that the whole series of the phenomena observed 

in tempered steel are to be regarded as purely mechanical in their character. It may be observed that the first manner of explanation does not 

necessarily conflict with the second. Both chemical and mechanical 

phenomena may coexist. But it is best in this place to hold the two 

hypotheses strictly apart. This is readily possible, because the different 

states of hardness obtainable from a glass-hard steel rod by annealing 

are all reached, practically, when the temperature of the annealing bath 

is still below 350°, a temperature insufficiently high for the conversion 

of uncombined into combined carbon.

43 Matthiessen: -Rep. Br. Assoc. Adv. Sc., 1866, p. 15.

44 Troost and Hautefeuille: Ann. de ch. et de phys. (5), IX, 1876,p. 70.

« Forquignon: Ann. de ch. et de phys. (5), XXIII, 1881, pp. 531-636.

(670)
BARUS AND BTUOUHAL.] CONSEQUENCES OF. THE CHEMICAL THEORY. 79

Suppose now that we abstract from physical considerations altogether 

for the time being, and endeavor to obtain from the older and more 

thoroughly investigated chemical hypothesis an explanation for the details of the phenomena of annealing discussed in an earlier chapter.46 

If sudden chilling is accompanied by chemical combination of the carbon in steel, then must the operation of annealing, which reverses the 

effects of the former, enable us to reconvert combined carbon into its 

original uncombined state.47 But we have shown that for each temperature of exposure during the annealing of a glass-hard rod there exists a distinct degree of hardness, cceteris paribus, characteristic of 

the temperature in question alone. It follows, therefore, that to each 

temperature of the annealing bath there must correspond a certain 

fixed ratio of combined to uncombined carbon, the time of exposure 

being indefinite. From the known behavior of steel in different states 

of temper, moreover, combined carbon, must be looked upon as electrically active, uncombined carbon as electrically neutral. Thus we have 

it in our power, with the aid of the simple process of sudden chilling 

combined with subsequent annealing, in so far as in this way, within 

certain limits, any given amount of an electrically active ingredient 

may be converted into an electrically passive form, to reach the same 

results which, in the case of alloys, for instance, are obtainable only by 

melting the two component metals together in a ratio which may be 

called for. We said "within certain limits": the superior limit here 

meant, is the total amount of carbon present in the given type of (normal) steel; the inferior limit, the small amount of combined carbon 

which even after most prolonged and gradual cooling cannot be made 

to appear in the uucombined state. With this chemical interpretation, 

finally, the remarkable linear relation between the thermo-electric constant and the specific resistance of steel passing continuously from the 

glass-hard to the soft state would at once appear to possess broader 

significance than that of being a special peculiarity of steel.

These are the reflections which induced us to undertake the present 

investigation. We were in hopes, moreover, that the results would 

prove of such a character as to enable us to derive inferences from them 

on the chemical nature of steel. At all events, the subject, considered 

from the standpoint of its own merits, is not undeserving of detailed 

attention. The number of data in hand on the relation in question is 

almost insignificant.

<8 Strouhal u. Barus: Wied. Ann., XI, p. 962,963, 1880. Chapter II, pp. 43 et seq.

47 Caron : 1. c., pp. 45,46. Unfortunately \ve have not been able to find any data 

relative to the effect of ordinary annealing (exposures below 400°) on the mode of 

occurrence of carbon in steel.

(671)
80 IRON-CARBURETS.^ IBUU.M,

. EXPERIMENTS WITH ALLOYS.

Earlier results inadequate. The literature on the electrical conductivity of alloys is very voluminous, but the exhaustive researches of 

Matthiessen48 contain all the essential data. At least, little has been 

developed that has a bearing on the present paper since the date of 

Matthiessen's main research.49 From the tables and graphical constructions there given, the conductivity of a large number of alloys can be 

at once deduced when the proportion in which the ingredients of the 

alloy are mixed is known. Similar remarks by no means, however, apply to our knowledge of the thermo-electric properties of alloys. Qualitative results are not lacking. Available quantitative data are, however, very rare.50 Pairs of values of both the electrical conductivity 

and the thermo-electric power of alloys are only to be found in isolated 

examples, if at all. At least we were not able to obtain other data 

than a few measurements incidentally made by Sundell.51

Matthiessen's numerous results made a special determination of data 

on the relation between percentage composition and either of .the electrical constants superfluous. Such measurements presuppose chemical 

analysis, which could not have been made without unduly sacrificing 

the greater part of our wires and material. By weighing out the ingredients, and careful fusion, we were able to obtain from Matthiessen's 

tables a satisfactory corroboration of our results.

Material, fusion, preparation, etc. The general plan adopted in our 

researches with alloys was such as would correspond to a progressive 

increase in.. the state of hardness of steel from the soft or thoroughly 

annealed to the glass-hard condition, premising the views discussed in 

the last section. We commenced with pure silver, to which more and 

more of a second metal was successively added, until finally mechanical 

difficulties were encountered such as prevented a drawing of the alloy to 

wire. In case of silver-gold alloys, a complete series, commencing with 

silver and ending with gold, were obtainable. The alloys examined are 

those of silver with gold, platinum, copper, and zinc. Silver and gold 

were obtained pure from the mint at Frankfort; platinum, from the 

shops of Heraeus in Hanau. The copper was deposited electrolytically 

from a copper-sulphate solution. In making the alloys we proceeded 

thus: A weighed amount of silver having been well fused on a boneash cupel by the aid of a blast-lamp, the proper quantity of the second 

metal was added to it. Solution is usually immediate. Having mixed

48 Matthiessen: Pogg. Ann., CX, pp. 190-221, 1860.

49 Matthiessen and Holzmann: Pogg. Ann., CX, pp. 222-234, 1860; Rep. Br. Assoc. 

Adv. So., 1863, p. 37.

50 We may, perhaps, mention Joule: Phil. Trans., 1859, I, p. 96 (Bi, Sb); Sundell: 

Pogg. Ann., CXLIX, 1873 (Bi, Sb, Sn).

61 Sundell: Hid., pp. 154-170.

(672)
BARUS AND BTKOUHAL.] ALLOYS THERMO-ELECTRIC DATA. 81

the two component inetals as thoroughly as possible by chasing the 

globule over the surface of the cupel, the flame was withdrawn and a 

glass bell-jar filled with hydrogen (the gas being continually resupplied 

through an aperture in the neck of the jar), quickly, placed over it. 

Oxydatiou, as well as absorption of oxygen by the melted globule, was 

thus avoided, the button cooling in an atmosphere of hydrogen. Only 

in the case of silver-copper alloys is this simple process to be regarded 

insufficient for the attainment of very accurate results.52 But the discrepancies thus introduced into our work, and which are due to absorption of oxygen by copper, are quite insignificant. Of this fact a 

comparison of Matthiesseu and Holzmaim's data with our own has fully 

convinced us. On the other hand, the variation of thermo-electric 

power and conductivity of alloys of silver and copper takes place within 

'limits so nearly coincident that the general character of the diagram 

which we will endeavor to construct below is in nowise distorted.

The buttons53 were hammered and drawn down to wires of appropriate 

diameter. These were then annealed at high red heat in a current of 

hydrogen by the aid of a dynamo-electric machine. We were able to 

regulate the intensity of current, and with it the glow, by introducing 

into the circuit a solution of copper-sulphate, in which the copper electrodes were kept at suitable distances apart. Accidental fusion of the 

hot wires was thus not to be apprehended. After this annealing they 

appeared soft and flexible. Only the middle parts of the wires, over 

the whole length of which the glow had been uniform, and which, for 

other reasons, were apt to be homogeneous, were reserved for the 

measurements.

Method of thermo-electric measurement. Results. The methods of 

measurement of thermo-electric power and specific resistance are 

identical with those employed in our earlier researches.54 The formeris throughout referred to pure silver as a datum, i. e., denotes the power 

of a thermo-element, one part of which is always silver; the other, however, the given alloy. Junctions were carefully soldered. The composition of all alloys is given in volume per cents, the data expressing the 

volume of the metal alloyed to silver in 100 volumes of alloy. It has 

been stated that these numbers are ,only approximate, since during 

fusion the two metals will hardly have been volatilized in like ratios.

With these remarks the following tables (35-39) will be readily intelligible. The thermo-electric constants a and & are calculated on the 

basis of Avenarius' 55 formula, e=a (T t)+b (T* tz). from six correM Cf. Matthiessen u. Holzrnann: I. c., pp. 222-224.

63 It would have been desirable to operate with larger quantities of metal, but these 

were not tit our disposal.

M See Chapter II, p. 31 et seq.

^Avenarius: Pogg. Ann.; CXLIX, p. 374,1873. e is the electro-motive force for the 

temperatures Taud t of the junctions of the given thermo-element whose constants are 

a and &.

(673) 

Bull. 14 6
82 IRON-CARBURETS. fBUU.. 14.

spending values of f, T, if, for each alloy, by the metbod of least squares. 

The measurements were originally made in Weber-Siemens' units, and 

then reduced to current values by the relation ohm=1.06 Siemens.

TABLE 35. Thermo-electric poiccr of alloys.

Alloy.

Sil ver-platinum ................

Do.......................

.

Do...............:.......

T)n

Vol. 

P. ct.

10

16

t

C.

 16.5

16.6

16.7 

16.7

16.8

16.8

ICO J.O. O

15.9

15.9 

16.0

16.1

16.1

17.1

17.1

17.1 

17.1

17.1

17.2

16.1

16.1

16.2 

16.2

16.3

16.3

T

C.

85.6

 75.7

64.1 

53.0

43.1

36.3

HO /» fc. O

69.3

60.9 

52.3

45.8

37.5

90.6

79.1

68.3 

55.4

45.2

35.2

90.2

74.0

62.9 

52.4

43.4

36.2

e 

observed.

microvolt.

-308.6

-261. 3

-206.7 

-159. 1

-111. 7

- 82.4

-413. 0

-340. 3

-288.2 

 230. 1

-186. 4

-132. 9

_ QQ4 ^

-49&3

' -405. 2 

-296. 8

-213.8

-134.4

-710.6

-539. 7

-425. 6 

-324. 9

-239. .4

-174. 0

e 

calculated.

microvolt.

-308. 8

-261. 1

-206. 7 

-159. 1

-111.9

- 82.3

-412. 5

-346,4

-288. 5 

-230. 1

-186.5

 -132. 7

-603. 4

 499. 6

-405. 0 

-296. 4

-213.7

-134.6

-709. 4

-539. 5

-427.1 

-324. 9

-239. 5

 173. 6

Diff.

-0~2 0. 2

0.0 

0.0

0.2

-0.1

-0.5

0.1

0.3 

0.0

0.1

-0.2

-1.0

1.3

-0.2 

-0.4

-0.1

0.2

-1.2

-0.2

1.5 

0.0

0.1

-0.4

a

]

1-3.95

J

.

|- -5. 72

)

 6.77

1

S -7. 90

.

*

6

-0.0051

-0.0090

-0.0164

-0. 0158

TABLE 36. Thermo-electric power of alloys.

' Alloy.

Silver-gold ....................

Do. ...................

TVi

Do...... .................

Vol. 

P.ct.

5

15

2

K t>

35

t

C.

15.5 

15.5

15.4 

15.4

15.4

15.4

15.4

15.5

15.5 

15.5

15. 6

15.6

1 C ft 13. 1

15.7

15.8 

15.8

15.8

15.8

13.9

13.9

13.8 

13.8

13.8

13.8

T

C.

85.1 

75.5

68.3 

62.0

50.6

40.0

89.5

80.6

7,1.5 

63.2

52.8

44.1

on uu. o &

82.6

66.3 

54. 3

44.9

35.9

88.3

79.7

72.3 

63.4

51.9

42.4

e 

observed.

microvolt.

-132.9 

-114.1

- 99.1 

- 87.8

.- 65.5

- 45.4

-209. 2

-181.5

-154.1 

-129. 7

- 99.3

- 74.8

-227.0

-201. 1

-14&3 

-110.8

- 82.5

- 55.9

-223. 6

-195.8

-172.3 

-144. 2

-109.2

- 80.9

e 

calculated.

microvolt.

-132.9 

-113.7

- 99.8 

- 87.5

- 66.5

- 45.4

-209. 5

-181. 6

-154. 0 

-129. 3

- 99.3

- 75.0

-227.0

-201. 3

-148. 0 

-110.7

- 82.3

- 56.1

-223. 7

-195.6

-172. 1 

-144.2

-109.2

- 80.9

Diff.

0.0 

-0.4

0.7 

-0.3

-0.0

-0.0

0.3

0.1

-0.1 

-0.4

0.0

0.2

0.0

0.2

-0.3 

. -0.1

-0.2

0.2

0.1

-0.2

-0.2 

0.0

0.0

0.0

a

1

_ 1 77

. -2. 38

1

^-2.54

J

.

S -2. 61

1

'

&

-0. OOli

-0.0043

-0. 0048

. -0. 0039

(674)
BAKUS AND RxnounAL.] ALLOYS THEEMO-ELECTRIC DATA. 

TABLE 37. Thermo-electric power of alloys.

83

Alloy.

Silver- gold . ......;.............

Do.......................

Do .......................

Gold...........................

Vol. 

P.ct.

50

75

onUV

100

t

c.

15.0

15.0

14.7 

14.7

14.7

14.6

14.1

14.1

14.1 

14.1

14.1

14.0

17.3

17.3

17.3 

17.3

17.4

17.4

15.3

15.4

15.5 

15.6

15.6

15.7

T

G.

87.1

78.2

65.6 

55.3

44.4

36.2

86.1

77.5

68.0 

53.3

42.1

30.5

91.0

80.2

68.1 

57.0

45.7

34.6

89.1

80.7

70..9 

60.5

51.4

40.3

e 

observed.

microvolt.

-202. 3

 175. 4

-138. 7

-rl08. 9

- 78.2

- 56.1

-151. 5

-135. 1

-111.9 

- 79.3

- 55.8

- 30.7

-116. 0

-100. 8

- 79.3 

- 61.2

- 43.3

- 25:-6

19.3

17.0

14.8 

12.2

9.6

6.5

e 

calculated.

microvolt.

-202. 6

-175.2

-138 5 

-108. 8

- 78.3

- 56.1

-154.4

-133. 5

-111.4 

- 78.5

- 54.7

- 31.5

-117.7

- 99.2

- 79.3 

- 61.0

- 43.1

- 25.8

19.3

17.2

. 14.7 

12.0

9.5

6.6

Diff.

0.3

-0.2

-0.2 

 0.1

 0.1

0.0

+2.9

-1.6

-0.5 

-0.8

-1.1

0.8

1.7

-1.0

0.0 

-0.2

-0.2

0.2

0.0

-0.2

0.1 

0.2

0.1

-0.1

a

^

1-2.39

1

J

1

I. -1.71

)

1

i-1.41

1

J

 +0.275

Z>

-0.0041

-0. 0043

-0. 0017

-0. 00012

TABLE 38. Thermo-electric power of alloys.

Alloy.

Do......................

Do......................

Do......................

Do......................

Vol. 

P.ct.

2

5,6

1 ^

50

75

t

C. 

14.6

14.6 

14.6

14.7 

14.7 

14.7

13.7

13.7 

13.8 

13.9 

13.9 

13.9

14.3

14.3 

14.3 

14.4 

14.4 

14.4

14.3

14.3 

14.4 

14.4- 

14.5 

14.5

16.2

16.3 

16.3 

16.3 

16.3 

16.3

T

C.

83.7

77.7 

68.2 

57.7 

48.0 

33.8

89.5

80.4 

72.8 

62.8 

52.2 

39.2

84.8

75.5 

65.3 

56.5 

46.3 

35.5

83.3

72.9 

63.4 

53.8 

43.9 

33.5

86.9 1

74.0 1 

64.8 

52.4 

41.7 

33.0

0

observed.

microvolt. 

0.3

-1.2 

-0.7 

-1.2 

-0.4 -0.2

1.6

1.2 

0.6 

-0.2 

0.5

a 8

4.0

2.6 

'2.5 

2.0 

1.4 

1.0 

O

11.6

9.0 

7.1 

5.5 

3.7 

.1.9

8.7

6.8 

5.2 

4.1 

2.0 

1.0

e 

calculated.

microvolt. -0.6

-0.6 

-0.8 

-0.6 

-0.5 

-0.4

1.0

0.9 

0.9 

0.8 

0.6 

0.4,

3.6

3.0 

2.4 

2.0 

1.5 

0.9

11.8

9.1 

7.1 

5.2 

3.5 

2,0

9.2

6.7 

5.2 

3.4 

2.1 

1.2

Diff.

0.9

-0.6 

-0.1 

-0.6 

0.1 

0.2

. 0.6

0.3 

-0.3 

-1.0 

-0.1 

0.4

0.4

-0.4 

0.1 

0.0 

-0.1 

0.1

-0.2

-0.1 

0.0 

0.3 

0.2 

-0.1

-0,5

0.1 

0.0 

0.7 

-0.1 

-0.2

a

> -0. 023

I H- 0.021

1+0.041

1+0.045

1+0.020

b

+0. 0001

 0.0001

+0. 0001

+0. 0013

+0. 0011

(675)
84 IRON-CAHBITRETS. 

TABLE 39. Thermo-electric power of alloys.

[BULL. 14.

Alloy. '

Silver- zinc, with larger amount

of zinc.

Silver-zinc, with smaller

amount of zinc.

Vol. 

P.ct. t

C.

15.5

15.5

15.5 

15.5

15.8

15.8

15.7

15.7

15.8 

15.8

15.8

15.9

T

C.

87.0

80.8

.71.5 

60.5

49.1

35.3

90.6

81,0

72.2 

58.3

48.0

40.7

e 

observed.

microvolt.

- 8.8

- 8.0

- 4.9 

- 4.3

- 3.2

- 1.3

-12. 8

-11.1

- 8.2 

- 7.1

- 5.7

- 4.1

e 

calculated.

microvolt.

- 8.6

- 7.4

- 6.0 

- 4.3

- 2.8

- 3.4

-12.2

-10. 7

- 9.4 

- 7.1

- 5.4

-4.2

Diff.

-0.2

-0.6

+1.1 

0.0

-0.4

+0.1

-0.6

-0.4

-1.2 

0.0

-0.3

0.1

a

-0. 024

J

)

1 

5- -0. 176

1

J

&

-0.0009

+0. 0001

Specific resistance. The following table contains our data for the specific resistance of the same alloys to which the foregoing tables (35-39) 

refer. .The first two columns-need no explanation. Column third contains the resistance in ohms per meter of wire at the temperature in 

column fourth. Under 2p the diameter and under st the specific resistance in micro-ohms at the temperature t is given. The constant a, 

finally, whose signification is apparent from st=s (1+art), enables us to 

calculate s, the specific resistance at zero centigrade, in micro-ohms.

It is to be remarked that all the measurements were originally made 

in Siemens' units (ohm=1.06 Siemens), and subsequently reduced. The 

temperature-coefficients used,#, are obtained from the results of Matthiessen, C. Vogt, and v. Bose,5G by calculating with the aid of their formulae, 

st for 100° and 0°, and then finding the mean coefficient (a) between 

these limits. This is obviously permissible in our case.

TABLE 40. Electrical resistance of alloys.

Alloy (soft).

Do .............................

Do............................. DO..........................;..

Do.............................

JJo. ............................

Do....................:........

Do ............................. DO......:........:.........,...

Do.............................

Do....,.:......................

Do .............................

Gold ..................................

 Do ............................

Do.............................

Do .............................

Do..............................

Do.............................

Vol. 

P.ct.

100

100

100

2

5

10

15/*;

15

25

35

50

50

75

on

100

5,6 1 15

50

75

W 1 m

oJvna. 

0. 2023

0. 1777

0. 1802

0. 2431

1. 0802

0. 8054

2.4027

0. 3887

0. 7483

0. 9886

1. 1350

1. 2098

1. 2190

0. 9177

0. 2772

0. 1137

0. 2049

0. 1036

0. 2292

0. 2370

- 0.2314

 0.1733

0. 2114

t

C.

15.2

15.4

15.0

11.3

15.2

11.0

15.2

15.5

15.6

15.7

15.1

15.4

15.2

16.2

11..2

18.0

15.0

11.0

16.8

16.2

16.7

17.4

15.6

2p

cm. 

0. 0319

0. 0337

0. 0335

0. 0495

0. 0330

0. 0496

0. 0347

0. 0337

0. 0337

0. 0339

0. 0338

0. 0337

0. 0337

0. 0339

0. 0493

0. 0495

0. 0338

0. 0496

0. 0344

0. 0358

0. 0352

0. 0500

0. 0500

cm St^t0

microhm 

1.619

1.589

1.586

4.67

9.21

15.53

22.74

3.463

6.686

8.906

10. 188

10. 700

10. 782

8. 295

5.283

2. 193

1.844

1.999

2. 131

2.383

2. 255

3.403

4.151

a

0. 00398

0. 00398

0.00398

0. 00130

0. 00072

0. 00043

0. 00033

0. 0025

0. 0012

0. 0008

0. 0007

0. 0007

0. 0007

0. 0009

0. 0016

0. 00395

0. 0036

C. 0034

0. 0032

0. 0029

0. 0031

(0. 0020)

(0. 0015)

cm 

s c^°°

microhm 

1.521

1.492

1.491

4.60

9.11

15.46

22.63

3.329

6. 561

8.790

10. 079

10. 585

10. 667

8.174

5.188

2.037

1.744

1.924

2.016

2.271

2. 138

(3. 28)

(4. 06)

56 Matthiessen u. v. Bose: Pogg. Ann., GUI, p. 412, 1858. 

(676)
HAUL'S AND BTBOUHAL ] ALLOTS THERMO-ELECTRIC RESISTANCE. 85

The following table (41) contains results of Matthiessen and others; 

a and b here are Matthiessen's constants for his relation between electrical conductivity and temperature. By means of these A and A', the 

electrical conductivity at 0° and 100°, respectively, were calculated. 

But, according to Matthiessen, A=100 for hard silver; A=1.656 for 

mercury, (0°). Hence

''=17 TOT log*,=2.19375-logA,

From these values of st the constant a, was then obtained, in the way 

already given, st=s (l+at).

TABLK -41. Specific resistance of alloys of silver. 

[Kesultsof Mattliiessen (and C. VogtJ.J

Metal.

Do.........

Silver-platinum 

Do.........

Do.........

Silver-gold ..... 

Do.........

Do.....:...

Do .........

Do .........

Do .........

Gold ...........

Do .........

Silver-copper...

Do .........

Do .........

Do .........

Do.........

Do.........

Hard 

or 

soft.

h

h 

h

h

h 

h

h

h

h 

h

h

h

h

h

h

Vol. 

Per ct.

100

100

2.51 

5.05

19.65

19.86 

52.08

79.86

19.86

52.08

79.86

100

100

1.53 

8.25

46.67

77.64

' 95.17

98.35

100

100

A atO° 

Ag(h) 

=100

100

ins 71

31. 640 

18. 031

6.696

21. 684 

15. 030

21. 335

21. 746

15.080

21. 584

77 964

79.327

79.708 

80. 284

74 940

69. 811

82. 300

89. 544

99 947

102. 213

a

0.38287

0.41570

0. 039363 

0. 013949

0. 002214

0. 019185 

0. 010120

0. 023212

0. 019753

0. 010864

0. 024539

0. 28648

0. 29149 .

0. 32868 

0. 22101

0. 21011

0.21194

0. 26758

0. 30886

0. 38681

0. 39557

b

0. 0009848

0. 0010624

0. 00003642 

0. 00001182

0. 00000139

0. 00001152 

0. 00000370

0. 00001694

0. 00001395

0. 00000746

0. 00002506

0. 0006582

0. 0006697

0. 00069C5 

0. 0003503

0. 0003961

0. 0004240

0. 0005717

0. 0007155

0. 0009208

Vat 

100° Ag 

(h)=100

71. 561

77. 794

28. 068 

16.754

6.489

19. 881 

14. 055

19. 183

19. 910

14. 068

19. 381

56. 875

53. 805 

61. 686

57. 890

52. 857

61. 259

65. 813

70. 270

71. 864

«CJ5.0° 

cm2

microhm. 

1. 5623

1. 4367

4.938 

8.664

23. 331

7.205 

10. 394

7.322

7.184

lu. 360

7.238

2. 0038

1. 9094

1.960 

1.946

2.085

2.238

1.898

1.745

I. 5631

1. 5297

^ 100° 

cma

microhm. 

2.1831

2. 0082

5.566 

9.325 <M effn

7.858 

11. 115

8.144

7 847

11. 105

8.061

2. 7948

2. 7468

2.904 

2.533

2.699

2.956

2.550

2.374

2. 2232

2. 1739

0°....100°

0. 003974

0. 003978

0. 001272 

0. 000763

0. 000319

0. 000908 

0. 000694

0.001123

0. 000923

0.000719

0.001137

0. 003947

0. 003947

0. 004810 

0. 003017

0. 002946

0. 003208

0. 003442

0. 003606

'0. 004223

0. 004211

Digest. Diagram. For the sake of perspicuity, the final results are 

tabulated again as follows.

TABLE 42. Corresponding values of the galvanic and thermo-electric constants.

Alloy.

Silver-copper. ........................ .._...............

Volume 

Per cent.

0

2 

5 

10 

15 

100

' 0

2 

5,6 

15 

50 

75 

100

«£HLoo cm-*

microhm. 

1 49

4.60 

9.11 

15.46 

22.63

*/O ft7\

13.44

1 dQ

1.74 

1.92 

2.02 

2.27 

2.14 

1.53

a 

( d6 \

\d(T-t)) (T+t)=0

0.00

 3.95 

 5. 72 

 6.77 

 7.90

/A OO\

o. ono

 0.023 0. 021' 

0.041 

0.045 

0. 020 

( 0.114)

' Applies for chemically pure metals, 

immediately derived from observations.

These values in parentheses are approximate, and are not

(677)
86 IRON-CARBURETS. IBULL. 14. 

TABLE 42. Corresponding values of the thermo-electric and galvanic consta?i/s Qout'd.

Alloy.

Silver-zinc ................................................

Volume. 

Per cent.

0

5 

15 

25 

35

50 

75 

90 

100 '0

< 

>

100

s-£Ho°

cm2

microhm. 

1 49

3*. 33 

6.56 

8.79 

10.08 

10.63 

8.17 

5.19 

2.04 

1.49

(3. 28) 

(4. 06) 

5.38

a 

/ de- \

\d(T t)/(T+t)=o

0.00

 1.77 

 2.38 

 2.54 

 2.61 

 2.39 

 1.71 

 1.41 

0.27

 0. 024 

 0. 176 

( 0. 098)

The results contained in the last table (42) are given graphically in 

figure 13, specific resistance being represented as abscissa, thermo-elec12

10

6

G

\

SP

V

tific Resist 

0 ° micro)

\

3TIQ. 13. Specific resistance and th'ermo-electric constant: steel, silver-gold, silver-platinum, silver 

% zinc.

trie constant as ordinate. In order to facilitate comparison the linear 

relation which holds for steel (see chapter II, page 63) is also drawn,

(678)
BAUUS AND BTKOUHAL.] ALLOYS ELECTRICAL BEHAVIOR. 87

and the interval of variation57 of the constants in question indicated by 

two small circles near the ends of the line. All the constants are given 

in microhms and micro-volts, respectively, and the thermo-electric position is referred to silver.

Discussion. A mere glance at the curves tells us that the relations 

under consideration are by no means of a simple character. Both properties, as exemplified by the thermo-electric constant and specific resistance, pass through maxima or minima, in such a way, however, that the 

said singular points do not coincide. i. e., are not properties of one and 

the same wire as regards composition. Equally difficult is it to observe 

any perspicuous law for the direction of the line joining the extreme 

points (those corresponding to pure metals) of the curves. The very 

simple relations which obtain in case of steel would apparently lead to 

the anticipation of some result of this kind.

The given curves, however, apply only for fixed conditions of temperature; the galvanic constant s only for the temperature £=0; the 

thermo-electric constant a for the mean temperature £(T+t)=0. But 

the temperature-coefficient, both for thermo-electric power58 as well as 

for specific resistance, varies in a marked degree as we pass from alloy to 

alloy. Hence it follows that for each temperature there exists a set of 

curves of the kind in question, characteristic of the said temperature. 

Change of temperature, therefore, involves a change in the curves both 

in figure and in position. It follows herefrom that a certain temperature 

must exist for which the figure of the curves is the simplest possible; 

our knowledge of the effects of temperature is, however, as yet insufficiently accurate to enable us to adduce further inferences. It is to be 

noticed that, at least as far as the above experimental matter is 'concerned, the magnitude of the given curves t. e., the range of variation 

of the involved electrical constants is qualitatively in the order of the 

differences of the specific volumes of the metallic components of the 

respective alloys. The very large loop, obtained in the experiments 

with silver-platinum alloys, corresponds to the marked increase of 

hardness which these materials experience with increasing additions of 

platinum to silver. On the other hand, in the case of silver-gold and 

silver-copper alloys, .a very great difference in the extent of the loop is 

apparent, unaccompanied by corresponding differences in the degrees of 

hardness59 of the respective alloys. That the bulge in the different 

curves must be wholly to the right of the lines joining the extreme

57 In later researches the superior limit was found to bo even above 50.

58 In reference to thcrino electric power we consider the quantity 26 in the equation 

e-=ar-\-l)T6 as a kind of temperature coefficient, since the therino-electromotive force

e for a given difference T, of temperature, increases linearly with?, the mean tern-

£

peratnro of the junctions.

5;l We shall iind below that hardness may also eiist in iron-carburets without a marked 

electrical equivalent.

(679) r . '
88 IRON-CARBURETS. [BULL. 14.

points is known. Finally it may be called to mind that the direction of

the initial tangent at the point " silver"( ~\ throughout the above \^s

results is negative.60 The thermo-electric effect of the addition of small 

amounts of other metals to silver would therefore appear to be a progression in a thermo-electrically negative direction.61 The number of 

alloys here examined is too small to permit us to attach much significance to this fact. Nevertheless it follows that the thermo-electric relation of any given metal to another does not, so far as can now be seen, 

enable us to predict the effect produced when the first metal is alloyed 

to the second. Gold and platinum, for instance, are both positive as 

regards silver; the initial alloys silver-gold, silver-platinum, however, 

are negative as regards silver.

THE GENERAL PHENOMENON OF TEMPER REGARDED FROM THE 

CHEMICAL AND FROM THE MECHANICAL STANDPOINT.

Inferences from the behavior of alloys. We now desire to consider the 

bearing of the above results on the electrical properties of steel. From 

the standpoint of the chemical theory of tempering, it is permissible to 

regard the linear locus, thermo-electric power varying with resistance, 

as the initial tangent of a loop of comparatively enormous magnitude. 

(See figure 13.) The increment of resistance with increasing hardness, 

or, in other words, with an increase of the ratio of combined to uncombined carbon, is to be considered analogous to the increase of resistance 

encountered on alloying small amounts of any metal to any given other 

metal. The linear relation can hardly be regarded striking, since in the 

case of steel the maximum amount of available carbon does not exceed 

one to two per cent. Finally, the magnitude of the variation or the extent 

of the loop might again have been anticipated, from the fact that here a 

metalloid is alloyed to a metal. The question, therefore, at once suggests 

itself, in how far these results are corroborated by the electrical behavior 

of cast-iron. In another paper we will show that the specific resistance 

of cast-iron, when in a condition corresponding to that of hard steel, 

t. e.j when by means of sudden cooling as much carbon has been conc/w< verted into the combined form as possible, may be increased to 100 ,0° cm2

microhm. That is, the specific resistance of chilled cast-iron is nearly as

60 The isolated negative value for the two per cent, copper alloy might be regarded 

suspiciously in consequence of the difficulties encountered iu endeavoring to obtaiu 

these alloys free of oxygen. But its specific resistance shows no anomalous behavior.

61 Thermo-electrically negative in Seebeck's sense. Cf. Wiedemann, Galvanisraus, 

3 ed., p. 248, 1883.

(680)
BAUUS AND BTROUHAL.I RESISTANCE A VOLUME-FUNCTION. 89

large as that of mercury. Suppose, now, we compare the variation of

specific resistance (superior limit 8=50^0° microhm ) in the case of \ cm2 J

steel, where the amount of combined carbon cannot exceed 1 to 2 per cent., 

with the corresponding variation of specific resistance ( superior limit

100^,0° microhm ) in the case of cast-iron, where the combined carcmr J

bon can be increased as high as 5 per cent.; then it apparently follows 

at once that the electrical behavior of cast-iron is such as we would be 

justified in predicting from the known relations in case of steel, if we 

accept the chemical hypothesis of tempering.62 Hence neither the simple relation of thermo-electric power and specific resistance discovered 

for steel, nor the pheuomeual variation of these constants with the state 

of hardness of this material, are further to be looked upon as remarkable. We will return to this subject again, below.

It follows from what has been said, that our hope of being able to 

throw additional light on the nature of the phenomenon of temper in 

case of steel from a detailed study of the analogous electrical behavior 

of alloys was not realized. For .although on the one hand the new data 

furnish no results antagonistic to the chemical theory, on the other they 

leave us without satisfactory or additional reasons for accepting the 

same. Under these circumstances it is necessary to contrast the theories 

which may be advanced for the explanation of temper with full regard 

to all known facts. This we will endeavor to do in the following, particularly so as the discussion will show where good work has been done 

done and where crucial data are still lacking.63

Electrical resislance a volume function. The discussion may be appropriately commenced with the examination of certain mechanical phenomena which accompany hardness in steel. It is known that the effect 

of tempering to glass-hardness is an increase both of the specific resistance ami the specific volume of steel. This, however, is analogous to 

the effect of temperature in the case of metals generally. The question 

is therefore at once suggested, in how far a given increment of volume 

in the case of steel, whether produced by temperature or by tempering 

will be accompanied by the same increment of specific resistance. We

62 Cf., however, p. 186.

63 In this place it will be well to refer to certain memoirs which have a definite bearing on the subject.-matter in hand. In addition to Karsten, Hausniaun (Molecularbeweguugen, 1856, p. 48), Tunner (Leob. Jahrbuch, x, p. 480, 1861), Jullien (Bullet.de 

la Soc.de 1'industrie inine'rale, I, p. 566; II, p. 202, 644), Hezner (Berg- u. Hiittenni. 

Ztg., 1862, p. 140), Deville (Dingler's Journal, clxviii, p. 174), Caroii (ibid., p. 36) 

have developed theories ou the causes of hardness in steel. For a discussion the 

reader is referred to Kerl's Metallurgy, 1870, Vol. Ill, pp. 25-7, translated by Crookcs 

and Rohfig. It is not our object to enter into a critical examination and comparison 

of these, as wo propose simply to consider the inferences which may be drawn from 

the electrical behavior of iron-carburets.

(681)
90 IRON-CARBURETS. [HULL. 14.

were fortunate in finding a sufficient number of data in the literature 

of steel to enable us to make a preliminary calculation or estimate.

Let v2 and v} denote the specific volume of steel in the glass-hard and soft 

states respectively. Then the results of Fromme M with steel rods whose 

diameters (0.27 centimeter and less) are nearest those of our own (0.10 

centimeter and less) may be thus expressed: 65

1003 v, 1012 1000 -fl^j ooo -, ( )

Suppose we put v2=v (l+3/?£), where j3=l'2: 10G , meaning thereby that 

the volume-increment v2 v is due to an increase of temperature t. Then 

we find

360°><>330° ....... (2)

Since /? will probably increase with temperature, this inequality might 

approximately be expressed £=300°.

Experiments on the resistance effect of high temperatures were originally made by Miiller.66 By the aid of his data for the resistance of 

iron at 21°, 285°, "oxide-tints appear" (300° to 350°), we deduce, if s'_ and 

s be the specific resistances of steel at 300° and 0°, respectively,

3.6>->2.5 ....... (3) s ^ '

where the superior limit is possibly too small. The more recent results

s' 

of Benoit,67 however, furnish us more accurate values. Let refer to x

an interval of temperature between 0° 330° and 0° 360°. Then 

Benoit's special formulae and constants for steel give us the relation:

3.7>->3.4 ...... (4) 8 V '

If, finally, s' and s denote the specific resistance of good steel in the 

glass-hard and soft states, respectively, then our results have shown 68

(5)

If we compare the estimates expressed in the inequalities (3), (4), (5), 

it becomes at once apparent that the results of Fromme, together with 

those of Miiller and Benoit, are more than sufficient for the explanation 

of .the enormous increase of resistance which a steel rod tempered to 

glass-hardness, .experiences. It follows that in the case of steel, a 

given increment of specific volume, whether produced by temperature

64 Fromme: Wied. Ann., VIII,. p. 354, 1879.

65 These inequalities are not general in their signification. Their purpose is merely 

that of expressing the extent of the interval within which the cited data were observed 

to lie.

^Miiller: Pogg. Ann., GUI, p. 17G, 1858. It is hardly necessary to distinguish between iron and steel here.

67 Beuoit: Comptea reud., LXXVI, p. 342, 1873 ; cf. Carl's Rep., IX, pp. 55-9, 1873.

gi 

68 The predominant influence of carbon ou the ratio will be referred to elsewhere.

(682)
BAKUS AND BTBOUHAL.] RESISTANCE A VOLUME FUNCTION. 91

or by tempering, is accompanied by increments of specific resistance of 

the same order. Of course, a result of this kind, since the rod remains 

homogeneous throughout in one case and is subjected to extremely complicated structural modification in the other, cannot be rigidly true. 

Nevertheless, the approximate data are of the greatest importance, 

because they demonstrate conclusively that the effects of the operation 

of tempering, even if regarded as of a purely mechanical character, 

must be attended by electrical phenomena of the same order as those 

which are actually observed.

(2) There is another question intimately connected with the one just 

discussed, viz, whether a given decrement of volume,69 produced either, 

by pressure alone or by temperature alone, is always attended by the 

same diminution of resistance for the same substance (metal); or 

whether it is necessary to postulate the existence of a purely thermal 

influence in the second case. Chwolson,70 who has subjected wires of 

copper, brass, and lead to pressure, infers that the resistance and the 

specific volume of these substances vary in like ratio.

In Chwolson's experiments the effects due to pressure are so nearly 

commensurate with the errors possibly introduced by temperature that 

we a.re justified in approaching his results with some diffidence. Marked 

compression is not readily attainable by piezometric methods. With 

steel, however, the result, which more than verifies Chwolson's inference on the resistance-effect of volume-reduction, may be thus illustrated.

Let S(=SQ (l+at). Specific resistance (st) is here regarded as a temperature (t) function. Then, if t be 'supposed to decrease indefinitely, 

the equation st Q would be satisfied at about

£=-2500 ....... (G)

provided, of course, the given relation holds.71 

On the other hand, let

S2=Sl 1+**=!! ....... (7,

where the specific resistances s2 and «i correspond, respectively, to the 

volumes v2 and v 1} and fc is a constant. Specific resistance is here regarded as a volume-function.

69 In the case of mercury, for instance. The results for solids would be distorted by 

the loss of structural homogeneity of the compressed solid resulting from external 

pressure. Large increment of volume is probably only obtainable by tempering steel, 

and to this enlargement of mean specific volume the remarks already made apply.

T° Chwolson, Carl's Rep., XIV, 26, 27, 1878.

n The temperature coefficient here accepted is the one found for soft steel in chapter 

I, p. 19, viz, a =0.004.

(683)
92 IRON-CARBURETS. [BUM,. 14.

In order to estimate the value of fc, we made a few preliminary experiments, the results of which are contained in this table: 72

No.

2

2

Temper.

Soft...... ....

Diameter.

cm.

0.575

0. 385

Length.

cm.

10.11

10.02

Specific 

gravity.

at 20°.

7. 6977

7.6145

7.6117

7. 5289

Specific 

volume.

m : vi .at 20°.

1. 0000

1. 0109

1.0000

1. 0110

Specific 

resistance.

microhm.

14.3

38.6

14.9

41.0

Specific 

resistance.

microhm.

15.5

40.2

16.2

42.7

k

)

| 149

It will be observed that, in the calculation of &, both - and 

were taken at 20°, because we as yet possess no data for the reduction 

of the former ratio to zero. Equation (7) implies, of course, that the 

same temperature (desirably 0° C.) occurs throughout.

Suppose, now, that by any mechanical means whatever the volume of 

steel has been isothermally so. far decreased that in equation (7), s2 =0. 

Then

If

(3)

Such a volume decrement, if the result of diminution of temperature, would correspond to a cooling of steel as far as [vt=v0 (1+3 fit)],

t== 3fi ~~v^~ ......

L e.j if the volume decrements in (8) and (9) be identical,

(9)

(10)

From a comparison of equations (6) and (10), we therefore again infer 

that variation of resistance is a necessary concomitant of variation of 

volume. No matter how the latter may have been produced, whether 

by temperature or by tempering, the increments of resistance due to a 

given increment of volume are of the same order. It is probable that 

this relation will apply to the resistance of non-electrolyzed solids generally. The results for steel are as nearly coincident as the excessively 

large sources of errors' unavoidably encountered permit us to anticipate. In addition to those already enumerated, we need only mention 

that Fromme worked with a different kind of steel from that used in 

our researches; that neither the coefficient of heat-expansion nor the 

galvanic temperature coefficient applies accurately for the large intervals of temperature met with, &c. A special error is introduced in 

consequence of the difficulty encountered in endeavoring to define 

values for the soft state.

72 Rods not thoroughly homogeneous, tempered after heating in a blast-flame.

(684)
BAUUS AND sTuouHAL.l RESISTANCE A VOLUME-FUNCTION. 93

(3) The results of Fromme73 andOhwolson finally contain a remarkable. 

analogy, to which attention has not yet been given. If the hardness of 

a glass-hard steel rod be supposed to decrease continuously, then the 

specific volume will be found to pass through a minimum, as Fromme 

.has emphasized, at a state of hardness corresponding to the annealing 

tint, "gray" (annealed at 300°-500°). Chwolson experimented on a 

very large number of metals and alloys. He found that the electrical 

effect of "drawn" hardness as well as the hardness due to sudden chilling vanishes on. exposure of the hard wire to high temperature, in such 

a way that after the first gentle ignition at low red heat the specific resistance of all metals passes through a minimum.74 Unfortunately 

Fromme has not interpolated a temperature which would produce an 

effect between "gray annealed" and " soft." Nevertheless it is difficult 

to avoid the conclusion that in all these examples of minima we encounter phenomena essentially of the same kind. Chwolson remarks that in 

case of steel his results were singularly striking. It would appear, 

therefore, that the mechanical effect (electrically measured) of sudden 

cooling is the same for almost all metals; that the magnitude of this 

effect differs from metal to metal, and is enormously pronounced in steel, 

fthis is the first evidence adduced that the given operation, tempering, 

produces qualitatively like effects on metals generally, the difference 

being in degree only.75 o

(4) In view of the increasing importance of density or of the values of 

specific volume in all these instances, the fact that in the above experiments with alloys the ranges of variation were found to be in the order 

of the differences of specific volume of the metals composing the alloy 

may again be called to mind. In case of steel the intimate relationship 

between specific resistance and thermo-electric power, described elsewhere, suggests that the cause of the increase of volume consequent 

upon sudden cooling is of a purely mechanical character, i. e., that it is 

not the direct result of the change of chemical condition of steel which 

tempering probably produces.

"Drawn" hardness. Matthiessen76 found that a hard-drawn wire of 

silver could be vep- perceptibly annealed (conductively decreased) by 

continued boiling in water. We obtained a good corroboration of this

"Fromme, 1. c.

"Lead and German silver are exceptions.

76 It must be borne in mind that this remark refers to the electrical indication of the 

(mechanical) effect of tempering. It is Avell known that while sudden chilling hardens 

steel, it is said actually to soften some of the other metals. It is, however, exceedingly difficult to distinguish between the degrees of hardness of brass or copper suddeuly chilled or slowly cooled from red heat, by ordinary mechanical means; and, moreover, sudden cooling may be accompanied by purely chemical effect in alloys and 

(not chemically pure) metals as it is in case of steel.

TC Matthiessen, und v., Bose: Pogg. Ann., CXV, p. 363, 366, 370, etc., 1662.

. (685)
94 IRON-CARBURETS. [BULL. 14.

result with drawn Germ an-silver wire,77 in which, after an exposure to 

steam at 100° of only an hour, a change of resistance of about 0.25 per 

cent, was perceptible. It follows, therefore, that not only tempered but 

drawn wires may be annealed to a very marked degree at comparatively 

low temperature.

Inferences from the behavior of iron-carburets. (1) In chapter I we saw 

that the temperature-coefficient of cast-iron is in good accordance with 

the coefficients of wrought iron and of steel in different states of temper, so that in this respect all the iron-carburets form a single connected 

series.

(2) This is by no means the case if we compare the relative galvanic and thermo-electric behavior of these products. From an inspection of figure 13 it is at once obvious that the position of cast-iron is 

isolated relatively to the linear locus which obtains for steel. !This observation shows conclusively that in the case of steel the cause of the 

electrical variation in question must be essentially different from that 

which determines the position of cast-iron. Below it is shown to be 

necessary to explain the distinctive electrical qualities of cast-iron as 

effects of chemical composition. Hence we infer with some assurance 

that the electrical behavior of steel on passing from one state of teniper to another, since the succession of values in no way suggests the 

electrical qualities of cast-iron, is conditioned by the cotemporaneous 

and purely mechanical changes which steel undergoes.

Phenomena of annealing chemically interpreted. On endeavoring to use 

the chemical hypothesis of tempering to account for the phenomena of 

annealing,78 we at once encounter serious difficulties. On the basis of 

this theory there must exist a fixed ratio of combined to uncombined 

carbon for each temperature of the annealing bath. Moreover, for 

a given temperature this ratio must be approached gradually (asymptotically) as time of exposure is prolonged indefinitely 5 for different 

temperatures it must decrease as temperature increases indefinitely, 

until finally a minimum value wholly independent of temperature is 

asymptotically reached.79 The minimum of the ratio of combined to 

uncombined carbon need not, of course, be zero. The last phase of this 

species of decomposition is in many respects similar to the phenomena 

of dissociation. The resemblance can, however, only be apparent, since 

continuous dissociation has not been observed except in the case of 

gases. At least, in our knowledge, there are no chemical examples in

"The results are these: Before boiling: 12°.4, r=6.8522; 12°.5, r=6.8523; 12°.6, 

r=6.8524. During boiling: 99°.8, r=7.0167, r=7.0182, r=7.0204; resistance (r) measured successively. After boiling: 13°.5, r=6.8691; 13°.6, r=6.8694; 13°.7 r=6.8696.

78 Strouhal und Barus: Wied. Ann., XI, p. 962, 1880.

79 In these cases of annealing slow cooling of the annealed rod after exposure to the 

annealing temperature is always presupposed. It is thus that annealing at red heat 

is synonymous with softening (" Ausgliihen"). This operation does not, however, convert all the carbon in steel to the imcombined form, in which case the said ratio would 

be zero.

(686)
BABUS AND BTROOHAL.] ANNEALING-EFFECTS AND VISCOSITY. 95

which solids are found to dissociate in accordance with the laws to which 

gases, in virtue of their physical state, must conform; and for this reason 

the explanation of the phenomena of annealing given by the chemical 

theory is remote and forced, and to be discarded. We gain no more by 

adopting Matthiessen's hypothesis, which considers all iron-carburets 

as solidified, more or less thorough solutions of carbon in iron.

Annealing physically interpreted.T It is not difficult, however, to find 

for the phenomena of annealing a satisfactory explanation of a purely 

mechanical character. We proceed in a manner analogous to the way 

in which, in the case of soft rods of the same dimensions, what is known 

as coercive force80 in magnetism is sometimes defined. To this analogy 

we will recur again.

(1) It will be permissible in this place to introduce a definition of viscosity which is conveniently adapted to our present purposes. We will 

suppose the viscosity of steel to be measured by the maximum of strain 

of a given kind (in the present research the strain accompanying hardness) which a steel rod of given dimensions, after previous condition of 

supersaturation, of itself, permanently retains. The process of tempering to glass-hardness, therefore, is essentially one by which energy is 

stored up, whereas during the operation of annealing the stored energy 

is again more or less gradually expended; and the maximum.energy 

permanently potentialized, under given circumstances of temperature 

(the same rod always presupposed), increases directly with the maximum 

intensity of permanent strain under the same circumstances. Practically, however, we possess no means for the absolute evaluation of either 

of these quantities. But in so far as both thermo-electric hardness and 

specific resistance (the rod being in the state of the maximum of permanent hardness as regards the given temperature) vary directly with 

strain and stored energy, we may accept either of the former quantities 

as furnishing a good general estimate of the magnitude of the latter. 

In the case of one and the same steel wire viscosity is an inverse function of temperature and of temperature only. In the case of wires which 

differ quantitatively though not qualitatively as regards carburation, 

.and are otherwise identical, viscosity is a function both of temperature 

and carburation (carburation < 2 per cent.), decreasing with the former 

and increasing with the latter magnitude.

(2) The difference between the phenomena of annealing and the phenomena of viscosity, as ordinarily studied and observed, is succinctly 

this, that in the latter case stress or a single force is applied from without to produce the gradual and permanent deformation through infinite 

time; in the former, however, stress exists in the rod itself (strain of 

hardness), but can be made to disappear in the asymptotic way characteristic of these phenomena by decreasing the viscosity of the rod as a 

whole; i. e., increasing its temperature. In other words, in the ordinary

80 Cf., for instance, Mousson: Physik, 2 ed., Vol. Ill, p. 86. 

(687)
yb IRON-CARBURETS IBULL. 14.

case of viscosity-measurement the phenomenon is evoked by sudden 

application of stress (torsion, tension, flexure, volume-compression) at 

constant viscosity; in the present case by sudden decrement of viscosity 

at initially constant stress. For instance, given a glass-hard rod at 

ordinary temperatures. Let its temperature be raised to 100°. The 

stress which was just permanently maintained at the lower temperature 

is in excess at the higher, because of the diminished viscosity of the 

rod, as a whole; and this excess must therefore disappear gradually 

through infinite time, precisely as we have observed it. If, furthermore, 

the diminution of viscosity be sudden and very large (annealing at high 

temperatures 200°, 300°, &c.), stress will disappear at a correspondingly 

rapid rate; etc.

In this way we are able, as a first approximation, to refer the phenomena 

of annealing to the general category of phenomena of viscosity.' But for 

the reason of the deformation accompanying the existence of internal 

stress, for the reason that the degree of heterogeneity of a hard rod 

varies to a greater or less extent with each variation of stress as well 

as temperature, it is difficult to form any clear conception of the viscosity 

of the rod, as a whole, except by the aid of such a definition as is given 

at the beginning of the present paragraph. We will waive a further 

development of these views here for the reason that the details of operation of tempering itself are in need of further experimental elucidation, in various directions. Here, however, an account of the occurrences which rob the theory just sketched of much of its clearness and 

perspicuity is in place.

(3) The most satisfactory conception which we can form of the nature 

of the strain of a glass-hard steel rod is that of abnormally condensed 

external layers surrounding, like an arch, an abnormally rare core. 

These two abnormal states of density mutually condition each other. 

It is the stress under which the internal layers exist which is the cause 

of the condensation of the relatively thin external shell, and the extreme 

limit of condensation of the latter, again, which prevents the internal 

layers from falling back to normal density. This view has much experimental evidence to support it,81 though it must be regarded as a mere 

diagram of the essential features of the vastly more complicated structure of the glass-hard rod. An increase of the temperature of a hard 

rod (annealing) is antagonistic to the existence of a strain of this character in two respects. In the first place it is obvious that the rare core 

will be in a condition of less intensity of strain at a high than at a low 

temperature, and this because of the volume-expansion due to temperature. For instance, the temperature may readily be chosen so high 

that an identical hot rod 'would normally have the same low density 

that originally existed in the strained core of the cold glass-hard 

rod. Increase of temperature, on the other hand, diminishes the den81 Cf. Mousson: Pbysik, 2. ed., pp. 224,225, Vol. I, 187. Fromme: 1. c.

(688)
BARUS AND hTiiouiAu] ANJfE AL1NG~EFFECTS AND VISCOSITY. 97

sit.y oi' t he external layers. In proportion, therefore, as tlie temperature 

of the annealing bath is higher, the inner layers of the originally hard 

rod approach the normal density for the respect.ive temperatures more 

and more nearly, and the surface condensation, because the conditions 

of its existence are being annulled, must therefore also disappear at a 

corresponding rate. When the temperature, £°, at which the stress in 

the inner layers is wholly gone has been reached, only as much of 

the surface condensation can have remained as is in conformity with the 

ordinary viscosity of steel at P. The rod if cooled from t° will therefore in the cold state be of greater density than an otherwise identical 

and homogeneous rod it being postulated, of course, that with the disappearance of strain the otempered rod itself approaches nearer and 

nearer the homogeneous state. If the annealing be carried to even 

higher temperatures than t°, the surface condensation will also more and 

more fully vanish, and the density of the cold rod as a consequence 

again decrease. Now, it is exceedingly remarkable and significant that 

the electrical effects due to the annealing of a glass-hard steel rod, enormous as they are, vanish almost entirely after the temperature of the annealing bath exceeds 300° to 400°, that, is at a temperature at which the 

density of a homogeneous hot rod is the same as the density of an identical cold glass-hard rod,8* or, in other words, very nearly at the temperature t° just discussed.83 Magnetic effects, however, as will be shown 

elsewhere, are still very marked for rods annealed at temperatures 

higher than t°. This is in conformity with the hypothesis of residual 

surface condensation, because magnetic phenomena are so largely dependent on the external layers of a rod. Finally, the actual existence 

of a maximum of density for rods annealed at temperatures near t° has 

been experimentally shown by Fromme.84

(4). With these remarks, however, the subject is by no means fully 

exhausted, even so far as our present purposes go. It is easily conceivable that a rod at 400° may be brought into a condition of strain 

(strain of hardness) which bears the same relation. to an identical homogeneous rod at 400° that an ordinary glass-hard rod does to an identical cold soft rod. We believe, however, that the viscosity of the hot 

rod is too insignificant to admit of the permanent retention of more than 

reduced intensities of stress, no matter how much of the strain peculiar to temper may by some ideal means85 have been imparted to it. 

In other w6rds, suppose that a sufficient and very great intensity of

82 Cf. pp. 90-93.

83 The condensed layers of the rod being thin in comparison with the rarefied parts.

84 Fromme: 1. c., p. 355.

86 To form a definite conception of an ideal process of tempering like the one in 

question, suppose the observer to have in control a sot of forces, by aid of which he 

is able to move each of the molecules of a (soft) sire] rod into such positions that the 

rod, as a whole, experiences a strain of glass-hardness of very great intensity. When 

this characteristic distribution of molecules within the volume of the (now) hard rod 

has been effected, let the action of the said forces be discontinued and the molecules

. ' (689)
98 IRON-CARBURETS. ' [BULL. 14.

the strain iu question is imparted both to an iron and to a steel rod of 

the same dimensions.. When the tempering influence has ceased, the 

steel rod will have retained a phenominal amount and exhibit glasshardness. The iron rod, on the contrary, will have lost nearly the whole 

of it. Analogous to the latter, the steel rod when at 400°, no matter 

how much stress maybe imparted to it, will permanently retain no 

more at 400° than the small amount which is consistent with the definition of viscosity above given.86 The present consideration, therefore, 

culminates in an experimental inquiry which may be formulated thus: 

Will a steel rod, if chilled from a given temperature in red heat in a 

liquid at any temperature below t°, and subsequently annealed by an 

exposure to i°, indefinite as regards time, always exhibit the same final 

intensity of stress or thermo-electric hardness barring of course all 

secondary effects, such as are due to decarburatiou, etc..

THE PHENOMENON OF GLASS-HARDNESS DISCUSSED FROM THE 

CHEMICAL AND FROM THE MECHANICAL STANDPOINT.

Chemical interpretation. We now proceed to the discussion of the 

effects of sudden chilling on steel. If we endeavor to explain the known 

phenomena mechanically, we encounter two grave difficulties. In the 

first place, we fail to find any obvious reason why the hardness of a 

chilled rod is not, as Chernoff87 discovered, a uniformly continuous 

function of the temperature of the rod before sudden cooling. In 

the second place, the important function of carbon in the process of 

tempering, and the necessary presence of this element in steel if the 

effects of sudden cooling are to be permanent, is.not easily discernible. 

Both these apparently weak points of the mechanical tjieory may be 

very easily explained chemically. It is only necessary to suppose that a 

certain high temperature must be reached before the uncombined carbon 

of soft or annealed rod is again either converted into the combined form 

or is dissolved.88 That such a temperature would lie, at lowest, in the

left to themselves. Then will the excess of stress gradually disappear, until, through 

infinite time, the intensity of strain which the given rod under the given circumstances of temperature of itself can just permanently retain, is reached. The (hard) 

rod is now in a condition of stable molecular equilibrium. The close analogy between 

this ideal method of imparting temper and magnetization is at once apparent. 

86 Cf. p. 95, (1).

87 Chernoff: Vortrag geh. in der Russ. Tech. Gesell., April u. Mai, 1878; cf. Jeans, 

op. cit., p. 644-7. A reprint of Chernoff's lecture kindly sent by the author showed 

us tliat Chernoff was the first to discover the remarkable phenomenon in question. 

Our own experiments, made independently of Chernoff and shortly after him, led to 

the same result, both as regards mechanical and thermo-electric hardness. (Cf. Barus; 

Wied. Ann., VII, p. 405, 1879; Strouhal and Barus: Wied. Ann., XI, p. 946, 1880.)

88 Cf. Karsfcen's theory on the existence of a " polycarburet," for instance, in PereyWeddiug, op. cit., p. 167; Jeans, op. cit., p. 646; etc.

(690)
BABUS AND sTROuiiAt,] GLASS-HARDNESS PHYSICAL CAUSES. 99

region of red heat is iiomediately probable. Sudden cooling.from temperatures below this critical value, in so far as carbon would remain

 imdissolved or uncombined, could not impart hardness to steel, but 

would merely anneal it the more thoroughly which is actually observed. 

It is particularly to be noted here, moreover, that, according to Jeans, 

in the cementation process iron will not absorb carbon until a certain 

definite high temperature has been reached.

Physical interpretation. (1) The first of the above-mentioned difficulties encountered by a mechanical theory must here be discussed with 

greater detail. The phenomenon is not without remarkable physical 

analogies. Gumming,89 for instance, and after him others, called atten-* 

tiou to the very sudden expansion exhibited by iron at a certain temperature in red heat. Tait 90 signalizes the abnormal thermo-electric behavior of iron under the same circumstances, Finally, the discovery due to 

Gore,91 which Baur 92 has recently studied with considerable detail, is to 

be cited here, viz., that the temporary magnetism of saturated iron at the 

said temperature suddenly vanishes from a foregoing very large value. 

There appears to be little reason to doubt that all of these phenomena 

are different manifestations of the same cause.93

(2) If, now, we bear in mind that a glass hard rod has retained a very 

large part of the increment of volume due to the heat expansion, at the 

temperature from which it was chilled; that furthermore very rapid 

cooling is the necessary condition of the appearance of glass-hardness; 

then the remarks just made at once suggest the inference that Cummiug's phenomenon plays a very important part in the process of tempering. It would follow, furthermore, that the said phenomenon must 

first fully have appeared if sudden cooling is to be accompanied by 

hardness. Hence the necessity of a critical temperature. Here, therefore, we encounter the first difference between iron and steel on the one 

hand, and all other metals and alloys on the other (these being without 

the said phenomenon), as regards conditions favorable to the production of hardness by chilling.

(3) The difference between iron and steel, however, appears even at 

ordinary temperatures whenever both materials are subject to the same 

kind of stress. If, for instance, we expose two like rods, one of iron and

8» dimming: Cf. Tait, 1. c. Gore: Proc. Roy. Soc., XVII, 260, 1869.

"oTait: Trans. Roy. Soc., Ediubgh., XXVII, 1872-73,'p. 125; Proc. R. S. E..VIII, 

p. 32, 1872-73.

«'Gore: Phil. Mag., (4), XXXVIII, p. 59, 1869; ibid., XL, p. 170, 1870.

<» Baur: Wied. Ann., XI, p. 408, 1880.

93 Tait refers the sinuous and broken character of the iron line in his thermo-electric 

diagram to Cuniming's phenomenon. Gore, and more thoroughly Baur, ascribe the 

anomalous behavior of temporary magnetism at red heat to the same cause, iul>oth 

cases attributed to Gore. The same irregular results would probably recur in the 

variation of electrical conductivity on passing the temperature in. question. The 

method of experimentation adopted by Beuoit (I. c.) led him to overlook this. With

 the discovery of Chernoff these interesting analogies are enriched by a new fact.

(691)
100 IRON-CARBURETS. [BULL. 14.

one of steel, to the influence of the same sufficiently intense magnetic field, 

the steel rod, after withdrawal, is found to have retained a very considerable part of its original magnetism permanently, whereas the iron is 

comparatively uninagnetic. Analogously we1 find that, although both 

iron and steel possess the essential property of sudden expansion at 

red heat discovered by Gumming, steel after sudden cooling has retained a phenomenal amount of the peculiar and characteristic strain 

accompanying hardness, while iron remains nearly soft and comparatively homogeneous. It appears, therefore, that the effect of sudden 

cooling on steel also admits of a physical explanation.

Physical and chemical changes simultaneous, There is one other consideration to be added here. If we compare the difference between 

steel and iron as regards their power for the retention of a given mechanical strain, with the respective retentive properties of steel at different temperatures, we may readily infer that under all circumstances 

the absolute amount of combined carbon in iron or steel is the essential 

factor. From this standpoint every gradually progressive change of 

strain from any original to any final value is to be looked upon as a 

physical phenomenon.; the fundamental cause of such gradual change 

of strain, in other words the cause for the necessary change of viscosity, 

is to be regarded as only dependent on temperature in such measure as 

temperature itself determines the ratio of combined to uncombined carbon j hence, also, the amount of combined carbon in the steel rod. Here, 

therefore, the thermo-electric hardness of a rod annealed for an indefinite length of time at t degrees is an indication of the amount of combined carbon in the rod at this temperature.

EXPERIMENTS WITH MALLEABLE CAST-IRON.

Above inferences not decisive. Endeavoring to review the above matter with the object of obtaining data for the discrimination between the 

physical and the chemical features of the process of tempering, we fail to 

find criteria sufficiently decisive to enable us to draw our inferences 

satisfactorily. We are induced even to acknowledge that there exists a, 

remarkably intimate relation between the two methods of interpreting 

the various phenomena; for not only are we able to explain even the 

more important details both from the chemical and the physical standpoint, but the development of either hypothesis continually suggests 

new means for the development of the other.

Electric behavior of malleable cast-iron. At this stage of our research 

it appeared probable that further and perhaps critical information might 

be obtained from a study of the electrical behavior of different species 

of cast-iron. We commenced our inquiry with an examination of what

(692)
BARU8 AND 6TROUHAL.] MALLEABLE CAST-IRON. 101

is known as " malleable cast-iron," 94 a material whichfrom its exceptional 

position in the series of iron carburets seemed particularly well adapted 

for the elucidation sought. This product is tough and tenaceous, though 

imperfectly malleable in the soft state, but after sudden cooling from 

red heat becomes almost as hard and certainly quite as brittle as hard 

steel. Forquingnon95 has shown that it is distinguished from steel, 

chemically, by the relatively very large amount of graphite which it 

contains. We were fortunate in obtaining rods of malleable cast-iron 

from M. E. Hartmann, in Wiirzburg.

The results of 'our measurements of thermo-electric power are given 

in the following table (42) on a plan identical to that adopted above for 

alloys. The rods were examined in three states of hardness, viz., in the 

commercial condition in which they reached our hands, then immediately after sudden chilling, finally after thorough annealing (softening) 

by slow cooling from red heat : 9fi

TABLE 42. Thermo-electric power of malleable cast-iron.

Eods.

ROD No. 1.

Soft...................................

ROD No. 2.

Chilled hard ...........................

Soft........................ ..........

t

C.

18.3

18:4: 

18.5 

18.6 

18.7

15.7

15.7 

15.7 

15.7 

15.7

17.9

17.9 

17.9 

17.9 

17.9

16,8

16.9 

17.0 

17.0 

17.1

12.0 

12.2 

12.3 

12.4 

12.5

18.2

18.2 

18.3 

18.3 

18.3

T

C.

79.7

68.8 

58.3 

47.4 

38.2

59.0

51.2 

43.4 

36.7 

30.1

86.1

-77.2 

60.5 

53.9 

43.1

75.9

66.3 

50.1 

45.2 

37.2

53.9 

46.3 

40.9 

35.5 

30.3

86.1

72.3 

55.5 

45.1 

35.1

e 

observed.

microvolt. 

-57.3

-39.4 

-25.0 

-13.4 

- 7.0

-81.6

-62.5 

-45.6 

-33.0 

-21.8

-69.8

-52.3 

-36.3 

-21. 5 

-11.9

-14.3

- 7.1 

0.0 

+ 3.7 

+ 5.5

-25.5 

-15.4 

 -11.1 

- 7.6 

-4.6

-43.7

-25.5 

- 9.5 

- 2.4 

+ 0.1

e 

calculated.

microvolt. 

-57.2

-39.2 

-25.1 

-13.7 

- 6.8

-80.8

-62.7 

-46.2 

-33. 2 

-21. 6

-68.5

-53.0 

-36.9 

-21.6 

-11.7

1=5 0

- 6.4 

+ 0.1 

+ 4.2 

+ 5.1

-24.4 

-10.3 

-11.5 

- 7.4 

- 4.4

-43.8

-25.2 

- 9.1 

- 3.0 

+ 0.3

Diff.

-0.1

-0.2 

0.1 

0.3 -0.2

-0.8

0.2 

. 0.6 

0.2 

-0.2

-1.3

0.7 

0.6 

0.1 -0.2

0 9

-0.7 

-0.1 

-0.5 

0.4

-1.1 

0.9 

0.4 

-0.2 

-0.2

0.1

-0.3 

-0.4 

0.6 

-0.2

a

) 

I +0.45

1-0.90

1+0.30

I +0. 98 

I +0. 37

1+0.72

b

-0. 014

-0. 013

-0.013

-0. 013 

-0, 014

-0. 013

94 Cf. Perry.Wedding, op. cit., p. 143.

"Forquingnoii, I. c., p. 536.

96 The usual process of surrounding the rods with ferro-ferric oxide in gas-pipe (closed), 

then heating the latter to redness in a charcoal furnace, in which the tube is left until 

the fire is completely extinguished, being adopted.

(693)
102 IRON-CARBURETS. IBULL.W. 

TABLE 42. Thermo-electric power of malleable cast iron Continued.

Rods.

ROD ~No. 3.

Chilled hard ..........................

Soft...................................

t

C.

16.1

16.2 

16.2 

16.3 

16.3

17.8

17.9 

17.9 

17.9 

17.9

18.9

18.9 

18.9 

18.9 

18.8

T

G. 

67.3

62.0 

50.3 

43.7 

37.3

58.2

51.1 

44-. 9 

37.9 

31.2

80.2

66.1 

53.1 

42.1 

33.2

e 

observed.

microvolt. 

7.6

8.3 

9.6 

10.5 

9.5

-22.9

-14.0 

-8.8 

- 4.2 

- 1.4

-31. 0

-10.8 

- 0.6 

+ 2.8 

+ 4.1

e 

calculated.

microvolt. 

6.8

8.6 

10.6 

10.4 

9.2

-22.1

-14.4 

- 9.0 

- 4.2 

- 1.3

-29.6

-12.0 

- 1.3 

+ 3.3 

+ 4'.1

Diff.

0.8

-0.3 

-1.0 

0.1 

0.3

-0.8

0.4. 

0.2 

" 0.0 

-0.1

-1.4

1.2

0.7 

-0.5 

0.0

a

I 1.00

I 0.73 

J

\ 1.15

1

Z>

-0.010

-0. 017

-0. 016

The following and final tables (43) contain our results for the specific 

resistance of malleable cast iron in each of the three states commercial, chilled hard, annealed soft (at red heat). In column third is given 

the actual resistance per meter of rod at the temperature t. The sections in cm2 are found under q. The specific resistances at t and 0 degrees are arranged under st and s, respectively, while the intermediate 

column a contains the temperature-coefficients for this reduction:

TABLE 43. Electrical resistance of malleable cast iron.

Bod.

1 

2 

3.

Remarks.

Chilled hard..........................

Soft...................................

Original condition .....

Chilled hard ..........................

Original condition. ....................

Chilled hard ..........................

Soft...................................

Win,

ohm. 

0. 0274 

377 

290

0. 0262 

323

285

0. 0262 

316 

290

t

C. 

15.5 

11.5 

14.5

15.5 

11.5 

14.5

15.5 

11.8 

14.5

Q

cm? 

(0. 308)2 

(0. 302)2 

(0. 290) 2

(0. 307) 2 

(0. 300) 2 

(0. 296) 2

(0. 303)" 

(0.297)' 

(0. 290)*

ftSSL,i° 

cm2

microhm. 

26.0 

34.3 

. 24.4

.24.8 

29.2 

25.0

24.1 

27.9 

24.4

a

0.004 

0.004 

0.004

0.004 

0.004 

0.004

0.004 

0.004 

0.004

«£!Eo° cm*

microhm. 

24/4 

32.7 

23.0

23.3 

27.9 

23.6

22.6 

26.6 

23. 0'

In the following digest the main data obtained for malleable cast-iron 

are given in more perspicuous form. Aa contains the range of variation 

of the thermo-electric constant a from soft to hard. As has the same 

signification as regards specific resistance:

TABLE 44. Thermo-electric power and specific resistance of malleable cast-iron.

.

Rod number.

1...... ..........

2................

3................

Thermo-electric power (a). \ Specific resistance.

1

Soft.

+0.30 

+0.72 

+1.15

Hard.

 0.90 

+0. 37 

+0.73

Soft.

23.0 

23.6 

23.0

Hard.

32.7 

27.9 

26.6

Aa

 1.20 

 0.35 

 0.42

As

+9.7 

+4.3 

+3,6

(G94)
BARUS AND 6THOUHAL.] ELECTRICAL EFFECT OF STRAIN. 103

Decisive character of the evidence. The first striking feature of the 

last set of results is the slight thermo-electric difference between the 

malleable cast-iron rods and silver. Hence the large values of thermoelectric hardness corresponding to the large values of specific resistance.

Far more remarkable, however, are the almost insignificant variations (Aa and As] produced by sudden cooling. Here, therefore, we 

have a valuable example of an iron-carburet in which the interval of 

mechanical hardness due to tempering; i. e., the difference of mechanical hardness between hard and soft is very great, whereas the corresponding change of the electrical constants scarcely reaches the electrical difference between "blue annealed" and "soft" for steel. In this 

respect, therefore, these measurements have critical value. It follows 

that the mechanical hardness possessed by chilled steel cannot be the 

only or even the principal cause of the enormous variation of the electrical constants; that the said cause of these variations must be sought 

in the secondary phenomena which accompany the presence of hardness; 

that they are therefore very probably due to the strains manifesting 

themselves, as a whole, in the volume expansion of hard steel.

This important deduction is further substantiated by certain experiments made with cast-iron by Joule.97 His results showed that castiron in the white, hard condition is therino-electrically nearest antimony; 

in the black,98 graphitic condition, however, nearest bismuth. All other 

. samples of cast iron examined occupied thermo-electric positions between 

these limits. If, therefore, the shifting of thermo-electric position produced by sudden chilling were to be ascribed to the conversion of uncombined into combined carbon, hard steel, like white cast-iron, would 

lie nearest antimony, soft steel nearest bismuth, whereas the actual 

positions of steel in these two extreme states of hardness is just the 

reverse of this. Hence it would follow, again, that the change of thermo-electric power of steel due to tempering must be referred to the 

increase of volume simultaneously experienced. In striking accordance 

with this inference are the results of Forquiguon : 99 " Le foiite malleable 

se distingue de 1'acier par ses faible allongements et sa forte teueur en 

graphite." It appears, therefore, that here again the absence of marked 

volume increase is the concomitant of the absence of marked electrical 

variation.

If we add to these deductions the remarks made in.pages 89,95, and 99, 

we arrive at the following final result: The existence of the peculiar 

strain accompany ing hardness in steel is the cause of electrical effects so 

enormous that such additional effects which any possible change of carburatiou may involve can be wholly disregarded, and all electrical results interpreted as due solely to variations in the intensity of the said, 

strain.

97 Joule: Plul.Traus., 1859. I, p. 97. ' '

98 That is, black at the surface of fracture, known to be rich in graphite. 

"Forquignon, 1. c., p. 536.

(095)
CHAPTER IV.

ON THE THERMO-ELECTRIC EFFECT OF MAGNETIZATION.

Earlier results. A number of facts go to prove that the molecular 

structure of an iron-carburet is materially affected both by the intensity 

and by the kind of magnetization which it receives. We know, moreover, from experiments of Joule, 100 Wertheim, 101 Mayer, 102 that the existence of magnetism in a bar exerts a stress bearing some analogy to a 

pull in the direction of the magnetic axis. This strain seems to be an 

inseparable concomitant of the magnetic quality. We therefore infer at 

once that if two identical steel rods be magnetized to different intensities, their original thermo-electric powers will have changed; that, 

moreover, the increments of this quantity in the two cases, in accordance with the difference of magnetic state premised, will be unequal. 

Similar remarks possibly apply to other physical constants of steel, in 

particular to its electrical conductivity. With regard to the latter, the 

results of earlier observers are either unsatisfactory or discordant.103 

The experiments of Beetz 104 furnish the first evidence of a decisive 

character. This physicist found that the resistance effect of longitudinal magnetization is an increment of from 0.03 per cent, to 0.06 

per cent.; that in the case of transverse magnetization, however, no 

variation (greater than 0.0005 per cent.) is appreciable. Beetz's result 

has been corroborated and supplemented by experiments of Auerbaeh,105 

Who maintains that while the specific resistance of hard steel increases 

continuously from the longitudinally to the circularly magnetized state, 

soft iroii and soft steel possess a minimum of resistance when unmagnetic.

The discovery of a thermo-electric effect of magnetization is due to 

Sir W. Thomson,106 and his experiments furnish the only results on 

the subject which have thus far been obtained. He found that an iron 

wire in the longitudinal or in the transversely magnetized state is thermo. 

electrically positive or negative,107 respectively, when compared with the

i°°Jonle: Phil. Mag., XXX, pp. 76, 225, 1847. ' 

101 Wertkeirn: Ann. d. Cliim. et de. Pliys. (3), XXIII, p. 302, 1848. 

102 Mayer: Phil. Mag. (4), XLVI, p. 177, 1873:

103 Cf. digest and partial discussion in Wiedemanu's Galvauismus, II a, p. 586 (ed. 

1874).

104 Beetz: Pogg. Ann., CXXVIII, p. 202, 1866. 

105 Auerbach: Wied. Ann., V, p. 289, 1878. 

106 Thoruson: Phil. Trans., Ill, p. 722, 1856. 

107 In Seebeek's sense. See preface.

104 (696)
BABUS AND STBOUHAL.] HARDNESS AND MAGNETIZATION. 105

same wire in the mimagnetic state; that is, there would be a thermocurrent from transversely magnetic to uumagnetic through hot, or from 

nnmagnetic to longitudinally magnetic through hot.

Relative electrical effects of hardness and magnetization. These facts, 

have an immediate bearing on the question in how far the method for 

the measurement of hardness which we employed in the case of unmagnetie rods is to be modified when we deal with magnets. For it is 

obvious, if the hardness of a steel rod is to be expressible in terms of 

its thermo-electric power, that magnetization, in so far as it produces 

no appreciable change of the mechanical quality, must to an equal extent be without influence on the value of its electrical equivalent.

The effect of transverse and of circular magnetization on the specific 

resistance is not distinctly marked. Beetz, L c., obtained no indication 

whatever. We are justified in accepting a similarly small interval of 

variation for the thermo-electric power, although Thomson, Lc., was able 

to adduce conclusive experimental proof of its existence. In its bearing on the especial purposes of the present series of papers, this effect 

is, however, of secondary importance; for which reason, and in view of 

the difficulties with which an exact measurement would be surrounded, 

we determined to neglect it in favor of the much more pronounced phenomenon now to be considered.

It is the evaluation of the electrical effect of longitudinal magnetization, therefore, which is carefully to be essayed. As regards the specific resistance, the results of Beetz furnish the datum of only about a 

half-tenth per cent, for iron in the most favorable case. Now the resistance effect of glass-hardening is as high as 300 per cent. It is 

obvious, therefore, that where the specific resistance is used for the 

definition of hardness of steel, the effect of magnetization is thoroughly 

negligible, since for steel it will probably fall even below the small value 

for iron; particularly so where permanent magnetism is alone of interest. 

Consequently this mode of measurement of hardness may be immediately applied to steel irrespective of its magnetic state.

In considering the thermo-electric behavior of steel in its dependence 

on magnetization, the following striking peculiarity is conspicuous at 

the outset. When the simultaneous variation of thermo-electric power 

and specific resistance is produced by tempering, the result is such 

that steel for continually increasing resistance moves constantly toward 

greater thermo-electrically negative values. When the simultaneous 

variation in question is produced by magnetization, however, a positive 

increment of resistance (Beetz) corresponds to a shifting of steel towards 

thermo-electrically positive values (Thomson). This at once points out 

a radical difference between these phenomena, a difference, however, 

which might have been anticipated both from the utter dissimilarity of 

the strains, as well as from* the fact that we necessarily deal with steel 

only in the first case, but with iron and steel (soft) respectively, in the

(697)
106 IRON-CARBURETS. [BULL. 14..

second where, moreover, the behavior of soft and of hard steel is not 

even qualitatively the same (Auerbach).

The magnetic result admits of the following interpretation. It has 

been 'stated that one of the results of magnetization is elongation in 

the direction of the magnetic axis and contraction at right angles to it 

in such proportions as leave the volume of the iron unchanged (Joule).. 

In this respect the stress is analogous to a pull. Now, Thomson discovered in the one case a current from transversely magnetized to 

longitudinally magnetized iron through hot; in the other a current from 

transversely strained to longitudinally strained iron through hot. 

Possibly, therefore, we have in hand more than an incidental coincidence. It is to be noted that both results apply for elongation withiir 

the elastic limits.J08

Method of experimentation. Thomson's results are qualitative. For 

our purposes, however, quantitative results are a necessity. With the 

object of deriving these the following experiments were made. The disposition of apparatus is diagrarnmatically given in Eig. 14. A soft iron;

FIG. 14. Disposition of apparatus.

wire about 0.08 centimeter thick and.40 centimeters long, the ends of 

which had been fastened to long terminals (c, d) of copper wire, was

'""Thomson, I. c., pp. 712, 713. Cohn, Wied. Ann., .VI, p. 385, lr?9. Beetz (Pogg. 

Ann., CXXVIII, p. 193, 1866) remarks that the resistance effect of magnetization is. 

probably to X>e referred to the occurrence of the magnetic strain, and in so far anticipates the above statement. But he possesses no direct evidence.

(G9cS)
BARUS AND STKOUHAL.] MAGNETIZATION. 107

thrust through a helix (AJ3] together with one of the copper wires, and 

fixed in its axis. At each of the ends of the helix, and as near its center as possible, a doubly tubulated spherical receiver, containing petroleum at the temperatures t and T, respectively, was placed. These receivers contained the junctions of the thermo-element (copper-iron). In 

other respects the disposition and method of measurement was the same 

as that employed in the previous chapter II, and the reader desiring 

further information is referred thither.109

The helix in question had a length of 22.3 centimeters, contained ten 

layers, each with about 55 windings of thick copper wire 0.3 centimeter in diameter.

A Siemens dynamo-electric machine was at our disposal as a source 

of strong current, the intensity of which, obtained by the aid of a large 

tangent compass, -under the given circumstances proved to be

=3 12 gt cmi 

sec

Let 2a be the length, r the radius of a given layer of the helix, n the 

number of turns of wire in the layer, 2& the length of the rod to be 

magnetized. Then will the magnetizing force oh the axis of the helix 

and at a distance b from its center be

-Y _7tni q-f- 1) a I) b

"j

J

and the mean magnetizing force of this layer referred to the given 

length (2&*) of wire

The following are the data describing the field actually used:

 5 -y- _OK -51 -y_KOQ </ ^J _A>. = O<J -*i -A «J^SO - cm* sec

It is unfortunate that the conditions of a more uniform field could notbe secured. But in view of the very large central intensities (X0 =940) 

the belief is warranted that the maximum of magnetization must atleast have been very nearly attained. A uniform field of the intensity, 

130 to 140, is usually regarded as sufficient to magnetically saturate iron. 

Our mean value (528) is about four times as large.

The actual measurement of the influence of magnetization on thethermo-electric power of iron was made in such a way that two separate 

series, each of five observations of electro-motive force and' temperature 

for the rod free from magnetism (i. e., without magnetizing current), 

included a single series of the same number of observations for the, 

magnetized rod (i. e., with current). The thermo-electric constants of" 

the first and third series were therefore to be regarded as identical,

lc»Chap. II -36. 

(699)
108 IRON CARBURETS. [BULL. 14.

while those of the second would differ from them by an amount equivalent to the magnetic effect to be measured. In order that all direct 

action of the helix on the galvanometers or parts of the circuit might 

be avoided, the former with its attached thermo-element was placed at a 

great distance (100 feet) from the latter. These remote parts of the set of 

apparatus being connected by copper wire of a given kind, no discrepancies due to extraneous thermo-currents in the connections were to be 

apprehended. On all these points we satisfied ourselves by special tests. 

Results. (1) The results of the three series of observations in question 

are contained in the following table. If e be the electro-motive force 

for the temperatures t and T of the junctions, we have

e=a(T-t)+b(T2 -t2 ) ........ (1)

a formula to be applied to the three cases. We proceeded as follows: 

Having calculated the constants a and b for the series of observations 

J and III (unmaguetic iron-copper) by the method of least squares, the 

mean of the two values of each was taken, and together with the temperatures Tand ^belonging to the series IJ, was used in deducing values 

of e for this series, bythe aid of formula (1). In the table the latter are 

given in parentheses. They are therefore such as would hold for the 

element unrnagnetic copper-iron under circumstances identical with 

those in which the element magnetic copper-iron was actually placed.

TABLE 45. Thermo-electric power of magnetic and umnaynetic iron.

t

°c.

15.5

15.4 

15.3 

15.3 

15.2

15.1

15.0 

15.0 

15.0 

14.9

14.8

14.8 

14.3 

14.7 

14.7

T

°C. 

71.9

60.1 

50.0 

39.7 

31.0

83.6

72.5 

58.2 

46.2 

35.9

90.8

79.3 

67.8 

54.0 

45.0

e 

observed.

microvolts. 

564.1

456.9 

364.7 

261.7 

171.3

674.2

'578. 8 

448.9 

332. 5 

229.5

733.8

. 635. 9 

536.2 

-J08.8 

325.7

e 

calculated.

microvolts. 

564.0

458.3 

363.3 

260.8 

171.9

(669. 3)

(575. 5) 

(445. 5) 

(329. 6) 

(226. 5)

732.3

637. 2 

536. 3 

409.2 

325.2

Diff.

+0.1

-1.4 

+1.4 

+0.9 

-0.6

1 A Q

+3.3 

+3.4 

-1-2.9 

+3.0

+ 1.5

-1.3 

-0.1 

-0.4 

+0.5

a- 11. 860

b=- 0.0213

&= 0.0211

1 Electro-motive force relatively to copper (given sample), as zero, in each of the three casea.

An inspection of the column of differences proves conclusively that 

longitudinally magnetic iron wire is thermo-electiically more positive 

than iron free from magnetism. We have, therefore, a'corroboration of 

Thomson's result.

Nevertheless, the differences in question are small, and if we compare 

them with the set of values for the series I and III in the same column 

we infer that they must be largely distorted by incidental errors. It 

.appears, therefore, that the observations are not adequately exact for

(700)
BARUS AND sTuouHAL.] MAGNETIZATION THERMO-ELECTRIC EFFECT. 109

the calculation of the constants of the element magnetic-uninagnetic 

iron with the desirable accuracy, though they do furnish a good estimate of their value.

(2) For this reason we made a second set of experiments differing 

from the above in so far as much greater intervals (T t) of temperature were chosen. T and t being kept as nearly constant as possible, 

measurements of e for .the magnetized and uninagnetized state of iron 

were alternately made. Supposing the resistances of Bosscha's zero 

method to have been so adjusted that for given values of T and t and 

unmagnetie iron no current was appreciable in the galvanometer, it 

was found that a permanent deflection at this instrument immediately 

occurred on closing the magnetizing circuit through the helix, of such a 

kind as to indicate an increase of thermo-electromotive force. That 

this effect is Of purely thermo-electric origin, and is not to be directly 

ascribed to extraneous influences, follows conclusively from the regularity of increase of e with increasing values of T. To produce different 

but temporarily constant values of the latter quantity the boiling point 

of water and of aniline and the melting point of lead were found serviceable.

The table below contains mean values of electro-motive force and 

temperature, the results being derived from a great number of measurements of e, with alternately open and closed magnetizing current, 

for each pair of values of T and t. The differences between the values 

of e corresponding to magnetic and unmagnetie iron respectively, enable us to calculate the constants a and & for the thermo-couple composed of two identical iron rods, one of which, however, is magnetically 

saturated, the other free from magnetism.

TABLE 46. Thermo-electric power of magnetic and unmagnetie iron.

Thermo-electric couple: magnetic-un-

£

°C 

16.5

15.4

17.

16.5

15.4 

17.

16.5

15.4 

17.

T

°C 

99.3

184.2 

328.

99.2

184.2 

328.

99.2

184.0 

328.

e 

observed.

micro volts. 

785

1250 

1173

788

1267 

1199

4.0

11.3 

25.4

e 

calculated.

microvolts. 

787

1251 

1178

790

1201 

1204

4.2

10.5 

25.8

Diff.

o

+5 

-5

o

+6 -5

-0.2

+0.8 

-0.4

a 12.49

&= 0.0240

b= 0. 0248 

a + 0. 035

6=+ 0. 00014

1 Thermo-electromotive force relatively to copper (given sample) as zero.

2 Thermo-electromotive force relatively to unmagnetie iron as zero.

Value of the effect. The thermo-electric effect of magnetization, aa 

given by the constant a, is therefore +0.035. The corrospomlnig effect 

due to tempering i. e., the difference between the constants a for the 

soft and for the glass-hard state attains values as high as 13.0. Hence,

(701) ' . , "
110 IRON-CARBURETS. [BULL. 14.

even if the behavior of iron and steel were qualitatively the same an 

unfavorable supposition not in accord with Thomson's observations 

the increment of thermo-electric power resulting from complete saturation would only amount to a few tenths per cent, of the thermo-electric 

interval between soft and glass-hard steel. But in our experiments we 

shall have to do with permanent magnetism only, whence it follows that 

the discrepancy will be reduced to a much smaller value. . We conclude 

that the thermo-electric hardness of a steel rod is practically independent 

of its magnetic state.

A remark on the general character of the strains met with in this 

chapter is in order here:

(1.) In the case of steel (cylindrical rods) hardened by tempering, we 

observe a dense external shell .surrounding an abnormally rare core, in 

such a way that greatest intensity of stress is exerted in the radial direction 5 i. e., at right angles to the axis of figure. Tempered steel has 

been shown to be thermo-electrically negative towards soft steel.

(2.) In the case of steel hardened by drawing through a wire-iron, we 

observe a compressed external shell (though of far lesser density than 

in the first case) surrounding a slightly rarified core, in such a way that 

greatest intensity of stress is exerted in an axial direction. Harddrawn steel is thermo-electrically positive toward soft steel.110

(3.) If an iron wire is longitudinally stretched and the deformation 

temporary, then the strain, so far as its electrical indications are concerned, is similar to the magnetic strain in iron.

"°Magnus: Pogg. Ann., LXXXIII, p. 469, 1851. 

(702)
CHAPTER V.

ON THE INFLUENCE OF HARDNESS ON THE MAXIMUM OF MAGNETIZATION WHICH THIN CYLINDRICAL STEEL RODS OF DIFFERENT 

DIMENSIONS PERMANENTLY RETAIN.

PLAN AND PURPOSE OF THE PRESENT EXPERIMENTS.

Earlier results. The relation existing between the magnetic properties and the state of hardness of steel has been made, the subject of a 

Tery large number of investigations'.111

Dimension-ratio andhardness. After the apparently discordaut.results

 of J. Mtiller, Pliicker, and Wiedeiaann, on the one hand, and Hansteeu 

and Lamont, on the other, had been interpreted by Ch. Ruths in a very 

thorough investigation subsequently corroborated by Fromine the 

present question may be said to have been answered in so far as the 

practically important factor, the ratio of dimensions of the material experimented upon, is concerned. It was herewith conclusively proven 

that both temporary112 and permanent magnetism show a totally different kind of dependence on the state of hardness of steel when the 

saturated rods are long than when they are short. On the basis of 

these researches our knowledge of the practically more important permanent magnetism, more particularly the maximum possible for a given 

cylindrical steel rod, may be summarily stated as follows:

So long as the ratio of length to diameter is smaller than a certain

111 Digests of the earlier papers may be found in J. Lament, Handbuchdes MagnetIsmus, p. 249, 1867; G. Wiedemann, Galvanismas, II a, p. 340, 1874. Among the 

snore recent publications (since 1876) the following are especially to be mentioned: Ch. Ruths, Inaug. Dissertiou, p. 34, Darmstadt, 1874; Ch. Ru'ths, Ueber den. 

Magoetismns weicher Eisencylinder, etc., Dortmund, 1876; J. M. Gangaiu, Comptes 

Eend., LXXXII, p. 144, 1876; C. Fromme, GottingerNachrichten, p. 157,1876; Treve 

et Durassier, Comptes Rend., LXXXII, p. 145, 1876; A. v. Walt^nhofen, Dingler's 

Journal, CCXVII, p. 357, 1876; ibid., CCXXXII, p. 141, 1879; Gray, Phil. Mag. (5), 

VI, p. 321-33-2, 1878; A. Righi, Beibltitter, V, p. 64, 1881 ; W. Metcalf, Beibliitter, V, 

j>. 895, 1881; A. Pictet, Arch, de Gen. (3), VI, p. 113-125, 1881.

The remarks made in this and the following chapters were originally published in 

the Verhaudl. der phys.-med. ges. zu Wiirzburg," N. F. XVII, p. 19,1882. The present paper differs from these in form, the observations having been reduced throughout 

to the current absolute electromagnetic units, and by containing a large number of

 experiments made since the date of original publication. It will be found that the 

latter have added essential corroboration to the inferences drawn. The reduction in

 question, presupposing a knowledge of the contents of Chapter I, has not until lately 

been feasible.

113 The terms "permanent", and "temporary" as used here have the- signification 

proposed by G. Wiedernaun in Beibliitter I, p. 67, 1877.

Ill . (703)
IRON-CARBURETS IBULL.H

limiting value, apparently characteristic of the material chosen, cylindrical rods are capable of retaining a greater intensity of magnetism 

permanently when in the glass-hard than when in the annealed state; 

but after the ratio in question increases to values above this limit, hard 

rods are overtaken in this respect by the yellow annealed j these in turn 

by the blue annealed. Soft rods, cceteris paribus, usually retain more 

magnetism than hard or annealed rods of the same dimensions, except 

when the ratio of axes is small.

Garburation. The results in hand for the specific magnetic effect of 

carburation are even more unsatisfactory. We possess at best cursory 

or isolated data, due to Barlow,113 Miilier, 114 Jainin,115 v. Waltenhofen,116 

Pictet.117 To our knowledge the only attempt at a systematic research 

with reference to the effect of carburation was made by Treve and 

Durassier.118 But the results of these observers are far from being even 

approximately complete. They are, moreover, seriously obscure, because insufficient attention is paid both to hardness and dimensions.

Taken as a whole, therefore, the work done, however valuable, can 

serve for orientation only. It is of the nature of a mere estimate. The 

full and minute analysis must introduce all those complications of a 

metallurgical kind which render the term k ' steel'-' itself indefinite. In 

this place the effect of carburation cannot even be discussed with advantage. It will, therefore, be waived, to be resumed in Chapter VII of the 

present memoir, where we shall have occasion to review the physical 

characteristics of the iron carburets in general.

Critical discussion. Eeturning from this digression to a discussion of 

the magnetic effect of the hardness and of the dimensions of steel rods, 

we find it undeniable, although the main features of the subject may 

be said to be roughly outlined, that the information gained is almost 

intangibly vague and unsatisfactory. In fact, the solution is at most a 

qualitative one. The data of the above researches, in other words, do 

not enable us to trace the continuous change of magnetic intensity of 

thin saturated steel rods, considered for the time being as a function of 

a single independent variable hardness only the steel passing from an 

initial (soft) to a final (hard) state through every intermediate state, 

dimensions and carburation being regarded as parameters. And yet it 

is only from results of this character that an intelligent insight into 

these complicated phenomena can be obtained.

There are two difficulties which have thus far stood in the way of 

more exact research in this direction. The first of these was the want of 

a sufficiently sensitive method for the discrimination between degrees of

113 Barlow: Phil. Trans. p. 117,1822. 

n'Milller: Pogg. Ann., LXXXV, p. 157, 1852. 

115 Jamin: Coraptes Rend., LXXVII, p. 89, 1373. 

1J6V. Walteuhofen : Pogg. Ann., CXXI, p. 431, 1864. 

11T Pictet: Arch, de Genfcve (3), VI, p. 113, 1881.

et Durassier, Mondes, XXVIII, pp. 587, 667,1875.

(704)
BAiuis AND STROUHAL.] EARLIER RESULTS CRITICISM. 113

hardness. The estimate furnished by the oxide tints, 119 if indeed rigidly 

reliable, is much too crude. The same would be true of any other of the 

more current methods. After we had found, therefore, how well the 

electrical properties of steel can be thus utilized after we had .seen, 

for instance, that the annealing effect of temperature as low as 50° C. 

can be. pursued and studied with the utmost nicety the application of 

our method to magnetic phenomena at once forcibly presented itself. 

Subsequently certain analogies, which appear to exist between hardness 

itself when measured electrically and permanent magnetic moment, rendered the application of our method even more desirable. With regard 

to the second difficulty, we want in this place again to emphasize that 

the behavior of rods of different dimensions cannot by any means be 

immediately compared unless, ccuterisparibus, the same thickness occurs 

throughout. Most of the observers cited, however, have obtained their 

results with rods for which different values of L : J) were secured120 

by retaining L constant and varying D. Now, it is, a priori, to be anticipated that glass-hardening, accompanied or not by subsequent annealing, will be productive of different effects, of states of hardness, 

which, even if temperature and time are identical, are structurally121 the 

more dissimilar in proportion as the rods subjected to these operations 

differ in diameter. Nor is this all. Difference of thickness usually implies a difference in chemical composition, unless, indeed, the specimens 

chosen are cut from the same piece of steel. To our knowledge, in none 

of the above researches (rods from 0.2 centimeter to 0.7 centimeter in 

diameter) was this done. How very different the behavior of rods frequently is, even when coming from the same source and nominally of 

the same kind of steel, will appear from several examples to be cited in 

the next paragraph.

Thomson's law, in accordance with which geometrically similar rods 

show equal moments per unit of mass when placed in identical magnetic 

fields, is probably true for iron, but cannot be immediately applied to 

the case of steel: possibly it may be applied to very soft rods; to a 

lesser extent to those in the annealed state; certainly not to glass-hard 

rods, inasmuch as here the peculiarities of internal structure resulting 

from the process of tempering manifest themselves, even in the case of

119 It is highly probable that a given oxide tint can he obtained in an infinite number 

of ways by varying temperature and time of exposure simultaneously : lower temperatures acting for very long intervals of time producing the same co]or effect as higher 

temperatures for short periods of exposure. Researches on this subject are in progress. 

Possibly the variation of color may correspond very closely with the actual variation 

of hardness, as discussed in'Chapter II.

120 All the above remarks apply to cylindrical rods of length L and diameter I).

121 Structure, as used here and elsewhere, refers to the variation of density encountered on passing along a radius from the axis of the rod to the circumference. In 

how far the structure of rods of different diameters will vary cannot even be conjectured. -» 

(705) 

Bull. 14 8
114 IRON-CARBURETS. [BULL. U.

geometrically similar figures, in a way that compels us to treat each 

thickness individually.122

TJw present experiments. The above remarks, we believe, clearly show 

that the whole of our knowledge on the relation of magnetism to the variables, carburation, hardness, and dimensions, is urgently in need not only 

of reconstruction, but of farther elucidation; and we took great delight 

in welcoming this opportunity for the practical application of the experience which the attention of many years to the physical properties of 

steel has given us. The first part of our projected magnetic researches, 

referring principally to long, thin rods, to annealing temperatures below 

500° C., and to the soft state, are herewith made public. The second 

part, on the behavior of short, thick rods, and on the influence of temperatures between 400° and 1,000°, will have to be reserved for another 

communication. We may add, more specifically, that for the 30 rods

examined in the present experiments the ratio of dimensions, a = ~,

varied between « = 120 and a = 10. But the data in this chapter enable us to predict the magnetic behavior, even for magnets in which the 

said ratio (a) lies below 10 or above 120, with a degree of probability 

amounting almost to certainty. But, in view of the importance of 

thick magnets, now so largely used in rnagnetometric and galvanometric work, a new research on this subject seems pertinent. Similar remarks apply to high annealing temperatures.

We conclude this paragraph with the appropriate remark that our 

knowledge of the excessively complicated phenomena under cousiderac 

tion can be advanced by tentative methods alone. The mathematical 

theory of the subject, even in case of homogeneous material, encounters formidable and almost insuperable difficulties. But we will be 

able to show in the sequel that the condition of internal structure is 

one of the most essential factors which determine the magnetic character of the (tempered) rod. Again, the investigation of the true nature 

of the structural properties of hard steel is surrounded with difficulties 

which will long baffle the experimentalist's skill. For in all such methods, like the one which Fromme pursued in order to obtain preliminary 

data on the condition of the interior of a steel rod, and in which the 

external layers are gradually and consecutively removed by acids or 

otherwise, we apprehend that the rod, for the very reason of this removal, will change its physical condition (strain) while in the hands of 

the operator. Long before we reach, the core of the rod its density and 

electrical properties must be conceded to have changed materially. 

Nevertheless, we infer that the structure of tempered steel is of a 

thoroughly definite and distinct character; that this is emphatically

122 This inference, wbicb we published in the same form in 1882, has since been corroborated by H. Meyer, in bis paper "Ueberdie Magnetisirungsfunction von Stahl u. 

Nickel," Wied. Ann., XVIII, p. 248,1883. Meyer contends that Thomson's law is true 

neither for soft nor for hard steel rods.

(706)
BARUS AND 6TUOUHAL.J DESCRIPTION OF THE STEEL. , 115

demonstrated by beautiful consistency and uniformity of our different 

series of results, obtained with different steel rods, tempered at different times.

ON THE MATERIAL USED.

The steel. The steel chosen was that described in the previous chapter. 

It was received in the shape of rods 30 centimeters long and from 0.084 

centimeter to 0.150 centimeter in diameter. These were hardened as 

shown above (Chap. II, pp. 29-31). Analyses are superfluous, as it is 

our intention at present to study the results for a single value of the 

variable parameter, carburation, only; or, in other words, to investigate 

the magnetic behavior of a given type of steel. From the large supply 

of tempered rods such were chosen as not only showed a maximum of 

thermo-electric hardness for the glass-hard state, but also, when tested 

for longitudinal homogeneity in the manner described in pages 38,121, 

gave the most satisfactory results.

Rods of lilce composition, thickness, temper. At the outstart we were 

inclined to infer that from rods of the same kind of steel (composition), 

of the same thickness, and tempered in the same manner in so far as 

the details of this process are at the observer's control comparable 

values of the maximum of magnetic intensity could be immediately derived. For the purpose of testing this supposition, rods of0 nearly the 

same thermo-electric hardness (II, p. 65), but of different lengths, were 

broken from different samples of the class of rods experimented upon. 

These, after having been subjected alike to the action of the same magnetic field in our case of unnecessarily great intensity and fairly uniform according to Thomson's law ought to have retained a moment per 

unit of mass such as would be expressible by the same function of the 

ratio of length to diameter. Moreover, as the thickness of the rods 

chosen was practically the same, this function would have to increase 

to a certain limiting value, as the corresponding lengths increased from 

zero indefinitely.

These anticipations were, however, by no means realized. In this 

place it will be well to add, by way of example, such results as are particularly applicable for the illustration of the consideration just made:

A magnet 4.1 centimeters long, 0.084 centimeter thick, weighing 

0.173 gram, specific resistance s=39.8 at 17.6 degrees, after saturation 

was found to have the specific magnetism w=43.0; whereas another 

specimen taken from a different rod, the magnet being only 3.05 centimeters long, 0.084 centimeter thick, weighing 0.131 gram, specific resistance «=39.4 at 18.5 degrees, after saturation had retained m=52.0; 

whence it appears that in the second case, notwithstanding the fact that 

the length (or ratio of dimensions) was only about three-fourths of that

(707)
116 IRON-CARBURETS. [BULL. 14.

in the first, a very decidedly greater intensity of magnetization was attainable. This is hardly referable to a difference of composition. In 

all probability the result is to be associated with peculiarities of the internal structure of the rods.

The following example is still more to the point:

A magnet (a) 5.0 centimeters long, 0.084 centimeter thick, weighing 

0.214 gram, of the specific resistance s=40.4 at 18.5 degrees, had retained the specific magnetism w=45.8; another taken from a second 

rod of the same thickness, the magnet (&) being 5.9 centimeters long, as 

before 0.084 centimeter thick, weighing 0.24.9 gram, of the specific resistance s=39.7 at 18.3 degrees, gave, after saturation, m=45.0.

In order to arrive at some inference as to the cause of this difference 

of magnetic state, both the magnets last mentioned were slowly annealed, at first for a period of ten hours in steam, thereupon for an 

additional period of ten hours in aniline vapor at 185 degrees, finally 

for one hour in melted lead at 330 degrees. After this both were softened by heating to redness and cooling slowly. For each of the particular states of hardness thus obtained the specific resistance was 

measured. The rods were then magnetized to saturation and their 

magnetic moment determined. The results of these precursory experiments are given in the following table:

10h in 100°..................... .....................................

10h in 185°. .........................................................

I1' in 330°.... .......................................................

Soft..............................................................

8

40.6

35.2

26.6

9fl 3

1fi Q

(a)

t

18

?,0

?0

9ft

on

m

45.8

43. 1

62.2

84 3

46.8

s

39.9

QS; i

26.4

20.1

1 o n

(b)

t

18

?,0

?0

20

OA

m

45.0

42.7

61.7

86.4

56.0

From an inspection of the table, or of Fig. 15, it is obvious that at 

330° (lead bath) the magnetic intensity of the longer magnet (b) has 

overtaken that of (a), but it is not until both magnets are quite soft 

(homogeneous) that the normal behavior fully appears. It is to be noted, 

however, that this experiment is not in itself perfectly conclusive. The 

influence of carburation is principally efficient in the glass-hard state ; 

L: D, if its value be as large as in the present case, less so. In the soft 

state, however, the effect of L: D predominates. It would be possible, 

therefore) with due consideration of the values of s, to ascribe the results 

obtained to a difference of carburation between (a) and (&). The nearly 

equal values of specific resistance for the soft state, especially when 

viewed in the additional light given by the first example, make the latter inference improbable.

- Eacli series of magnets originally integrant parts of the same liard rod,. 

The individuality of behavior of different rods (i e., such as are not

(708)
BAttUS AND STKCK'IIAI, ] STRUCTURAL PHENOMENA. 117

pieces of the same homogeneous rod, though otherwise identical) appears, therefore, to be conclusively demonstrated.123

- 9-

-49- Resistance

4- 'f (an-. tnicrolaii)

FIG. 15. Specific magnetism of rods annealed from 0° to 1000°.

Eesults of this kind a number of other examples might be cited 

urged the inference upon us that only in the case where magnets are 

broken from one and the same longitudinally homogeneous hard rod, 

can comparable and harmonious results be expected. Add to this the 

fact that the frequent reheatiugs to redness, necessary in drawing a wire 

to small diameter, imply a difference of carburatiou in different samples, 

for this reason alone. However insignificant this may appear to be, we 

were convinced that its effect, where accurate results are called for, is 

by no means negligible. These instances are adequate to give emphasis 

to the statement above made, that each rod must be examiued and 

treated separately. Indeed, a better opinion of the longitudinal homogeneity of a wire can be formed subsequently from an inspection of the 

-behavior of the different magnets taken out of it, than could be formed 

at the outset by the aid of the electrical properties of different parts of 

the rod in question.

Unfortunately, thiu (diameter = 2p = 0.084 centimeter) glass-hard 

rods, of the same hardness throughout their length, out of which magnets of the kind desired, having different values for the ratio of dimension (L : D), can be Broken, are only obtainable with great difficulty.

123 It is quite clear that even the details of the process of tempering have an important 

bearing on the magnetic intensity'of hard rods. A single rod repeatedly rehardened 

shows very marked differences in the maximum of permanent magnetization for nominally the same state.

(709)
118 IRON-CARBURETS. [BULL. 14.

Even those which were here finally accepted as the best for the present 

purposes, after the test for homogeneity was applied, proved to be satisfactory for only two-thirds of their length. The remaining third had 

to be discarded. There are some drawbacks in the way of heating a 

thin steel rod uniformly by means of the electric current. Greater difficulty is encountered in chilling it suddenly and alike throughout its 

length, in consequence of the large rate at which radiation takes place. 

Our thick rods (diameter = 2p = 0.150 centimeter) were much more uniform. The samples selected from our supply showed differences of electrical conductivity for different parts of their lengths, amounting to only 

a few tenths of one'per cent.

METHOD OF MAGNETIZATION.

Helix. Magnetic field. Magnetization was effected by the inductive 

action of a galvanic current in a helix. As a source of current the 

Hefner-Alteneck dynamo-electric machine of the Physical Institute of 

Wiirzburg was at our disposal. A magnetic field of very great intensity 

c.ould thus easily be produced, and discrepancies due to non-saturation 

were therefore not to be apprehended.

The helix referred to (length 2a=22.3 centimeters, inner radius r=2.1 

centimeters, outer radius r=5.3 centimeters) contained ten layers, in 

each of which there were w=55 turns of thick copper wire.

If a current, «, circulates through the helix, the magnetizing force Xb 

at a point on its axis at a distance & from its center will be

_7tnir a+1)

~

a &

In our case the mean value of current was

;=30 Amperes

see

If this value is introduced into the formula specified and the aggregate of the value of Xb calculated, the total intensity 2Xt of the magnetic field at different points & (cm) on the axis varied as follows:

b= 0

884

1

882

2 

879

3

874

4

865

5 

851

(cm) 

( g* \

\cmit sect

If it be remembered that the diameter of our magnets was less than 

1 millimeter, these figures show in how far the field by which magnetization was effected may be said to have been uniform. The longest 

magnet was 10 centimeters. In this extreme case the variation of force 

throughout its length amounted to less than 4 per cent. In the more

(710)
BARUS AND STKOUHAL.J MAGNETIZATION. 119

usual case of magnets of lesser leugth much smaller variations present 

themselves. On the other hand, where permanent magnetism is alone 

of interest and the field of great intensity, the desideratum of uniformity 

is perhaps of minor importance.

The mean intensity X of the magnetizing force due to a single layer 

of wire and corresponding to a length 2b (cm) symmetrically located 

with respect to the center of the helix is

In the present case the aggregate 2X of these means, or the mean 

intensity of the field due to the whole helix, corresponding to the part 

26 of the axis situated as specified was

b2X=0

884

1

883

2

882

3

880

4

877

5

874

i

(cm) !

cm^aec ' 

1

The largest values of 2X employed by Euths, for instance, in his 

researches on temporary magnetism, were 2X=<iO for iron and 5X=147 

for steel. There can be no doubt, therefore, that in our case the most 

complete saturation possible was actually attained. Indeed, we had 

frequent occasion to convince ourselves that successive magnetization 

produced no additional effect equivalent to one per cent, of the Avhole 

moment.

Magnetization. In the case where magnetism is induced by means of 

a helix, the question in reference to the manner in which the magnets 

'are to be introduced and withdrawn from its action is always of importance. Some observers, among them J. Wiedemann and C. Fromrne, 

placed their magnets in the helix after the current had been closed and 

withdrew them before breaking it. In this way the complications due 

to certain undesirable induced currents are avoided. At the same time, 

however, the advantages of a uniform field are lost and a normal distribution of magnetism possibly interfered with. For the last mentioned 

reasons, Holz and Fromme preferred to open and close the current while 

the rod to be magnetized lay in place. Both methods have been made 

the subject of an experimental comparison by Fromme.124

We gave preference to neither of these methods, but chose a plan 

which., under the circumstances, was also the most convenient. It consisted in allowing the current to increase from zero to its maximum value 

gradually and then again to wane in the same manner. This may be 

satisfactorily accomplished by appropriately applying the power to the 

dynamo-electric machine. We think we are justified in the belief that 

in this way the permanent magnetic moment is finally weakened only 

to a negligible extent, at least to a smaller amount than in either of the 

other methods.

12->C. Fromuie, Wied. Auu., V, p. 345, lb?8. 

(711)
120 IRON-CARBURETS. [UULI.. 14.

In order to give the magnets the desired symmetrical position, relatively to the helix, a glass tube was secured coaxially with it. Into one 

end of this the little rods were introduced to be drawn into its center 

by the force of magnetic attraction. Each rod was magnetized twice, 

an interval of about 30 seconds125 intervening.

MEASUREMENT OF MAGNETIC MOMENT.

Apparatus. The magnetic moments of the wires were derived from 

the deflection of a small magnetized steel mirror, observed after the 

manner of Poggendorf with telescope and scale. We made use of an 

appliance due to Professor Kohlrausch, by means of which the attached 

magnets could always again be brought into the same position relatively 

to the mirror, and rotated 180° around the vertical. Both the first and 

the second method of Gauss were applied.

The apparatus consisted of a solid brass ring provided with leveling 

screws, from which two vertical columns of the same metal arose supporting a circle graduated in degrees. An alhidade, with two verniers, resting on conical bearings, occupied a central position within the 

latter. A horizontal brass bar, in connection with the middle of the 

alhidade, and adjustable with reference to the vertical, carried on its 

lower edge the special device above referred to, by the aid of which 

the magnets were appropriately fastened in position. This apparatus 

was fixed in place and adjusted at the outset, and the distance between the axis and that of the needle determined once for all. In this 

way the relative values of the moments of our magnets (and it is from' 

these that the results of the present paper are principally deduced) are 

independent Of discrepancies introduced by errors in the determination 

of the distance betAveen magnet and mirror.

Method. In calculating the results we made use of the ordinary 

formulae

M-^ Ttm^ 9

for the first, and

Kf r* T tan£ V Jj/JL ^^ 12

for the second of the positions of Gauss, where T is the horizontal intensity of terrestrial magnetism at the place where the observations are

(

o^ \ in our case T 0.196 jfjj^r )> r *ne distance between magnet

and needle (in our adjustment r=26.34 centimeters), q> the angle of de125 Frankenheirn was the first to show that the number of times a magnet is exposed 

in a given field, and not the duration of such exposure, is of marked influence on the 

resultant moment (Pogg. Ann., LXXIII, p. 49, 1864).

(712)
BARUS AN-D STBOUHAL.] HARDNESS MEASUREMENT. 121

flection, I the distance between the poles. We assumed I 0.85 L where 

L is the length of the magnet. This approximation is sufficient because 

the term of the above formulae involving I is only of the nature of a 

correction.

The measurements were made at ordinary temperatures, varying between 18° and 21°. The effects of the changes in the magnetic moment, 

as well as those due to variation of terrestrial magnetism, we regarded 

negligible. This is also true with reference to the torsional discrepancy 

of the silk fiber (the torsion-coefficient was found to be only 0.00032).

In addition to the magnetic moment M of the whole rod we shall give 

throughout the moment m per unit of mass (1 g.). To this quantity 

the name specific magnetism has been given. In the case where a number of different magnets are compared it is a more perspicuous result 

than the former.

DETERMINATION OF THE DEGREE OF HARDNESS.

Resistance measurement. Of the two methods of estimating the hardness of the rods proposed in Chapter II, one of which depends upon 

thermo-electric properties, the other upon the specific resistance of 

steel, we chose the latter because of its greater simplicity. Here again 

it was our object, primarily, to arrive at accurate relative values, and 

fliis we were able to accomplish satisfactorily by the aid of Matthiessen 

and Hockin's modification of the bridge. In one of the branches of 

Wheatstone's combination, the bridge cylinder of F. Kohlrausch (diagramatically represented in Fig. 16 by the straight line AB] was inserted j in the other the steel wire Di-^2? 

whose resistance is to be measured, and 

a tenth Siemens unit Z-3Z^ the whole being 

appropriately connected with thick copper wire, Flat clamp-screws of brass 

pressed* the steel rod down firmly upon a 

plane surface. In this way the danger of 

breaking the very brittle magnets was less

seriously to be apprehended. The normal riG. t6._Dispositionofnatusroi, ro. 

Z$Zi was made of heavy German sil ver wire siatance measurement. 

soldered to thick terminals. These were amalgamated and in galvanic connection with the bridge by means of mercury. From the 

points A and B the copper-connecting wires lead to a galvanometer, 

the deflections of which are observed Avith telescope and scale. As a 

source of current two Smee elements were found sufficient.

In figure 16, if the points Z>i, D2 , Z-A , Z± correspond to the points If,, 

M2 , M3, Jf4 , in such a way that when connected respectively with the

(713)
122 IRON-CARBURETS. [BULL. 14.

terminal of the battery, the current in the galvanometer (8) is zero, we 

have

Pi, A Jfi, 3f»

To obtain the points of contact D] and D2 , we made use of two steel 

needles, the points of which had been flattened wedge-shaped. These 

were fastened parallel to each other, and at a fixed distance apart, in a 

small piece of wood. To their tops the ends of two long thin copper 

wires were soldered. This arrangement, after having been screwed to 

a longer reshaped piece of wood, along which the copper wires were 

led, represented as a whole a kind of tripod, two of the feet being the 

steel needles mentioned. During the measurements the latter stood 

on the steel rod to be tested. Small clamp-screws served for connecting the battery- wires with the terminals of this apparatus, these being 

sufficiently long and thin that the successive clamping and unclamping 

did not interfere with the adjustment in such a way as to slide the 

points J>u A along the steel rod, for instance.

This simple contrivance, which is easily improvised, gave us results 

of the most satisfactory kind. Our resistances were rarely larger than 

a few hundredths ohm. Nevertheless they were determiuable with an 

accuracy of a few tenths per cent, with certainty. Our mirror- galvanometer enabled. us to adjast the sliding contact on the bridge-cyliuder 

of Kohlranseh to -&> a scale-part, or roihro °f tne length of the wire A, 

E. In virtue of a fixed distance D1? D2 we possessed a number of these, 

arrangements to be used according as a larger or a smaller wire was to 

be operated upon in view of the stability of the apparatus as a whole, 

and of the fact that all operations were conducted in a room of practically constant temperature, an unusual a.ccuracy iu the relative data 

was attained.

It is obvious that this method is applicable at once as a test for the 

degree of uniformity of hardness along the length of the wire. By 

placing the contrivance just described on different consecutive lengths 

without making any further alteration in the adjustments, the respective resistances of these parts could be subjected to a minute comparison. 

This furnishes us with the criterion desired.

Great difficulties were encountered in the measurement of the 

sections of the steel wires. We determined the diameter microscopically, with the aid of an ocular micrometer of known factor. Two readings, corresponding to diameters at right angles to each other, each 

pair taken at a number of different, approximately equidistant parts of 

the wires were made. The mean of these individual values was accepted. 

This plan was fairly good in so far as the error made in the measurement 

of the sections does not influence the relative values of resistance.

From the observed resistance of any wire at t degrees, the value of this 

quantity per meter, in ohms ( w), was calculated. A knowledge of the tern
BAHUS AND STKOUHAL.] METHOD OF ANNEALING. 123

perature-coefficients of steel126 then enabled us to deduce herefrointhe specific resistance (resistance in microhms between opposite faces of a cubic

centimeter) for the temperature 0°. This value, s ( ^5L 0° microhm Y

7 \GUIZ J

has been adopted as a measure of hardness.

From s, the thermo-electric hardness of our wires may be* calculated 

by the aid of the formula

fc=0 .412 s

In this way the present scale of hardness is made identical with that 

previously employed in our work on the phenomena of annealing. The 

data h are therefore proportional to the specific resistances of the steel 

rods and have a very simple connection with the respective thermoelectric constants a, as has been shown elsewhere. 127

METHOD OF ANNEALING.

Systematic plan. In the different series of experiments the glasshard state was chosen as the point of departure. After the rods had 

been examined with reference to their hardness in the way described, 

they were magnetized to saturation and their magnetic moment determined. Thereupon we exposed them to the annealing effect of steam 

at 100°. A sufficiently small decrement of hardness resulted by continuing the operation for one hour at first,and then for additional two, three, 

and four hours, amounting in the aggregate to ten hours of exposure. 

This is sufficient to bring the rod as near the limiting state, or the maximum of permanent hardness corresponding to 100° as is easily practicable.

The magnets were now subjected to the action of aniline vapor at 

185°, during successive intervals of twenty minutes, forty minutes, two, 

four, and finally six hours.

A lead bath, at 330° was next chosen. At first the magnets were annealed therein for a time of one minute only. Then the action was prolonged to one hour. In the later experiments the melting point of tin 

(240°) as well as that of zinc (420°) were found serviceable as temperatures of annealing.

Finally the rods were thoroughly softened in the usual way, by heating to redness and cooling very slowly. To avoid oxidation of the magnets we imbedded them in pulverized artificial ferro-ferric oxide, surrounded this with fire-clay, and finally enveloped the whole with a 

piece of gas-pipe.

In this way we obtained about twelve distinct states of hardness, distributed "with fair uniformity between the glass hard aud soft states, as

12o Of. Chapter I. «"Chapter II, p. 63. 

(715)
124 IRON-CARBURETS. [BULL. 14.

extremes. It is only between the soft condition and that corresponding 

to the temperature 300° of the annealing bath that a greater number of 

degrees of hardness, as our results eventually showed, would have been 

desirable. Particularly in the case of long magnets there appear within 

this interval changes of magnetic capacity of a very significant character, 

changes, moreover, which cannot be satisfactorily supplied by a process 

of interpolation based on the data for neighboring states.

After the magnets had been taken out of the annealing bath it was 

our custom to put them aside for some time in order to allow a complete 

cessation of possible "after" effects. Thereupon the test for hardness 

was applied.

Results of the annealing. The progress of annealing in the different 

experiments is fully given in the following tables:

TABLE 47. Thin icire. 

[2p=0.084 centimeter.]

Description of temper.

Specific resistance -5 - 0° microhm. cm2

Rod I.

38.5 

36.3 

34. 8 

33.9 

33.4 

29.5 

28. 4 

27.1 

25 9 

25.0 

20.4 

18.8 

15.7

Hod II.

37.3 

34.7 

33.0 

32.2 

31.0 

27.4 

20.3 

24.9 2'-'. 7 

22.8 

IR. 9 

17.4 

14.5

TABLE 48. Thick icire. 

[2p=0.15 centimeter.]

Description of temper.

Eod IX.

47.2

42.0

39.5

38.2

37.4 3i <\

29. 7

27.9

26.2

24.8

24.0

20.3

17.5

15.7

EodX .

46.8 '

41.7

39.3

38.0

07 1

31.4

29.6

27.7

26.0

24.6

23.8

20.1

17.2

15.6

Eod XL

43.8

38.6

36.5

35.1

34.3

29.0

27.5

25.6

24.2

22.9

22.2

19.0

16.2

14.9 ,

Eod XLI.

43.5 '

38.4

36.2

34.9

34.0

28.7

27. 3

-23.9

22.7

2'.'. 0

18.7

10.0

14.9

Specific resistance - 0° microhm. cin2

(716)
UAUUS AND BTHOUIIAL.] MAGNETISM, HARDNESS, DIMENSIONS. 125

In how far we are justified in regarding the scale of hardness for rods 

in the magnetized state as ccBteris paribus identical with the scale corresponding to the unmaguetized state has been fully discussed in the previous chapter on the thermo-electric effect of magnetization.128

MAGNETIC RESULTS FOR RODS OF LARGE DIMENSIO1ST-RAT10.

Description of magnets. The results of the experiments, the plan of 

which has been fully detailed in the preceding paragraphs, are given in 

the following tables.

The first experiments were made with wire of smaller diameter. 

Breaking rod No. I into three parts, we obtained the magnets Nos. 1,2, 

3; and, similarly, the raagnets Nos. 6, 9,10, from rod No. II. Accidentally, the longest of these, No. 10, during the course of the experiments, 

was further broken into parts, which, however, in their turn, were available for magnets. Nos. 5,7,8 were thus obtained. All magnets are numbered in the order of their respective lengths. The following table (49) 

contains certain important physical constants of the ten rods. We 

measured their dimensions first while they were in the glass-hard state j 

then after the various stages of annealing; finally, before and after 

thorough annealing at red heat. In this way we were able to arrive at 

numerical data for the simultaneous volume-contraction with some accuracy. Mean values are given in the tables. In calculating the specific 

gravity, 4, from the mass and dimensions of the individual rods, our 

main object was that of checking the measurement. In view of the 

small diameter, A will not be correct within 1 per cent.

TABLE 49. Constants of magnets.

Rod 

2 p cm, A

L f

A=7.70 |

II.

A=7.69

Magnet 'No.

1 

2

3 

4

5

6

7

8 

9

10

Mass

M

g

, 0. 086 

172

249- 

336

068

126

197

236 

413

502

Length

cm.

2.00 

4.05

5.85 

7.90

3.63

3. 03

4.72

5.60 

9.92

12.06

Dim. ratio, 

a

23.9 

48.4

69.8 

94.3

19.6

36.5

56.8

68.1 

119.5

145.1

The degree of homogeneity of these rods may be satisfactorily inferred 

from the data for s. In the case of Nos. 1, 5, 6, the method for the 

measurement of resistance could not readily be applied, the rods being 

too short. We, therefore, preferred to accept in place of such direct

»» Wied. Ann., XIV, p. 54, 1881. Cf. W. Beetz, Pogg. Ann., CXXV1II, p. 193, 1866.

(717)
126 IRON-CARBURETS. [BULL. 14.

results, the values deducible by interpolation from those obtained from 

rods of like origin. Data of this kind are, however, distinguished in 

the next table by an asterisk (*) preceding the numbers.

Magnetic data. The magnetic measurements were made in the second 

position of Gauss. The^numerical values of the constants occurring in 

the formulae 

are as follows:

i~'!&A&

T=0.196cm*8ec r=26.34cm jR=207.4cm 

The results of the magnetic measurements are these:

TABLE 50. Relation between the magnetic constants of steel and hardness. 

1. Magnets in the glass-hard state.

Eod.

,

CL. \

*

Magnet

No.

1

2

3

4

6

9

10

a

24

48

70

94

36

120

145

Wlm

ohm.

*0. 726

0.734

0.727

0.716

*0. 719

0.723

0.714

t

00.

*1&2

17.6

18.3

18.7

*18.5

18. 5

18.5

cm flo

8 cm*

microhm.

*38. 5

38.8

38.6

38.1

*37.3

37.5

37.1

n

cm.

1.34

3.46

5.28

7.68

2.58

10.77

13.78

M

abs. H.

2.89

7.41

11.20

16.06

5.54

22.11

27. 65

TO

abs. E.

33.7

43.0

45.0

47.9

43.9

53.5

55.1

2. Magnets annealed 1 hour in steam.

'{

*~\

1

2

3

4

6

9

10

24

48

70

94

36

120

145

*0. 687

0.695

0.688

0. 679

*0. 670

0.673

0. 667

*18.4

18.2

18.4

18.6

*18.6

18.6

18.6

*36.3

36.7

30.4

35.9

*34.7

34..S

34.6

1.33

3.38

5.19

7.51

2.53

10.61

13.53

2.85

7.23

11.01

15,70

5.44

21.78

27.15

33.3

42.0

44.3

46.8

43.1

52.8

54.1

3. Magnets annealed 3 hours in steam.

( ' 1

J II.. .j*

1

2

3

4

6

9

10

24

48

70

94

36

120

145

*0. 662

0.669

0.665

0.653

*0. 641

0.644

0.638

*20. 1

20.0

20.2

20.2

*20.1

20.2

20. 1

*34. 8

35.1

34.9

34.4

*33. 0

33.2

32.9

1.30

3.30

5.08

7.41

2.50

10.41

13.29

2.80

7.06

10.78

15.49

5.36

21.38

26.67

'32.7

41.0

43.3

46.2

42.5

51.8

53.2

4. Magnets annealed 6 hours in steam.

fI

I... <

I

,

n. \1

i

2

3

4

6

9

10

24

48

70

94

36

120

145

*0. 648

0.654

0.651

0.638

*0. 626

0.630

0.623

*21.1

20.9

21.3

21.2

*21.0

21.0

21.0

*33.9

34.2

34,1

33.5

*32. 2

32.3

32.1

1.28

3.23

5.00

c 7.29

2.47

10.22

13.05

2.76

6.91

10.60

' 15. 24

5.31

20.98

26.19

32.2

40.1

42.7

45.4

42.0

50.8

52.2

(718)
BAUUS AOT STROUHAL.] MAGNETISM, HARDNESS, DIMENSIONS. 127

TABLE 50. Relations letiveen the magnetic constants of steel and hardness Continued. 

5. Magnets annealed 10 hours in steam.

Eocl.

H

Mncnet 

No.

1

2

3

4

5

6

7

8

9

a

24

48

70

94

20

36

57

68

120

TFlm

ohm.

*0. 637

0.645

0.640

0.627

*0. 614

*0. 614

0.614

0.612

0.017

t

oc

*20.1

20.2

20.1

20.0

*20.1

*20.1

20.2

20.3

19.-8

 cm

microhm.

*33. 4

33.7

33.6

33.0

*31.6

. *31. 6

31.6

31.4

31.7

n

cm.

1.28

3.24

5.00

7.30

.0.93

2.42

4.28

5.30

10. 26

M:

dbs. E.

2.75

6.93

10.60

15. 25

2.01

5.19

9.13

11.20

21.06

m

abs. E.

32.1

40.2

42.7

45.4

29.6

41.1

46.4

47.8

51.0

6. Magnets annealedZO minutes in aniline vapor.

,..{

n.J

I

1

2

3

4

5

6

7

8

9

24

48

70

94

20

36

57

68

.120

*0. 566

0.572

0.568

0.559

*0. 536

*0. 536

0. 534

0. 536

0.539

*20.1

20.1

20.1 20-1

*20. 0

*20. 0

20.0

20.0

20.0

*29.5

29.7

29.6

29.2

*27.4

*27.4

27.3

27.4

27.5

1.28

3.45

5.38

7.85

0.92

2.56

4.51

,5.69

11.05

2.76

. 7. 38

11.41

16.41

1.98'

5.51

9.62

12. 12

22. 69

32.2

42.8

45.9

48.9

29.1

43.6

48.9

51.3

55.0

7. Magnets annealed 1 hourir, aniline vapor.

,..(

 .{

1

2

3

4

5

6

7

8

9

24

48

70

94

20

36

57

68

120

1

'0.545

0.550

0. 540

0.538

*0. 514

. *0. 514

0.515

0.512

0.514

*18.9

19.0

19.0

18.8

*18. 8

*18. 8

19.0

19.0

18.5

*28.4

28.7

28.5

28.1

 *26. 3

*26. 3

26.4

26.2

26.3

1.36

3.63

5.64

8.27

0.94

2. 08

4.75

5.96

11.66

2.93

7.77

11.96

17.29

2.04

5.75

10.14

12.69

23.94

34.1

45.1

48.1

51.5

30.0

45.6

51.5

53.7

58.0

8. Magnets annealed 3 hours in aniline-vapor.

,...{

I

f ""I

1

2

3

4

5

6

7

8

9

24

48

70

94

20

86

57

68

120

*0. 520

0. 523

0.523

0.514

*0. 488

*0. 488

0.487

0.486

0.490

*18.9

18.8

18.9

19.0

*18.8

*18.8

18.7

18.8

19.0

*27. 1

27.2

27.3

26.8

*24.9

*24.9

24.9

24.8

24.9

1.44

3.93

6.17

8.99

1.00

2.90

5.16

6.46

12.68

3.09

8.41

13.08

18.'80

2.16

6.23

11.01

13.76

26.03

36.1

48.8

52.6

50.0

31.8

49.3

55.9

58.2

63.1

9. Magnets annealed 7 hours in aniline vapor.

,

y I

A. ... <

I

1

2

3

4

5

6

7

8

9

24

48

70

94

20

36

57

68

120

*0. 500

0. 503

0.502

0.495

*0. 466

*0. 466

0.465

0.467

0. 467

*20. 0

20.0

20.0

20.0

*20. 0

*20.0

20.0

20.0

20.0

*25.9

26.1

26.0

25.7

 *23. 7

*23.7

23.6

23.7

23.7

1.51

4.29

6.72

9.89

1.09

3.11

5.63

7.11

13.88

3.25

9.19

14.26

20.67

2.36

6.69

12.02

15.14

28.50

37.9

53.3

57.3

61.6

34.7

53.0

61.0

64.0

69.0

(719)
128 IRON-CARBURETS. [BULL. 14.

TABLE 50. delations between the magnetic constants of steel and hardness Continued. 

10. Magnets annealed 13 hours inaniline vapor. ,

Eocl.

x (

I

 =....!i

Magnet 

No.

1

2

3

4

5

6

7

 8

9

a '

24

48

70

94

20

36

57

68

120

Tflrn

ohm.

*0. 483

0.483

0.485

0.480

*0. 449

*0. 449

0.445

0.449

0.454.

t

C C.

*19. 9

19.9

19.9

19.9

*19.9

*19. 9

19.8

19.0

20.0

om «cm*°°

microhm.

*25. 0

24.9

25.1

24.9

*22.8

*22. 8

22.0

22. 7

23.0

n

cm.

1.59

4.60

7.19

30.50

1.11

3.30

C. 01

7.66

14.69

If

abs. E.

3.42

9.85

15. 2.3

21.95

2.39

7.09

12.83

10.31

30.16

in

abs. E.

39.9

57.1

61.3

65.4

35.2

56.2

65.1

69.1

73.1

11. Magnets annealed 1 minute in melting lead.

,...{I

f II.. M

I

I

i

2

3

4

5

6

7

8

9

24

48

70

94

20

36

57

68

120

*0. 397

0.399

0. 397

0.394

*0. 374

 0.374

0.374

0. 373

0.375

*18.6

18.4

18.7

18.7

*18. 5

'18.5

18.5

18.7

18.4

*20.4

20.5

20.4

20.3

*18. 9

*18.9

18.9

18.8

18.9

1.57

5.68

9.44

14.06

0.99

3.58

7.25

9.32

18.91

3.38

12.16

20.02

29.40

2.15

7.68

15.47

19.85

38.82

39.4

70.5

80.5

87.6

31.5

60.9

78.5

84.0

94.0

12. Magnets annealed 1 hour in melting lead. 1

 ....! 1

I

1

2

3

4

5

6

7

8

9

24

48

70

94

20

36

57

68

120

*0. 367

0.370

0.307

0.365

*0. 346

*0. 346

0.345

0.345

0.348

*18.8

18.8

18.8

18.7

*18.8

*18.8

18.8

18.8

18.7

*18. 8

18.9

18.8

18.7

*17. 4

*17. 4

17.4

17.3

17.5

1.45

5.06

10.13

15. 27

6.94

3.59

7.62

9.96

20. G2

3.11

12.76

21.48

31.92

2.03

7.71

16.25

21. 22

42.34

36.3

74.0

86.4

95.2

29.8

61.1

82.5

89.8

102.6

]3. Magnets annealed at red heat (soft). ' i

,...1I

1

2

3

4

5

6

7

8

9

24

48

70

94

20

36

57

68

120

*0. 302

0.310

0.308

0.299

*0. 288

*0. 288

0.292

0.292

0.279

*15.1

18.2

18.2

9.0

*15.4

*15.4

18.3

18.3

9.6

*15.7

15.7

15.7

. 15.6

*14.6

*14. 6

14.6

14.6

14.5

0.32

2.57

6.2L

10.85

0.31

1.39

4.22

6.07

16.23

i

0.69

5.70

13.18

22.63

0.25

2.99

9.00

12.93

33.55

8.0

31.9

53.0

67.6

3.7

23.7

45.7

54.7

80.7

RESULTS WITH RODS OF SMALLER DIMENSIONAL RATIO.

Description of magnets. The rods used in the present experiments 

differ from the others principally in two respects: in the first place, the 

maximum of attainable hardness is here of much larger value than in

(720)
1JAUU8 AND STUOUHAL.] CONSTANTS OF MAGNETS. 129

the earlier work; in the second, the degree of longitudinal homogeneity in the glass-hard state (and we may accept this as a fair evidence of structural uniformity throughout the chosen lengths) far surpasses that hitherto obtained. Hardness was carried even as far as

6- = 47.5 ( ^5 0° microhm microhm J ) In consequence of the exceptional hoin- '

ogeneity mentioned, we find that the magnetic data are in excellent accordance.

With the object of arriving at corroborative results, two pairs of wires 

of approximately identical degrees of galvanic hardness were selected. 

These are numbered IX, X, and XI, XII.130 Each of these was broken 

into magnets such that the dimension-ratios a = 10, 20,30, 40,50, obtained.131 Certain important physical constants of these 20 magnets, 

Nos. 21 to 40, have for convenience of reference here been tabulated. 

The remarks which precede Table 49 apply to Table 51.

TABLE 51. Constants of iiiagnets.

Bod 

2 p cui, A

1X { A=7.'<6 j --. - . - "" 

) X { A=?!58 5 '" - -......-.......

XI | A=7.70 ] " - - - 

V1T (2p=0.151| ^M A=7.65 ) - -" "- - - - " 

'

Magnet 

No.

1

f

1

r

1

j

I

f 

1

21

22

23 

24

25

26

27

28 

39

30

31

32

33 

34

35

36

37 

38 

39

40

Mass

g

0.184

0.372

0.570 

0.764

0.953

0.194

0.386

0. 593 

0.789

0.998

0.194

0.401

0.578 

0.799

0.979

0.208

0.413 

0.034 

- 0.827

1.040

Length 

L.

cm.

1.45

2.94

4.50 

6. ('4

7.52

1.46

2.32

4.49 

5.99

7.56

1.47

3.01

4.33 

6.00

7.38

1.51

3.03 

4.62 

6.04

7.58

Dim. ratio 

a

9.9

20.0

30.6 

41.1

'51.2

9.8

19.6

30.1 

40.2

50.7

9.9

20.8

29.2 

40.5

49.8

10.0

20.-1 

30.6 

40.0

50?2

. Homogeneity. The criterion for homogeneity was applied in the manner described in p. 121 by carefully examining the rod under experiment 

with reference to the electrical resistance of. the parts between six equidistant points, about 5 centimeters apa,rt. We believe it expedient to

m The maximum hardness observed with the older material waa 8 = 0.48 Siemens

units at 18° therefore about « = 44.5 (^HL-O0 microhm). Cf. Wied. Ann., xi, p. 945, 'cm* '

1880. .

ls°Tho rods III to IX and the magnets Nos. 11 to 20 are discussed in the following 

chapter.

ir" Of course this can only be done approximately. It is not easy to break a glasshard rod accurately at a given point.

Bull. 14 9 (721)
130 IRON-CARBURETS. [BULL. 14.

take the present opportunity of communicating some of these results 

by way of example. Table 52 contains (columns 2 to 5) the readings 

immediately taken from a Kohlrausch bridge. The measuring wire 

of this had been previously calibrated, with due allowance for the 

small corrections thus resulting. Column 1 shows which of the consecutive lengths (5.07 centimeters) of the steel rod corresponds to the 

given bridge reading, and the portion of the bridge-wire equivalent to 

0.1 Siemens unit. Herefrom the absolute resistances (ohms) of the 

steel rods per 5.07 centimeters at t° are calculated, and the values 

given in columns 6 to 9. In view of these very satisfactory results, we 

were justified in simplifying the subsequent work by testing the homogeneity of the four longest magnets only.

TABLE 52. Results for homogeneity.

1

2 

3 

4 

5

o. is.tr. 

t=

Bridge reading; scale parts.

IX.

70.1 

70.4 

70.6 

 70.8 

70.7.

468.1 

10.8

X.

69.0 

68.9 

'69.0 

68.9 

69.0

474. 3 

10.8

XI.

67.2 

67.1 

67.2 

67.5 

67.5

488.3 

11.0

XII.

66.1 

66.1 

66.2, 

66.3 

66.3

502.0 

11.0

Resistance pei length 5. 07 cm. 

(ohm).

IX.

0.017

0.026 

0.033 

0.037 

0.040 

0.039

10.8

X.

0.013

0.085 

0.083 

. 0.085 

0.083 

0.085

10.8

XI.

0.013

0.011 

0. Ot.9 

O.OU 

0.016 

0.016

11.0

xn.

0.012

0.054 

0.054 

0.056 

0.058 

0.058

11.0

Magnetic data. In making the magnetic measurements we used the 

first position of Gauss. The numerical values of the constants occurring in the fonnulse

 -STtgv ... n

m M

are as follows:

gH '

T=0.194cmHsec- r=24.90 cm. JK=232.S cm. 

The magnetic results of our experiments, finally, are given in the 

series forming table (53): . '

TABLE 53. Relation between the magnetic constants of steel and hardness. 

1. Magnets in thr glass-hard state.

Eod.

= i1

Magnet 

No.

21

- 22

23

24

25

a

9.9

20.0

30.6

41.1

51.2

TFlm

ohm.

0.283

0.283

0.283

0.283

' 0. 283

t

°C.

10.8

10.8

10.8

10.8

10.8

«5ELo°

cm2

microhm.

47.2

47.2

47.2

47.2

47.2

71

f,m.

2.60

8.32

14.86

21.37

28.18

M

abs. E.

4.17

13.31.

23.62

33.64

43.86

. m

abs. E.

22.7

35.8

41.4

44.0

40.0

(722)
BAHUB AND BTBOUHAL.] MAGNETISM, HARDNESS, DIMENSIONS. 131

TABLE 53. Relation between the magnetic constants of steel and hardness Continued. 

1. Magnets in the glass-hard state Continued.

Rod.

f

X J

i

n f

1

,

XII. J

. I

Magnet

No. 

26

27

28

29

30

31

32

33

34

35

36

07 Of

38

39

40

a

9.8

19.0

30.1

40.2

50.7

9.9

20.3

29.2

40.5

49.8

10.0

20.1

30.6

" 40.0

50.2

TFlm

ohm.

0.273

0.273

0.273

0.273

0.273

0.259

0.259

0.259

0. 259

0.259

0.248

0.248

0.248

0.248

0.248

t

°C.

11.2

11.2

11.2

11.2

11.2

11.0

11.0

11.0

11.0

11.0

11.0

11.0

11.0

11.0

11.0

«£Eo° 

cm2

microhm.

46.8

46.8

46.8

46.8

46.8

43.8

' 43.8

43.8

43.8

43.8

43.5

43.5

43.5

43.5

43.5

n

cm.

2.82

8.88

15.82

22.45

29.75

2.99

10.27

17.16

25.77

32.98

2.98

9.53

17.32

24.33

32.28

. M

aba. E.

4.53

14.21

25.14

35.36

46.30

4.80

16.43

27.30

40.59

51.40

4.79

15. 24

27.50

33.30

50.22

TO

obs. E.

23.3

30. 8

42.4

44.8

46.4

24.8

41.0

47.2

50.8

52.5

23.0

' 36.9

43.4

46.3

48.3

2. Magnets annealed 1 hour in steam.

n I

i

x f

1

r

i

~V\ J

\

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

9.9

20.0

30.6

41.1

51.2

9.8

19.6

30.1

40.2

50.7

9. 9

20.3

29.2

40.5

49.8

10.0

20.1

30.6

40.0

50.2

0.252

0.252

0.252

0. 252

0.252

0.244

0.244

0.244

0.244

0.244

0.229

0.229

0.229 0. 2'.'9

0.229

0. 219

0. 2J9

0.219

0.219

0.219

11.8

11.8

11.8

11.8

11.8

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

42.0

42.0

42.0

42.0

42. 0

41.7

41.7

41.7

41.7

41.7

38.6

38.6

38.6

38.6

38.6

38.4

38.4

'38.4

. 38.4

 38. 4

2.43

7.80

13.92

20.05

26.47

2.66

8.30

14.88

21. 08

27.95

2.82

9.83

10.42

24.69

31.63

2.86

9.20

16.70

23.43

31.15

8.90

12.48

22.12

31.56

41.21

4.27

13.28

23. 65

33.20

43.50

4.53

15.73

20.12

38.89

49.29

4.59

14.72

26. 52

36.89

48. 47

21.2

33.6

38.8

41.3

43.2

22.0

34.4

39.9

42.1

43. C

.23.3

39.2

45.2

48.7

50.4

22.1

35.6

41.8

44.6

46.6

3. Magnets annealed 3 hours in steam.

-ii

xl"i

I

XI {

i

21

22

23

24

25

26

' 27

28

29

30

31

32

33

34

35

36

37

38

39

40

9.9

20.0

30.6

41.1

51.2

9.8

19.6

 30.1

40.2

50.7

9.9

20.3

29.2

40.5

49.8

10.0

20.1

30.6

40.0

 50.2

0.238

0. 238

0.238

0.238

0.238

0.230

0:230

0.230

0.230

0.230

0.216

0.216

0.216

0.216

0. 216

0.207

0.207

0.207

0.207

0.207

11.9

11.9

11.9

11.9

11.8

11.8

11.8

11.8

 11.8

11.8

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

39.5

39.5

39.5

39.5

39.5

39.3

39.3

39.3

39.3

39.3

36.5

36.5

36.5

36.5

36.5

36.2

36.2

30.2

36.2

36.2

2.46

7.72

13.69

19.72

25.89

2.70

8.21

14.62

20.65

27.34

2.83

9.68

16.16

24.21

30.94

2.88

9.12

16.50

23. 09 . 30.57

3.94

12.34

21.76

31.05

40.30

4.34

13.13

23.23

32.52

42.55

4.54

15.49

25.70

38.13

48.22

4.63

14.59

26.21

36.35

47.57

21.4

33 2

38.2

. 40.6

42.3

22.4

34.0

39.2

41.2

42.6

23.4

38.6

44.5

47.7

49.3

22.2

35.3

41.3

43.9

45.7

(723)
132 IRON-CARBURETS. [BULL. 14.

TABLE 53. Helation between the magnetic constants of steel and hardness Continued. 

4. Magnets annealed 6 hours in steam.

Rod.

-!1

f "V J

\

= 1

JU...<(

I

Magnet 

No.

21

22

23

21

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

, Ol 0

9.9

20.0

30.6

41.1

51.2

9.8

19.6

30.1

40.2

50.7

9.9

20.3

29.2

40.5

49.8

10.0

20.1

30.6

40.0

50.2

TTlm

chm.

0.230

0.230

0.230

0. 230

0.230

0.223

0. 223

- 0. 223

0. 223

0.223

0.209

0.209

0.209

0.209

0.209

0. 199

0.199

0.199

0.199

0. 199

t

°C

11.9

11.9

11.9

11.9

11.9

11.9

11.9

11.9

11.9

11.9

11.8

11.8

11.8

11.8

11.8

11.8

11.8

11.8

11.8

11.8

«?5o° cm*

mic rohm.

38.2

38.2

38.2

38.2

38.2

38.0

38.0

38.0

38.0

38.0

35.1

35.1

35.1

35.1

- 35.1

34.9

34.9

34.9

34.9

34.9

n

cm.

2.48

7.72

13.70

19.63

25.80

2.70

8.21

14.53

20.55

27.24

2.82

9.68

16.09

24.05

30. 82

2.84

9. 12 ° ie! 39

22.92

30.41

M

abs. E.

3.98

12.35

21.77

30.90

40.16

4.34

13.13

23.09

32.37

42.39

4.53

15.49

25.60

37.88

 48.03

4.56

14.59

26.03

3(5. (58

47.32

ra

abs. E.

21.6

33.2

38.2

40.4

42.1

22.4

34.0

38.9

41.0

42.5

23.3

38.6

44.3

47.4

49.1

21.9

35.3

41.1

43.6

45.5

5. Magnets annealed 10 hours in steam.

>J\

x {1

nfI

21

22

23

24

25

26

28' 27

29

30

31

32

33

34

35

36

37

38

39

40

9.9

20.0

30.6

41.1

51.2

9.8

19.6

30.1

40.2

50.7

9.9

20.3

29.2

40.5

49.8

10.0

20.1

30.6

40.0

50.2

0.226.

0.226

0.226

0.226

0. 226

0.218

0.218

0.218

0.218

0.218

0.204

0.204

0.204

0.204

0.204

0.195

0.195

0.195

. 0. 195

0.195

11.8

11.8

11.8

11.8

11.8

11.9

11.9

11.9

11.9

11.9

11.9

11.9

11. 9

11.9

11.9

11.9

11.9

11.9

11.9

11.9

37.4

37.4

37.4'

37.4

37.4

37.1

37.1

37.1

37.1

37.1

34.3

34.3

34.3

34.3

34.3

34.0

34.0

34.0

34.0

34.0

2.46

7.73

13.69

19.66

25.83

2.70

8.19

14.57

20.60

27. 25

2.81

9.61

16.06

24.03

30.74

2.87

9.09

16.34

22.87

30.37

3.95

12.37

21.76

30.95

40.21

4.34

13. 10

23.16

32. 45

42.41

4.51

15. 37

25.54

37. 85

47.91

4. '61

14.54

25.95

36.01

47.25

21.5

33.3

38.2

40.5

42.2

22.4

33.9

39.0

41.1

42.5

23.3

38.3

44.2

47.4

48.9

22.2

35.2

40.9

43.5

. 45. 4

6. Magnets annealed 20 minutes in aniline vapor. ,.{

*!\

-I1

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

9.9

20.0

30.6

41.1

51.2

9.8

19.6

30.1

40.2

50.7

9.9

20. '3

29.2

40.5

49.8

ic.-o

20.1

30.6

40.0

50.2

0.191

0.191

0.191

0.191

' 0. 191

0.185

0.185

0.185

0.185

0.185

0.173

0.173

0.173

0.173

,0. 173

0.165

0.165

0.165

0.165

0.165

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

31.5

31.5

31.5

31.5

31.5

31.4

31.4

31.4

31.4

31.4

29.0

29.0

29.0

29.0

29.0

28.7

28.7

28.7

28.7

28.7

2.31

7.97

14.60

21.15

28.02

2.60

8.45

15.48

22.22

29.58

2.54

9.75

16.70

25.52

32.87

2.67

9.28

17.31

24.52

32.75

3.71

12.75

23. 21

33.30

. 43. 62

4.18

13. 52

 24. 60

34.99

46.04

4.08

15.60

26.56

40.20

51.23

4.29

14.84

27.49

38.60

50.96

20.2

v 34.3

40.7

, 43.6

45.8

21.5

35.0

41.5

44.4

46.1

21.0

38,9

46.0

50.3

52.3

20.6

35.9

43.7

46.0

49.4

(724)
BARUS AND sTRouiiAL.l MAGNETISM, HARDNESS, DIMENSIONS. 133

TABLE 53. Relation between the magnetic constants of steel and hardness Continued. 

7. Magnets annealed 1 hour in aniline vapor.

Kod.

= |

1

x {

1

xi 1

1

XII...

Magnet 

No.

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

a

9.9

20.0

80.6

41.1

51.2

9.8

19.6

30.1

40.2

50.7

9.9

20.3

29.2

40.5

49.8

10.0

20.1

30.6

40.0

60.2

Flm

chm.

0.179

0.179

0.179

0.179

0.179

0.175

0.175

0.175

0.175

0. 175

0.164

0.104

0.164

0.164

0.164

0.157

0.157

0.157

0.157

0.157

t

°C.

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

«2Eo°

cm2

microhm.

29.7

29.7

29.7-

29.7

29.7

29.6

29.6

29.6

29.6

29.6

27.5

27.5

27.5

27.5

27.5

27.3

27.3

27.3

27.3

27.3

n

cm.

2.33

8.30

15.38

22.37

29.75

2.52

8.79

16.81

23.60

31.46

2.57

10.08

17.49

26.83

34.64

2.C6

9.60

18.19

25.88

34,63

M

alts. E.

3.75

13. 28

24. 45

35.22

46.31

4.05

14.06

25.92

37.17

48.97

4.13

16.13

27.82

42.20

53.99

4.27

15.36

28.89

40.75

53. 89

in

abs. E.

20.4

35.7

42.9

46.1

48.6

20/9

36.4

43.7

47.1

49.1

21.3

40.2

48.1

52.9

55.1

20.5

37.2

45.6

49.3

51.8

8. Magnets annealed 3 hours in aniline vapor.

-I1

ll1

= 11,

1 xn.J

1

I

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

9.9

20.0

30.6

41.1

51.2

9.8

19.6

30.1

40.2

50.7

9.9

20.3

29.2

. 40.5

49.8

10.0

20.1

30.6

40.0

50.2

0.169

0.169

0.1C9

0.169

0.169

0.164

0.164

0.164

0.164

0.164

0.153

0. 153

0.153

0.153

0.153

0.147

 0. 147

0.147

0.147

0.147

11.7

11.7

11.7

11.7

11.7

11.8

11.8

11.8

11.8

11.8

11.8

11.8

11.8

11.8

11.8

11.9

11.9

11.9

11.9

11.9

27.9

27.9

27.9

 27.9

27.9

27.7

27.7

27.7

27.7

27.7

25.6

25.6

25.6

25.6

25.6

25.5

25.5

25.5

25.5

25.5

2.41

8.99

16.93

24. 75

32.94

2.62

9.56

18.08

26.23

35.06

2.61

10.71

18. 98'

29.25

37.83

2.75

10. Zff

19. 81

28.37

38.16

3.87

14.38

26.91

38.97

51.27

4.21

]5.30

28.73

41.31

54.56

4.19

17.13

30.19

46.07

58.95

4.42

16.46

31.46

44.67

59.37

21.0

38.7

47.2

'51.0

53.8

21.7

39.6

48.5

52.4

54.7

21.6

42.7

52.2

57.7

60.2

21.2

39.8

49.6

54.0

57.1

9. Magnets annealed 7 hours in aniline vapor.

K {1

,11

S1 {1

21

22

23

24 25

26

27

28

29

30

31

32

33

34

35

36

37

38

39 ' 40

9.9

20.0

30. C

41.1

51.2

9.8

19.6

30.1

40.2

50.7

9.9

20.3

29.2

40.5

49.8

10.0

20.1

30.6

40.0

50.2

0.159

0.159

0.159

0.159

0.159

0.154

0.154

0.154

0:154

0.154

0.145

0.145

0.145

0.145

0.145

0.138

0.138

0.138

0.138

0.138

12.0

12,0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

 12.0

12.0.

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

26.2

26.2

26.2

26.2

26.2

26.0

26.0

26.0

26.0

26.0

24.2

24.2

24.2

24.2

24.2

23.9

23.9^

23.9

23.9

23.9

2.53.

9.80

18.73

27.65

37.03

2.68

10. 30

20.06

29.31

39.39

2.63

11. 40

20.69

32.19

41.96

2.80

11.01

21.73

31.32

 42.37

4.06

15.68

29.76

43.53

57.65

4.30

16. 58

31.88

46.16

61.31

4.22

18. 24

32.92

50.70

65.39

4.50

17.61

34.51

49.31

65.93

22.1

42.2

52.2

57.0

60.5

22.2

42.9

53.8

58.5

61.4

21.8

45.5

56.9

63.5

66.8

21.6

42.6

54.4

59.6

63.4

(725)
134 IRON-CARBURETS. [BUU,. 14.

TABLE 53. Belation lehveen the magnetic constants of steel and hardness Coutinned. 

10. Magnets annealed 13 hours in aniline vapor.

Eod.

(

IX \

i

x f1

2I I 1

Magnet 

No.

21

22

23

24

25

26

27

28

29

30

31

32

33

34

 35

36

37

38

39

40

a

9.9

20.0

30.6

41.1

51. 2

9.8

19.6

30.1

40.2

50.7

9.9

20.3

29.2

40.5

49.8

10.0

20.1

30.6

40.0

50.2

TFlm

ohm.

0.151

0.151

0.151

0.151

0.151

0.146

0.146

0.146

0.146

0.146

0. 138

0.138

» 0. 138

0.138

0.138

0.132

0.132

" 0. 132

0.132

0.132

t

00.

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

« Lo°

cm2

microhm.'

24.8

24.8

24.8

24.8

24.8

24.6

24.6

24.6

24.6

24.6

22.9

22.9

22.9

22.9

22.9'

22.7

22.7

22.7

22.7

22.7

n

cm.

2.50

10.25

20.09

30.02

40.25

2.64

10.79

21.59

31.87

42.96

2.53

11. 59

21.68

34.53

45.08

2.73

11.30

22.90

33.50

45.60

Jlf

abs. E.

4.02

16.40

31. 93

47.26

62.66

4.24

17.20

. 34. 3-2

50,20

60.87

4.06

18.54

34.49

54. 39

70; 20

4.38

18.08

36. 37

52.74

70. 90

m,

abs. E.

21.8

44.1

56.0

61.9

65.8

21.9

44.7

57.9

63.6

67.0

20.9

46.2

59.7

68.1

71.8

21.1

43.8

57.4

63.8

68. :>

11. Magnets annealed 10 minutes in melting tin.

Ix f1

xi1

f1 TTT XI.. J<j

I

(

xn.J

1

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

fjrt 36

37 38

39

40

99

20.0

30.6

41.1

51.2

9.8

19.6

30.1

. 40.2

50.7

9.9

20.3

29.2

40.5

49.8

10.0

20.1

30.6

40.0

50.2

0.147

0.147

0.147

0.147

0.147

0.141

0.141

0.141

0.141

0.141

0.134

0.134

0.134

0.134,

0.134

0.127

0.127

0.127

0.127

0.127

11.7

11.7

11.7

11.7

11.7

11.5

11.5

11.5

11.5

11.5

11.6

11.6

11.6

' 11..6

11.6

11.7

11.7

11.7

11.7

11.7

24.0

24.0

- 24.0

24.0

24.0

23.8

23.8

23.8

23.8

23.8

22.2

22.2

22.2

22.2

22.2

22.0

22.0

22.0

22.0

22.0

2.46

10.37

20.64

30.97

41. 92

2.60

10. 98

22. 23

33.11

44.78

2.46

11.70

22. 17

35.60

' 40. 70

2.68

11.37

23.47

34.58

47.29

3.95

16.59

32. 80

48.75

65.25

4.18

17.57

35.41

52. 10

69.70

3.95

18.72

35. 27

 56. 07

72.78

4.30

18.19

37. 27

54.44

. 73. 59

21.5

44.6

57.5

63.8

68.5

21.5

45. 5

59.7

60.1

69.8

20.4

46.7

6t.O

70.2

74.3

20 7

44.0

58.8

65.8

70.8

12. Magnets annealed 1 minute in melting lead.

= 1

JJL..^[

r

i

"V J

1

= (1

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

9.9

20.0

30.6

' 41.1

51.2

9.8

19.6

30.1

40.2

50.7

9.9

20.3

29.2

40.5

49.8

10.0

20.1

30.6

40.0

50.2

0.124

0.124

0.124

0.124

0.124

0.120

0.120

0.120

0.120

. 0. 120

0.115

0.115

0.115

0.115

0. 115

0.109

0.109

0.109

0.109

0.109

11.9

11.9

11.9

11.9

11.9

11.3

11.3

11.3

11.3

11.3

11.9

11.9

11.9

11.9

11.9

11.9

11.9

11.9

11.9

11.9

20.3

20.3

' 20.3

20.3

20,3

20.1

20.1

20.1

20.1

20.1

19.0

19.0

19.0

19.0

19.0

18.7

18.7

18.7

18.7

18.7

2.26

10.88

24.04

38.43

52. 53

2.33

11.14

25. 34

40.08

55.46

2.30

11.71

24.71

 42. 45

56.53

2.46

11.18

25. 95

41. 39

58.01

8.60

17.40

38.19

60. 51

81.77

. 3.74

17.83

40.27

63.12

86.32

3.69

18.72

39.30

66.87

88.10

3.95

17.89

41.21

65. 16

90.26

19.7

46.8

67.0

79.2

85.8

19.3

46.2

67.9

80.0

86.5

19.0

46 7

68.0

83.7

90.0

19. 0

43 3

C5. 0

78.8

86.8

(726)
BARUS AND BTBOTOAL.J MAGNETISM, HARDNESS, DIMENSIONS. 135

TABLE 53. Relation between the magnetic constants of steel and hardness Continued. 

13. Magnets annealed 1 how in melting zinc.

Eod.

r

IX ix.. 11

I

.1

1

n!

1

Magnet 

No.

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

a

9.9

20.0

30. C

41.1

51.2

9.8

19.6

30.1

40.2

50.7

9.9

20.3

29.2

40.5

49.8.

10.0

20.1

30.0

40.0

50.2

TT1 m

ohm.

0.107

0.107

0.107

0.107

0.107

0.102

' 0. 102

0. 102

0.102

0.102

0.098

0.098

0.098

0.098

0.098

0.093

0.093

0.093

0.093

0.093

t

°C.

10.3

10.3

10.3

10.3

10.3

10.3

10.3

10.3

10.3

10.3

10.3

10.3

10.3

10.3

10.3

10.3

" 10.3

10.3

10.3

10.3

/JE5-00 cm"

microhm.

17.5

17.5

17.5

17.5

17.5

17.2

17.2

17.2

17.2

17.2

16.2

16.2

10.2

16.2

16.2

16.0

16.0

16.0

16.0

16.0

n'

cm.

1.85

10.15

26.02

43.90

61.65

1.83

9.82

26.89

46.03

65.10

1.74

10.06

20.87

47.63

65.29

1.93

9.95

27.14

46.73

G7. 60

Jf

abs. E.

2.98

16.24

41. 35 .

69. 12

95.96

2.94

15.71

42.64

72.49

101.32-

2.79

16.09

42.74

75.03

101. 74

3.10

15.91

43.10

73.57

105. 17

in

abs. E.

16.2

43.7

72.5

90.5

100.7

15.2

40.7

72.1

91.9

101.5

14.4

40.1

72.6

93.9

103. 9

14.9

38.5

68.0

89.0

101.1

14. Magnets annealed at red heat (soft).

-!E.-I

,{

*lXI..

I

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

9.9

20.0

30.6

41.1

51.2

9.8

19.6

30.1

40.2

50.7

9.9

20.3

29.2

40.5

49.8

10.0

20.1

30. C

. 40.0

50.2

0.096

0.096

0.096

0.096

0. 096

0.093

0.093

0. 093

0.093

0.093

 0. 096

0.096

0.096

0.096

0.096

0.087

0.087

0.087

0.087

0.087

10.0

10.0

10.0

10. 0

10.0

10.1

10.1

10.1

10.1

10.1

10.2

10.?.

10.2

10.2

10.2

10.2

10.2

10.2

10.2

 10.2

15. 7

15.7

15.7

15.7

15.7

15.6

15.6

15.6

15.6

15.6

14.9

14.9

14.9

14.9

14.9

14.9

14.9

14.9

14.9

14.9

0.52

2.72

7.94

10. 87

28.49

0.46

2.52

7.59

15.72

29.15

O.S2

2.55

6.80

15.13

26.63

0. 57

3.15

8.25

16.32

29.42

0.83

4.35

12 62

26.56

44.35

0.74

4.03

12.06

24, ?3

45. ^6

0.84

4.08

10.82

23.83

41.50

0.92

5.04

13.10

.25. 69

36.36

4'. 5

11.7

22.1

34.8

46.5

3.8

10.5

20.3

31.4

45.4

4.3

10.2

18.7

29.8

42.4

4.4

12.2

20.7

31.1

44.0

(727)
136 IRON-CARBURETS. [BULL. 14.

DISCUSSION.

Digest. Our present purpose will be greatly facilitated by a tabular 

comparison of the essential features of the results in hand. The following digest (Tables 54 to 59) contains, besides brief descriptions of temper, 

the hardness as represented by the specific resistance s, together with 

the corresponding magnetic moments per unit of mass, m, of the several

rods.

TABLE 54. Rod I.

Description of temper.

Soft.........................................................

Hardness, 8.

QS 5

36.3 

34.8 

33.9 

33.4 

29.5 

28.4 

27.1 

25.9 

25.0 

20.4 

18.8 

15.7

Specific magnetism, m.

No. 1.

33.7 

33.3 

32.7 

32.2 

32.1 

32.2 

34.1 

36.1 

37.9 

39.9 

39.4 

36.3 

8.0

No. 2.'

43.0 

42.0 

41.0 

40.1 

40.2 

42.8 

45.1 

 48.8 

53 3 

57.1 

70.5 

74.0 

31.9

No. 3.

45.0 

44.3 

43.3. 

42.7 

42.7 

45.9 

48.1 

52.6 

57.3 

61.3 

80.5 

86.4 

53.0

No. 4.

47.9 

46.8 

46.2 

45.4 

45.4 

48.9 

51.5 

56.0 

61.6 

65 4 

87.0 

95.2 

67.6

TABLE 55. Rod, 1L

Description of temper.

Annealed 1 hour in steam 100° .............. 

-Annealed 3 hours in steam 100° ... .°. .......

-Anneah'd 20 minutes in aniline vapor 185° . . 

-Annealed 1 hoar in aniline vapor 185° ......

-Aoinealed 9 hours in aniline vapor 185° ..... 

-Annealed 7 hours in aniline vapor 185° .. . . . 

-Annealed 13 hours in aniline vapor 185° ....

rgoft. ...................................... .

Hardness, 8.

37.3

34.7 

33.0 

32.2

31.6

27.4 

26.3 

24.9 

23.7 

22.8 

18.9 

17.4 

14.5

Specific magnetism, m.

No. 5.

........

29.6 

29.1 

30.0 

31.8 

34.7 

35.2 

31.5 

29.8 

3.7

No. 6.

43 Q

43.1 

42.5 

42.0

41.1 

43.0 

45.6 

49.3 

53.0 

56.2 

60.9 

61.1 

23.7

No. 7.

........

46.4 

48.9 

51.5 

55.9 

61.0 

65.1 

78.5 

82.5 

45.7

No. 8.

.......

47.8 

51.3 

53.7

58.2 

64.0 

69.1 

84.0 

89.8 

54.7

No. 9.

53.5 

52.8 

51.8 

50.8 

51.0 

55.0 

58.0 

63.1 

69.0 

73.1 

94.0 

102.6 

80.7

No. 10.

55.1 

54.1 

53.2 

52.2

TABLE 56. Rod IX.

Description of temper. .

Annenled 1 minute in lead bath 330°................

Soft.................................................

Hardness, s.

47.2 

42.0 

39.5 

38.2 

37.4 

31.5 

29.7 

27.9 

26.2 

. 24.8 

24.0 

20.3 

17.5 

15.7

Specific magnetism m, for the dimensionratios;

9.9

22.7 

21.2 

21.4 

21.6 

21.5 

20.2 

20.4 

21.0 

22.1 

21.8 

21.5 

19.7 

16.2 

4.5

20.0

35.8 

33.6 

33.2 

33.2 

33.3 

34.3 

35.7 

38.7 

42.2 

44.1 

44.6 

46.8 

43.7 

11.7

30.6

41.4 

38.8 

38.2 

38.2 

38.2 

40.7 

42.9 

47.2 

52.2 

56.0 

57.5 

67.0 

72.5 

22.1

41.1

44.0 

41.3

40.6 

40.4 

40.5 

43.6 

46.1 

51.0 57.0' 

61.9 

63.8 

79.2 

90.5 

34.8

51.2

46.0 

43.2 

42.3 

42.1 

42. .2 

45.8 

48.6 

53.8 

60.5 

65.8 

68.5 

85.8 

100.7 

46.5

(728)
BARUS AND STROUHAL.] MAGNETISM, HARDNESS, DIMENSIONS.

TABLE 57. Rod, X.

137

Description of temper. Hardness, a.

46.8 

41.7 

39.3 

38.0 

37.1 

31.4 

29.6 

2?. 7 

26.0 

24.6 

23.8 

. 20.1 

17.2 

15.6

Specific magnetism m, for the dimneaionratio=

9.8

23.3 

22.0 

22.4 

22.4 

22.4 

21.5 

20.9 

21.7 

22.2 

21.9 

21.5 

19.3 

15.2 

3.8

19.6

36.8 

34.4 

34.0 

34.0 

33.9 

35.0 

36.4 

39.6 

42.9 

44.7 

45.5 

46.2 

40.7 

10.5

30.1

42.4 

39.9 

39.2 

38.9 

39.0 

41.5 

43.7 

48.5 

53.8 

57.9 

59.7 

67.9 

72.1 

20.3

40.2

44.8 

42.1 

41.2 

41.0 

41.1 

44.4 

47.1 

52.4 

58.5 

63.6 

60.1 

80.0 

91.9 

31.4

50.7

46.4 

43.6 

42.6 

42.5 

42.5 

46.1 

49.1 

54.7 

61.4 

67.0 

69.8 

86.5 

101.5 

45.4

TABE 58. Mod XL

Description of temper. Hardness, e.

43.8 

38.6 

36.5 

35.1 

34.3 

29.0 

27.5 

25.6 

24.2 

22.9 

22.2 

19.0 

. 16.2 

14.9

Specific magnetism m, fortho dimensionratio =

9.9

24.8 

. 23.3 

23.4 

23.3 

23.3 

21.0 

21.3 

21.6 

21.8 

20.9 

20.4 

19.0 

14.4 

4.3

20.3

41.0 

39.2 

38.6 

38.6 

38.3 

38.9 

40.2 

42.7 

45.5 

46.2 

46.7 

46.7 

40.1

10; 2

29.2

47.2 

45.2 

44.5 

44.3 

44.2 

46.0 

48.1 

52.2 

56.9 

59.7 

61.0 

68.0 

72.6 

18.7

40.5

50.8 

48.7 

47.7 

47.4 

47.4 

50.3 

52.9 

57.7 

63.5 

68.1 

70.2 

83.7 

93.9 

29.8

49.8

52.5 

50.4 

49.3 

49.1 

48.9 

52.3 

55.1 

60.2 

66.8 

71.8 

74.3 

90.0 

103.9 

42.4

TABLE 59. Rod XII.

Description of temper.

Soft ................................................

Hardness, 8.

43.5 

38.4 

36.2 

34.9 

34.0 

28.7 

. 27.3 

25.5 

23.9 

22.7 

22.0 

18.7 

16.0 

14.9

Specific magnetism m, for the dimension-ratio=

10.0

23.0 

22.1 

22.2 

21.9 

22.2 

20.6 

20.5 

21.2 

21.6 

21.1 

20.7 

19.0 

H.9 

4.4

20.1

36.9 

35.6 

35.3 

35.3 

35.2 

35.9 

37.2 

39.8 

42.6 

43.8 

44.0 

43.3 

38.5 

12.2

30.6

43.4 

41.8 

41.3 

41.1 

40.9 

43.4 

45.6 

49.6 

54.4 

57.4 

58.8 

65.0 

68.0 

20.7

40.0

46.3 

44.6 

43.9 

43.6 

43.5 

40.7 

49.3 

54.0 

59.6. 

03.8 

65.8 

78.8 

89.0 

31.1

50.2

48.3 

46.6 

45.7 

45.5 

45.4 

49.0 

51.8 

57.1 

63.4 

68.2 

70.8 

8G.8 

101. 1 

44.0

Plan of the discussion. These results may be discussed from two distinct stand-points.. In case of one and the same wire, the specific 

t magnetism of the magnets taken out of it varies both with their degree

(729)
138 IRON-CAEBURETS. [BULL. 14.

of hardness and with the ratio of length and diameter. In place of a 

diagram in three dimensions, however, it is expedient to regard the one 

or the other variable, as an arbitrary constant, while the other passes 

through all possible values. We thus represent all relations by plane 

diagrams. Our results are compared in this way. It is, however, convenient to replace Tables 54 and 55 by others satisfactorily deducible 

from them by graphic interpolation, since the ratio of dimensions in the 

earlier experiments (Tables 54 and 55) do not compare well with those 

in the later (Tables 56 to 59). In other words, without such reconstruction of the former results, the difference of magnetic behavior of the 

two kinds of steel employed cannot be readily discerned. For this 

reason the Tables 60 and 61, following, have been prepared. The data 

contained are such as would have been found if the ratio of dimensions 

had been a=20, 40, 60, 80, and 100, respectively, in place of the values 

which actually obtained.

TABLE 60. Rod I.

Description of temper.

Annealed 1 hour in lead-bath 330° ...........'.......

Soft ................................................

Hardness, 8.

38.5 

36.3 

34.8 

33.9 

33.4 

29.5 

28.4 

27.1 

25.9 

25.0 

20.4 

18.8 

15.7

Specific magnetism in, for the dimension-ratio =

20

31.4 

30.5 

30.1 

29.9 

29.8 

29.6 

30.3 

31.8 

33.6 

34.7 

32.2 

26.0 

6.0

40

40.2 

39.2 

38.5 

38.3 

38.0 

40.0 

42.3 

46.2 

50.4 

52.6 

63.4 

65.3 

21.3

60

44.3 

42.9 

42.2 

42.0 

41.8 

44.5 

47.4 

51.6 

56.0 

60.0 

77.3 

81.4 

43.0

80

46.5 

44.7 

43.9 

43.8 

43.8 

47.2 

50.3 

54.4 

59.1 

63.4 

84.2 

90.3 

59.4

100

48.0 

46.0 

45.2 

' 45.0 

45.2 

49.4 

52.3 

56.5 

61.4 

65.8 

89.2 

97.2 

70.3

TABLE 61. Rot II.

Description of temper.

Soft ................................................

Hardness, 8.

37.3 

34.7 

33.0 

32.2 

31.6 

27.4 

26.3 

24.9 

23.7 

22.8 

18.9 

17.4 

14.5

Specific magnetism m, for the dimension-ratio=

20

' 31.5 

30.4 

30.0 

29.9 

29.9 

29.4 

30.0 

32,8 

34.3 

35.0 

33.0 

30.0 

6.0

40

45.0 

43.4 

42.8 

42.7 

42.7 

45.3 

47.3 

50.9 

54.7 

58.0 

64.3 

65.3 

27.8

60

49.5 

47.8 

47.3 

47.2 

47.2 

50.1 

52.2 

57.3 

62.3 

66.4 

80.7 

84.6 

47.5

80

51.3 

49.7 

49.0 

48.8 

48.8 

52.5 

55.0 

60.0 

66.0 

70.8 

88.6 

95.0 

63.3

100

52.4 

50.5 

49.9 

49.8 

49.7 

54.0 

56.6 

62.2 

68.0 

72.0 

92.2 

100.8 

74.0

General inferences. A detailed comparison of the results expressed 

in Tables GO and 61 with those in Tables 58, 57. 58, 59, and all of these 

among themselves, shows conclusively that the magnetic behavior of

(730)
IVAUUS AND BTBOUHAL.J MAGNETISM AND HARDNESS. 139

each particular wire is of a distinct and individual character. More 

perspicuously, even, the same fact is observable in a graphic representation of the data. The curves obtained for the several wires are by 

no means coincident. The thicker wire shows greater magnetizability 

than the wire of smaller diameter. In the case of both kinds of steel, 

gal vaiiically hard rods are magnetizable to a lesser degree than soft rods. 

Moreover, there appears to exist a relation between the density and 

maximum permanent moment, in so far as the latter in general increases directly with the former. This effect is particularly apparent for 

the thicker wire. But the fundamental inference is this, that the relation between specific magnetism and hardness expressed galvanically, 

as exhibited by all the wires, is essentially of the same kind.

Magnetism and hardness. The general contours of the families of 

curves expressing the functionality between magnetic moment, per unit 

of mass, hardness, ratio of dimensions, are of very great interest. It 

appears clearly that the latter variable by no means deserves the exclusive importance which, has hitherto been attributed to it, at least not 

in the accepted sense that a certain critical value exists (Etiths, for instance, puts it, a-=35) below which magnets differ in a pronounced way 

as regards magnetizability, from magnets with a larger dimension-ratio. 

The variations of the series of curves belonging to magnets taken from 

one and the same wire are obviously of like nature; in other words, 

obtained from a definite law by the mere change of a parametric constant, a. In general, all magnets, whether long or short, after incipient 

annealing diminish in magnetizability, until a well-marked minimum of 

this quality is reached. If thereafter annealing be continued maguetizability again increases, attains a maximum, and finally decreases 

again to the value for the soft state.

The causes which led earlier observers into partially erroneous inferences are not far to seek. With the ordinary very rough method of 

estimating the degree of hardness of steel by the aid of the oxide tints, 

the character of the curves, as a whole, did not appear. Hitherto data 

for only four points for each rod, corresponding to the hard, the yellow, 

the blue, and the soft states, were available. Irrespective of the vagueness of degrees of hardness thus defined it will readily be seen that 

where the full contours of the curves are unknown the grouping of these 

points is such as to suggest the said imperfect inference of a critical 

dimension-ratio.

The effect of a variation of dimensions is particularly apparent in its 

bearing on the position and value of the minima and maxima of the 

permanently saturated magnetic state. In proportion as the length of 

the magnets, or more accurately the ratio of dimensions increases, these 

singular points, which are nearly coincident in very short rods, move 

apart, the minimum occurring in the glass-hard state, the maximum 

passing at a very rapid rate toward the soft state. At the same time 

the maximum increases enormously in value, and for long, thin rods is

(731)
140 IRON-CARBURETS. [BULL. 14.

greater than twice the equivalent of the permanently saturated magnetic moment of the same rod when hard. As we approach short rods, 

as will be seen, the maximum flattens out, moving toward the minimum at a more rapid rate than the minimum progresses in the opposite 

direction. But the variations are such that for very short magnets, i. e., 

such for which the ratio of dimensions is below 5, the minimum will 

probably lose its marked character altogether,'and eventually come 

into Ml coincidence with the maximum. Here, therefore, a uniformly 

continuous decrease of magnetizability from the glass-hard to the soft 

states is to be anticipated.

Graphic representation. All these results may be made to appear 

with striking clearness by representing them graphically. It will be 

sufficient for this purpose to accept the mean of the two series of results 

for the thin sample of steel wire, and then to compare this with the 

mean or combined results (four series) obtaining for the thicker sample 

of wire. These mean values are given in the following tables, 62 and 63:

TABLE 62. Progressive states of magnetizability, varying with hardness. 

[Thick wire, 2p=0.15 centimeter.]

Mean hardness

(gal van).

45.3

40.2

37.9

36.6

35.7

30.2

28.5

26.7

25.1

23.8

23.0

19.5

16.7

J5.3

Mean specific magnetism m, for the dimension-ratio =

10

23. 5

22.2

22. 3

22.3

'22. 3

20.8

20.8

21.4

21.9

21.4

21.0

19.3

15.2

4.3

20

37.6

35.7

35.3

35.3

35.2

36.0

37.4

40.2

43.3

44.7

45.2

45.8

40.8.

11.2

30

43.6

41.3

40.8

40.6

40.6

42.9

45.1

49.4

,54.3

57.8

59.3

67.0

71.3

20.5

40

46.5

44.2

43.3

43.1

43.1

46.2

48. 8

53.8

59.6

64.3

66.5

80.4

91.3

31.8

50

48.3

46.0

45.0

44.8

44.8

48.3

51.2

56.5

63.0

68.2

70.9

87.3

101.8

44.6

TABLE 63. Progressive states of magnettealility, varying with hardness. 

[Thin wire, 2p=0.084 centimeter.]

Mean specific magnetism w, for the dimension-ratio Mean hardness 

(gal van).

37.9

35.5

33.9

33.1

32.5

28.5

27.4

26.0

24.8

00 Q

£O. y

n

19. 7

18.1

15.1

20

31.5

30.5

30.1

29.9

29.8

29.5

30.1

32.3

33.9

'34.8

32.6

28.0

6.0

40

42.6

41.3

40.7

40.5

40/3

42.6

44.8

48.6

52:6

55.3

. 63.8

f5.3

24.5

60

46.9

45.4

44.8

44.6

44.5

47.3

49.8

54.4

59.2

63.2

79.0

83.0

45.3

80

48.9

47.2

46.5

46.3

46.3

49.8

52.7

57.2

62.6

67.1

86.4

92.7

61.4

100

50; 2

48.3

47.6

47.4

47.4

51.7

54.5

59.4

64.7

68.9

90.7

99.0

72.2

On the basis of these tables the two families of curves, Figs. 17 and 

18r have been constructed.

(732)
BAKUS AND STKOUIIAL.] MAGNETISM AND HARDNESS. 141

Specific TncufTtdisrru ( C. (r.S.)

P PPP

(733)
142 IRON-CARBURETS. [BULL. 14.

Magnetism and dimension-ratio. Of equally great interest, moreover, 

is the other phase of these phenomena in which magnetizability is regarded as a function of the independent variable, the dimension-ratio, 

whereas hardness appears merely as an arbitrary constant. We "will 

endeavor in this place to give an account of our data, sufficiently detailed to admit satisfactorily of a comparison with results of earlier 

observers. In the absence of a better means of estimating hardness 

the oxide tints were largely made use of, and the wires examined, therefore, classified as hard, yellow annealed, blue annealed, and soft. In 

conformity with this method of description, we will attempt to give the 

parameter (hardness) in our own results, such values as will correspond 

with the said four States. The following special experiments furnish approximate data for the expression of the degree of hardness corresponding to any given oxide tint in our own galvanic scale:

Cm / Cm2, 0° microhm. 

Glass-hard......................... ...... ................. .. .s=45.7

Yellow annealed ....... ....... ....... .....:. .............8=26.3

Blue annealed.......................... .................... . . ....8=20.5

Soft .......................................................................s=15.9

It is well to note that the logarithmic interval between yellow annealed and blue annealed is about equivalent to the same interval between blue annealed and soft, and about twice as large as that between 

glass-hard and yellow annealed. Referred to our method of tempering, 

the values for yellow annealed and blue annealed would agree very 

nearly with three hours of annealing in aniline vapor (mean s=26.7 and 

26.0) and one minute of annealing in melting lead (mean s=19.5 and 

19.7), respectively.

The smaller galvanic values for these states correspond to the smaller 

values for the soft state (mean s=15.3 and 15.1), respectively, and the

difference is, therefore, obviously due to carburation. Hence for our 

present purposes it is fully sufficient to select from tables 62 and 63 the 

following mean values of magnetism .for the degrees of hardness in

question:

TABLE 64. Thick wire.

Mean specific magnetism m, for the dimension-ratio =

Glass hard

Soft.....................................

10

93 <\

21.4

19.3

4.3

20

07 a

40.2

45.8

11.2

30 .

43.6

49.4

67.0

20.5

40

46.5

Vt 8

80.4

31.8

50

4fl Q

5fi 1

87.3

44.6

TABLE 65. Thin wire.

Soft...... ...............................

Mean specific magnetism m, for the dimension-ratio =

20

3L5 

32.3 

32.6 

6.0

40 '

42.6 

48.6 

63.8 

24.5

60

46.9 

54.4 

79.0 

45.3

80

48.9 

57.2 

86.4 

61.4

!

100

50.2 

59.4 

90.7 

72.2

(734)
BAHU8 AND STUOUIUT..] MAGNETISM AND DIMENSIONS. 

Specific TTutfjnetr'srms ( C. GSJ *

Sr> ^

I F

143

\

Specific -irta.tjruitisi;i. ( C. (r-Xj 

I 1

(733)
144 IRON-CARBURETS. [BULL. 14.

Graphic representation. These data enable us to. construct the curves 

in Figs. 19 and 20.

The curve glass-hard is concave as regards the axis of abscissae 

throughout. Eising very rapidly at first it finally ascends to a distinct limiting value, or horizontal asymptote. The curve soft, on the 

other hand, rises very slowly in its earlier stages, and is convex as regards the axis of abscissae. From here it passes rapidly upward 

through a point of circumflexion into concavity towards X, and then 

above the former curve. Finally the rate of ascent again decreases so 

that a horizontal asymptote must eventually also be reached, but apparently at a later stage of the progress than is the case with hard 

wire. From either of these two curves, which describe the variations 

of the extreme states, we may, by the process of annealing, pass continuously to the other; but the manner of such passage from the one to 

the other, resulting from a continuous change of parameter (hardness), 

is excessively complicated. Incipient annealing of a glass-hard rod 

produces a distinct though small descent of the original curve as a 

whole. .As annealing progresses, the farther end of the curve is always 

the first to rise and pass above the original curve in such a way that 

the point of intersection of the new curve and the original curve, glasshard, moves rapidly from greater to smaller values of the dimensionratio. When the curve "yellow annealed" is reached the part between 

a=14 or 18, respectively, and or=oo has already been elevated above 

the curve glass-hard. In the case of the "blue annealed" curve we 

observe the part between a=15 or 20, respectively, and a=co to have 

risen enormously; but on the other hand the part of this curve between 

a= 0 and <*=15 or 20, respectively, having descended gradually, is now 

distinctly convex as regards the axis of abscissae. Passing from blueannealed to soft, we find the left-hand part of the curve falling at a more 

rapid rate, While the right-hand branch still rises slowly, reaching a 

superior limit and then falling rapidly into coincidence with the curve 

for the soft state, already discussed.

We have remarked that the phenomenon of variation of maguetizability, regarded as a whole, does not by any means seem to present a 

certain critical value for the dimension-ratio, below which magnets behave differently than above it. If only the four curves hard, yellow 

annealed, blue annealed and soft were known, as they appear in Figs. 19 

and 20, there, would appear to be reasons for considering o-=15 or 20, 

respectively, as a critical value of this kind; for it is here that the three 

curves approximately intersect each other. How unjustifiable, however, such conclusions are, will be obvious from a mere glance at Figs. 

17 and 18, in which the curves for this value of a manifest no change of 

character whatever.

Magnetism and density. We may remark here that when the rodis very 

long in comparison with its diameter, its specific magnetism (saturation 

presupposed) becomes coustaut-or independent of the dimensions.

(736)
DAUUS AND STROUIIAL.I MAGNETISM AND DENSITY. 145

In Green's equation for the distribution of magnetism in a cylinder 

of finite length, 21, and radius r.

A. = nKX pr -jr

where A, is the linear density of free magnetism at a distance x from the 

middle of the cylinder, K the coefficient of magnetization, X the magnetizing force, p a numerical quantity related to K; let KX be accepted 

as the expression for coercive force, JP, and put for greater simplicity

rlg-=p.

 y -L

If now we evaluate

/

{ 2 nwFT FT 1 v~l "kxdx = L I 4- , r Igv L Igv v-1

and furthermore put

tylfy srr* M _ *zm ______

M

yu n r2 1 d 

we find that if I (or better- = a) be supposed to increase indefinitely,

m will pass through

m== 2_F ( l _ JL_ I 

. d \ pa)

into a constant value, depending only on the material. Biot 132 put p = 

0.124, approximately.

JSTow it is remarkable that in this case, in which moreover the expression for the linear distribution of magnetism attains its simplest form, 

we are led to infer that the (linear) rods are capable of retaining more 

magnetism permanently in proportion as they are softer. But this 

general deduction will not hold good as far as the soft state. Figure 

20 gives as yet no decisive answer to this question. However, in passing from the blue annealed to the soft condition, steel passes through 

a state of maximum density; and our results thus give warrant to the 

surmise that the greatest attainable magnetization can be imparted to 

steel, when the hardness of the necessarily linear rod has that particular 

value which is characterized by maximum density. This digression suggests itself naturally here, but will be made the subject of a special inquiry. From figure 17, however, it is already quite apparent that the 

said unique maximum will be considerably larger than 785 c. g. s. units' 

of intensity (magnetic moment per unit of volume), the value thus far 

assumed and derived from an incidental result of Kohlrausch.133

132 Biot: Trait6 do Phys., Ill, p. 76, 1816.

133 Of. Gordon: Electricity and Magnetism, I, p. 156, London, 1886.

(737) . 

Bull. 14 10
146 IRON-CARBURETS. I BULL. 14.

Earlier results interpreted. It will now be in place to compare oar 

results with those of Euths. We will select from his data the series 

contained on p. 47 of his memoir, as these may be regarded typical. 

Here again, those alone can be considered which refer to magnets as 

nearly as possible in the permanently saturated state. In the place of 

the absolute magnetic moment of his steel rods we have deduced the 

corresponding values for specific magnetism from his data. This greatly 

facilitates comparison.

TABLE 66. Ruths' magnetic results.

Length = 12. ^

I.

0.10

70

1.99

68.7

88.6 

92.0

n.

0.24

50

4.31

66.1

71 

71

III.

0.29

40

6.22

74.7

79.1 

90.2

IV.

0.38

30

10.55

61

52 

61.3

V.

0.49

25

17.50

66.6

38.6

48.2

VI.

0.59

20

25.65

51

29.7 

28.4

Diameter.

Dim. ratio, approx.

Mass.

Glass-hard. ~> Yellow annealed. > Spec. Magnetism. 

Blue annealed. )

The first comment to be made in this connection has reference to our remarks given in p. 117, on the structural influence of tempering. Ruths' 

magnets were all of the same lengths, whereas the thickness varied from 

0.2 centimeters to 0.6 centimeters. To i inpartlike degrees or similar states 

of hardness to rods varying in thickness to this very large extent, is manifestly impossible, even if the material were throughout perfectly identical. It follows thatthe divers values of specific magnetism obtained cannot even be compared one with another. Hence the attempt to arrive at 

the nature of the functionality between permanent magnetism and ratio 

of dimensions from these results, must necessarily be futile. Euths' data 

are unavailable, therefore, for the construction of curves, corresponding 

to those in figure 19. We infer from Euths' table that in general the 

specific magnetism increases with the dimension-ratio. In the case of 

the thicker magnets (IV, V, VI) Euths found values for specific magnetism much larger than our own. In accordance with these, the intersection of the curves glass-hard and blue annealed would occur for (x 3Q'f 

the corresponding point for blue annealed and yellow annealed lying at 

«=2S. In accordance with Euths' results, moreover, figure 19 would 

have to be changed in such a way that the curve, glass-hard (to agree 

with Euths' large values) rise at a more rapid rate, thus falling short of 

intersection with the other two curves until these have intersected each 

other at about «=20. Then its passage is through blue annealed at 

about «=25, and through yellow annealed at about a=40, where the 

latter curve is also supposed to rise more rapidly than is the case in our 

results. But with this apparently satisfactory interpretation, the equivalence of blue annealed and yellow annealed for <*=50, is wholly in 

discordance.

Fromme uses eight rods, all of the same length, four of which are of

(738)
BA3U8 AND sTKOuiiAL.J MAGNETISM AND HARDNESS GRAY'S RESULTS. 147

like small diameter, the other four of like larger diameter, to corroborate 

Kuths' results. The dimensions are these:

First four: a==15', second four: «==50 '

His results for the ratio of mass (/*) and square of the time (t) of 

vibration are the following:

a=15

1982

1508

1118

a=50

413

448

440

These values would put the point of intersection of blue annealed 

and yellow annealed at #=50. agreeing with Baths' result for his magnet II. But this by.no means removes the discordance between the 

data for a=5Q and those of Ruths for #<50, because the latter refer 

this point to <*=20.

An extended series of observations on the relation between moment of 

permanent magnetism and hardness, of exceptional accuracy, has been 

published by Gray134 All the rods have the same dimension-ratio, a=50. 

Unfortunately he does not carry one and the same hard rod through all 

possible states of inferior temper. Although the material is identical 

throughout, the results are therefore necessarily distorted by structural 

discrepancies, in addition to the effects due to differences of hardness 

in the glass-hard state. In operating with low temperatures Mr. Gray 

neglects the (then unknown) time-effect of annealing.

In Chapter II, pp. 40-43, we discussed the results obtained with rods 

tempered in a way nearly identical with that employed by Mr. Gray, hard 

wires being immersed in linseed oil, the temperature of which was raised 

very gradually by the aid of a Bunsen flame, and batches of wires removed from the bath at different stages of the heating. If we take into 

consideration the great irregularity of distribution of temper which the 

rods so treated manifest, the causes of relatively large discrepancies 

occurring in Mr. Gray's results are apparent at once. For the same 

reasons we are not able to compare them in detail with our own.

One striking difference between the two sets of results is, however, 

to be noticed. Mr. Gray has observed no minimum of magnetizability 

in the region of glass-hardness. The specific magnetism, in general, is 

found to increase rapidly between glass-hard and annealed at 100°; is 

fairly constant between the latter state and annealed at about 280°; and 

after this increases rapidly again until the highest annealing temperature employed (310°) is reached. As a whole, however, the observed 

range of variation (72 to 80 0. G, S. units of magnetic moment per 

gramme) is remarkably small when compared with our own (45 to 85

134 Gray : 1. c. 

(739)
148 IRON-CARBURETS. [DULL. 14.

and 42 to 75, respectively, C. G. S. units of magnetic moment per 

gramme). The following tabular comparison between Mr. Gray's mean 

results and our own will exhibit this perspicuously:

Table comparing the mean results'of Gray and of B. and S. 

[Gray. Z=5.000, 2p=0.097 centimeters.] [B. and S. Z=7.50 centimeters, 2p=0.15 centimeters.]

Eod. No. 

Ito5....... ........

6to 10.... ..........

11 to 15.. ...........

16 to 20. ............

21 to 25..... ........

26 to 30..... ........

31 to 35. ............

36 to 40. ............

41 tn 4"?

51 to 55...... .......

56 to 60- ............

Annnealed 

at15«

1000

150°

200°

OfiflO

260°

27«o

280°

2900

3000

3100

Mag. mom. 

(C. G. S.), 

per gramme.

C 71. 82

i 74. 33

C 75.64

\ na no

C 75. 60

I 76. 50

C - 75.76

i 76. 04

77.42

7fi fiQ

7C QO

77 P»Q

76.51

76.14

f 78. 60

i 70 no

79.24

Eod No.

IX to XII..

IX to XII..

IX to XII.

IX to XII.

IX to XII.

IX to XII.

IX to XII.

IXtoXIE.

IX to XII.

IX to XII.

IX to XII..

IX to XII..

IX to XII.. ixtoxn..

Annealed 

at^-

20°

100°

1000

lOflo 100a

185°

185°

185°

1850

185"

210°

330°

440"

1000°

Daring 

the 

time.

!>>

3*

&

10*

. 20"

I*31-

7h

13>>

10"

lm

I*

Mag. mom. 

(C. G. S.), 

per gramme.

48.3

46.0

45 ft

448

44.8

48.3

51.2

56.5

63.0

68.2

70.9

87.3

101.8

44.6

Hardness, 8.

41 1

40.2

37 9

36.6

35.7

30.2

28.5

26.7

25.1

93 a

23.0

19.5

16.7

15.3

The large though unavoidable discrepancies encountered by Mr. Gray, 

notwithstanding his careful manipulation and precision of measurement clearly show the difficulties with which the problem in question 

was then surrounded. We possess no data for the magnetic effect produced by tempering in oil. The only satisfactory method of accounting 

for the above discordance would be that of supposing that Mr. Gray 

operated upon a less highly carburized steel than was used in our experiments. In such a case, greater values of specific -magnetism for the 

hard state and small values for the soft state in Mr. Gray's results, as 

distinguished from our own, are anticipative.

CONCLUSION.

The general problem. The results in this paper offer only a partial solution of the general problem. Irrespective of the effect of carburation, 

concerning which remarks have already been made, the temporary and 

permanent magnetization induced by magnetic fields of an intensity insufficient to saturate steel, are new subjects of importance. A fifth

(740)
iiAiius AND STOOL-HAL.] MAGNETISM AND HARDNESS CONCLUSION. 149

variable, the intensity of the field, therefore, suggests itself. If we remember how intimately magnetic phenomena are associated with the 

structural condition of a rod, and how absolutely devoid of reliable facts 

our knowledge of this actually is, we see how little advancement can be 

hoped from theory. The mathematical analysis, again, even when starting from the simplified premises of homogeneity, encounters formidable 

difficulties. On the other hand, the possibility of a solution of the general problem, by the application of the method which we have endeavored to develop in the above, we dare say is undeniable. Snch an attack we have in view.

Practical bearing. The present investigation has a practical bearing 

of some importance. For cylindrical rods it gives a satisfactory solution 

of the problem as to what degree of hardness is to be chosen in order 

that a given steel rod may possess the maximum magnetizability, It

is a remarkable result, that for very small values of the dimension-ratio 

considered as one extreme case, the rods can be most intensely magnetized when in the very hard states, whereas for very large values of the 

dimension-ratio regarded as the other extreme case, similarly favorable 

conditions are offered by the softer states, with the probability that a 

state of singular excellence in this respect lies between blue annealed 

and soft.

But it does not by any ineansQbllow herefrom that in the construction of magnets for practical purposes they are to be made glass-hard 

if short and thick, and soft if long. This question involves elements 

of quite another character. The problem -is so to construct a magnet 

that with a maximum of intensity it may be best qualified to withstand 

the hurtful influence of atmospheric changes of temperature, of shocks, 

and such like effects; in short, to produce a magnet which, under like 

circumstances, shall always show practically identical values of the intensest available magnetization. This will be made the subject of the 

next chapter.

ADDENDUM,: ON THE DENSITY-EFFECT OF INCIPIENT ANNEALING

OF HARD STEEL.

In Chapter V we adverted to the relation probably existing between 

the maximum of permanent magnetism of linear, steel rods and their 

density. We there, moreover, state the grounds why the conditions 

most favorable for the appearance of such a relation are encountered in 

the case of linear rods. The question is therefore immediately suggested whether the characteristic minimum of magnetizability of steel 

rods corresponds to an analogously singular point in the variation of 

density. We commenced experiments with the object of discussing the

(741)
150 IRON-CARBURETS. [BULL. 14.

matter, with a steel rod 1.91 centimeters in diameter and 5.40 centimeters long, tempered glass-hard in the usual way.

State of hardness.

Annealed 4h at 100° ....... |

Annealed 8h at 100° ....... J

Annealed 12h at 100° ........

Specific 

gravity 

at 20°.

7. 8320

7. 8313

7. 8035

7. 8033

7. 8032

7. 8040 

7. 8039

7. 8052 

7. 8052

7. 8058

Specific 

volume.

1 1. 00000

1 1. 00363

1. 00365

1 1. 00355

{ 1. 00339

1. 00332

The first result obtained from these data is a striking corroboration 

of a result of Froinme's, viz, that the maximum increase of specific volume experienced by a hard-tempered steel rod diminishes as the diameter of the rod increases. Fromme's results for thickness on specific 

volume of tempered steel rods are these:

2p= Thickness (cm.) = 

v = Sp. volume =

0.7 

1. 00772

0.42 

1. 01000

0. 265 

1. 01285

0.255 

1. 01210

u

The result for the above rod 2p = 1.91 and v 1.00363 is in excellent 

accordance with these data. In drawing this inference it is necessary 

to bear in mind that serious discrepancies may be introduced by the 

possible differences in carburation of the respective rods. Nevertheless, 

all these results taken together are so satisfactorily consistent that it is 

difficult to avoid the deduction made.

The second result shows, that the increment of specific volume due to 

tempering in general decreases as time increases. But this variation 

takes place at a more rapid rate at the middle stages of the operation 

than either at its early or closing stages. The curve, therefore, contains 

a point of circumflection, and the possibility of a maximum near the inception is by no means excluded. To obtain definite and decisive results, however, it will be necessary to operate with thin rods, for which 

the density effect of tempering is so much more clearly pronounced.

The plausible inference that the anomalous electrical behavior of steel 

on incipient annealing, discussed in Chapter II (page 67), and the minimum of magnetizability investigated in this chapter, may find an analogous variation in the density of similarly treated hard steel, cannot as 

yet, therefore, be said to have been disproved.

(742)
OHAPTEE VI.

THE TEMPERING OF STEEL CONSIDERED IN ITS BEARING ON THE 

POWER OF MAGNETIC RETENTION, OR ON THE CONDITIONS OF MAGNETIC STABILITY OF THIS MATERIAL.

INTRODUCTION.

Temporary and permanent magnetic effects of annealing. The influence of temperature on the moment of permanent magnetism of steel 

rods is characterized by a temporary and a permanent effect, usually 

superimposed. If a steel rod magnetized to saturation at the temperature t° is heated to T° (T>£) and then again cooled to <°, it will be 

found to have experienced a loss of magnetic moment. If the process 

is repeated the temperatures t and T being the same as before an additional diminution, decidedly smaller, however, than the first, will 

manifest itself. Continuing in this way we shall find that the permanent loss converges to zero. The rod is now in a condition for which 

the magnetization lost during the passage from P to T° is again restored when the original temperature tP is regained.

Kesearches on this important subject have been made in great numbers.135 The result has usually been that magnets which are to be used 

between the atmospheric temperaturess t and T should be heated and 

cooled between these or greater limits for an indefinite number of 

times, in order that a condition of magnetic permanence or of perfect 

magnetic elasticity, as it has been called, may be assumed.

Simultaneous mechanical effects hitherto disregarded. To the venture of 

resuming a topic which has been so elaborately and apparently so exhaustively discussed, we were primarily induced by certain new and important facts which our researches on the hardness of steel had developed. 

Curiously enough among those who operated with glass-hard rods and 

it was to these that we. at first, desired to confine our attention only a 

few have given even cursory consideration to the important factor, the 

change of the mechanical state of the material. We have shown that 

temperatures 20° or 30° above that of the water in which during temia6 The earlier literature is systematized in J. Lament, Maguetismue, p. 386,1807; G. 

Wiedenianu, Galvauismus, II a, p. 603,1874; A. Mousson, Physik, 3 Aufl., III., p. 110. 

Among the more recent papers (since 1876) we desire to mention: G. Wiedeman, Pogg. 

Ann., CLVII, p. 257, 1876; J. M. Gaugain, Comptes rend., LXXXII, p. 1422; 

LXXXIII, p. 661, 1876; LXXXVI, p. 536,1878; G. Poloni, Beiblatter V, p. 67, p. 802, 

and p. 614,1881; Elettricista, I.I, p. 193, 1878; J. Trowbridge, Am. Journal (3), XXI, 

p. 316, 1881

(743) 151
152 TRON-CARB¥RETS. [BULL. 14.

pering the rod was chilled, when acting on glass-hard rods can be made 

to produce annealing effects of definite and accurately definable magnitude.

If, therefore, it is our object to investigate the functionality between 

magnetization and temperature, it is manifestly necessary at the very 

outset to exclude all permanent and simultaneous changes in the material carrying the magnetic quality. This is what none of the former 

observers have done. Temperatures as high as 100° are frequently applied. Under these circumstances the hard rod assumes diiferent mechanical properties while in the hands of the operator, and the results 

will necessarily be stripped of the claims to accuracy which the care 

frequently bestowed would otherwise justify.

. Eetentiveness. There was a second consideration which suggested 

the present series of experiment. This was the desire to utilize certain 

earlier data in the endeavor to construct magnets possessing great 

power, of retention. It is not necessary to advert to the important 

bearing of this problem, not only on all absolute magnetic measurements, but more particularly even on those of a relative character. 

That the methods now employed are inadequate is conceded by the observers of highest authority and experience. Old magnets subserve 

best the purposes of measurement; but even these, where a constancy 

of moment under like circumstances is to be presumed are carefully 

to be protected from shocks and larger changes of temperature.

Thepresent work. In the following pages our experiments will be cited 

chronologically. Some of them are merely corroborative as regards 

results which have already been pronounced by others. But the intimate connection between these and our subject proper, together with 

the new interpretation which has frequently been given them, vindicates

their appearaoce here,

The method of magnetization and the calculation of the magnetic 

moment as well as the measurement of hardness was identical with that 

detailed in Chapter V.

RETENTIVENESS AS REGARDS VARIATION OF TEMPERATURE.

Preliminary experiments. Our first experiments were incidentally 

made with six little steel parallelpipedons, of the same material which 

had been used in a series of experiments described elsewhere. The dimensions (cm.) and mass (</) of these, after being tempered to glasshardness, were as follows:

Breadth ..............

I.

3.0

0 ^

0.3

0.328

II.

2.5

O K

0.3

0.278

m.

3 rt

0.4

0.3

0.278

IV.

2.5

0.4

0.3

0.232

V.

3.0

0

0

0.2

0.133

YL

2.5

0.3

0.2

0.113

(744)
BARUS AND 6TKOUHAL.] RETENTIVENESS AND TEMPERATURE. 153

When magnetized with a large Funkler's magnetic battery (50 kilos 

portative force) of the horseshoe form, these retained the following 

quantities of specific magnetism:

I.

16.4

II.

12.0

in.

18.6

IV.

14.8

V.

25.0

VI.

20.7 cm*

01 see

Hereupon the magnets were transferred from a water-bath at 15° 0. 

to another at 50° 0. and then returned. This was repeated ten times, 

with an allowance of about ten seconds of immersion for each. After 

this process the respective values of specific magnetism were found to 

be 

m=

I.

16.1

II.

12.7

III.

18.4

IV.

14.6

V.

24.6

VI.

20.3

The losses are therefore small as a rule, only about f per cent. The 

temperature 50° appears to be relatively low in so far as its effect in producing the variation in question is concerned. If it should be our purpose to reach a limiting value in this way the operation would have to 

be repeated a great number of times. Possibly several hundred repetitions would even be inadequate.

For this reason we decided to continue the work with the aid of 

higher temperatures. The magnets were exposed in steam. 0 Previously, 

however, we remaguetized them to saturation. This was done with a 

large and powerful helix, through which the current of a dynamo-electric machine circulated. The mean intensity of 'the magnetizing force 

when referred to the lengths 2.5 cm. to 3.0 cm. of the magnets, and for 

the current 3.0 cmM gM/sec, was found to be 

It is obvious that these powerful forces 136 were far more than sufficient 

to effect the saturation.

The magnets were now exposed in steam at 100° for consecutive intervals of 20, 40 minutes, then for 1, 2, 3, and finally 4 hours. After 

each withdrawal from the steam-bath they were laid aside for some 

time in a room in which the temperature varied between 10° and 15°. 

After this we made the measurement of the magnetic moment. The

136 For divers other data relative to this lielix conf. Chapter V. 

(745)
154 JRON-CARBURETS. [BULL. 14.

results of this series of experiments are shown in the following table

for m:

TABLE 67. Limits of magnetic stale.

Description of temper.

Annealed 40m more in fteam 100° .

Annealed lh more in steam 100°. . .

- Annealed 2h more in steam 100°. . .

Annealed 3h more in steam 100°. . .

Annealed 4h more in steam 100°. . .

I.

18.07

14.08

11.68

10.34

9.42

8.86

S.65

It.

14.90

10.74

9.05

8.11

7.32

7.07

6.6D

ni.

21.34

15. 80

13.45

12.21

11.21

10. 68

10.29

IV.

17.08

19 49

10.42

9.00

8.85

8.21

8.03

V.

28.70

20.94

17.00

15.68

14.16

13.63

12.98

VI.

23.55

16. C6

13.92

12.22

11.04

10.24

9.91

If these results be constructed graphically, time of exposure as abscissa and specific magnetism (at ordinary temperature) as ordinate, we 

obtain a series of curves of regular and similar contour. Their general

 characteristic is that of an initially rapid descent, which as annealing 

continues is soon retarded until finally an asymptote parallel to the

 axis X, is approximately reached. These results corroborate the older 

results for the effect of the time of exposure on the variations of the 

magnetic state of a bar. The phenomena were first studied by Moser and 

Riess, 137 somewhat later by Holmgren, 138 and particularly emphasized 

by the latter in a way at variance to the views of the former observers. 

Physicists were inclined, however, to refer Holmgren's apparently anomalous results to other causes,139 whereas Laniont140 pointed out that Holmgren had operated with glass-hard rods, while the magnets of Moser 

and Eiess were uutempered. Quite recently G. Poloni 111 has given the 

effect of the time of exposure due prominence. He fails, however, 

clearly to discriminate between the results obtained in cases of differently tempered bars, or, in other words, confounds the effect due to 

change of temper with the magnetic effect. We shall show in the sequel 

that they are entirely distinct and can be separately studied.

Simultaneous magnetic and mechanical effect of annealing. But there 

is another inference of greater relevancy to our iramediate inquiry. The 

curves under consideration are strikingly similar to those formerly ob 

taiued while investigating the electrical effect produced by a change of 

temper of steel (annealing).142 In fact, the analogy is sufficiently evident 

to induce us to associate the observed decrement of magnetic intensity 

and the cotemporaneous change of mechanical state of glass-hard rods

 as phenomena intrinsically related. In other words, we were inclined 

to regard annealing as the primary, and the diminution of magnetic intensity (in by far the greater part) as tbe secondary occurrence; or more

137 L. Moser and P. Riess: Pogg. Ann., XVII, p. 403, 1829.

13(5 K. A. Holmgren: ActaSoc. Scierit. Upsala(3)I; Fortschritted. Physik,p.536,1856.

139 Of., G. Wierleinann: Galvanisuius, II a, p. 614, 1874.

140 J Laraonfc: Magnetismns, p. 385, 1867.

141 G. Poloni: Elletricisfca, II, p. 139. Beibl. II, p. 523, 1878. 

142 Strouhal and Bams: Wied. Ann., XI, p. 030, 1880. Chap. II.

(746)
DAUUS AND 6TUOUHAL.] MAGNETIC EFFECTS OF TEMPERATURE. 155

accurately, to distinguish between a primary or purely magnetic (permanent) effect of temperature, a direct effect; and an indirect effect of 

temperature, due to the influence of the rearrangement of molecules in 

consequence of mechanical annealing, upon the existing intensity of 

magnetism of the rod.

With the object of verifying this hypothesis we selected a sample out 

of our supply of glass-hard rods which, when tested, showed great 

uniformity of hardness throughout its length. This was broken into 

two nearly equal parts Nos. 11 and 12.143 The constants of each were 

found to be 

Length ... 

Mass......

No. 11.

10.0 

0.417

No. 12.

10.0 

0.418

cm. 

8-

These were now magnetized to saturation with the helix, and then annealed in steam at 100° during consecutive intervals of 10, 20, and 30 

minutes, 1, 2, 3, 4, 5, and 6 hours. After each of these we made a determination of hardness using specific resistance s at the atmospheric 

temperature t as a datum for this purpose. Furthermore, in order to 

arrive at the desired comparison, IsTo. 12 was remagnetized to saturation after each interval of annealing, whereas No. 11 was tested for 

specific magnetism in the condition in which it left the annealing bath, 

that is without repeated magnetization.

The results of these experiments are contained in the following table. 

The specific magnetism is represented by m* and TO, according as tne 

magnetic datum in question was obtained with or without, remagnetization respectively. W here denotes the observed electrical resistance 

of the respective rods per meter of length at the temperature t, s the 

corresponding specific resistance (cm./cm.2 0° microhm).

TABLE 68. Diminution of hardness, magnetisation, and maynetteability.

Description of temper.

Annealcd+30m in LCO° ...................

Auncalecl+ lh in 100° ..................

Magnet No. 11.

W

0.755 

741 

724 

708 

689 

671 

656 

646 

639 

. 634

t

18.3 

18.7 

20.1 

21.0 

19.9 

20.2 

18.7 

19.2 

20.0 

19.9

s

39.5 

38.7 

37.6 

86.7 

35.7 

34 8 

34.1 

33.5 

33.1 

32.8

m

6?. 6 

59.5 

56.0 

52, 0 

50.0 

47.3 

46.1 

45.1 

44,3 

43.8

Magnet No. 12.

W

0.761 

746 

728 

712 

693 

670 

660 

651 

644 

638

t

18.5 

18.7 

20.1 

21.0 

20.0 

20.1 

18.7 

 19 0 

20.0 

19.9

«

39.9 

39.1 

38.0 

37.1 

36.1 

35.2 

34.5 

33.9 

33.5 

33.2

m

"59." ?' 

58.2 

57.5 

56.5 

56.1 

56.4 

50.5 

56.3 

56.5

ra*

62.5 

62.4 

61. !> 

60.6 

60.2 

59.5 

59.4 

59.3 

59.1 

59.0

43 The magnets Nos. 1-10, were used in the work detailed, in Chapter V.

(747)
156 IRON-CARBURETS. [BULL. 14.

Mere inspection of this table discovers at ouce the striking parallelism 

in the successive values of specific resistance s and specific magnetism 

m. If the two series of results be represented graphically, time of exposure as abscissa, s and m respectively as ordinate, we obtain (Fig. 

21) two curves of an obviously allied character. Indeed there can be

4.5

[40

'35

00

BO

40

30

20

10

^ jrsff

\f4- '08

14-

6 3 70 12 

Timje, of expasta'e to 1OO", inJvours ,

FIG. 21. Diminution of specific magnetism and specific resistance produced by continued annealing

(low temperatures).

no doubt that the occurrence of the continuous diminution of magnetic 

moment here observed is largely conditioned by the variation of hardness which occurs contemporaneously. It is particularly to be noted 

that in both instances the asymptotic limit is reached after the lapse of 

the same time, approximately.

If now we regard the values for m* as obtained with the magnet No. 

12, there appears in the first place a diminution of the quantity of magnetism which the saturated rod permanently retains, which soon however, as annealing continues, reaches a certain minimal value in a way 

consistent with the results of the former experiments. Furthermore, 

from a comparison of the values of m and m*, it follows that during the 

progress of the annealing the influence of the higher temperature (100°), 

regarded in connection with the time during which it acts, becomes less 

and less pronounced, in proportion as the magnet itself has reached

(748)
BABUS AND STRODE.] MAGNETS SUCCESSIVELY ANNEALED. 157

the limiting state of hardness for the temperature (100°) under consideration. But it also appears that the same limiting value of specific 

magnetism gradually reasserts itself, no matter how often the combined 

process of magnetization and subsequent indefinite annealing may be 

repeated. Moreover, a magnet which has approximately reached the 

limiting hardness for the given temperature, if remagnetized to saturation and annealed again at the same temperature, reaches a limiting 

magnetic condition, the value of which is nearly independent of the 

time of exposure.

The purely magnetic effect (permanent}. The inference enunciated at 

the end of the last paragraph still needs additional proof. Accordingly, 

our magnets Nos. 11 and 12 were now magnetized afresh and then exposed to steam in the uniform manner described. We thus arrived at 

the following results:

TABLE 69. Specific magnetism, TO, of saturated rods successively annealed at 100°.

Time of exposure to 100°. No. 11.

59.0

57.3

56.6

55.7

55 7

55.7

59.0

57.2

. 56.6

56.0

56.0

06.0

No. 12.

59.0

57.1

56.6

55.9

55.6

55.6

58.7

57.1

56.4

55.9

55.9

55.8

We also remagnetized the steel parallelopipedons Nos. I ... VI, with 

which the original experiments were made, and then annealed them in 

steam, in the usual way, repeating the whole process a number of times. 

The following table contains the values of specific magnetism obtained:

TABLE 70. Specific magnetism, m, of saturated rods successively annealed at 100°.

Time of exposure to 100°.

1 hour more in steam at 100°......

2 hours more in steam at 100°. ....

1 hour more in steam at 100°. . ....

50 minutes more in steam at 100°. .

1 hour more in steam at 100° ......

I.

17.82

16.34

]6.24

16.12

37.84

16.28

16.24

17.77

16. 25

16.10

16.07

II.

13.96

12.78

12.69

12.66

13.94

12.69

12.66

13. 91

12.73

12.59

12.54

III.

20.14

18.r>4

18. 3H

18.29

20.12

18.47

18.37

20.09

38.31

18.24

18.26

IT.

16.22

14.75

14.60

14.54

16. 03

14.73

14.69

16.00

14.54

14.54

V.

27.20

25.44

25. 24

25. 12

25. 42

25. 34

27.25

25.60

25.34

25.31

VI.

22.58

21. 07

20.93

20.41

22.80

9fi Q3

20.97

21.01

20.93

20.86

If the present behavior of the magnets, where the steel has practically reached its limiting mechanical state for 100°, is contrasted with 

the above, where temper varies simultaneously with magnetism, a much

(749)
158 IRON-CARBURETS. [BULL. 14.

smaller and thoroughly uniform loss of specific magnetism is everywhere apparent. In the case of No. 11 the original loss amounted to

"*' ~ *' =30 per cent, nearly; whereas at present the average loss is 

only ' ~ J' =5.3 per cent. Similarly, the average Joss of specific

magnetism of the rods I ... VI was originally " 'lftTr * = 55 per

Zt\Jt i O

19 69 17 9S Cent, nearly. Now we have only an average loss of ~ ' * = 8.C per

19.62

cent. But owing to the fact that these magnets had been specially 

treated at the outstart repeatedly heated from 15° to CO0 an immediate 

comparison between the last results and those for No. 11 is not to be 

made.

We have thus arrived at a partial corroboration of certain results obtained by Moserarid Eiess, 141 and subsequently also by Dufour. 145 Following Moser and Riess, we have for the successive losses of a hard needle :

Per cent. 

After the first magnetization ...... ...... . . ...... ...... ...... ...... ...... ...... 44.0

After the second magnetization ............................................... 6. I

After the third magnetization ...... ...... ...... ... ........................... 4.4

But with this last result our observations are at variance. As has 

been stated, our data have invariably shown that when the maximum of 

permanent hardness corresponding to any temperature has once been 

attained, then the magnetic effects of repeated application of the same 

annealing process are identical, the losses of specific magnetism experienced by saturated rods constant.

The direct and indirect effect of temperature. We conclude, therefore, 

that if it be oar object to perspicuously represent the law of the phenomena in question, it is essential to discriminate between two speciesof magnetic loss. If the magnet is in such a condition for instance 

glass hard that the higher temperature (2) produces a mechanical 

effect, then this is invariably accompanied by a magnetic effect peculiar 

to itself, and as experiment has shown, of relatively very large intensity. 

The reasons for this behavior are obvious. The existence of magnetism is conditioned by a strain of a particular and characteristic kind. 

The same is true of hardness. It is very probable, therefore, that the 

partial disappearance of one of these strains from any cause whatsoever 

will materially interfere with the intensity of the other. 146 Why the influence of the time of exposure to 100° is marked when the state of 

hardness is such that annealing produces both a mechanical and a rnagM4Moser u. Riess : Pogg. Ann., XVII, p. 403, 1829.

145Dufour : Fortschr. der Physik, 1857, p. 438.

H6Whether mere magnetization produces a change in the temper of glass-hard steel 

is still to be investigated. In consequence of the very small variation of dimensions 

the anticipative effect must, of course, necessarily be small.

(750)
BARU8 AND 8TBOUHAL.J MOSER AND RIESS* RESULTS. 150

netic effect, is readily seen. For the latter effect must continue to vary 

until the limit of variation of the former has been fully reached; and 

the annealing effect of 100° in case of glass hard steel is a diminution of 

hardness occurring at a very gradually decreasing small rate through 

infinite time.

When this has occurred i. e., When the final state of hardness due 

to an exposure to T has been reached we have to do with a purely 

magnetic phenomenon only. A rod magnetized to saturation and annealed at T° experiences a direct effect a loss of specific magnetism 

which is relatively small, nearly independent of the time during which 

T acts, and the cause of which may be loosely ascribed to a smaller coercive force at T and to the effect produced by the thermal expansion on

 the magnetic strain. We may add that while in the first case, where 

the rod itself undergoes a change of state, a limiting value of specific 

magnetism was not fully reached even after 22 hours of annealing; in

 the second, the action is certainly complete after the lapse of an hour,, 

and occurs in such a way that the principal part of the magnetism is 

lost within the first ten minutes.

The reasons fully appear why Moser and Eiess found that when soft 

and annealed rods were used the losses were not only small, but occurred 

with the characteristic rapidity of those here enunciated. In this case 

an annealing effect due to 100° is manifestly impossible, and the peculiarities of the purely magnetic phenomenon are alone observed. It 

would moreover appear that the latter for a given temperature, T, is independent of the material used, of an intrinsically magnetic nature. At 

least Moser and Eiess found for this loss

Per cent 

When the needle was soft ...... .......... .................................... 13.6.

When tempered blue ......................................................... 13.4

When tempered cherry red ................................................... 13. 7

We will waive this matter here, as it is our object to investigate it 

specially, paying particular attention, moreover, to the effect incident 

upon a variation of the dimensions L/D. Such an effect is already,, 

though somewhat obscurely, apparent.

Pre-existing magnetization. If the inference derived in the foregoing 

paragraph be correct, 'then must it be immaterial whether a glass-hard 

unmagnetic steel rod is first annealed, say in steam, at 100°, until the 

final mechanical state for this temperature has been practically reached 

and then magnetized to saturation, or whether the rod, originally saturated, is annealed and then reinagnetized, as in the previous case. 

The ultimate result must, in other words, be independent of pre-existing 

conditions so long as these are effects of a lower order than correspond 

to the given temperature.

In order to give this question, which partakes of the nature of a 

crucial test, due experimental consideration, two rods, Nos. 13 and 14, 

of equal length, were broken from a glass-hard sample of the same

(751)
160 IRON-CARBURETS. [BULL. 14.

thickness (0.084 cm.) and material as Nos. 11 and 12. The constants of 

the new magnets are:

Length .....

No. 13.

9.1 

0.379

No. 14.

9. 1 cm. 

0.381 fir.

Of these, No. 14 was magnetized to saturation,; No. 13, however, left 

unmagnetized. Both were then exposed to the action of steam, and 

the progress of the annealing investigated by repeated measurements 

of the specific resistances of the rods. Unfortunately, a piece of No. 13 

was accidentally broken off in clamping. The new rod (No. 13) was 

8.7 cm. long and weighed 0.363 g. The two wires in their present condition would not, however, permit us to discuss the question from a sufficiently broad standpoint, and we, therefore, selected three other wires 

of the diameter 0.2 cm., so chosen as to present nearly the same specific 

resistances, viz:

No. V.. .......

No. VI. .......

No. VII.......

8 = 42. 4 ( 7^3 0° microhm. )

\ cm-" / 

8 42.6 Do.

8 42.2 Do.

The rods were tempered by sudden cooling after heating to redness 

in the flame of a blast-lamp. Out of the first but a single magnet was 

taken, No. 15, and but one, No. 16, from the second; while to the third 

and most homogeneous of the three.the two shorter magnets, Nos. 17, 

and 18, owe their origin. It was intended to have the lengths of Nos. 15 

ami 16 and of Nos. 17 and 18 identical, but it is difficult in the case of 

wires of this thickness to break theni off at a prescribed mark. Small 

variations of length are, therefore, unavoidable. The constants of the 

four magnets (0.21 cm. thick) are:

Length .cm. 

Hasa .....g.

No. 15.

7.2 

1.90

No. 16.

7.3 

1.92

No. 17.

2.90 

0.773

No. 18.

2.95 

0.776

These were now treated in a manner analogous to that applied to 

Nos. 13 and 14; 11 hours of annealing in steam at 100° transferred 

them into the final state of temper for this temperature, not completely, 

it is true, but sufficiently so for the purposes. All were now remagnetized. Nos. 15,16,17,18, acted on by steam for some time, and their 

magnetic behavior examined, were then'remagnetized again, and once 

more annealed. Nos. 13 and 14, however, were first exposed to a lower 

temperature, that of boiling methyl alcohol at 66°, during a certain in. 

terval; and not until the magnetic limit for 66° had been fully reached

(752)
BARUS AND STHOUHAL.] PRE-EXISTING MAGNETIZATION. 161

were they exposed in steam, in order that the limiting value of permanent specific magnetism corresponding to the new temperature (100°) 

might in its turn appear. The data expressing the magnetic effect of 

these operations are detailed in the following tables, 71 and 72. As 

before, W denotes the resistance per meter of length of rod at tf°, s the 

corresponding specific resistances at zero.

TABLE 71. Limits of magnetic state at 100°.

Time of exposure.

Qla'ss-hard.

10m in 100°.. .........

420m iu 100°. ....:....

+ 3b in 100°. ..........

+ 4>> in 100°.....- ....

I1" in «C° ............

+ 2b in 66°...... ......

4- 3b in 660.... ........

+ 3" in 100°... ........

Magnet No. 13.

IF

ohm. 

0.734 

721 

701 

683 

666 

646 

632 

622

t

C. 

9.0 

9.0 

9.0 

8.0 

9.0 

9.0 

9.0 

9.3

s

microhm. 

39.7 

39.0 

37.9 

37.0 

35.9 

34.9

34.1 

33.5

m

abs. E.

48.3 

48.0 

48.0 

47.5

47.5

Magnet No. 14.

W

ohm. 

0.741 

726 

707 

688 

609 

650 

634 

626

t

C. 

9.1. 

9.1 

9.0 

8.1 

9.0 

9.0 

9.0 

9.8

g

microhm. 

40.1 

39.3 

38.2 

37.2 

36.1 

35.0 

34.2 

33.6

m

dbs. E. 

51.4 

48.7 

45.8 

43.4 

40.3 

39. ? 

38. 

37.; 

49.'. 

48. < 

47.1 

47.4 

47.1 

47.1

TABLE 72. Limits of magnetic state at 100°.

Time of exposure.

Glass-hard. 

Om inlOO°...........

One day after tempering 

10"' in 100°...........

+ lb in 100°...........

+ 2>> in 100°...........

+ 3h in 100°...........

+ 4b iu 100°...........

10m in 100° ..........

-WO-inJOOO... .......

4-30 in 100°.... .......

101" in 100° ...........

-f-2010 in 100° ...........

-j-30ro in 100°...... ....

+ 3" in 1000... ........

Magnet No. 15.

W

6. 1277 

1219 

1165 

1128 

1087 

1048 

1021 

1011

t

8.7 

9.3 

9.6 

9.7 

9.0 

9.1 

9.3 

10.0

S

42.4 

40.4 

38.6 

37.3 

35.9 

34.6 

33.7 

33.3

m

43.6

41.8

41.7

41.6

43.4

42.1

41 9

41.7

41.6

Magnet No. 16.

TF

0. 1282 

1218 

1167 

1129 

1084 

1049 

1024 

1008

t

8.8 

9.3 

9.8 

9.7 

9.0 9.1- 

9.5 

10.00

S

42.5 

40.3 

38.6 

37.3 

35.9 

34.7 

33.0 

33.2

m

48.1

47.2 

37.4 

33.2 

30.3 

27.8 

26.0 

24.8 

24.5 

45.3 

43.7 

43.6 

43.6 

45.2 

44.0 

43.7 

43.5 

43.4

No. 17.

m

.......

........

29.2 

27.8 

27.6 

27.4 

29.3 

27.8 

27.6 

27.4 

27.3

No. 18.

wt

32.3 

31.5 

21.4 

17.5 

liV.2 

13.4

n.«

11.2

10.7 

30.1 

28.0 

28. 2 

28.2 

30.0 

2«.8 

28.4 

28.4 

. 28.3

Magnetic effect of annealing Final result. In this series of results 

our views are fully corroborated. A"Vhen the limiting state of hardness 

conditioned by the temperature of annealing T has once been reached, 

then it is wholly immaterial, in so far as the subsequent magnetic behavior is concerned, whether the rod was originally a magnet or not. 

The consecutive values of m for Nos. 15.and 16, as well as Hos. 17 and 

18, after 11 hours of annealing and remagnetization have been applied, 

manifest a perfectly similar progress throughout. The same is true of 

Nos. 13 and 14, both while in vapor of methyl alcohol and while in 

Bull. 14 11 (753)
162 IRON-CARBURETS. [BULL. 14.

steam. It will be observed that the limiting magnetic state for 66° 

differs from that of 100°, although neither is able to effect any further 

change in the qualities of the material. Whence it follows, in complete 

analogy with the results formerly found in the case of simple annealing, that in the present case each given temperature, after having been 

applied to a glass-hard rod to produce and consummate the mechanical 

effect, and thereupon to the remagnetized rod for magnetic effect, has 

its particular and characteristic magnetic limit.

Simultaneous variation of specific resistance and magnetism (low temperature). In Fig. 21 the diminution of specific resistance, together with 

the simultaneous variation of specific magnetism due to annealing at 

100°, has been graphically represented. The results are those above 

given for the magnets Nos. 11,14,16,18. The similarity in the two 

sets of curves suggests an inquiry into the mutual dependence of these 

quantities. In figure 22 we have plotted specific resistance as abscissa

60

41)

30

o

Z 1.1 a. =10$

'SO 4.0 3O S.O

Hardness ( specific "resistance, microhm,)

FIG. 22. Simultaneous variation of specific magnetism and specific resistance in case of continued an

nealing (low temperatures).

and specific magnetism as ordinate. The points are found to lie on loci 

of small curvature, approximately parallel to one another. The members of the family appear the more nearly linear the greater #=75

and therefore the simpler the linear distribution of the magnetism. All 

are, of course, ouly the initial parts of far more extensive curves to be 

obtained by continuing the annealing at temperatures higher than 100°. 

The data for Nos. 11,14, 16, and 17, moreover, show in how far the 

diminution of specific magnetism from the original to the final value, as

(754)
BABUS AND STROUHAL.] MAGNETISM AND RESISTANCE. 163

resulting from annealing, is dependent on the ratio of dimensions a. 

We have the following values for the amounts lost :

8 No. 11,

No. 14, 

No. 16 

No. 18.

=30 per cent, a--

=2S Per cent. , __ =

=- P-ent , __ .

It appears, therefore, that long, thin magnets lose decidedly less than 

those of small length. But the initial intensity is not without influence. 

For instance, although both No. 11 and No. 14 were originally saturated, 

the former retained a larger quantity, whether in virtue of its state of 

hardness or from small differences of chemical composition does not 

appear; for the loss of No. 11 is greater, or else that of No. 14 smaller, 

than the other values would indicate.

In a similar manner the influence of hardness appears in a series of 

experiments made with ten small steel parallelopipedons of nearly the 

same dimensions. These magnets (designated by No. VII to No. XVI), 

2.5 cm. long, 0.4 cm. broad, and 0.3 cm. thick, of the same material, 

were glass-hardened in the same way in so far as this is possible in the 

ordinary method of tempering-r-and finally magnetized to saturation by 

the action of the same magnetic field (helix). The following tabular 

comparison of the results, however, shows variations of a kind such 

that few consistent inferences, with the exception of that emphasizing 

the effect of hardness, can be deduced from them. But from this very 

fact the importance of structural effects is again clearly indicated.

TABLE 73. Limits of magnetic state at 100°.

Weight (g) .............................

Specific magnetism :

Loss in per cent, of original value (m) :

VII.

2.53

11.18

2.70

10.05

7.91

70

21

vm.

2.45

. 14. 11

2.89

12. 20

11.06

en

10

IX.

2.48

14.03

3.93

12.31

W QP

72

12

X.

2.47

15.11

4 3<1

no OP;

19 flQ

71

9

XI.

2 CO

14. 1 f\

4 C6

1 9 7O

U 41

71

11

TABLE 74. Limits of magnetic state at 100°.

Weigbt (x) .............................

Specific magnetism : 

Glass-bard, saturated ... ................

Loss in per cent, of original value (m) :

XII.

2.51

12.47 

 4.09

11.50

9.80

67

15

xm.

2.41

14.05 

3.08

13.00

11.82

78

9

XIV.

2.48

14. C4 

4.53

13.61

12.45

69

9

XV.

9 QO

1C. 56 

5.55

15.72

13.70

67

13

XVI.

2.43

15.76 

4.55

14.85

13.34

71

10

(755)
164 IRON-CARBURETS. [BULL. 14.

Specific resistance and specific magnetism Higher temperatures of annealing. The following final experiments on the relation between magnetic moment per unit of mass and the respective specific resistance, in 

case where a" diminution of both qualities is effected by annealing, give 

further insight into the nature of this functionality. Two magnets, Nos. 

19 and 20, were broken from a glass-hard rod, No. VIII (diam. 0-147 cm.), 

and exposed for different lengths of time in hot baths. The constants 

of the magnets are these:

Dimension ratio ......

L \. 50

H 0. 193

a =10. 2

1. 172 g

61.9

The results obtained by examination at different stages of the operation of annealing are given by the following table:

TABLE-75 Simultaneous variations of magnetization and galvanic hardness, for continued annealing.

Magnets Nos. 19 and 20.

Time of exposure.

20m in 100°. ...............

+ 2h in 100°................

+10 in 185°. ......... ......

+ 6h in 185°.... ............

+ lm in 330°...... ..........

TVlm

Ohm

0.283

0.267

0.245

0.202

0.162

0.120

t

°C. 

11.5

12.0

19 A

11.6

n

o

10.0

s

microhm. 

47.0

AA O

40 5

33.4

26.7

19 6

m 

No. 19

91 9^

12.56

7.74

3 no

2.45

0 25

m

No. 20

OQ 1

oo *\

99 3

18.8

n

K

14.4

These curves (figure 23) pass from convexity as regards the axis a? 

through a point of circumflexion into concavity. Both loci are very

50 4O ~ 30 20 , 

Hardness (specific resis/.ancefrrucroihmsj decreasing.

FlG. 23. Simultaneous variation of specific magnetism and specific resistance in case of continued annealing (high temperatures).

much alike, decreasing rapidly near the origin as well as near their extreme points (annealed at 330°). Short magnets lose their magnetiza-

(756)
BARUS AND BTRouHAL.1 DIRECT AND INDIRECT ANNEALING, 165

tion when exposed to temperatures at more rapid rates than1 long ones. 

The latter, on the whole, show greater magnetic permanence than the 

former.

The interpretation of these phenomena is difficult. But it is in place 

to present the salient points to be considered here. For the reasons 

given on page 145, a perspicuous relation between magnetism and resistance "can only be anticipated in case of linear rods. The results in 

hand conform with this view to the extent that the observed curvature diminishes in marked degree in proportion as a increases 

(cf. Fig. 22). In general, moreover,' there are two phenomena su; 

perimposed: the direct magnetic effect of temperature and a much 

larger indirect effect, the latter being the magnetic effect of a change 

of hardness (annealing) produced by temperature, simultaneously. In 

the case of a given rod (a constant and large) the direct effect is a function of time and temperature. The indirect effect, on the other hand, 

must be expressible as a function of s since this quantity shows the 

amount of change of mechanical state. Take rod No. 11, in which 

a is large, for instance, and deduct the direct effect given in Table 69 

from the superimposed effects given in Table 68; the variation of magnetic moment (m1 ) and hardness for the indirect effect alone is given in 

this table:

Time of annealing.

0.... ...................

Direct effect.

m= 

62.6

59.5

56.0

52.6

50.0

47.3

46.1

45. 1

44.3

43.8

Indirect effect.

r>i'= 

62.6

61.3

58.4

55.6

53. G

.50.3

4.9.1

48.1

47.3

46.8

8

39.5

83. 7

37.6

36.7

35.7

34.8

34.1

33.5

33.1

32.8

Here, therefore, the relation between m' and s is approximately linear. 

Thus far, however, inagnetizability has decreased; its variation is small.

A passage to higher annealing temperatures is accompanied by a 

marked increase of inagnetizability. The actual magnetism possessed 

by the rod after thorough annealing in the lower temperature (100°), 

may. therefore, fall so far short of the attainable saturation at a higher 

temperature as not to be affected sensibly, either by the direct or the 

indirect influence of the said higher temperature. This inference is 

substantiated by the data in Table 75 for the rods !Nos. 19 and 20. The 

slight variation of specific magnetism in the case of higher annealing 

temperatures (185°, 330°) is exhibited in Fig. 23 by the approximately, horizontal parts of the corresponding curves. It follows, therefore, that before the relation of magnetism and resistance can be 

thoroughly discussed, the character of the relation between maximum 

of permanent magnetism and hardness, which in Figs. 17 and 18 is

(757)
166 IRON-CARBURETS. , [BULL. 14.

graphically given for ordinary temperatures, must be known for all 

other temperatures. In other words, a family of curves such as given 

by Figs. 17 to 20 exists with equal definiteness for higher temperatures (100°, 200°, 300°, etc.) and from the co-ordination of such series 

of families the value of the direct or purely magnetic effect of temperature is deducible for any given circumstances.

Furthermore, the increments of the superimposed magnetic effects 

and the simultaneous increments of specific resistance should be compared when obtained under circumstances such that the (linear) rod re- 

.mains, as nearly as possible, in a state of magnetic saturation. It is, 

therefore, essentially necessary to compare increments. The character 

of the direct effect being known, that of the indirect effect follows.

It will be observed that the difficulty encountered here is the result of 

variation of magnetizability. Moreover, the direct and indirect effects 

need not necessarily vary independently of each other when superimposed.

MAGNETIC RETENTIVENESS AS REGARDS THE EFFECTS OF PERCUSSION AND TIME.

 Effects of temperature, percussion, time. The use of annealed in the 

place of glass-hard magnets for magnetic instruments, procures for us 

the decided advantages of a diminished sensitiveness as regards the 

influence of temperature. If a magnet, which is thus to be used, is 

annealed at a given higher temperature T° we will continue to suppose it produced with steam, a method both convenient and satisfactory until the limit of hardness characteristic of this temperature 

has been attained, then will this material be perfectly passive in so far 

as temperatures below T° are concerned. If the rod is then magnetized 

to saturation how often soever this may have been previously done is 

entirely without consequence and again thoroughly annealed at T°, 

then the magnet will in a comparatively short interval of time arrive 

at a stable and limiting magnetic state, which when exposed to temperatures below J° will in its turn be equally passive, i. e., suffer no 

permanent magnetic variations. But where magnets are to be used for 

purposes of measurement, a full guarantee for their stability as regards 

permanent effects from changes of atmospheric temperature is not the 

only desideratum. The efficiency of the magnet is conditioned almost 

to ah equal extent by its power of magnetic retention against such influences as percussion of rapid vibration, or indeed the prolonged effect 

of time. That the methods previously employed for the construction of 

magnets for practical purposes are invariably deficient in this respect 

is well known, and it will therefore be adequate to add in this place a 

single authoritative statement only.

.(758)
BABUB AND STROUHAU] MAGNETIC PERMANENCE WILD'S RESULTS. 167

Observations of Wild. In the "Annalen des physikalischen Centralobservatoriums," St. Petersburg, p. 63, 1878, H. Wild discusses the efficiency of Edelmann's bifilar magnetometer and refers to the magnet of 

this apparatus as follows:

Obgleich der Magnet nacb seiner Magnetisirung abwecheelnd einer Temperatur von 

0° und 30° ca. 30 Mal ausgesetzt worden war, nm ihn permanenter zu machen, fand 

doch eine scbnelle Abnahme des magnetischen Momentes statt, so dass sie rnehrfache 

Verstellungen und Veranderungen erforderte. Damit niimlich die Scala noch nicht 

ganz aus dem Gesichtsfelde herausriicke, musste schon am 17. April (seit Anfang December) der Torsionswinkel um 1° 51'. 5 vermindert werden, um wieder die Mitte der 

Scala in das Gesicbtsfeld des Fernrohrs zu bringen . . . Da die Vermiuderung des 

Magnetischen Momentes des Stabesauchin folgendenMonaten ungeschwacht fortclauerte, so befiirchtete ich, es sei der Magnet schlecht und liess nach dem Muster clesselben einen neuen herstellen.

A numerical estimate of these variations is furnished by the following data : The magnet in question was 8.0 centimeters long, 2.1 centimeters broad, and 0.22 centimeter thick; its magnetic moment M and 

specific magnetism m were found initially, after the change of temperature mentioned, to be 

after 9 months : . ' .

,¥=914.5 m=27.14

The mean loss per month was therefore as high as 0.46 per cent, of 

the original value, but the new magnet was hardly found to be preferable to the old. On page 8 of the "Annalen des Centralobservatoriuras, 

etc.," 1879, H. Wild reports as follows :

Audi der neue Magnet verier nacb der Aufhangung am Bifilar noch fortwahrend 

bis zum Schlusse des Jahres so viel Magnetismus, class eine Bearbeitung der Beobachtung an diesem Bifilar nicht erfolgen konnte.

This magnet had also been subjected in the usual manner to 16 successive changes of temperature between 0° and 56°. 

The following data show the extent of these variations accurately: 

On the 29th 'of December, 1878, immediately after magnetization the 

magnetic moment M and the specific magnetism m of the bar were

M=IS52 m=55.0 

Some time after, on the 4th of February, 1879,

M=115Q m=52.1 

After 16 changes of temperature between 0° and 55°,

J/=1694 w=50.3

The explanation of these results on the basis of our investigation is 

no longer difficult. It was customary following Eiess and Moser, who 

considered the time of exposure to the higher temperature as of no 

consequence to put the principal stress on the condition of a change 

of temperature. As a result, the magnet was subjected to the influence 

of the higher temperature only long enough to heat it uniformly throughout. Even Holmgren contended that permanent and hurtful effects of

(759)
168 IRON-CARBURETS. [BULL. 14.

temperatures between given limits (0° and 100°) could be made to vanish 

by repeated alternations of temperature from the inferior (0°) to the 

superior (100°) limit, and with this end in view heated and recooled his 

magnet fully 213 times. Possibly this might actually suffice. If, however, as is usual, only 20-40 alternations are made (and even this is 

tedious and troublesome, consuming much time), a sufficiently advanced 

state of annealing can hardly have been attained. To a much smaller 

extent even will this be the case where temperatures only as high as 

50° are employed. The magnet therefore practically remains in an extreme of glass-hard state, a condition in which strains of an intensity so 

enormous exist in the rod, that irrespective of other causes, changes of 

mechanical state purely the results of time may be anticipated. By the 

process of annealing, these abnormal strains, so to speak, are diminished 

to values which insure far greater stability of mechanical state.

Better results are obtained by application of higher temperatures than 

50°, if the action of these is sufficiently prolonged. For instance, a magnet, destined to become a part of the bifilar at. the Physical Institute 

at Wurzburg, was, after magnetization, held for ten minutes in boiling 

water and then adjusted in place. The original specific magnetism was

found to be

m = 28.95 M - 2397

After the annealing

m = 24.43 ill = 2023

Since that time the biftlar has been in continual use, and the behavior 

is quite satisfactory. Tf we observe how great is the initial change of 

hardness, relatively speaking, during the first ten minutes of exposure 

to 100°, we infer that even this amount of annealing is sufficient to reduce the hurtful excess of strain to a degree that insures fair stability. 

A constancy of magnetic moment under like conditions is the result.

Obviously, however, results of better permanence will be reached 

where the annealing at the practically convenient temperature of 100° 

is sufficiently prolonged to leave the magnet in the limiting mechanical 

state characteristic of this temperature. But unfortunately such a process would diminish the magnetic intensity very materially;. indeed, in 

the usual case of a ratio of dimensions a =10 . . . . 20, a loss of even 

more than 70 per cent, is frequently met with in the above. If, however, the bar is again magnetized to saturation, the original intensity 

will be v.ery nearly regained; whereupon, if the process of annealing is 

once more applied, a limiting magnetic state possessing the desired stability, is reached, with a loss of magnetization amounting- to only 5 to 

10 per cent.

Maximum hardness and magnetization for 100°, stable at 0°. Now, 

there is .ampie reason for the belief that rods in this singular magnetic 

state possess the best available qualities of magnetic retention. If a 

glass-hard saturated magnet be dropped, the result is invariably a loss

(760)
BABUB AND sTKOtHAL.] RETENT1VENESS AND PERCUSSION. 169

of magnetic moment. Tbis is by no means the case with rods subjected 

to the treatment specified. Even if a sharp blow be intentionally administered, or the magnet be thrown with violence upon the floor, the 

action is without apparent magnetic effect. As an example we will cite 

the following observations made with a short and thick magnet. It is 

known that the retentiveness of such is much inferior to that of long, 

thin rods.

The magnet was 2.5 centimeters long, 0.4 centimeter broad, and 0.3 

centimeter thick. At the outset it was purposely boiled for but 4 hours 

in water; then magnetized to saturation, and subjected during 2 hours 

to the action of steam. Our magnetometer showed the following average deflection of five readings (scale-parts millimeters):

n = 27.00

Then the magnet was placed on a block of wood, and, with the aid of a 

second block, sharply struck 30 times at right angles to the direction of 

its magnetic axis, and 20 times in a direction with it. After placing the 

magnet aside for a timej in order that its original temperature might be 

reassumed, the reading at the magnetometer was

n = 26.97

The same process was repeated, with the result

w = 26.93

Even if the slight diminution from 27.00 to 26.93 about 0.3 per cent. 

had existence in fact that is, was not due to errors of observation, but 

to magnetic moment lost still, as it represents the magnetic effect of 

100 powerful blows, it is certainly negligible. But this magnet has not 

yet reached the maximum of permanent hardness for 100°. Whence it 

follows that, from a rigid application of our method, results more satisfactory even than this are to be looked for.

Experiments of a determinate and final character were made upon a 

liollow cylindrical magnet, weighing 109.32 g. The length of the tube 

was 16 centimeters, its outer radius 1.6 centimeters, its inner radius 1.2 

 centimeters. After tempering to glass-hardness it was magnetized to 

.saturation, then annealed in steam at 100° for a period of 30 hours.' 

After this the cylinder was once more magnetically saturated and thereupon reanuealed in steam for 10 hours. The specific magnetism, determined from time to time, showed the following values:

Magnet glass-hard, saturated ................ m = 41.0

10 hours in steam at 100°.................... m = 26.1

20 hours in steam at 100°.................... m 25.2

30 hours in steam at 100°... ....... ........ m = 24.8

Magnet annealed, resaturated... ............. m 39.9

5 hours in steam at 100°......:.............. m = 33.8

10 hours in steam at 100°............. ... .. m = 33.1

(761)
170 IRON-CARBURETS. [BULL. 14.

In the last instance the needle of our magnetometer for a distance of 

72.9 centimeters of the magnet and a rotation of the same of ISO0, was 

deflected over w=475.6 scale-parts (millimeters), where 250 centimeters 

intervened between mirror and scale and the whole measurement was 

subject to the conditions of Gauss's second position.

The magnet was now introduced into a long and wide glass tube and 

allowed to fall vertically for a distance of 1.5 meters, impinging on a. 

block of wood. This was done once with the north pole and again with 

the south pole downward, whereupon the deflection was found to be 

w=475.2 scale-parts, and 10 minutes later w=475.6 scale-parts.

We then allowed the same magnet to fall in horizontal position from 

a height of £ meter upon the floor. After ten of these descents the magnetometer showed n 474.7 scale-parts, and five minutes later w=475.0' 

scale parts.

Finally the magnet was again introduced into the glass tube and 

dropped in vertical position from a height of 1.5 meters, with the 

north and south poles alternately foremost. After ten repetitions of 

this treatment we observed the deflection n = 473.3; after three minutes, w=474.0; after thirty minutes, w=475.5.

The observed difference may therefore safely be referred tp temporary 

thermal variations, partly incident to the percussion experienced by the 

rod, partly due to contact of the latter with the hand of the operator. 

A destructive effect due to percussion cannot be said to be apparent 

at all, despite the intense shocks to which the magnet was exposed. 

The temperature of the room (=6°.0) did not vary during experiment..

After these results, the inference is warranted that the magnetic retentiveness of rods tempered and saturated in the manner set forth will 

be proof against effects of cold of the same order, sucti for instance asare met with by observers in the polar regions. Direct researches on 

this point are contemplated. Whether or not cold is capable of producing a mechanical annealing effect is unknown. Certain it is that it 

would be discernible only by such sensitive methods as are employed in 

Chapter II. But the marked magnetic effect produced by reduction of 

temperature has long been understood. Indeed, J. Trowbridge, by the 

use of carbonic acid and ether, was able to diminish the magnetic moment in this way fully 66 per cent. In the case, however, where a rod 

is in the magnetically stable condition as regards an elevation of temperature of say 100°, it is altogether probable that if cooled to a similar 

extent it will continue to possess the desirable quality in question.

We believe, therefore, in the method described, actually to have found 

a process for the construction of magnets of exceptional constancy and 

of powerful magnetic reteutiveuess. In how far this quality may be 

preserved in the lapse of time, will have to be deferred to the verdict 

of observers by whom such magnets may possibly be used. How much 

more reliable and satisfactory measurements made in different parts of 

the earth will be, when the magnets are no longer liable to injury from

(762)
BABU6 AND 6THOUHAL.] MAGNETIC PERMANENCE. 171

the shocks and blows unavoidably encountered during transportation,, 

needs no further comment.

In conclusion, we desire to add the following rules for the practical 

construction of magnets:

1. Eods tempered glass-hard are never to be used as essential parts of 

magnetic instruments.

2. After having tempered the rod in a way that insures a uniformity 

of glass-hardu'ess throughout its length, expose it for a long time (say 

20 to 30 hours; in the case of massive magnets even longer intervals 

are preferable) to the action of steam at 100°. The operation may be 

interrupted as often as desirable. The magnet has now reached the 

highest or hardest of the mechanical states which are no longer influenced by temperatures below 100°.

3. Magnetize the rod, no matter Whether originally a magnet or not,, 

to saturation, and then subject it during a period of about 5 hours (in 

the case of large massive magnets even longer intervals are preferable) 

to the action ot steam at 100°. Then the magnet will have reached the 

highest and most powerful of the magnetic states which are no longer 

influenced by temperatures equal to or less than 100°. The magnet is 

now ready for use..

It may be added that the advantages of using steam are two fold: In 

the first place, the process is exceedingly convenient and economical.144 

In the second, it will be remembered that the temperature 100° ultimately leaves the rod in a condition in which the change of capacity for 

magnetization, as hardness decreases, takes place along the contours of" 

a very flat minimum. 145 Even if slight changes of hardness should 

subsequently occur, their magnetic effect would be reduced to insignificance, in virtue of the singular variation just mentioned.

ADDENDUM.

f

RESULTS OF PROF. H. WILD, OF ST. PETERSBURG, WITH REFERENCE TO MAGNETS TEMPERED AND MAGNETIZED BY THE METHOD 

PROPOSED IN THIS CHAPTER. 146

We are fortunate in being able to cite in this place some results confirmatory of the efficiency of the method for the treatment of magnets 

proposed in this chapter bearing the authority of Professor Wild. In 

his work on the absolute value of Siemens' mercury unit. Professor Wild

144 A flask with a long neck will be found serviceable. The steam condensing in the 

latter runs back into the bulk of boiling water. Or tho suspended magnet may 

simply be boiled. t The prolonged action of steam is in no way deleterious or corrosive. 

The rods are etched uniformly black and may thus be polished.'

146 Cf. Chapter V, p. 141.

146 H. Wild: M6moires de I'Acade'mie imp6riale des sciences de St.-Pe"tersb., VIIe s6r.,. 

T. XXXII, No. 2, p. 36.

(763)
172 IKON-CARBURETS. [BULL. 14.

made use of a large magnet constructed with exceptional care by H. 

Freiberg, out of "Eibiswalder naturhartem Wolfram-Stahl." Its dimensions (rectangular parallelopipedon) and weight are these: length, 29 centimeters; breadth, 3.6 centimeters; thickness, 1.2 centimeters ; weight, 

1,030 grams. This magnet was carefully tempered by heating to low 

redness and sudden cooling in lime-water at 20°. After being magnetized to saturation between the poles of a powerful electro-magnet, it 

was kept at 100° for 35 hours; thereupon again magnetized and exposed 

to steam for 10 hours more. The following are the observed magnetic 

moments (0. G. S.) at 20°: .

1883. 

April 27

April 30

May 1 After 10 hours' further exposure to 100° .

32.60X10 3

24. 56X10 3

31.48X103

29. 15X10 3

On June 21,1883, at20°, Wild obtained for the same quantity, 28.8 x 10s. 

The magnet, despite the treatment which it had experienced, therefore, 

still lost about 1 per cent, of its total moment, during the intervening 

three months. But this variation is little more than 0.0001 of the total 

intensity per day, if the loss were proportional to time. Eeferred to 

July 1, however, when the actual measurements were commenced, the 

said decrement cannot be estimated as above 0.00005 per day particularly so if it be borne in mind that the diminution in question must 

gradually vanish at a continually decreasing rate through infinite time, 

or that a final and definite moment is being asymptotically approached. 

Indeed, the said limit was practically reached in the second third of 

.July, as the following results show. Wild further remarks that final 

magnetization of 28 O.G.S. units of magnetism per gramme is to be con- 

 sidered as a satisfactory value. The results in question are as follows:

Date.

July 21 

July 22 

July 26 

Aug. 3 

Aug. 4 

Aug. 5 

Aug. 10 

Aug: 11 

Aug. 13

M: 103=

28. 8018 

28. 7846 

28. 7749 

28. 7760 

28. 7771 

28. 7834 

28. 7844 

28. 7754 

28. 7870

Mean If .-103=28.7803

Differs from the mean by

. +0. 00043 

_ 54.

 43 

 32 

+ 31

+ 41 

 49 

+ 67

±0.00045

The value for July 21 is not included in this mean.

We venture to remark that with so unusually large a magnet even 

better results could have been obtained by repeated boiling and remagnetization. In consideration of the dimensions, the decrement of 1 per 

cent, is by no means surprising. The tubular magnet discussed in the 

above was operated upon three successive times by our method, before 

 definite adjustment for absolute work. We are not aware, however, 

whether it will not take some time, in order that a magnet kept at 100° 

may thoroughly regain the state of molecular equilibrium for 20°.

(764)
CHAPTER VII.

A PHYSICAL DEFINITION OF STEEL BASED ON THE ELECTRIC BEHAVIOR OF IRON WITH GRADUALLY INCREASING DEGREES OF CARBTJRATION.

INTRODUCTION.

Nature of the problem. A detailed and thoroughly exhaustive study 

of the problem in hand, viz, in how far the effect of carburation on the 

galvanic and thermo-electric properties of iron is available for the general classification of iron-carburets, calls for working facilities at a puddling furnace, for instance, or other technically satisfactory agency for 

the decarburation or carburation of iron. Possibly, however, similar 

work might be done on a small scale in the laboratory, if the necessarily complicated apparatus or opportunities for constructing the same 

were at the observer's disposal. These advantages were not within our 

reach.

The problem is of a kind, moreover, which is apt to mislead the inve»tigator into insuperable and almost infinite complications. To avoid 

these it is absolutely necessary to conduct the experiments with reference to some thoroughly preorgauized plan. In the absence of the 

above-mentioned metallurgical apparatus we were obliged to contend 

ourselves with commercial products, and the main purpose of the present 

memoir has therefore been restricted to the development of a plan or 

scheme of operations for the general and tentative study of the electrical 

behavior of iron-carburets. These efforts have not been unsuccessfulj 

indeed they appear to be of considerable promise. They have already 

afforded us a method for the physically exact definition of steel which 

we regard as important. As a whole, the present chapter furnishes an 

essential and interpretative sequel to our researches on the hardness of 

steel.

Electrical manifestation of mechanical properties. The very remarkable effect of rapid and of prolonged cooling from red heat, respectively, 

on the physical and chemical properties of iron-carburets has always 

been a subject of great metallurgical interest.147 In the case of steel 

the contrast between the two states or conditions thus produced is particularly well marked and of the greatest practical value. Experience 

has shown, however, that the said processes may be applied, with much 

advantage, to most of the other iron-carbon products. It is thus that

H7 On Earsten's theory, relative to the nature of these effects, see Percy's Metallurgy, 

. edited by Wedding and others, Vol. II, p. 167, et seq., Braunschweig, 1864.

(765) 173
174 IRON-CARBURETS. [BULL. 14.

the question naturally suggested itself to us, whether the remarkable 

parallelism discovered in tbe variation of the degree of hardness of 

steel and its galvanic and thermo-electric properties was not to be considered as only a special case of the behavior of iron-carburets gener 

ally, under analogous circumstances. In this respect we believed ourselves justified in predicting that those characteristic mechanical qualities which distinguish steel from other iron-carburets must necessarily 

be sharply outlined in a general electrical diagram adapted to the classification of iron-carburets as a whole. A similar idea, as we subsequently 

found, seems incidentally to have occurred to Joule, 148 since he remarks, 

after having given the necessary experimental data: J 'I believe the excellence of the latter metal (steel) might be tested by ascertaining the

 amount of change in thermo-electric condition which can be produced 

by the process of hardening." But neither Joule nor others have given 

the subject more than this inadequate consideration, and it was not 

until our investigations on steel had been fully developed that the problem attracted our attention.

Critical operations. At first sight a comparison of the electrical intervals comprehended between the hard tempered, and soft annealed 

states, appeared to be rich in promise j but the processes of slow and of 

most rapid cooling possible, from red heat, are as yet not sufficiently defined, e^en if we abstract from decarburation, etc., for obtaining iron

 carburets in two characteristic physical states. In the case of slow 

cooling the temperature in red heat to which the specimen has been

 exposed, as well as the time during which exposure takes place are 

important items, particularly when the cast-irons are under examination. In the case of rapid cooling the temperature to which the redhot rod is suddenly and permanently lowered is additionally to be con-, 

flidered. It would not, however, be difficult to define the two processes

an question succinctly. A rod, for instance, suddenly chilled from red 

Obeat in water at ordinary temperature and then annealed by long exposure in ether vapor at 35° might appropriately be termed glass-hard; if 

annealed in vapor of sulphur (500°) or of cadmium (700°), soft. For the 

very large and physically important class of iron-carburets, wroughtiron, low-carbureted steel, and steel, these details, fortunately, do not 

" produce any serious distortions ; the thermo-electric hardness and the 

specific resistance of steel, no matter what the process may have been 

by which a given rod was softened, remain very nearly constant in 

value at least when compared with the enormous range of variation of 

these qualities due to tempering. The same is true for the hard condition of the carburets between iron and steel, where it is only neces-

 sary to choose the temperature before sudden cooling sufficiently high 

£o insure the appearance of hardness, and to chill in water at ordinary

'«Joule: Phil. Trans. 1859,1, p. 96. 

(766)
'BARU8 AND 6TROUUAL.] SLOW AND RAPID COOLING. 175

room-temperature. Decarburation is, however, under all circumstances 

to be avoided,149 and the exposures to high temperature must not be 

prolonged. It follows therefore that it will be expedient to commence 

the present investigation by a consideration of the electrical properties

 of the carburets in question, that is such in which the total carbon is 

less than about 2 per cent. To this may be added that within the interval (0 2 per cent.) those modifications in the mode of occurrence of 

the carbon in iron, which are the cause of such great diversity in the character of the different species of cast iron, are as yet comparatively without 

marked influence. Thus it appears that our results for this set of products'may be considered as satisfactory and definite. In order to complete the discussion conveniently, however, it is desirable to include 

certain essential properties of the cast-irons, or in other words to prolong the loci of our diagrams into the region of cast-iron, without going 

into any details. That this is readily pdssible will appear in the sequel.

A further introductory remark may be added here. Commercial ironcarburets are never pure, but contain in greater or smaller amounts 

vitiating impurities like phosphorus, sulphur, silicon, and the like. 

Each of these produces its own electrical effect, as has been seen in the 

earlier chapter (III) on alloys. The discrepancy thus introduced need 

not by any means be negligible, and full consideration is given to it in 

a later paragraph. For the present it will be expedient to suppose 

this secondary electrical effect to be absent, or that the material in 

band is a pure iron-carbon product.

Nomenclature. As a convenient nomenclature to be used throughout, 

we will designate the process of softening steel, that is cooling from 

red heat as slowly as necessary by the Roman numeral " J"; the pro-. 

cess of sudden cooling from the same temperature (hardening, tempering, 

glass-hard) by the Roman numeral " JJ." In like manner all constants 

which refer to J or JJ, are to be marked with the subscript 1 or 2, respectively. For instance, 7il5 S] . . . h2 , s2 . . . In like manner we may, 

without confusion, consider " soft state" and "glass-hard state," "state 

J" and "state JJ," respectively identical, etc.

H9 In this place it is well to call to mind an important result of Forquignon's (Ann. de

 Claim et de Phys. (5) XXIII, p. 538, 1881). He found that steel kept at red heat for 

©eventy-two hours, in an envelope of hematite, lost nearly one-half of its total cajjbon. 

This corresponds to the loss of nearly four-fifths of total carbon, due to continued exposure of cast iron to reel heat in the preparation of malleable cast iron (Percy op. cit.,

 p. 143.) In many physical experiments with steel, particularly in magnetic work, it is 

often necessary to soften steel by heating it to redness for some time. It is therefore

 obvious that the product thus obtained cannot be considered identical, as regards total

 carburation, with the original carburet. Possibly this method of eliminating carbon 

may be available for obtaining points in an electric diagram corresponding to ironcarburets lying between iron and steel.

(767) ,
176 IRON-CARBURETS. [BULL. 14.

WROUGHT-IRON.

Electrical data. Pure iron subjected to the process J/is mechanically 

indistinguishable from the same metal when subjected to I. So also 

the electrical difference between these two states is practically insignificant. This is true approximately for commercial iron with less than 

0.2 per cent, of carbon, and the more nearly true, moreover, the smaller 

the amount of this element. 

For the electrical conductivity of iron Chwolson150^gives the folio wing 

results : If a hard-drawn wire is ignited at low redness its electrical resistance is found to vary about 0.4 per cent. If the ignition be intense 

about +5.3 per cent. The process II produces a variation of only 0.7 per 

eent. in comparison with the hard-drawn state. If, therefore, we compare the rod in the state II with the same rod in the state I, we find a 

total electrical change about +L1 per cent, or 4.6 per cent., respectively, according as / was produced by gentle or by intense ignition.

For results of this kind, with reference to the thermo-electric behavior of iron, we searched in vain. But the relation between the variations 

of thermo-electric and galvanic constants is initially (i. e. for very small 

amounts of a foreign element alloyed to any given metal) linear, as we 

proved both in the case of steel and of alloys of silver. Hence results 

of the same order as Chwolson's may be at once predicted for the thermoelectric behavior of commercial iron. Sir William Thomson151 found that 

the thermo-electric hardness152 of iron, like that of steel, is increased by 

the process II. Joule153 finally remarks, U I find that in steel the (thermo-electric) change is in the same direction as in iron, but of enormously 

greater magnitude."

These small variations amounting to less than 2 per cent, of the total 

resistance or thermo-electric hardness, are for the present purposes at 

least, quite negligible; particularly so when contrasted with the corresponding change of the electrical constants of steel (200-300 per cent.). 

Where great accuracy is sought for, special measurements may be 

made. For this reason we accept for wrought iron the values for the 

electi^cal constants given in the following table (76). Here thermoelectric hardness is represented by h, specific resistance by. s ; hi refers 

to iron subjected to process J; 7i2 to the same wire subjected to process 

IT, etc., as has been stated. Furthermore dh=hz hi; 4s=s2 *i

150 Chwolson : Bulet. de St. Petorsb., X, p. 379, 1877; also Carl's Rep., XIV, p. 26, 1878, 

161 Thomson: Phil. Trans., 1856, III, p. 722.

152 On the definition o'f thermo-electric hardness, see our paper in Wied. Ann., XI, p. 

970,1880, or this memoir, Chapter II, p. 65. 

Jw Joute : Phil. Trans., 1859, I, p. 95-97.

(768)
BABUS AND 8TBOUHAL.] ELECTRICAL. CHARACTER OF IRON AND STEEL. 177

h=log lit log lh', d log s log $2 log alv The object of these differences 

will appear below. For h and s the values obtained elsewhere154 are 

given. Microvolts, microhms, and square centimeters are the fundamental units: log refers to Brigg's logarithms.

TABLE 76. Electrical constants of wrought-iron.

Material.

Thermo-electric hardness.

hi

Microvolt. 

4.7

hi

Microvolt. 

4.7

Specific resistance.

cm, »W°°

Microhm. 

12.2

cm «»-SP°°

Microhm. 

12.2

Afc

Zero.

As

Zero.

A log ft

Zero.

Alog«

Zero.

STEEL.

Electrical data. If we suppose the degree of carburation of iron to 

increase continuously from zero to about 1.5 per cent., the difference 

in mechanical hardness between states I and JJ will likewise increase 

continuously until steel is reached. For the purpose of defining the 

relatively enormous interval peculiar to the latter substance technically, metallurgists are in the habit of using some empirical criterion for 

instance, the power to give sparks with flint.155 It is, moreover, of the 

greatest practical importance that this phenomenal change of mechanical condition is confined to state JJ, and that state J, as regards hardness at least, is not readily distinguishable from wrought iron.

A large number of results on the electrical behavior of steel were 

discussed above. It will therefore only be necessary, in this place, to 

recall to mind the electrical interval JJ-J for this substance in a table 

constructed on the plan of the preceding, and therefore needing little 

further elucidation. For state JJ the largest values156 occur in case of 

rod No. 28.

fc=17.7 and s=41.5

But later experiments157 furnished considerably harder wires, the results

164 Chapter II, p. 61. The mean values for the three iron wires there examined are 

here given.

165 Cf. Karsten: Karsten's und v. Dechen's Archiv, XXV, p. 223. at seq., 1853; also 

Jeans, "Steel, its history," etc., London, Spon, 1880, pp. 533-542. 

16<»Cf. Chapter II. 

167 See our paper, Wied. Ann., XX, p. 640,1883.

Bull. 14- -12

(769)
178 IRON-CARBURETS. [BULL. 14.

for which are not given in the digest in question. The hardest of these 

showed s=4:7.5. If we pat h=ns, there follows,

ft=19.6 and s=47.5 

The minimal values for state II are those of rod No. 39:

7i=15.1 and s=34.9 

The largest values for state I are given by No. 46:

/i=6.9 and s=16.0 

and the smallest by No. 47:

fc=5.0 and «= 14.0

The following table (77) contains both extreme and mean values for the 

different constants, the largest being put on the horizontal row I, the 

smallest on the row s, the mean on the row m. All of these are obtained 

from a combination of the data just cited.

TABLE 77. Electrical constants of steel.

I

8

m

Thermo-electric hardness.

A,

Microvolt. 

5.0 

6.9 

6.0

*,

Microvolt. 

19.6 

15.1 

17.3

Specific resistance.

«'W° cm

Microhm. 

14.0 

16.0 

15.0

cm «« w°

Microhm. 

47.5 

34.9 

41.2

AA

14.6 

8.2 

11.3

As

33.5 

18.9 

26.2

UP* 

A log A

460

103 x 

A log 8

440

From the remarks made in the above it follows obviously that the 

magnitude of the interval II-I will depend very essentially on the degree of carburation of the steel tested. We experimented with silver 

steel158 of excellent quality. But commercial varieties of steel may be 

readily found in which the said interval II-I is even less than one-half

that given in the table.

CAST-IRON.

Thermo-electric data. In his experiments on cast-iron Joule159 found 

that the difference of thermo-electric position between state I and state 

II is about 2-ory °f the thermo-electric interval bismuth-antimony. In 

case of steel he found the change of thermo-electric position II-I to be 

in the same sense as in'cast-iron and as large as -^ of the said interval. 

Furthermore, " that the metal (cast-iron) is brought nearer bismuth (i. 

e., thermo-electric hardness is increased) as the quantity of carbon in 

combination is increased," and in much larger ratio than would be commensurate with the additional amounts of carbon.

168For silver steel see Percy, op. cit., pp. 237-240; also Faraday and Stoddard, Quar. 

Jour. Science, 1820, p. 325. 

159 Joule: 1. c., p. 96.

(770)
BARUS AND BTKOUHAL.I THEEMO-ELECTRICS OF CAST-IRON. 179

As accurate a knowledge as possible of the electrical qualities of castiron is a matter of such importance as to call for a special examination 

of a variety of products. These were made with as much material as 

we found available. The results for thermo-electric power are given in 

the following tables (78-79), where e denotes the electromotive force referred to silver in microvolts, observed or calculated as specified, corresponding to the temperature T and t of the junctions. On the basis of 

the formula of Avenarius, e=a (T fy+b (T2 <2 ), the constants a and 6 

were calculated, usually from five sets of observations, by an application of the method of least squares. In how far the measurements are 

satisfactory may be seen by consulting the column of differences (Diff.) 

between e observed and e calculated. Eods No. 1, 2, 3 were of German 

cast iron; No. 1 soft and of excellent quality; Nos. 2 and 3, though 

also of good iron, so hard160 as not to yield readily to a file. White castiron cannot be put in the form necessary for measurements like the 

present without encountering very great mechanical difficulties. But 

its properties are well represented by rods Nos. 2,3, which were specially 

cast thin. Eods No. 4 .... 12 are of good American cast-iron, so soft 

as to be easily touched with a file. They were planed dov^n to approximately square and uniform sections for us by Mr. William Grunow, of 

New York. All the rods were examined in three states: the original 

or commercial condition in which they reached our hands; after sudden 

cooling from red heat (II) ; after annealing soft at red heat (I).161 

We considered chemical analyses superfluous for the reasons given near 

the beginning of this paper. A few isolated results of this kind are 

valueless.

TABLE 78. Thermo-electric power of cast-iron. German material.

Bod.

1

'

2

Bemarks.

Annealed at red heat (I) ......

t

°C.

19.2

19.8

19.9 

20.1

20.3

15.7

15.9

10.0

10.1

16.2

T

°C.

83.4

70.1

59.9 

50.2

40.2

59.9

51.6

44.4

37.9

32.2

e 

observed.

microvolt.

 385. 5

 296. 9

 230. 8 

 171.7

 110. 7

-343. 2

 274. 1

 215. 8

 164. 3

 120. 3

e 

calculated.

microvolt.

-386.4

 296. 0

 231. 1 

 171. 0

 111.0

 342.8

 274. 1

 216.1

 164.7

 120. 0

Diff.

0.9

 0.9

0.3 

 0.7

0.3

 0.4

0.0

0.3

0.4 0.3

a

 4.94

7 ni

6

 0. 0106

 0.0095

Rod broken. Too abort for measurement.

16.7

16.7

16.8 

16.8

16.8

76.9

69.5

59.7 

49.9

39.1

 512.6

 446.2

 360.2 

 275. 5

 184. 2

 512. 3

 446.6

 360. 1 

 275. 7

 184. 1

 0.3

0.4

-0.1 

0.2 0.1

 7.89 0.0067

160Eods Nos. Si and 3 being only 0.2 . . 0.3cm. in diameter, it was found impossible to 

cast them without the appearance of a steel-like and brittle hardness, 

'si Cf. Chapter II, p. 60.

(771)
180 IRON-CARBURETS. [BULL. 14. 

TABLE 78. Thermo-electric power of cast-iron. German material Continued.

Bod.

2

3

Remarks.

Annealed at red heat (I),hard <

I

I

!

'

f

Suddenly cooled (II), hard . . <

1

I

«

°C.

18.1

 18.1

18.0

18.0

18.0

17.5

17.5

17.6

17.6

17.7

17.8

17.9

18.0

18.1

18.2

17.9

17.9

17.8

17.8

17.8

18.0

18.0

18.1 

18.1

18.1

T

°C.

55.2

49.6

44.7

39.3

34.8

84.5

74.5

63.9

54.8

42.9

79.8

70.8

59.7

49.3

39.6

58.8

52.6

46.1

38.9

33.0

88.2

78.6

66.4 

52.2

44.9

e 

observed.

microvolt.

 339. 7

-289. 2

 236. 4

-192. 4

 149. 8

 551. 9

 461.6

-368. 1

 291.4

 193. 3

 526. 0

 446.4

 354.5

 261. 1

 187. 6

 377. 2

 318. 4

 255. 7

 189. 0

 140. 1

 569.2

 481.6

 376. 7 

 259. 6

 200. 6

e 

calculated.

microvolt.

-341. 0

 287. 5

 237. 1

 191. 7

 150. 3

 551. 7

-461. 6

 368. 3

 291. 3

 193.2.

-527.2

-448. 2

 350. 9

 261. 3

 178. 3

 377.8

 317.4

 256. 1

-188. 8

 140. 2

 568.4

 482. 6

 377. 1 

 259. 1

 200. 8

Difl.

1.3

-1.7

0.7

 0.7

0.5

-0.2

0.0

0.2

 0.1

 0.1

1.2

1.8

 3. 6

0.2

0.7

0.6

 1.0

0.4

-0.2

0.1

-0.8

1.0

0.4 

 0.5

0.2

a

 a so

 a 84

 8.08

-8.12

1

^ 6.61

*

b

-0.0121

-0.0136

-0.0043

-0.0145

 0. 0140

TABLE 79. Thermo-electric power of cast-iron. American material.

Hod.

4

5

6

Bemarks.

{

'

.

,-

Annealed at red heat (I), soft<|

I

f

Original condition, soft ..... <|

1

t

°C.

24.6

24.4

25.0 

25.1

23.3

20.5

20.4

20.2 

20.2

20.1

19.1

19.1

19.1

19.2

19.3

12.8

13.1

13.4

13.7

13.9

13.5

14.0

14.3

14.6

15.0

16.0

16.4

16.7

17.0

17.4

14.9

15.3

15.5

15.6

15.7

T

°C.

89.6

74.7

49.9 

39.9

31.6

55.6

49.5

43.5 

38.9

32.4

88.7

77.5

62.1

53.8

42.1

80.8

68.0

56.0

47.0

35.2

55.8

49.8

39.6

33.4

27.6

79.0

65.7

56.6

43.9

35.3

83.2

75.4

63.2

50.0

39.6

e 

observed.

microvolt.

 500

 374

 175 

 103

 56

-245. 0

 201. 5

 159. 0 

 129. 0

 83.5

 428.7

 351. 2

 246. 0

 193. 0

-123. 8

 486

 380

 290

 224

 140

 315.6

 268. 2

 184.6

 137. 5

 90. 7

 360. 5

 274. 5

 213. 1

 140. 1

 90.3

 462

 399

 310

 215

 147

e 

calculated.

microvolt.

 499

 375

 176 

 102

 56

-244.7

 201. 6

-ICO. 4 

 128. 1

 83. 6

 429. 7

 349. 5

 246. 6

 193. 8

 123. 4

 484

 382

 290

-223

 140

 317.1

 266. 4

 185. 6

 136. 8

 91.0

 361. 3

 272. 4

 214. 8

 139. 4

- 90.5

 462

 400

 309

 216

 147

Diff.

 1

1

1 

 I

0

-0.3

0.1

1.4 

-0.9

0.1

1.0

 1.7

0.6

0.8

 0.4

 2 2

0

 1

0

1.5

 1.8

1.0

 0.7

0.3

0.8

 2.1

1.7

 0.7

0.2

0

1

 1

1

0

a

1

| 5.88

1

1I

S-6.42

J

 >

1

S-4.42

I

J

 5.96

1

[ 6.78

1

J

 4.21

 5.32

b

-0. 0158

 0. 0073

 0.0162

 0.0123

 0.0104

 0. 0161

 0.0140

(772)
BABUS AND BTKOUHAL.J THERMO-ELECTRICS OF CAST-IRON. 181 

TABLE 79. Thermo-electric power of cast-iron, American material Continued.

Bod.

6

7

8

9

10

Remarks.

{

,

Suddenly cooled (II), not very 1

hard. ' \

I

,

Original condition, soft .....{

{

,

Original condition, soft . . . . .<

I

I

t

°C.

14.4

15.0

15.3

15.9

16.2

22.8

23.0

23.0

23.0

23.0

18.2

18.3

18.4 

18.6

18.6

14.7

15.2 

15.6 

16.0

16.4

21.4

21.4

21.6

21.6

21.6

17.4

17.4

17.4

17.0

17.0

17.5

17.9 

18.2

18.7

19.0

10.5

10.8

11.1

11.2

11.5

12.7

12.8 

12.8

12.9

12.9

18.9

19.2 

19.5 

19.9

20.2

16.2

16.4

16.6

16.8

16.9

19.4

19.3

19.1

18.8

18.7

23.4

23.4

23.5

23.7

23.8

T

°C.

57.7

48.9

40.7

34.8

29.4

83.3

75.2

63.2

53.8

41.5

71.9

67.3

58.8 

51.3

44.5

57.9

50.6 

43.0 

37.1

31.7

82.6

69.4

56.5

47.0

39.5

86.9

80.5

72.3

52. 9

38.9

57.1

50.8 

45.3

40.1

35.4

87.7

75.3

62.9

52.0

42.7

72.3

64.0 

52.2

43.0

37.0

58.3

52.6 

44.9

37.1

33.6

89.8

81.8

72.5

60.7

51.6

86.4

73.6

56.1

43.8

35.0

57.8

50.9

47.1

42.6

37.4

e 

observed.

microvolt.

 270. 6

 206. 6

 151.4

 111.7

 77.4

 361.2

 308.0

 225. 5

 168.7

- 98.8

 372

 335

 273 

 217

-170

 321.2

 260. 0 

-195. 2 

 149. 5

 108. 6

 359. 0

 273. 3

 189. 5

 135. 6

 94.0

 502

 445

 382

 236 '

 139

 261. 6

 212.0 

 172. 1

 137. 2

 103. 4

 437.3

 350.7

 274. 8

-205. 7

 154.1

 411

 347 . 

-262

 195

 154

 300. 4

 251. 1 

 187. 2 

 126. 6

 97.5

 457.8

 388.1

 327. 7

 245. 2

 187. 3

 473

-372

 243

 160

 103

-235. 3

 185. 0

 157. 8

 1^6.5

 89.8

e 

calculated.

microvolt.

 269.7

 207. 1

 152. 2

 111. 8

 77.1

 361.6

 305.4

 227. 4

 169. 6

 98.1

 371

 336

 272 

-217

-170

 320.4

 258. 8 

 197. 3 

 150.1

 107. 7

-358.9

 272. 1

 191. 2

 135. 6

 93.6

 500

 447

 381

 236

 139

 259. 8

 213. 3 

^ 173. 9

 136. 0

 103. 3

 436.9

 352. 0

 272.8

 207. 2

 153. 7

 411

 347 

 261

 196

 154

 299. 5

 251. 4 

 188. 7 

 126.0

 97.0

 454.5

 393. 1

 325. 6

 245. 1

 187. 3

 472

 372

 244

 160

 102

 234. 8

 185. 6

 158. 3

 126. 0

 89.9

Diff.

 0.9

0.5

0.8

0.1

 0.8

0.4

 2.6

1.9

0.8

-0.7

_j

1

 1 

0

0

 0.8

 1.2 

2.1 

0.6

 0.9

-0.1

 1.2

1.7

0.0

 0.4

 2

2

»1

0

0

 1.8

1.3 

1.8

 1.2

 0.1

 0.4

1.3

 2.5

1.5

 0.4

0

0 

 1

1

0

 0.9

0.3 

1.5 

 0.6

 0.5

 3.3

5.0

 2.1

-0.1

0.0

 1

0

1

0

 1

-0.5

0.6

0.5

 0.5

0.1

a

1

^ 5.17

J

 4.27

-6.72

1 6.20

J

 4.82

-5.34

 5.60

-4.03

1 5.72

-

-0.54

 3.98

 5.61

.

-5.95

b

 0.0147

 0.0161

 0.0182

 0.0165

-0.0148

-0.0178

-0.0129

 0.0166

 0. 0138

 0. 0187

 0.0208

-0.0145

-0.0108

(773)
182 IRON-CARBURETS. [BULL. 14. 

TABLE 79. Thermo-electric power of cast iron. American material Continued.

Hod.

' 10

11

12

Eemarks.

.

Original condition, soft . . . . . -j

I

Suddenly cooled (II), hard. . «

I

Annealed at red heat (I), soft. (

,

I

Suddenly cooled (II), hard.. <

I

Annealed at red heat (I) , soft. 

1

t

°C.

20.1

20.0

19.1

19.7

19.6

21.6

21.6

21.5 

21.4

21.4

25.8

25.7

25.6 

25.6

25.5

19.0

19.0

18.8

18.7

18.5

22.5

22.5

22.5

22.4

22.4

12.1

12.5

12.7

13.' 1

13.2

19.5

19.5

19.4

19.4

19.3

T

°C.

86.2

78.3

69.2

59.6

50.1

74.9

67.4

60.3 

51.4

43.3

57.6

50.5

46.3 

42.6

36.8

89.6

80.3

67.8

60.6

51.6

86.2

75.9

63.9

51.6

40.7

57.9

50.0

44.5

38.2

34.3

87.9

80.2

67.3

54.1

45.9

e 

observed.

microvolt.

 383. 8

 335. 1

 275. 7

 214. 5

 160. 0

 364

 309

 258 

 195

 141

-234. 8

 181. 1

 151. 7 

 124. 7

 81.8

-888. 1

 331.1

 254. 3

-211.8

 162. 6

-449

-369

-279

-190

 118

 312. 7

 249. 5

 208. 9

 164. 3

 137. 3

 399. 4

 348. 3

 267. 8

 184. 5

 140. 4

e 

calculated.

microvolt.

 386.2

 333.0

 274. 2

 215. 6

 160. 0

 364

 308

 258 

 196

 141

 234.6

 182. 0

 151. 4 

 124. 1

 82.1

-389. 9

 329. 6

-253. 8

-212. 2

-162. 9

-449

 368

-279

 192

 117

 311. 0

-250.8

 210. 3

 164.0

 136. 7

 399. 9

 348. 3

 266. 1

 186. 3

 139. 8

Diff.

2.4

 2.1

 1.5

1.1

0.0

0

 1

0 

1

0

 0.2

0.9

 0.3 

-0.6

0.3

1.8

 1.5

-0.5

0.4

0.3

0

 1

0

2

I

 1.7

1.3

+1.4

 0.3

 0.0

0.5

0.0

 1.7

1.8

 0.6

a

}

} -4. 12

1

1

 5.59

-6.93

-3.83

j

S 5.53

1

J

,

I

1 5. 83

J

-4.34

b

 0.0163

 0.0129

-0.0054

 0.0156

 0. 0139

-0.0137

-0. 0141

Resistance. WQ give in the following table (80) the results for the

electrical resistance of cast-iron. The rods are respectively identical to 

those for which the Tables 78 and 79 apply. Under W are contained 

the resistances per meter of length at the temperature £, in ohms; under 

q the two sides of the rectangular section of the rods, in centimeters; 

st and 8 are the specific resistances at t° and 0°, the reduction having 

been effected by aid of the constant a, determined elsewhere.162 The 

rods are tested in the three states: original or commercial; after sudden cooling from red heat (II) ; after annealing at red heat (I).

«» Cf. Chapter I, p. 22.

(774)
BARUB AND STROUHAL.J RESISTANCE OF CAST-IRON.

TABLE 80. Electrical resistance of cast-iron.

GERMAN IRON.

183

Rod.

'1

?52 ?

 )

Condition.

Suddenly cooled (II) . .......

W 1m

ohm. 

0. 01235

1537

1070

O A7OO

791

674

0. 0750

790 

683

t

°C. 

10.0

11.2

14.5

15.5

10.6

14.5

15.5

11.4 

14.5

9

cm2 

0. 771 0. 771

0. 771 0. 771

0. 758 ' 0. 758

0. 309 0. 309

0. 309 ' 0. 309

0. 297 ' 0. 297

0. 307 ' 0. 307

0. 307 0. 307 

0. 293 ' 0. 293

cm "c^£°

microhm. 

73.4

91.4

61.5

fid 8

75.8

59.5

70.6

74.4 

58.8

a

0. 0013

12

13

0. 0013

13

13

0. 0013

13 

13

cm _ 8 c^°°

microhm. 

71.9

90.2

60.4

68 4

74.8

58.4

69.2

73.8 

57.7

AMERICAN IRON.

4

 {

 1 '1

 {

 I

-{

-1

19 /

Thoroughly annealed (I) ......

Thoroughly annealed (I) ......

Suddenly cooled (II) .......... 

Thoroughly annealed (I) ......

Thoroughly annealed (I) ......

Thoroughly annealed (I) ......

Thoroughly annealed (1) ......

Thoroughly annealed (I) ......

0. 00981

1200

ftQAQ

0. 00991

1244

0872

0. 00931

1025

0877 

0. 01377

1720

1214 

0. 01352

1561 

1267

" 0. 01403

1720

1265 

0. 02072

1950 

0. 02173

2075 

0. 02173

2624

2060

23

29

16

OE

25

16

25

.29

16

91

25

16

9"»

29 

20

25

18

16 

23

OK

20 

25

18

20 

25

25

20

0. 977 0. 936

0. 977 0. 936

0. 977 ' 0. 936

0. 959 0. 957

0. 959 0. 957

0. 959 ' 0. 957

0. 951 ' 0. 950

0. 951 ' 0. 950

0. 051 0. 950 

0. 813 0 803

0. 813 ' 0. 803

0. 813 0. 803 

0. 807 0. 805

0. 807 0. 805 

0. 807 . 0. 805

0. 790 ' 0. 7P9

0. 790 0. 789

0. 790 0. 789 

0. 656 0. 640

0. 656 ' 0. 640 

0. 643 0. 642

0. 643 ' 0. 042

0. 643 0. 642 

0. 647 ' 0. 646

0. 647 0. 646

0. 647 0. 646

89.7

109.7

77.5

91.0

114. 2

80.0

84.1

92.6

79.3 

89.9

 112.3

79.2 

87.8

101. 4 

82.3

87.4

107.2

78.9 

87.0

81.9

89.7

109. 9

85.7 

90.8

100.7

86.1

0. 0012

12

12

0. 0012

12

12

0. 0012

12

12 

12

1.2

12 

0. 0012

12 

12

0. 0012

12

12 

0. 0012

12 

0. 0012

12

12 

0. 0012

12

12

87.3

106.0

76.1

88.3

110.9

78.5

81.6

89.5

77.8 

87.5

109.0

77.7 

flu a

98.0 

80.4

84.9

104.9

77.4 

84.7

80.0 

87.1

107.5

83.7 

88.2

100.5

84.1

Digest. In the following table the important results in Tables 78, 79 

and 80, above, are systematically arranged for convenience in reference. 

It will be at once intelligible. We need only remark that in case of 

No. 1 the measurement of a was no longer possible for the soft annealed 

(I) condition, the rod having been accidentally broken. For this reason 

the value of a for the original state is taken for «i in the formation of 

Ja, and All. This, however, is quite permissible since the rod was originnally soft. It may be added that in the tables the logarithms are 

primarily deduced, the antilogarithms from these. This table furnishes 

us with mean values fcr cast-iron. They are given in the final horizontal row.

(775)
184 IRON-CARBURETS. 

TABLE 81. Electrical constants of cast-iron.

[BULL. 14.

Rod.

No. 1

No. 2

No. 3

No. 4

No. 5

No. 6

No. 7

No. 8

No. 9

No. 10

No. 11

No. 12

Means

ThermoeL constant a, referred 

to soft silver, for

J (2M-«)=0 (in

microvolt).

ai

( 4. 94)

 6.84

 6.61

 4.42

-4.21

 4.27

-4.32

 408

 3.98

-4.12

 3.83

 4.34

 4.66

as

 7.04

 8.30

 8.12

 6.42

-& 78

-5.17

 6.29

 5.60

-fl.54

 5.95

 6.93

 5.83

 6.58

Aa

2.10

1.46

1.51

2.00

2.57

0.90

1.97

1.57

2.56

1.83

3.10

1.49

1.92

Thermoel. hardness, deduced from a 

and ft=15.18-o, for J (T+<)=0 (inmicrovolts).

hi

(20. 12)

22.02

21.79

19.60

19.39

19.45

19.50

19.21

19.16

19.30

19.01

19.52

19.84

hi

22.22

23.48

23.30

21.60

21.96

20.35

21.47

20. 78

21.72

21.13

22.11

21.01

21.76

AA

2.10

1.46

1.51

2.00

2.57

0.90

1.97

1.57

2.56

1.83

8.10

1.49

1.92

log hi

1. 3036

.346fl

.3383

.2923

.2876

. 2889

.2900

.2835

.2824

.2856

.2790

.2905

log ht

1. 3467

.3707

.3674

.3345

.3416

.3086

.3318

.3176

.3369

.3249

.3446

.3224

VP&logh

43.1

27.9

29.1

42.2

54.0

19.7

41.8

34.1

54.5

39.3

65.6

31.9

40.3

Specific electrical resistance sC-^-0° cm*

(in microhms).

81

60.4

58.4

57.7

76.1

78.5

77.8

77.7

80.4

77.4

80.0

83.7

84.1

74.4

82

90.2

74. «

73.3

106.0

110.9

89.5

109.0

98.0

104.9

102.3

107.5

106.5

97.8

As

29.8

16.4

15.6

29.9

32.4

11.7

31.3

17.6

27.5

22.3

23.8

22.4

23.4

log si

1. 7809

.7663

.7610

.8812

.8949

.8907

.8906

.9052

.8885

.9029

.9225

.9246

log 82

1. 9551

.8736

.8651

.0255

.0448

.9517

.0375

.9911

.0209

.0100

.0316

.0273

10*4% «

174

107

104

144

150

61

147

86

132

107

109

103

119

DISCUSSION.

Plane diagram. The experimental material in hand is sufficient for 

the discernment of the main and characteristic features of the relation 

which exists between the mechanical and chemical properties of ironcarburets, and their electrical behavior. We will arrive at our end 

soonest by proceeding graphically, using ascthe basis for our construction the general mean values given in Tables 76-77 and at the end of 

Table 81. As regards the interpretation of these data we derive very 

valuable clews from our earlier researches on the electrical properties

of alloys. If to a given metal small amounts of a second metal be 

alloyed, the electrical constants are found to vary in a uniformly continuous way. Now, the total carbon in steel amounts to only 1-2 per 

cent; in cast iron to less than 5 per cent. We may therefore predict a 

mode of variation of specific resistances and thermo-electric power which 

shall be analogous to that observed for alloys. In other words, a uniformly continuous change in the electrical qualities of iron-carburets 

with the amount of carbon contained may justifiably be assumed. With 

the ultimate object in view of developing our diagram, let the percentage of total carbon, therefore, be represented as abscissa, the electrical 

constants h and s as ordinate. Carbon, however, occurs differently in 

iron-carburets when in the condition I than when in the other extreme 

condition, II. It is therefore necessary sharply to distinguish between 

the constants hi and Si belonging to the first or thoroughly annealed 

state, and the constants h2 and s2 for the hard state. Our data therefore 

furnish points belonging to two essentially different loci. Unfortunately for each of these, only three such points are in hand: the first

(776)
BARUS AND OTBOUHAL.J IRON-CARBUKETS ELECTRICAL BEHAVIOR. 185

corresponding to wrought-iron and the abscissa, #=0; the second to 

steel where, approximately, x=l.5; the third to cast-iron, where we 

may roughly put x=5.Q. The mean values of ordinate belonging to 

these abscissae may be taken from the following little table:

TABLE 82. Mean electrical constants of iron-carburets.

Material.

Steel........................

X

0

1.5

5.0

hi

4.7

6.0

19.8

hi

4.7

17.3

21.8

AA

11.3

1 Q

103 X 

A log h

40

Sl

19 9

15.0

74.4

82

199

41.2

97.8

As

26.2

23.4

10'X 

A log*

JJ.A

With these data and the qualitative results just referred to, our attention will be first directed to the hard state, II, of iron-carburets.

Between o?=0 (iron), and #=1.5 (steel), iron-carburets vary in marked 

degree as regards hardness, a circumstance observable both in the me-, 

chanical and electrical properties (h^ s2 ) of these products. Beyond this, 

approaching castiron, the variations are slight. The curve rises rapidly 

at first, finally at a gradually decreasing rate, and is therefore as a whole 

concave towards the axis of abscissae.

7

17

\

Carbur itian, i >L f.r ei rUs . Caa-bu ration., r'rt, -ptr <xn.fa .

PIG. 24. Diagram of the mean variation of the thermo-electric hardness and the specific electric 

. resistance of iron-carburets, with their degrees of carburation; 1, thoroughly annealed state; 2, suddenly cooled state.

A result almost the inverse of this is encountered in the case of the 

"soft" state I. Here the initial variations are insignificant, soft iron 

and soft steel differing slightly, not only in their mechanical states of 

hardness, but also in the electrical manifestation (/H, sx ) of this quality. 

It is not until we pass beyond a?=1..5 and enter the region of the castirons that the present curve I rises at a relatively rapid or accelerated 

rate. The curves, 1, are therefore on the whole convex as regards the 

axis of abscissae.

From these points of view the curves in the above diagram h2, 8%

(777)
186 IRON-CARBURETS. [BULL.14.

and hi, «i have been drawn. It may be plainly argued, moreover, that 

their general character does not change during the progress from #=0 

to o?==5; in other words, we accept concavity and convexity respectively throughout the given extent of the curves, to the exclusion of 

points of circumflexion. With this probable inference postulated, we 

observe that the two sets of curves h2j s2 and h^ «! must intersect in the 

region of cast-iron, that is, near #=5.

Curiously enough we found in certain data of Joule163 the evidence for 

such intersection. If we reduce Joule's figures to our scale of thermoelectric hardness, his results for white cast-iron and gray cast-iron are 

approximately these:

First extreme: cast-iron, black fracture (with much graphite), h=25.

Second extreme: cast-iron, white fracture (very hard), h=l2. All 

other samples of cast-iron which he examined lay between these limits. 

The large values for h and s obtained164 for malleable cast-iron (known 

to be graphitic165 ) are also in accordance with Joule's results. The first 

mentioned of the cast-irons above (h=25) is therefore to be referred to 

condition I (soft, carbon uncombined), the second (7i=12, carbon combined, hard) to condition JJ, which gives evidence in favor of the intersection of the respective curves.

Superimposed electrical effects. To this inversion of the electrical 

properties of iron-carburets as the quantity of total carbon is increased 

we have already adverted,166 and it is therefore essential to any discussion of the phenomena before us to take cognizance of the mechanical 

as well as the chemical causes of the same. These are three in number: 

(1) Effect of uncombined carbon; (2) effect of combined carbon; (3) 

effect of the peculiar strain accompanying temper.

In the curves hi and Si the first of these factors is primarily active, 

the second of small importance, the third inactive. The material is approximately homogeneous. In the curves Ji2 and s2, however, all factors 

produce their own specific results, though the influence of the first is 

relatively small. Here, therefore, we are confronted by a complex 

superposition of effects; such however, that between wrought-iron and 

steel the mechanical cause (3) is almost solely efficient; between steel 

and cast-iron the chemical causes (1, 2) predominate.

Character of All. As the result of the opposed character of the curvatures of the loci /(soft state) and II (hard state), the first being convex, the second concave, as regards the axis of abscissae, we are able to 

draw an inference of fundamental importance. For if we put dh=h2 hi 

and Js=s2 sx , then it follows obviously that the new variables J/i and 

/Js, regarded as functions of #, must each pass through a maximum. 

This remarkable result may be formulated thus:

The diagram which expresses the electrical behavior of commercial

163 Joule: 1. c. 163 Forquignon: I.e. 

164 Chapter III, p. 102. ""Chapter m> P- 103>

(778)
UABUS AND BTBOUHAL.] IRON-CARBURETS ELECTRICAL BEHAVIOR. 187

iron-carburets distinctly indicates the existence of a singular product, 

possessing the unique capability of occurrence in the greatest number 

possible of mechanical states a member, in other words, for which the 

difference of thermo-electric hardness between condition II and condition J is a maximum. This is a necessary but not a sufficient condition 

for the definition of that valuable product to which the term "steel" is 

applicable. For, irrespective of the fact that z//i=max. and z/s=max. 

need not necessarily select the same product, a definition based solely 

on the absolute value of the interval of variation does not necessarily 

exclude the occurrence of any marked change of hardness as regards 

the soft state. Yet this is essential. The mere fact, in other words, 

that for the unique iron-carburet in question the state II is furthest removed with reference to hardness from the state I, might even be true 

of a product brittle in the latter (soft) state.

Character of A log h. To meet this objectionable feature of the above 

definition, therefore, it is expedient to give preference not to the absolute variations of h and s, but to the relative variations h2 : h\. 82 : s^ of 

pairs of values of li and s. For this reason the logarithmic interval is 

considered. If J/&=log /t2 log hi and /4s=logs2 log«i, then we have 

for the definition of steel Jlog 7i=inax., or A log s= max. Between 

these we have yet to decide. In the first place it is to be noted that 

the equations z//t=max. and J,s=max., determine x=2 and #=3, respectively, and so far as can as yet be foreseen; whereas A log 7t=max. 

and Jlogs=max., apply for #=1.5 and #=2.0, respectively. In the 

latter case, therefore, not only are the two carburets defined chemically 

much more nearly coincident, but their mean position in the diagram is 

such as to select from all the iron-carburets the one which may stand as a 

type for the products commercial^ termed steel. And we may add here 

that, in so far as the variation of a function like the one in hand in the 

neighborhood of a maximum is usually small, a group of iron carburets disposed on either side of the said maximum will possess properties sufficiently alike to enable us to consider them as practically and 

commercially identical with the accurately defined type. Now it is 

very probable, if material of sufficient purity could be obtained, that 

both the equations /71og/t=max. and Jlogs=max. wilt be found satisfiable by the same a?, and this from the fact that as far as steel, at least, 

the relation between thermo-electric hardness and specific resistance is 

linear. But after subjecting any iron-carburet to the process of sudden 

cooling, the external layers will usually have been transferred into the 

state II more thoroughly than the core, particularly in case of thick 

rods and highly carburized iron. But it is from the external layers that 

A log h is practically determinate, irrespective of the figure and dimensions of the carburet operated upon. A log s is not readily determinable 

except for the mean condition of a carburet of definite figure.

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188 IRON-CARBURETS. [BULL. 14.

Definition of steel. Preference is, therefore, to be given to the former 

of the two critical equations and J log li = maximum to be accepted as 

the physical definition of steel. This equation is to be interpreted thus:

Let each member of the whole series of non-carburets be subjected 

successively to the following two operations:

1. A process of very slow cooling from a given temperature in red 

heat.

2. A process of most rapid cooling possible from the same temperature.

If now the carburets be examined with reference to the hardness produced in the two instances, there will be found among them a certain 

unique member whose properties are such that while process I has more 

nearly identified it with pure soft iron; process II will have moved it 

farther away from this initial carburet107 than is simultaneously the case 

with any other iron-carbon product; or which, in other words, is capable 

of occurring in the greatest number of states of hardness relative to the 

soft state possible. To this unique product the term "steel" is to be 

applied.

In so far, however, as the softest steel, for the very reason of its being 

essentially an iron-carburet, can never reach pure iron, it is obvious 

that there must remain a difference between the mechanical properties 

(Young's modulus, simple rigidity, tenacity, etc.) in general of soft iron 

and soft steel, on account of which preference will be given to one material or the other, as the needs of the engineer suggest. To this carburet (/I log /i = max.), finally, the maximum capacity for the retention 

of a strain of any given kind which may be imparted to it, seems also 

to belong. The strain accompanying magnetism, and the strain peculiar to hardness, of each of which steel retains a phenomenal amount, 

may be cited as examples.

COMMERCIAL OR IMPURE IRON-CARBURETS.

Series of iron-carburets. Thus far no attention has been paid to the 

unavoidable impurities like sulphur,. silicon, phosphorus, manganese, 

etc., which in addition to carbon are always present in commercial ironcarbon products. But it is easy to extend the considerations just made 

in such a way as will make them applicable to iron-carburets, pure and 

impure, generally. Let any iron-carburet be given. To this belong a 

whole series of iron carburets so constituted that, while in other respects 

the composition is identical throughout, carbon alone passes through 

the interval from zero to about six per cent.168 To each such series (see

167 That is, soft iron for which x=0.

168 0f course, the increment in C in this case presupposes a decrement in total Fe, so 

that there may be no variation in the percentage presence of the impurities.

° (780)
BAKUS AND BTKOtJHAL.] THERMOELECTRIC HARDNESS. 189

below, p. 191) a definite and characteristic pair of curves, h2 and h^ will 

correspond, and that particular impure iron-carburet which is selected

by the equation

A log h = maximum

is the steel for the given class of impure iron-carbon products. These 

relations, may be tersely exhibited as follows. Let

where #1 denotes the thermo-electric hardness of a given sample of 

impure iron- carburet, a, &, c . . . . , are parameters expressing the respective amounts of the impurities present in per cents, by weight of 

the whole, x (independent variable) representing the total carbon present, also in per cents, of the whole.

Let

*« /« K &, c, . . . a?)

be interpreted in like manner. Now suppose the functions %i and za to 

belong simultaneously to the same product, or in other words, to apply 

when the said given product is in the state I and the state IT, respectively.169 Then will these equations, if x be allowed to increase continuously from zero to about six, express the critical electrical properties 

of the whole given series of impure iron-carburets. Again by varying 

any one or all of the parameters, «, &, c . . ., we may pass from a 

given series of this kind to any other.170 Finally the function, in the case 

of a given series,

A log #=log #2 log zl

possesses the important property that for wrought iron its value approaches zero; for cast-iron its value is some positive number, and for 

steel we shall have A log 2=maximum. In order to determine the position of any iron-carburet in its own series a knowledge of the functions #! and z2 is fully sufficient.

Thermo-electric hardness general interpretation. With these new inferences we are able to give the results of an earlier chapter (It), a 

much more comprehensive interpretation. The extreme values of 

thermo-electric hardness, zl and #2 , corresponding to thorough annealing 

and sudden cooling, respectively, describe any given member of any 

given series of iron-carburets with reference to its chemical properties; 

i. e., z-i and #2 , together, determine its position in a diagram of classification peculiar to iron-carburets. The intermediate values of z, in 

other words, those lying between zl and #2 , and obtainable by the annealing of the previously chilled carburet, describe the same product 

with reference to its mechanical properties; i. e., the value of z deter169 In practice /i and/2 will be interpoJatory functions of like character. 

mlt is to be borne in mind here that these remarks apply principally for iron-carburets, in which x does not exceed 2. The final generalization is given below.

(781)
190 IRON-CARBURETS. [BULL. 14.

mines its position in a scale of hardness peculiar to the particular ironcarburet (#1, 22 ) in hand.

Herewith we have succeeded in expressing the general conception of 

a problem, of which our research on the hardness of steel (Chapter II) 

is to be regarded as only a special solution.171

FINAL GENERALIZATION.

t

Qualitative and quantitative carburation. In the above discussion the 

general features of the electrical behavior of iron carburets, whose 

degree of carburation is above 2 per cent., has already been given. But 

a more detailed consideration must take cognizance of the fact that even 

in case of the vsame chemical composition we encounter iron-carburets 

differing enormously in their physical properties, and we are led into a 

host of complications not readily to be surveyed. The mode of occurrence of carbon in iron, or what may be called the quality of carburation, becomes more and more dominant in effecting changes of physical 

character of these products, as the amount of total carbon present is 

increased. The temperature in red heat from which the conditions I 

(thoroughly annealed) and II (suddenly cooled) are reached, as well as 

the time during which exposure to the same takes place, here possesses 

essential importance.

Classification-function.^ The prolongation of the critical curves 7ii and 

^2 from steel into the region of cast-iron can therefore be made in a 

great variety of ways. For each particular path definite premises must 

be laid down, viz., that the increase of carbon shall take place, qualitatively as well as quantitatively, in a way such as is in accordance with 

the manner of carburation of the sample of cast-iron, in which the particular path in question is to terminate. Perhaps these relations are 

expressible with greater clearness in this wis*e: Suppose that with reference to the height and duration of the temperature from which thorough 

annealing (J) and sudden cooling (II) is to be effected, etc., certain fixed 

assumptions have been made. But beyond this let it be unrestricted, 

so that it may even lie beyond the melting point of the carburets operated upon. Furthermore, suppose the percentage amount (parameter) 

of foreign admixtures and impurities other than carbon present in iron 

be constant throughout. Then let the relations here involved be represented graphically in three dimensions: Thermo-electric hardness parallel to the axis Z; carburation quantitatively considered (percentage

171A good example of the difference between mechanical and thermo-electric hardness is given by malleable cast-iron, results for which are given elsewhere (Chapter 

III. p. 102).

(782)
BARU8 AND 8TROUHAL.] CLASSIFICATION-FUNCTION. 191

of total carbon) parallel to the axis X; finally qualitative carburation,172 

i. e., a quantity which expresses the mode of occurrence of carbon ia 

iron, parallel to the axis Y. With this understanding a characteristic 

surface will correspond both to condition I and condition II; and if 

analogously to the above (p. 189), we deduce the difference zHogz, its 

form will be

=.F(a, 6, c, . . . . y, x )

where the parameters a, 6, c, ... refer to the impurities present.

Every plane parallel to XZ cuts this surface in a curve, expressing 

the electrical behavior of a series of iron carburets as above defined 

(p. 188). All such curves of intersection are characterized by the presence of a maximum defining the steel corresponding to the impure iron, 

F (a, &, c, . . .y, 0), the initial carburet of the particular series under consideration.

Every plane parallel to HZ cuts the surface A log z in a curve, expressing the electrical behavior of all carburets possible in case of a 

selected fixed amount of total carbon in the iron carburet. Two such 

curves will differ more as their distance apart as well as from the initial 

plane "YZ is greater. It will be seen that the further step in the present research must be that of suitably varying the elements of the operations I and IT173 in such a way as to throw additional light on all these 

complications, among which those last mentioned are as yet the most 

obscure and imperfectly understood.

Classification diagram. Notwithstanding the dangers encountered in 

representing views in part theoretical with the aid of a diagram, we are 

able to bring to the mind of the reader all that has been said so perspicuously in this way, as readily vindicates the venture of a rough construction of the probable contour of the surface A log z. In the following figure (25) the XZ plane cuts the surface /Jlog z (rstno) in a line coinciding with the axis X. This is supposed to be an hypothetical carburet, iron-graphite, which remains iron-graphite both in state I and in 

state II. The extreme plane parallel to XZ represents the series of

mAs an example of the nature of the variable y, suppose it, for instance, to be the 

mean ratio of combined to uncombined carbon for the two states, I and II, or,

j,=i5 ( C0mb!nedl W C°m^ne^V ;. Should a single quantity, ,,, be in- } \ uncombined C )l \uncomllnne(lCy/Z >

sufficient to express the qualitative occurrence of carbon, so that a number of such 

variables y, y', y", ...... are necessary, then while' any given one, y for instance,

passes all values, the others are to be regarded as parameters i. e., constants during 

this variation. The presence of graphite, amorphous carbon, and combined carbon 

in iron may suggest two variables, y, y'.

173 Much, for instance, could be learned from continuous electrical ignition of ironcarburets, in vacuo and gases, respectively, and examination of the test sample from 

time to time; more from a detailed exploration of these phenomena, made conjointly 

by a physicist and a chemist. Carburation produced by ignition in gaseous hydrocarbons, and subsequently in vacuo, suggests itself as a first convenient method of 

experimental attack.

(783)
192 IRON-CARBURETS. [BULL. 14.

iron-carburets (rst) in which all carbon is combined, at least in state II. 

White cast-iron may be supposed to belong to this series. The plane

A log

...... -Oiermo-clcctrio 7uxr3nc$g<

carbwatiom

d,'lft c, ... respective ammaxta of-i- 

.iii,-tlie. Iron*

FIG. 25. Classification diagram.

YZ intersects the surface /J log e in the iron line approximately coinciding with the axis Y. The extreme plane (mtn) parallel to YZ corresponds to about 00=6. The most interesting feature of the diagram is 

the totality of steel maxima (svp). If ordinates be let fall from each of 

these, the resulting cylinder will intersect the plane XY in a curve 

(peg), expressing both qualitatively and quantitatively the carburation 

of the infinite steels possible in case of a given impure iron-carburet

F (a, 6, c,. . .y, x). It is hardly necessary to add that the number of 

such possible surfaces (rstno) is again infinite; since any variation of 

the parameters a, &, c, . . . or the accessary variables y,' i/," - - involves 

the construction of a new one. Practically, however, a finite number 

of typical surfaces suffice.

The figure finally contains an illustrative intermediate section, in 

which v is the steel of the series of iron -carburets uviv.

Concluding remarks. The perusal of the above pages will have shown 

that the problem in hand, considered in its full generality, is exceedingly complicated. Nevertheless, we presume to believe that the 

method of attack which has been briefly developed in this chapter contains promise of success. Both the intimate relationship between the 

mechanical properties of iron-carburets and their electrical behavior, 

as well as the incomparable sensitiveness of the functions involved, 

emphatically commend our electrical diagram to the metallurgical engineer. Indeed, it is remarkable that metallurgists have thus far given 

no attention to a class of physical properties which, from their simplicity

(784)
BARUB AND BTBOUHAl.] CLASSIFICATION-FUNCTION. 193

and pronounced character, seem above all others to be adapted for purposes of discrimination and classification. Magnetic functions, as we 

have shown elsewhere, admit much less readily of satisfactory interpretation, varying as they do enormously with the figure and dimensions of the sample under examination. The interest of the present 

ohapter, however, centers in the important product, steel. Curiously 

enough, the large range of variation of mechanical properties which 

renders this substance so indispensably useful have not as yet been 

found available for its accurate definition. The electrical qualities of 

steel, however, furnish a means to this end, which can conveniently be 

pushed to greater detail and nicety than will be necessary for any 

metallurgical or even physical purposes. It is in this respect that we 

believe with the present publication to have opened a new field of research, useful alike in its bearing on the practical and the theoretical 

prpblems concerning iron-carburets.

(785) 

Bull. 14 13
CHAPTER VIII.

BKEEF SUMMARY OP THE PKENCIPAJL DATA.

Introduction. The remarks in this memoir refer almost exclusively 

to the species of hardness known as temper, and which may be imparted 

to iron-carburets by sudden cooling from red heat combined with more 

or less subsequent annealing.

It falls within the scope of the work to develop so far as possible the 

very close analogy which exists between tempering and magnetization.

If we define the structure of a hard cylindrical steel rod as being the 

law of variation of density encountered on a passage from axis to circumference along any radius of the rod, then structural identity in case 

of two given geometrically similar rods of the same composition a priori 

implies identity of diameter. In what way structure may vary with 

diameter is not even conjecturable. It follows that immediately comparable magnetic data are to be anticipated only where the rods of 

variable hardness and length retain the same thickness and composition throughout the course of the experiments.

Chapter I. Like the specific resistance, the galvanic temperaturecoefficient of the iron-carburets exhibits a phenomenal range of variation, passing from the values for wrought iron and soft steel, 0.0052 and 

0.0043, respectively, to the values for hard steel and cast iron, 0.0016 

and 0.0013, respectively. The said coefficient decreases continuously 

and uniformly as resistance increases, more rapidly than the latter during the earlier stages, much more slowly during the later stages of a 

progress from iron to cast iron. An inferior limit of the temperaturecoefficient would therefore seem to appear much before the iron-carburet 

reaches the superior limit of resistance. If classified with reference to 

the relation between resistance and temperature, the iron-carburets as 

a whole form one continuous series.

Chapter II. If the temperature from which steel is suddenly cooled 

be supposed to increase continuously from a very low value to the 

highest admissible, the hardness of the chilled rod will remain comparatively inappreciable until a certain critical temperature in red heat 

is reached. At this stage and a little beyond hardness increases at 

exceedingly rapid rates with temperature, after which the rate again 

decreases.

The largest observed variation of thermo-electric power produced by

194 (786)
BABUB AND STKODHAL.] SUMMARY. ' 195'

tempering is 12.8 microvolts per degree centigrade at 0°. The largest 

ratio of the respective resistances of hard and soft steel

45 (cm /cm2 , 0°, microhm) : 15 (cm /cm2, 0°, inicrohni)=3.

Since hard and soft steel lie on opposite sides of pure silver iii the 

thermo-electric scale, maxima and neutral points of electromotive force 

(thermo-electric inversions) are a common occurrence.

The annealing effect of any temperature acting on glass-hard steel 

increases gradually at a rate diminishing continuously through infinite 

time diminishing very slowly in case of low temperatures ( < 100°), 

very rapidly at first, then again slowly in the case of high temperatures 

(> 200°); so that the highest and hardest of the inferior states of hardness possible at any given temperature is approached asymptotically.

The ultimate annealing effect of any temperature t° is independent

of the possibly pre-existing effects of a temperature t'°, and is not in 

any way influenced by subsequent application of the latter, provided 

f>t'. In case of partial annealing at t° (time finite) this law applies 

more fully the more nearly the said ultimate effect of t° is reached. 

, If hardness of steel is to be expressed thermo-electrically, it is inexpedient to use the soft state, as a point of departure. The thermoelectric difference between soft steel and soft iron (say 1) when compared with the corresponding difference between the) extreme states of 

steel (say 10) is small. In soft steel, however, the effect of foreign 

ingredients (impurities: S, P, Si, Mn, etc.) is still too pronounced to 

admit of a desirably accurate determination of the thermo-electric 

position174 of this metal.

In the case of steel, the relation between thermo- electromotive force 

per degree centigrade at 0°, and specific resistance at 0° (s), is linear 

throughout the whole of the phenomenal range of variation of these 

qualities with hardness. This law suggests the introduction of the 

new variable thermo-electric hardness (fe), defined thus : Suppose the said 

law of linear variation to be true indefinitely ; then will the electromotive force (microvolt) per degree centigrade at 0° of a thermo-element consisting of steel in the imaginary normal state whose specific 

resistance (cm / cm2 0° microhm) is zero, and steel in any given state, be 

the thermo-electric hardness of the latter. The thermo-electric position 

of steel in the stated normal condition, with reference to pure soft 

silver, is

w=15.18 microvolts

per degree C. at 0°. Finally in the fundamental equation fe=w«,

Chapter III. The chemical theory of the* phenomenon of temper 

leads to this ulterior inference. By the simple process of sudden cool174 It may be added here that, even if chemically pure steel were available, its thermoelectric position would, very probably, be seriously variable in consequence of unknowable differences in the mode of occurrence of the carbon contained.

(787)
196 . IRON-CAKBURETS. [BULL. 14.

ing, combined with subsequent annealing, applied to steel, inasmuch as 

in this way, within certain limits, any given amount of an electrically 

active ingredient (carbon) may be converted into an electrically passive form, the same results are reached which in the case of alloys are 

obtainable only by melting the two component metals together.

In the case of alloys, the plane locus determined by thermo-electric 

power (microvolts) per degree centigrade, at 0°, and specific resistance (cm /cm2 0° microhm) shows maxima (or minima) for both properties, so disposed that the said singular points, at the temperature 0° 

at least, do not coincide. The range of variation of the electrical properties in question appears to increase with the difference of specific volume of the (two) ingredients of the alloy. Applied to steel, the results 

 interpret the observed linear locus for the metal .(steel) as being the 

initial tangent of a curve of comparatively enormous magnitude.

Variation of resistance is a necessary concomitant of variation of 

volume; no matter how the latter may have been produced whether 

by temperature or by tempering the increments of resistance (s) due 

to a given increment of volume (v) are of the same order. A purely 

thermal effect in the one case does not therefore appear. If we put

Jc = £U : 2~ l 150, a first approximation.

«i «i

Gentle ignition after a previous state of (hard) temper appears to be 

generally accompanied by a passage of both resistance and volume 

through minima.

The annealing effect of temperature and time in the case of drawn 

hardness is quite analogous to the said effect in the case of temper.

The position of cast iron is isolated with respect to the locus expressing the simultaneous variation of thermo-electric power and specific resistance due to changes of temper in case of the other carburets (steel). 

Cf. this re'sume', Chapter I.

The chemical theory does not suggest nor account for the observed 

phenomena of annealing. Considered physically these are at once referable to the category of viscous phenomena. In the ordinary cases 

of viscosity measurement, the phenomenon is evoked by sudden application of stress (torsion, flexure, tension, volume compression or extension, etc.) under conditions of constant viscosity; in the case of annealing, by sudden decrease of viscosity under conditions of initially constant stress. Thermal expansion interferes with the purity of these 

phenomena by destroying the conditions of existence of the characteristic strain which accompanies hardness, and this in proportion as the 

expansion is greater. The final evidence in favor of the given interpretation (viscosity) of the phenomena of annealing is this: that the maximum of permanent hardness which can in any way be imparted to steel

(788)
IURUS AND STUOU1IAT,.] SUMMARY. 197

(i. e., the maximum intensity of strain which a steel rod is of itself able 

to maintain) decreases rapidly as temperature increases. (Of. Chap. 

Ill, p. 97.)

The temperature condition (cf. Chapter II of this re'sume') to which 

the appearance of glass-hardness is subject, is readily suggested by the 

chemical theory. Physically the state of red heat of iron and of steel is 

remarkable for the occurrence of certain characteristic phenomena: sudden volume-expansion (Cumining); anomalous thermo-electric behavior 

(Tait) j disappearance of the magnetic quality (Gore); sudden appearance of glass-hardness in steel chilled from this temperature (Cheruoff). 

An anomalous variation of resistance may be additionally inferred. 

As regards conditions favorable to glass-hardness Cumming's phenomr 

enon distinguishes iron and steel from all other substances. The difference between iron and steel, finally, is exhibited in like degree by the 

maximum of permanent magnetization, by the maximum of permanent 

hardness (Strain), and probably by the maxima of other strains which, 

these metals, under like conditions, respectively retain. °

In the substance malleable cast-iron there is encountered a remarkable example of the occurrence of mechanical hardness unaccompanied 

by an equivalent variation of the electrical properties.

The existence of the characteristic strain in glass-hard steel is the 

cause of electrical effects so enormous that such additional effects which 

any change in carburation may involve can be wholly disregarded, and 

all electrical and magnetic results interpreted as due solely to variations in the intensity of the said strain.

Chapter IV. Both the galvanic and the thermo-electric effects of magnetization are negligible in comparison with the corresponding electrical ' 

effects of tempering the former amounting to less than 0.3 per cent, of 

the latter in the most unfavorable case.

The absolute value of the said thermo-electric effect for magnetically 

saturated iron is +0.035 microvolts per degree centigrade, at zero;

The thermo-electric effects of a temporary tensile strain in iron and of 

magnetization are qualitatively alike. Hence we infer that the latter 

effect is to be attributed to the strain which accompanies magnetism.

Chapter V. Rigidly comparable data of the relation between magnetism and hardness are not readily obtainable except with magnets 

which were originally integrant parts of the same (hard) steel rod of 

uniform temper throughout its length. The plan of experimentation is 

expediently made to conform with a passage from hard to soft.

If magnetic moment (C. Or. S.) per unit of mass (</) be regarded as a 

function of hardness, the family of curves obtained exhibits the following general character: Magnets, whether long or short, after incipient 

annealing from the glass-hard state diminish in magnetizability to a pronounced minimum of this quality. If the annealing be continued magnetizability again increases to an enormously developed maximum in 

case of rods of large dimension-ratio, to a flat or indistinct maximum in 

case of small dimension-ratio. On passing from long to short steel rods

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198 IRON-CAEBURETS. [BULL. 14.

the minimum is found to move in a direction from hard to soft, at very 

slow rates, thus remaining in the region of glass-hardness; the maximum, on the other hand, in a direction from soft to hard, at somewhat 

more rapid rates. The unique maximum of permanent magnetizability 

will probably be exhibited by a linear steel rod, annealed from glasshardness as far as the physical state of maximum density. The value 

of the unique maximum is demonstrably much above 785 C. G. S. units 

of intensity, or 100 C. G. S. units of moment per gramme-mass. Continued diminution of the dimension-ratio finally, will probably bring the 

said minima and maxima into coincidence in such a way that permanent 

magnetizability decreases uniformly from hard to soft.

The family of magnetic curves must be separately investigated for 

each given diameter (structure) and each given degree of carburation. 

If magnetic moment per unit of mass be regarded as a function of the 

dimension-ratio ( a = length /diameter), the family of curves obtained 

(conveniently described with the aid of the four type curves: "glasshard]" ''yellow annealed," "blue annealed," "soft,") exhibit the following general character:

The curve "glass-hard" is concave as regards the axis of abscissae 

(dimension-ratio) throughout. Rising very rapidly at first, it finally 

ascends to a distinct limitiug value or horizontal asymptote. The curve 

"soft," on the other hand, rises very slowly in its earlier stages, and is 

convex a>s regards the axis of abscissae. From here it passes rapidly 

through a point of circumflexion into concavity, and then above the 

former curve. Finally, the rate of ascent again decreases, so that a 

horizontal asymptote is also reached, but apparently at a later stage of 

progress than is the case with hard steel.

From either of these two loci expressing the variations of the extreme 

states, we may by annealing pass continuously to the other. But the 

manner of such passage, from the one curve to the other, in consequence of the continuous change of parameter (hardness), is exceedingly complicated. Incipient annealing of glass-hard steel produces a 

distinct, though relatively small, descent of the original curve as a 

whole. As annealing progresses, the farther end of the curve is always 

the first to rise and to pass above the original curve in such a way that 

the point of intersection of the new curve and the original curve (glasshard) moves along the latter with great rapidity, from greater to smaller 

values of the dimension-ratio. When the curve "yellow annealed" is 

reached, the part of it between a small value of the dimension-ratio, a 

(=14 and 18, in the above measurements, for diameters 2p = 0.08 cm. 

and 0.15 cm.), and a= oo, has been already elevated above the curve 

"glass-hard." At the stage of progress given by the blue annealed 

curve, the part between another small value of a (a 15 and 20 in the 

above results) and a= oo has risen far more rapidty than before, while, 

on the other hand, the advancing part of curve between a=0 and the 

said small value (or=15 or 20, respectively) having descended very grad-

(790)
BARU8 AND BTHOUHAL.J SUMMARY. 199

ually, is now distinctly convex downward. Passing from "blue annealed" to " soft,";, the part of the curve above smaller dimension-ratios 

continues to fall, in general at greater rates, finally to merge into the 

curve " soft." The remaining part, above greater dimension-ratios, still 

rises slowly, reaching its superior elevation, from which it then falls 

rapidly into coincidence with the extreme curve "soft" also. During 

this last phase of progress the point of intersection of the advancing 

curve and the curve glass-hard passes along the latter from smaller to 

larger values of the dimension-ratio.

Chapter VI. In considering the permanent magnetic effect of temperature on steel permanently saturated, it is necessary to discriminate 

sharply between two species of magnetic loss: .

1. The direct effect, due simply to the action of temperature, and to 

be ascribed to diminution of coercive force and to interference of thermal expansion with the magnetic strain.

2. The indirect effect, due to the action of temperature in producing 

mechanical annealing, and to be ascribed to the interference of the rearrangement of molecules resulting, with the magnetic strain.

The two effects are frequently superimposed. Considered separately, 

the latter (indirect effect) is by far the greater in amount, and its character, with regard to magnitude and duration, fully typified by the concomitant phenomenon of ordinary mechanical annealing. The former 

(direct effect) is not only of smaller magnitude, but subsides completely 

within a very much smaller interval of time. A third (temporary) effect. 

of temperature does not fall within the scope of the present work. 

If the contemporaneous effects of the action of. temperature on permanently saturated glass-hard magnets, viz., reduction of magnetic moment 

per unit of mass (ordinates) and *of specific resistance (abscissa), be 

compared graphically, the loci of the relation pass from pronounced 

convexity, as regards the axis of abscissae, almost horizontally through 

a point of circumflexion into pronounced concavity. It must be borne 

in mind that both the direct and indirect effcts are here superimposed. 

The said curves, if constructed for different dimension-ratios, are approximately parallel, presenting greater curvature, however, for smaller 

dimension-ratios than for larger. The immediate bearing of temper on 

the indirect effect is strikingly shown by the fact that, in the case of 

long, hard, permanently saturated steel rods, the relation between permanent magnetism per unit of mass and resistance, where both variations are simultaneous and due to changes of temper only, and where 

the latter occurs between the maximum of permanent hardness for ordinary temperature and the maximum of the same quality for 100°, is 

ultimately (a = oc) linear.

The maximum of permanent magnetization for any given temperature, 

<°, which can be imparted to a steel rod exhibiting the maximum of 

permanent hardness for the same temperature, t°, is wholly independent of the possibly pre-existing states of magnetization. If t = iOO°,

(791)
200 IKON-CARBURETS. [BOLL. 14.

such magnets possess exceptional retentiveness both as regards effects 

of (atmospheric) temperature and time and of percussion.

The following rules for the practical treatment of magnets, where 

great reteutiveness is the principal desideratum, we believe to be justified in submitting:

1. Eods tempered glass-hard are not to be used as essential parts of 

magnetic instrument's.

2. Having tempered a given steel rod in such a way as insures uniformity of glass-hardness throughout its length, expose it for a long 

time (say 20-30 hours; in case of massive magnets even longer intervals of exposure are preferable) to the annealing effect of steam (100°). 

The operation may be interrupted as often as desirable. The magnet 

will then exhibit the maximum of permanent hardness for 100°.

3. Magnetize the rod whether originally a magnet or not is quite 

immaterial to saturation, and then expose it again for about 5 hours 

(in case of massive magnets even larger intervals of exposure are preferable) to the annealing effect of steam (100°). The operation may be 

interrupted as often as desirable. The magnet will then exhibit both 

the maximum of permanent magnetization as well as the maximum of 

permanent hardness corresponding to 100°. Its degree of magnetic 

retentiveness against effects of temperature (<100°), time, and percussion is probably the highest conveniently attainable.

Chapter VII. Given any iron-carburet, pure or impure.

Suppose carburation to vary continuously from 0 per cent, to 6 per 

cent, by weight of the whole; in any definite manner, and in such a way 

that increment in total carbon is compensated by decrement in total 

iron. Let there be no further change in the ingredients of the carburet. 

In this way we generate a special series of iron-carbides of which the 

given carburet is a particular member.

Such a series of iron-carburets exhibits the following characteristics:

If cooled from a temperature in red heat as rapidly as possible, thermoelectric hardness varies continuously with carburation, at a gradually 

retarded rate, and in such a way that the locus ascends rapidly during 

the earlier stages of progress, very slowly during the later stages. As a 

whole, therefore, the curve shows pronounced concavity downward.

If cooled from the same temperature in red heat with all desirable 

slowness, thermo-electric hardness varies continuously with carburation, 

at a gradually accelerated rate, and in such a way that the locus ascends 

slowly during the earlier stages of progress, very rapidly during the 

later. As a whole, therefore, the curve shows pronounced convexity 

downward.

The difference between the Values of thermo-electric hardness for the 

same carburation passes through a maximum in the region of steel.

The difference between the logarithms of the respective values of 

thermo-electric hardness for the same carburation passes through a pro-

(792)
BAKUS AND STKOUHAT,.] SUMMARY. 201

nounced maximum, denning a carbide, the mechanical properties of 

which are those of a type steel, and may be fully given thus:

Let each member of the whole series of iron-carburets be subjected 

successively to the following operations:

I. A process of very slow cooling from a given temperature in red heat.

II. A process of most rapid cooling possible from the same temperature.

If now the carburets be examined with reference to the hardness produced in the two instances, there will be found among them a certain 

unique member, whose properties are such that while process I has more 

nearly identified it with pure soft iron, process II will have moved it 

further away from this initial carburet than is simultaneously the case 

with any other iron-carbon product; a unique member, in other words, 

which is capable of occurring in the greatest number of states of hardness relative to the soft state, possible. To the said product the term 

" steel" is to be applied.

Similar deductions may/be made from the critical values of specific 

resistance of iron-carburets.

The variation of a function like the one in hand in the neighborhood 

of a maximum is small. Hence a group of iron-carburets disposed on 

either side of the said maximum will possess properties sufficiently alike 

to be practically or commercially identical with the accurately defined 

type.

The general statement of the problem of which a special solution is 

contained in Chapter II is this:

The extreme values of thermo-electric hardness, i. e., the values cor- 

. responding to sudden cooling and thorough annealing, respectively, describe any given member of any given series of iron-carburets with reference to its chemical properties. In other words, the said extreme values 

fix its position in a diagram of classification peculiar to iron-carburets. 

The intermediate values of thermo-electric hardness, i. e., the values lying between the extremes and obtainable by annealing of the previously 

chilled carburet, describe the same product with reference to its mechanical properties. In other words, the said intermediate values determine its position in a scale of hardness peculiar to the particular ironcarburet in hand.

Given the same iron-carburet pure or impure, as before. To this belong another series of carburets, so generated that while chemical composition remains unchanged, the mode of occurrence of carbon passes 

from an initial extreme phase to a final extreme phase. In the simple 

case, where carbon is present in the combined and uncombined modifications only, com me =0 may be regarded as the initial phase,

 m t i ^ = 1) as tue nnal phase of occurrence. The character of the

variation of thermo-electric hardness with the generating variable con.

(793)
202 IRON-CARBURETS. [BULL. 14.

veniently termed qualitative carburation cannot as yet be enunciated. 

The totality, or whole class of iron carburets of which the given sample 

is a particular.member, finally, may be expressed by a diagram in three 

dimensions, in which thermo-electric hardness appears as ordinate, 

quantitative carburation (total carbon in per cents.) as one independent 

variable, #, qualitative carburation as the other independent variable, y. 

In the general equation of such a surface, impurities (S. P. Si. Mn. etc.) 

including any further modification of carbon, are indicated by arbitrary 

constants (parameters). Any variation of each or all of these is equivalent to a passage from one definite classification-surface to another.

In constructing the diagram use was made of a class of easily measurable physical properties, thermo-electric hardness and specific resistance, ^which in the case of iron-carburets, from their simplicity and 

pronounced character, seem above all others to be adapted for purposes 

of discrimination and classification. In addition to these, however, 

both the density and magnetic quality (magnetic moment per unit of 

mass of permanently saturated linear rods) of iron-carburets are similarly, though less conveniently, available. On the basis of the above 

magnetic researches it may be safely affirmed that the given plan of discussion, if applied in turn to these functions, must lead to a classification-diagram differinig in no essential respect from the above.

(794)
APPENDIX.

ON .THE RELATION BETWEEN THE THERMO-ELECTRIC PROPERTIES, 

THE SPECIFIC RESISTANCE, AND THE HARDNESS OF STEEL, (1879).ITS

1. INTRODUCTORY REMARKS.

The experiments which gave rise to the following paper were commenced with the view of further studying the relation between the 

maximum of permanent magnetism, hardness, and form of steel, a subject proposed for inaugural work by Professor Kohlrausch.

Although this question has elicited considerable experimentation ever 

since Coulomb's 176 time, it was not until comparatively recently that harmonious results were arrived at, chiefly through the labors of Ruths,177 

Rowland, 178 Gaugain, 179 Fromine,180 Treve and Durassier,181 and Gray.182 

All these observers, however, classified steel, with reference to its hardness, either simply into hard and soft, or accepted the colors of the oxide 

film on the tempered bar as a criterion of distinction sufficient for their 

purposes. It seemed, therefore, that the most probable method of further 

elucidating the magnetic subject referred to would consist in attempting 

to find some method by which the hardness of steel can be more distinctly and more rationally expressed. My endeavor was, in other 

words, to give the very vague notion hardness, as applied to steel, a 

quantitative signification. So long, however, as the ultimate nature of 

hardness does not admit of accurate definition, it is sufficient for the 

accomplishment of this end to examine some of the other properties of 

steel, which likewise vary with its hardness, and by considering the 

magnetic moment, cceteris paribus, as dependent on the former, to eliminate, as it were, the notion of hardness between them. My attempt is, 

in short, to find an expression of the more complicated functions of

178This is here printed for its bearing upon the discussion of steel, in the form of 

its original publication in the Phil. Mag. (5), VIII, pp. 341-368, 1879.

178Coulomb: Biot. Phys. Ill, p. 108, &c.; Hansteen: Pogg. Ann., Ill, p. 236, 1825; 

Miiller: Pogg. Ann., LXXXV, p. 157, 1852; Plilcker: Pogg. Ann., XCIV, p. 28,1855; 

Wiedemann: Pogg. Ann., CVI, p. 169,1859; Lamont: Handbuch. d. Magnet., pp.223, 

249-253.

""Ruths: Inaugural Dissertation, p. 34. Darmstadt, 1874.

178 Rowland: Phil. Mag. (4), L, p. 361, 1875.

179 Gaugain: Comptes rend., LXXXII, p. 145, 1876.

18°Fromme: Gott. Na<j|r., No. 7, 1876, p. 157 et seq.

i8i Treve and Durassier: Ann. de Chim. et de Phys. (5), V, p. 266, 1875.

" Gray: Phil. Mag. (5), VI, pp. 321-3,1878. . .

(7«5) 203
204 IRON-CARBURETS. [BULL. 14.

hardness, cceteris paribus, in terms of the more simple. Of the latter, 

the thermo-electric properties and the specific resistance of steel, both 

admitting of accurate and easy determination, appear most suitable.

But the experiments on hardness and the electrical properties alluded 

to, although only introductory in their character, gave rise to a number 

of new results. I determined, therefore, to publish them separately. 

To obtain as complete a picture as possible of these phenomena I have 

made free use of all the information on the subject within my reach. 

In each case the author borrowed from is cited.

2. APPARATUS FOR HARDENING THIN STEEL WIRE.

For reasons which become apparent below183 the principal experiments 

of the following paper are confined to thin rods cut from the same coil."* 

The rather difficult task of hardening these homogeneously throughout 

their length, without giving rise to a change in their chemical composition (either from oxidation or carburation), I believe to have accomplished by the aid of the following apparatus:

A glass tube 200 to 300 millimeters long, 8 millimeters wide, was provided at a distance of about 80 millimeters from one end, with two 

opposite apertures aa, Fig. 26. each about 3 millimeters in diameter. 

This part was then surrounded with a cork, A, perforated perpendicularly to the axis of the tube ia 

a manner to correspond with the holes aa. This 

arrangement is fastened vertically in a suitable iron 

stand (not shown in the figure). The wire to be 

hardened is introduced into the tube and fastened 

below to a brass rod, M, fitting tightly in the perforation baabj and above to the spring d.K. For 

the purpose of fastening the lower end it was found 

sufficient, after having previously wound it around 

the rod bh so as to form a. coil which could easily 

be made to slide off, to push the rod through baab 

and the coil, the latter having been introduced into 

the tube from the top. The spring dK, round the 

lower half of which the other end of the wire was 

wound, the upper half being provided with a clampscrew gg, was fastened to a second arm of the 

stand (also omitted in the figure). By properly 

FIG. 26. Apparatus for hard- adjusting the rod bh and the arms of the stand the 

emng.. wirQ could be brought into coincidence with the 

axis of the tube and stretched as far as was neces^ry. 

183 Difficulties due to structure, vide § 7, d.
BARUS AND STROUHAL.] APPENDIX. 205

A powerful galvanic current heated the wire to the degree of redness 

desired. The former entered gg and passed back to the battery through 

bh (as shown in the figure). To prevent the oxidation of the wire during the heating, a current of dry CO2-gas,184 was passed through the 

tube, entering by means of the hose C attached to the lower end.

After the wire had attained a steady uniform glow the hose C was 

closed by the fingers, its connection with the carbonic-acid apparatus 

disadjusted, the open end being connected with a neighboring hydrant 

instead; hereupon the fauceot of the latter was quickly opened, the galvanic current being at the same time interrupted; the water dashing 

up the tube (as an unbroken column, however) with great velocity, imparts to the wire the hardness desired. Before each experiment the 

parts of the apparatus were well dried in a current of air.

The apparatus described presents the following advantages:

(1) By employing currents of different intensity, thus heating the 

wire to different degrees of redness, we are able to obtain corresponding degrees of hardness, which, though scarcely distinguishable mechanically (all appearing equally hard and brittle), have very different 

effects on the magnetic and electrical properties of steel. 185

(2) From the fact that the wire is kept in a state of continual tension 

by the spring dK, and from the particular method of chilling, the wires 

remain straight after being hardened.

(3) The very slight oxidation noticeable on the hard wires is probably due to the contact of water and steel in the act of hardening.

Disadvantages, however, arise from the fact that the use of the apparatus is confined to thin bars, and that the wires obtained may be in 

a state of circular magnetization. This would partly prevent their employment in (certain) subsequent magnetic experiments. The difficulty 

may however be avoided by opening the galvanic current a little before 

opening the faucet.

3. METHODS OF MEASURING THE HARDNESS *OF STEEL ELECTRICALLY.

(a) Thermoelectric position and hardness of steel. In this place it will 

be expedient to leave the special consideration of steel for the moment,

184 Having accidentally employed moist carbonic-acid gas, a small flame was observed 

at the top of the tube. .This is probably due to the combustion of H3 and CO, the 

former being generated by the decomposition of aqueous vapor by the hot steel, the 

latter by the action of the nascent H produced on the C02.

185 See IX. The coercive force of steel being a minimum at a point in incipient redness, it is possible that this apparatus might be used in obtaining intense circularly 

or longitudinally magnetic "wires. In the first case, the wires should be cooled without breaking the current; in the second, the wires surrounded by a'.tube through 

which, during the act of hardening, a powerful galvanic current flows. (See Holtz, 

Wied. Ann., VII, p. 71,1879.)

(797)
206 IRON-CARBURETS. [nuji.14.

giving attention to the electromotive force of a thermo-element composed of any two different metals A' and A".

Kohlrausch 188 has shown that the phenomena included under the head 

of thermo-electricity can be explained on the hypothesis that the heat 

current is always accompanied by an electric current, whose intensity 

is proportional to the number of caloric units passing tie same section. 

He thus arrives at an expression for the electromotive force between 

any two metals (A' and A"), which, if for simplicity we suppose the cold 

end to be kept at zero,187 has the following form :

where Er is the electromotive force corresponding to the difference of 

temperature, r, of the ends; (3' 3"), a constant, specific for the combination. 

This expression of Kohlrausch is very convenient, inasmuch as it 

allows us to separate the actual electromotive force into two terms, of 

which the first,

is dependent only on the metal A' and r, the second, 3" r [l-f-/(r)j, only 

on A" and r.

Now, we know that the thermo-electric position of a metal is dependent not only on its chemical nature, but also on its mechanical condition (hardness). Let us therefore put

where 307 and 30" are to represent the (absolute) constants dependent 

on the chemical nature of A' and A", respectively, 8' and 6", however, 

varying with the hardness of the metals. Thus the above equation 

becomes :

But suppose that A' and A" are not different metals, but represent 

two rods to which different degrees of hardness have been imparted, 

which were originally, however, cut from the same wire. In this case 

[3'- 30"1=0, whence

Er=[6'-6"} r

dependent only on r and the difference of hardness of the rods.

It will be shown below that the electromotive force of an element of 

soft and hard steel varies continuously with the difference of temperature T and with the difference of hardness of the rods. We will therefore put 6", the constant belonging to the soft bar (i.e., one which has 

been heated above redness and allowed to cool slowly in a badly conducting medium), equal to zero, as it is in this that the molecules will

»* Kohlrausch: Pogg. Ann., CLVI, p. 601, 1875.

187 The thermo-electromotive force being, according to Tait, Avenarius, Hankel, and 

others, a function of the temperature of the two ends.

(798)
BABU8 AND STROUHAT,.] APPENDIX. 207

most probably have assumed normal positions. If, furthermore, we 

replace Er 61 r [l+/(r)] by jE7T =o.r-f&T2, a sufficient approximation for

fl TP ' r/t 7f ~~\ ' practice, we derive -jrl=a+2br and -p " =a, for r=0. 

ar \_ dr J0

This expression, L e., the limiting value of the electromotive force of 

a thermo-element composed of a soft rod and one of any degree of hardness to the corresponding difference of temperature188 when the latter o 

converges towards zero, will, in the sequel, be taken as the measure of 

hardness of the harder bar. I shall apply the term thermo electric 

hardness abbreviated (T.E.H.) to it, throughout the following paper.

The relation between the thermo-electric properties and the hardness 

of steel, notwithstanding its comparative importance, has never to my 

knowledge been made the subject of detailed and exclusive study. All 

the experiments thus far. published (the principal being those, of Magnus,189 Sir William Thomson,190 and E. Becquerel191 ), are of a qualitative 

nature, the results being derived from the direction of the current observed on bringing together, in one way or another, wires of different 

hardness.

The experiments of Magnus, being limited to hard-drawn wires, do 

not properly fall within the scope of the present paper. The same is 

true of a number of the experiments in the excellent paper of Sir William Thomson. With regard to the effects of annealing Professor 

Thomson- observes: "In cases of round steel wire, of steel wire flattened 

through its whole length, by hammering, and of steel watch-spring, the 

thermo-electric effect of annealing portions after the whole had been 

.. suddenly cooled, was a current from unannealed to annealed through 

hot." This result comprehends all that has thus far been done.

(6) Specific resistance and hardness of steel. With reference to the 

specific resistance and the hardness of steel, I shall proceed in a manner analogous to the preceding. Denoting the observed specific resistance of a bar by $, that part of £ which is due only to the chemical 

nature of the rod by $0, that due to hardness by A S0, 1 have

Now, as it follows from results given below that the specific resist^ 

ance of steel increases continuously with its hardness, it will be convenient to put AS(> for the soft bar equal to zero. The value of J$0 for 

a bar of any degree of hardness, thus numerically determined, will in 

the following be accepted as a second measure of that property. The 

work thus far published on the relation between specific resistance and

188 The colder end being supposed at 0°. 

189 Magnus: Pogg. Ann. LXXXIII, p. 486, 1851. 

«» Thomson: Phil. Trans., Ill, pp. 709-727, 1856. 

191 Becquerel: Ann. de Chim. et de Phys., (4), VIII, p. 402, 1866.

(799)
208 IRON-CAEBURETS. LBULL. 14.

hardness of steel is due principally to Mousson.192 Of late, results have 

been announced by Chwolson.193 The data of both observers agree only 

qualitatively with mine, and among themselves.

4. DETERMINATION OF THERMO-ELECTRIC HARDNESS. APPARATUS.

(a) Method of measurement. In the determination of thermo-electric 

force the procedure known as Ohm's method was first employed. Afterwards it was found expedient to. measure these forces (as Kohlrausch 

and Ammann194 had done in similar experiments before) by a zero method, 

the object being to avoid the species of polarization due to Peltier's 

phenomenon. My method can easily be deduced from that proposed 

by Bosscha, the latter, in the case where small electromotive forces are 

to be measured, admitting of simplification. In the diagram, Fig. 27, 

E denotes the compensating element (1 Daniell's element = 11.7 Weber x Siemens' units), e the thermocouple whose electromotive force is to be determined, 

both acting as shown in the figure, C a Weber's commutator (employed for reasons given below), G the 

galvanoscope. Let the resistance of the branch db 

' 27a73°ustion °f be represented by a?, that of the branch aEb by W+ fc, 

where W represents the large resistance of a rheostat 

interposed, k that of the remainder of the branch (about equal to 1 

Siemens' unit) including E. When the current in 0 is zero we have,

P

But as -= is small, and therefore of necessity also x (maximum value jit * '

=10 S. U.), in comparison with W+lt+x (20,000 Siemens' units), I may 

with sufficient approximation, put

e- e ~wE xx

the experimental accuracy attainable allowing me to neglect (ft -f x) in 

 comparison with W. In the experiments the branch ab was a small 

Siemens' rheostat.

The precise moment at which the current in the galvanoscope is zero 

oan be best determined by observing whether the needle on closing and 

opening the circuit remains at rest. This, however, is only possible 

when the opposed currents, from e and E which pass through the galvanoscope are closed simultaneously. To accomplish this the little

192 Mousson: N. Deuksch. d. Schw. Gesellsch. (8), XIV, pp. 1-90, 1855.

193 Chwolson : Mel. Phys. de St. Pe"tersbourg, X, p. 379, 1877. See also Carl's Report., 

XIV, p. 15, 1878.

194 Kohlrauscli and Ammann: Pogg. Ann., CXLI, p. 450, 1870.

(800)
BAIIUB AND BTUOUHAL.] APPENDIX. 209

cups at the end of the rods 1 and 2 of the commutator were (juite filled 

with mercury, those of 3 and 4 only partially. By this device, on closing-, <7i and 02 are first brought into contact, and the current ECZ G\ 

7;a WJ7, not passing through the galvanometer, comes into action ; in the 

next moment (03 and C* being joined) the current from e and the partial current from E referred to are closed simultaneously. In this way 

also induction-currents which may possibly be generated in the rheostat, 

are without disturbing effect. The commutator merely serves the purpose of a double key.

As the electromotive forces to be measured were all very small, the 

large resistance W could be left unaltered, so that e const, x. Now, 

the resistance x was so chosen that the intensity of the current from 

e exceeded that of the partial current from E by the minimum possible. 

The thermo-electric force, however, decreasing with the temperature, 

T t = r of the ends, a moment soon arrives at which the intensities of 

the two currents are equal, and the deflection of the needle = 0, in consequence. At this point the thermometers are read off.

(b) Description of thermo-element. Instead of measuring the electromotive force Of soft and hard steel directly, it was found expedient to 

compare all the rods with one and the same piece of copper wire. By 

this means the apparatus could be considerably simplified and many 

practical difficulties avoided. The construction of the copper-steel 

couple is given in vertical section in Fig. 28.

To raise the ends of the rod to different temperatures two doublytubulated receivers, each about 10 centimeters in diameter, were used. These, held 

in position by movable supports of poorlyconducting material, and so placed that 

the tubulures A and B were horizontal, the 

other two vertical, were connected by a 

glass rod cd fitting water-tight in the perforated corks adapted to the horizontal Fic" 28-~0riginainef£tm °f therm°-elctubulures. This rod served a double purpose. By uniting the receivers as one it prevented breakage of the very 

brittle steel rods, at the same time allowing the receivers to be easily 

adjusted and removed; on the other hand the receivers could by means 

of it be placed at any distance apart, this being necessary, as the rods 

to be examined were of very different lengths. . On one side of the glass rod the copper wires which acted as poles 

of the instrument were inserted once for all; on the other two appropriate holes served for the introduction of the steel rods ss to be tested. 

The ends of the latter were connected with the corresponding ends of 

the copper wires by small flat clamp-screws of brass.

The apparatus being thus ready for experiment the two receivers 

were filled with distilled water at T° and <°, respectively, where t was 

so chosen as to differ but slightly from the temperature of the room. 

Bull. 4 14 (801)
210 IRON-CARBURETS. IBUI.L.M.

The thermometers (introduced through the vertical tubulures). were 

read off with a telescope as follows : The deflection of the needle having become very small, t was determined, after which, when the current 

in Gf = 0, T, whereupon another check-reading of t was made. Before 

each observation the water in the receivers was well stirred.

(c.) Galvanoscope. The galvanoscope used was a very delicate instrument of Sauerwald's, provided with mirror and astatic needle. The 

deflection of the latter was read off with telescope and scale. As the telescope of this instrument stood side by side with the telescope for the 

thermometers, both readings could conveniently be made by the same 

observer.

5. DETERMINATION OF SPECIFIC EESISTANCE.

For determining the specific resistance of steel rods use was made of 

Wheatstone-KirchhofFs bridge. An appropriate commutator allowed 

the observer to exchange the unknown resistances without altering the 

value of those belonging to the bridge proper. Thermo-electric disturbances were avoided as far as possible by closing the current (1 Smee 

with large resistance) only for very short intervals of time. Finally 

they were eliminated completely by replacing the hydro-electromotive 

force by Weber's magneto-inductor. 195 The resistances of all rods were 

determined in terms ,of an arbitrary standard 6 (0.0312 Siemens unit 

at 0°), chosen to correspond in magnitude with the unknown resistances. 

The galvanometer used was the one already mentioned above.

As the resistances to be measured were all very small (0.1 to O.C1 

Siemens unit), great care had to be taken to exclude all disturbing resistances -due to insufficient contact. Soldering could not be resorted to, 

as it was believed that the ends would thereby be annealed. The method 

adopted was as follows: The ends of the rods having,been well cleansed 

were covered to about 1 centimeter with a thin adhesive film of galvanically deposited copper, which was thereupon amalgamated (easily accomplished by plunging the freshly-covered part in mercury). The rod 

thus prepared was then fixed together with a glass rod in two corks, in 

a manner similar to that employed in the case of the thermo-element, 

and the whole, except the amalgamated ends, covered with a thick coat of 

varnish. Suitable wooden cups, provided with horizontal and vertical 

apertures, completed the connection of the rods with the respective parts 

of the bridge by means of mercury.

The efficient length was determined by deducting from the total length 

that of the amalgamated ends. For the measurement of diameter use

195 Weber: Pogg. Aim., CXLII, p. 418,1871. The use of the magneto-inductor in connection with the bridge was suggested by Kohlrausch. This physicist also showed 

that the method is applicable even when the resistances to be determined are in form 

of coils, the extra currents produced being calculable. I found the application of 

great convenience, inasmuch as the observer always has the needle of a delicate galvanometer completely under his control.

(802)
BARUS AND STKOUHAL.J APPENDIX. 211

was made of the microscope. A determination of this dimension from 

known weight, specific gravity, and length was impracticable, inasmuch 

as the use of the pycnometer, which alone would have given sufficiently 

accurate results, would have compelled me to break the rods.

6. EXPEEIMENTAL RESULTS.

A. Thermo-electric hardness of rods suddenly immersed in cold water 

while in different states of red heat. The following (older) results were 

obtained directly by Ohm's method. ET was put = constant r, acondition 

nearly fulfilled by couples of soft and hard steel between zero and 80°, in 

which case T. E. H. and the constant of proportionality are identical. 

The rods were hardened in the apparatus described in §2; diameter = 

0.0678 cm.; the numbers preceded by the point (.) were afterwards 

checked by the. method of compensation. T. E. H. is expressed in 

Weber x Siemens units.

The third column of the following table contains the number of large 

Bunsen cells employed in heating the wire, the fourth the observed degree of redness at the time of sudden cooling.

TABLE I.

No.

1

.2

< 3

) 4

C .5

c

< 7

] .8

( 0

f.10

< H

I 12 

C.13

] 14

( 15

T. E. H.

0. 0000004

0. 000003

0. 000012

0. 000000

0. 000000

0. 000000

0. 000052

0. 000049

0. 000054

0. 000056

0. 000057

0. 000063 

0. 000064

0. 000065

0. 000064

Bunsen 

elements.

4

5

5

6

6

7

7

7

8

8

8 

9

P

9

Remarks.

Soft, cooled slowly from red heat.

Below redness.

1

|

> Ignited dark red.

J

Ignited brick red.

The Bunsen cups were introduced without altering the remaining 

part of the circuit. The length of the wire heated was not in all cases 

the same.

B. Further thermo-electric data. Hard steel. Thefollowingdeterminations were made in the summer of 1878; temperature of the room very 

constant and at about 20°, this, as already observed, being nearly the 

same as <, the temperature of the water in the colder receiver. The 

method of compensation was employed throughout. The determination 

of T was effected b3r aGeissler normal thermometer (graduated in 0°.l), 

that of t by an ordinary instrument (graduated in 0°.2) which had, however, been carefully compared with the former.

In Tables II and III the difference of temperature of the ends of the 

steerrod is given under r, the corresponding electromotive force for the 

elements copper-steel under Er ; a and ft are constants which satisfy

(803)
212 IRON-CARBURETS.

the equation Er = «r fir2 . These were calculated by first computing 

their approximate values out of two distant observations, and then adding to them corrections deduced from five of the most satisfactory observations, by the method of least squares.

If, now, we denote by a and 6 the constants of an element soft-steel and 

hard-steel, corresponding to those «, ft, «', ft1 of the same rods, when coinpared with copper, we shall have, since_$T = ar flr* and E'? = a'- />'r2,

ET -ET'=(a-a)r-(/3-/3>)T*

But J£T J57T '=ET , the electromotive force of the element steel-steel; 

so that, since also ET = ar &r2,

fl^a-a1 l)=/3-p

The constants a and & are given in the last two columns, a may be 

regarded as numerically equal to the T, E. H. above defined, as Er is 

nearly a linear function of r.

TABLE II. Rods 0.0678 centimeters thick.

No.

1

 I

c

"IV^

1

I

,

4V

1

f

BVlJ

I

 [ "viz -!

'

"IX*

T

13.92

25.68

39.78

49.34

62.65

17.90

31.39

47.58

56.53

63.72

20."25

29.20

46.50

59.90

61.35

18.07

21.93

47.76

61.32

63.44

'l5.75

31.84

43.51

45.06

59.42

19.04

34.08

53.64

63.40

68.30

18.42

31.15

45.00

62.10

65.40

ET 

Observed.

0. 001464

2635

3981

4859

6031

0. 001815

3104

4567

5328

5972

0. 001112

1522

2283

2752

 2810

0. 000878

1054

2108

2576

2635

0. 000703

1347

1756

1815

2283

0. 000761

1288

1874

2108

2225

0. 000644

1054

1464

1874

1932

- Er

Calculated.

0. 001457

2636

3985

4862

6030

0. 001807

3100

4572

5349

5956

0. 001095

1526

2268

2761

2810

0. 000881

1056

2105

.2571

2640

0. 000700

1343

1765

1818.

2278

0. 000764

1288

1867

2112

2225

0. 000658

1062

1454

1871

1943

a

1

I 0. 0001071

.1 .

0.0001038

1

J- 0.00005811

)

0. 00005156

]

} 0.00004660

j

J

0. 00003807

0. OOOOH807

0

0. 0000001733

0. 0000001629

0. 0000002006

0. 0000001568

0. 0000001390

0. 0000001529

0. 0000001279

a=T.E.H.

Nil.......

0. 0000031

0. 0000490

0. 0000555

0. 0000005

0. 0000641

0. 0000690

0. 0007&0

b

Nil.

0. 0000000104

 0. OC00000273

0. 0000000165

0. 0000000343

0. 0000000204

0. 0000000454

1 Heated above redness and allowed slowly to cool in wood ash; "soft." 

' 2 Heated galvanically below redness, then suddenly cooled; "soft." 

3 Heated to dark redness, then suddenly cooled; "glass-hard." 

4 Heated to redness, then suddenly cooled; "glass-hard." 

6 Heated galvanically to brick-redness, then suddenly cooled; "glass-hard.'.' 

8 Heated galvanically to brick-redness, then suddenly cooled; "glass-hard." 

7 Heated to yellow-ignition, then suddenly cooled; "glass-hard." 

8 Heated to yellow-ignition, then suddenly cooled; "glass-hard."

* This determination was made at a later date; with reference to its accuracy the remarks tinder 

0 and D apply.

(804)
BAHUS AND 8TROUHAL.J APPENDIX. 213

TABLE III. Rods 2.65 millimeters thick, tempered by Mr. Bartli, mechanician.

2sTo.

'/>.

,

] *c{

I

I

,

I »JBJ

I

«4-

^

32.28

45.55

46. 88

55.54

56. 24

20. 32

31.88

32.90

47.93

49.80

32.40

33.08

50.47

61.00

62.25

10.86

27.20

43.75

58.12

60.37

Er 

Observed.

0. 002928

4040

4157

48GO

4918

0. 001639

2518

2576

3689

3806

0. 001991

2049

3045

3030

3689

0. 000117

351

644

937

995

Er 

Calculated.

0. 002918

4042

4153

4859

4915

0. 001628

2517

2580

3678

3811

0. 002004

2044

3043

3623

3690

0. 000121

351

642

942

993

a

1

}> 0.00009447

1

J

 >

1

\ 0.00008265

J

1

\ 0.0000646

J

J

1

I

\ 0.00000999

J

J

J8

0. 0000001257

0. 0000001229

0. 0000000864

0. 0000001068

a=T. E. H.

0. 00001263

0. 00002445

0. 0000424

0. 00011710

. b

0. 0000000476

0. 0000000504

0. 0000000869

0. 0000000605

'Soft; gently ignited, slowly cooled.

2 Tempered blue.

* This rod (as also those of the following section G) is electronegative with, reference to copper.

3 Tempered dark yellow.

4 Glass-bard.

B'. Specific resistance of the same material. The following Tables IV 

and V contain the specific resistances of the rods already cited in Tables 

II and III. The data are given in terms of mercury. The column S 

contains the total specific resistances, 4S0 the corresponding excess of

the latter over that of the normal rod I. Of the ratio -rf- mention

JL. Hi. JLL.

will be made hereafter.

Let the resistances of the two parts of the first branch of the bridge, 

on each side of the sliding contact, be denoted by a and &; let the resistances of the corresponding parts (thick copper wire) of the second 

branch of the bridge be denoted by K1 and K". Into the latter the 

unknown resistances W and R are to be inserted, respectively. Finally, 

let 6 be the standard of comparison above referred to, in terms of which 

W and E are to be measured. When the current in the galvanometer 

is zero, we shall have for a particular position of the commutator:

(1) W and E alone a_W+K' 

1)-R+K"

(2) W and R with 6 on the right 

a'_ W+K1 

V~R+K"+d

(3) W and R with d on the left 

a"__ W+K+ S 

l"~ R+K" 

Three similar equations may also be derived from the other position of

(805) 
214 IRON-CARBURETS. [BULL. 14.

the commutator, as only W and R are interchanged. From these six 

equations we deduce:" 

First position 

R K" 1

Second position 

W. K" R

a1 a b7~b

a" a

K1 .E?' and were determined in the same way previous to the experiments, and their values checked from time to time. In comparing the 

resistances I... IX and A . . . D, the following plan was observed:

W:S

R:8

T

11

IV

n

TV

V

vm

VII

vrn

IX

i

TT

1

I And in the same way

j "with A to D.

J

Each of the data is therefore derived as a mean of four determinations. Possible heterogeneity of the wire a+b thus becomes less 

effective.

As an example, I will add results obtained for the rod C (resist. = 

0.0051 Siemens units):

1st position..... 

2d position ......

W:S = 

W:i=

Mean..

Compared "with A.-

0.1648 

0. 1630

0. 1639

Compared with 

Ji.

0. 1654 

0. 1632

0. 1643

Compared with 

D,

0. 1C49 

0. 1639

0. 1644

For the rod I (resistance=0.0542 Siemens units) on different occasions, 

1.735 and 1.741 were found for W: d.

As will be seen, the principal stress was put on relative values of the 

resistances. To facilitate orientation, however, the results were approximately reduced to Siemens units by determining the standard S 

in that denomination.

Assuming the coefficient for temperature for steel to be the same as 

that for copper, the results obtained will be good for 00 (7 directly, d 

having been previously reduced. Although this is only approximately 

true, the influence of this difficulty on the relative values of the resistances will be but slight, as the temperature of the room remained 

nearly constant.

(a06)
UAUU8 AND STliOUHAL.] APPENDIX. 

TABLE IV.

215

No.

I.

II. *IVi

V.

VI.

VII.

VIII.

. *IX.

Resistance.

0. 05417

0. 04305

0.11130

0. 110GO

0. 07840

0. 08740

0. 15330

0. 09417

S

0. 1361

0. 1400

0. 2337

0. 2483

0. 2592

0. 2648

0. 2779

0. 2810

AiSo

Nil.

0. 0039

0. 0976

0. 1122

0. 1231

0. 1287

0.1418

0. 1449

A So

T.ti.H.

1260

1990

2020

2030

2010

2050

2070

'The resistances marked with an asterisk were determined by using the'magneto-inductor as a current generator. In the others a Smee element was employed.

TABLE V.

No.

D

0

B

A

0. 00209

0. 00512

0. 00595

0. 00908

rt

0. 1654

0. 2065

0. 2271

0. 3804

0. 0293

0. 0704

0. 0910

0.244S

A So

T. E. H.

2320

2860

2150

2090

The experiments now following, under the heads G and 7), have more 

a descriptive character than one of precise measurement; the results 

are therefore given with one decimal less. For the determination of 

T.E.H. the rods coming under these heads were compared indirectly 

with rod VIII (Table II) for the'T. E. H., of which the number 0.000069 

(as above found) was assumed.

C. T. E. H., and AS0 for glass-hard rods, diameter=2.3Q millimeters. 

These were hardened by the aid of the blast lamp. The flame of the 

latter was for this purpose directed horizontally and placed directly 

over a trough containing cold water. In this way the red-hot rod could 

be transferred with great rapidity out of the flame into the water.

TABLE VI.

No.

 [!!! *rmi

*[IV] *m

"[V]' *[ini'

T W 77

0. 000138 

131

130

180 

116 

136 

133

0.0121

0. 0129 

107 

123

o

0.421

0.442 

0.336 

0.430

0.285

0.306 

0.230 

0.294

A So

T. E. H.

2100

2300 

2000 

2200

Ignited yellow and chilled.

Do.

Do. 

Icrnited red and chilled. 

? [III] u. [V] Twice re-igniD. T. E. H. and /l#0, of rods 0.678 millimeter in diameter, hardened196 

in the apparatus §2, afterwards annealed by immersion in hot linseed oil.

wo The T. E. H. of these rods iu the glass-hard condition varied from GO: 10(i to GO: lO^.

(807)
216 IRON-CARBURETS. 

TABLE VII.

No.

*1

*2

*3

*4

*5

*6

*7

*8 

*9

no*11

*12

Soft

iron.

m rr TT J. , Ju. Jtz.

0.000010

13

11

14

12

18 

24

33 

31

36

57 

58

-0.000004

Resistance.

0. 0540

0616

0537

0691

0592

0763 

0659

0746 

0807

0731

0. 1088 

0. 1155

0. 0420

ct

a

0.157

158

159

163

166

177 

185

20.i 

206

209

250 

261

0.133

A So

0.021

022

023

i27

030

041 

049

069 

070

073

114 

125

-0. 003

A So

I. E. H.

2100

1700

2100

1900

2500

2300 

2000

2)00 

2200

21)00

2000 

2200

750

r

Jtt6DlfirK3 1

,

1 Glass-hard and gradually.

}> heated to 300° in linseed

oil. 1

J

> Similarly annealed at 280°.

> Similarly annealed at 240°.

Similarly annealed at 200°.

? Similarly annealed at 150°.

Heated to redness in Bunsen's blast-lamp and

slowly cooled.

1 Eods 1 to 5 remained in the bath during the whole process; the others were immersed but for 2m to 

3m. The temperature at which the rods 6 and 7 were annealed could not be determined with certainty, 

a microscopic air-bubble in the neck of the mercury reservoir having given rise to rupture of the thread.

E. Corroborative measurements. The resistances thus far determined 

being very small, it was feared that in spite of the continuity.apparent 

in their variation, errors from insufficient contact might have conspired 

in producing illusory results. For these reasons check-experiments 

with longer wires were made, the resistance of some of which (I to V) 

is sufficiently great to admit of direct comparison with the Siemens 

mercury unit (e"talon). To insure a more homogeneous hardening, these 

wires were spirally wrapped around a round stick of wood, and the 

length and diameter of the coils resulting so determined that the whole 

during the process of heating could be brought within the mantle of the 

blast-flame. In other respects the method given under C was pursued.

TABLE VIII.

No.

I

II

III

IV 

V 'VI

*vn ^vni

Resistance.

0.643

379

245

121 

105 

OJ69

0155

0169

Length.

0. 880m

917

928

932 

556 

733

732

740

Diameter.

0.67

96

1.19

1.83 

1.62 

2.15

2.15

2.15

S

0.260

296

293

342 

391 

354

325

352

1

A So

0.124

160

157

206 

255 

218

J89

216

Remarks.

Ignited yellow ; then suddenly cooled.

Do.

Do.

Ignited red ; then suddenly cooled. 

Ignited light yellow ; then suddenly cooled. 

Ignited red-yellow ; then suddenly cooled.

Ignited red-yellow ; but ends darker.

Ignited red-yellow ; then suddenly cooled.

Spirals II and IY were afterwards softened by heating to redness in a 

Bunsen burner. Their specific resistance in this condition was found

to be

 II. #o=0.154 *IV. flo=

Finally, in order to compare the results obtained with induction currents with those in which a Smee element was employed, certain of the 

experiments were repeated. The agreement was entirely satisfactory.

(808)
BARU8 AND 6TROUIIAL.1 APPENDIX. 217

7. HARDNESS AND THERMO-ELECTRIC PROPERTIES OF STEEL: DEDUCTIONS AND SUPPLEMENTARY EXPERIMENTS.

(a) Thermo-electric and mechanical hardness. From the data contained in Tables II, III, aud VII, we derive that the thermo-electric 

position of steel progresses continuously with its degree of hardness, 

or, in other words, thermo-electric and mechanical hardness are direct 

functions one of another.

This statement involves the assumption that the rod cannot pass 

from the glass-hard (maximum) to the soft state (minimum) without 

passing through every intermediate stage; or that by proper methods 

of annealing, every state between the maximum and minimum can be 

produced, This, I dare say, will generally be admitted.

As of further interest I may add: (1) that rods Cut from the Same 

wire and glass-hardened in the same way possess also the same thermoelectric hardness (Table VI); (2) this is the case even when the rods 

are carefully rehardened (rods [HI]', [V]', Table VI); (3) that if we 

start from like maxima, the thermo-current always passes from less to 

more annealed, through warm. (The direction of the current was independently observed.)

(b) Variation of T. E. H. with differences of material and of thickness. 

From an examination of the data obtained for different material, we 

infer that the T. E. H. of soft and similarly annealed rods approximates 

to the same value; 197 that the value of this constant for glass-bard rods 

is remarkably different. The rods in Table VI, for instance, possess a 

T. E. H. amounting nearly to 140:106 ; whereas in the rods in Table II 

the maximum 198 value found does not exceed?70:106 . This may be due 

to a difference in thickness, or, more probably, to a difference in the coinposition of the rods examined.

These phenomena were further studied through the following experiments :

1. Commercial rods of different diameters were glass-hardened and 

examined with reference to the current produced when one end of a 

couple was cooled with a wedge-shaped piece of ice. In general a 

maximum of T. E. H. was observed in rods whose diameters lay between 

1 and 2 millimeters. These experiments, however, are unsatisfactory, 

inasmuch as the composition of the rods enters as an element of dis197 In order to compare the degree of hardness corresponding to a particular oxide 

tint with that corresponding to a given temperature of the oil bath, use was made of 

the tables found in Frick's Physikal. Techuik, 3 ed., p. 377; also Wagner, Chetn. 

Tech., 8 ed., p. 29. On the authority of these works 230° corresponds to yellow, 290° 

to blue, annealed. We shonld therefore expect rods 6, 7, and 8, 9 (Table VII) to 

agree with the rods C and B (Table III) respectively. This is sufficiently the case.

lil8These rods (Table II), even when heated to the utmost white and suddenly cooled, 

remained strongly electro-positive towards copper. T. E. H., even in this extreme 

case, was much less than 107=106.

(809)
218 IRON-CAKBURETS. [BULL. 14.

turbauce which cannot be allowed for. For this reason experiments 

were made on thick bars, the parts of which had been filed to different 

diameters.

2. The halves of each of two pieces cut from the same rod, 5 millimeters in diameter, were reduced199 by filing to thicknesses of 3 millimeters 

and 1 millimeter, respectively, and glass-hardened. During the process of heating care was taken to raise all parts of the bars to the same 

degree of redness. On connecting the ends with the galvanometer and 

applying the ice wedge at the middle (where the diameter enlarged), 

very decided currents were observed, passing from thin to thick through 

warm. Hereupon two cones were filed of the same material (5 millimeters thick at base and 50 millimeters long). Point and base of the 

cones (previously glass-hardened) being connected with the galvanoscope, the ice wedge applied at any point produced in each case currents 

from apex to base through warm, thus harmonizing with the previous 

experiments. Near the points only the results became uncertain. On 

bringing together the cones with the rod [IV] (Table VI) the points 

were found to be thermo-electrically harder, the base softer than the 

rod. On the other hand, the point of a fine needle prepared from the 

same material gave contrary indications. The point, therefore, was 

apparently softer than rod IV.

3. Finally two very gradually tapering cones were prepared from 

another steel rod, 2.8 millimeters in diameter. Connection with the 

galvanometer being made, the application of the ice wedge to parts 

near the base generated a current from thin to thick through warm ; to 

parts near the apex, a current in the opposite direction. Finally, between these a position was found at which the application of the ice 

wedge produced no current at all. This occurred at parts about .5 

millimeters in diameter. The other cone gave like results.

4. When the bases of two similar cones of the same materials are 

connected with the galvanometer and their apices brought in contact, 

upon warming the latter, a current in one direction or another will be 

produced; this from the fact that the points are rarely equally hard. 

Experiment shows that by consecutively warming parts which lie symmetrically to the right and left of the apices in contact, currents in opposite directions are the effect. Herefrom it follows that the currents 

originate each in a single cone.200

5. In endeavoring to generalize from these experiments, attention 

must be paid to the following points: a, the maximum value of T. E. H. 

attainable is dependent on the quantity of carbon contained in the 

steel. The thermo-electric difference between rods of soft and sud199 It is TO be observed that the thinner parts of these pieces sooner arrive at red heat 

and remain longer in this condition than the thicker parts. This applies equally to 

the cones.

200 Tlie experiments with two separate cones were equally successful when the conical forms were only part of the same continuous piece.

(810)
1JAUUS AX1> STUOUHAL.] APPENDIX. 219

deuly cooled wrought iron can, for instance, be neglected in comparison 

with the corresponding difference between hard and soft steel, fc, T. B. H. 

is influenced by the temperature of the rod when suddenly chilled (VII c), 

as well as by the time of heating, the latter affecting the composition. 

c, By the form of the piece of steel and the method of sudden cooling, 

the internal structure of the mass being thereby modified (VII d}. 

d, Finally, we might add that, in the time elapsing between-the removal 

of the rod out of the fire and the subsequent immersion, the loss of 

heat by radiation will be relatively greater in the case of thin than in 

the case of thick rods.201 With these facts in mind we may conclude 

that the maximum values of T. E. H. attainable by glasshardening 

rods of the same composition increases as thickness diminishes; that 

as this dimension continues to decrease a diameter is reached at which 

the negative effects of decarburizatiou are equal and finally overcome 

by the positive effects due to diminution of diameter.

(c) Effect of the temperature from which steel is suddenly cooled in hardness. Chemical and mechanical hardness. From the results contained in 

Table I there follows: The hardness of steel does not increase continuously with its temperature at the moment of sudden cooling, but 

at a point in dark red heat the glass-hard state is suddenly attained. 

From this point on, however, the degree of glasshardness (measured electrically) continues to increase with the temperature. This observation 

conduces to the conclusion that the change of state due to glass-hardening is chemical in its nature^ In this opinion, I believe, most chemists at present also concur, it being assumed that the unconibiued 

carbon in soft steel is, by sudden immersion, converted into the chemically combined. In summing up the facts by which the hypothesis is 

furthermore supported, I will mention in the first place the detailed 

analogy202 which exists between the white pig (used in the manufacture 

of Bessemer steel) and glass-hard steel, on the one hand, and ordinary 

(gray) cast-iron and soft steel on the other; the former containing 

carbon only in the combined, the latter also in considerable proportion 

in the uucombined, state. Secondly, hardening by a process of wirepulling, hammering, etc., will, in all probability increase the specific 

gravity of steel; hardening by sudden cooling, as is well known, di201 1 will add hero (1864) that another possible source of error was overlooked in .the 

above. 1 refer to the electro-rnotive«force of superficial layers in case of loose contracts, as investigated by Franz (Pogg. Aim., LXXXV, p.-388, 1852), Jenkin (Rep. 

Br. Assoc., 1861, (2), p. 34), Gaugain (C. R., XXXVI, p. 612-16, 1853, Ann. de Chim. 

et de Phys. (3). LXV, p. 75-102,"1862) and others. But I feel confident that these 

phenomena are not contained in the above: I, because loose contacts were avoided; 

2, the metals were always bright and polished; 3, the results were the same when 

difference in diameter (double cone) occurred in one and the same continuous piece 

of steel; 4, from the variety of experiments made and the uniformity of the results 

obtained.

-l)3 See Wagner: Ch'eni. Tech.. 8 ed., pp. 14,15,29. These analogies refer to mechanical propertieSj method of preparation, color.

(811)
220 IRON-CAEBURETS. [BULL. 14.

minishes it. In the former case the thermo-electric current usually 

passes from soft to hard through warm; 203 in the latter, in the contrary 

direction. In drawn wire the specific resistance is smaller,204 in hard 

tempered greater than that of. the same wire in the soft state.

Considering these facts as a whole, we are perhaps justified in distinguishing between a process of chemical and a process of mechanical 

hardening. This, however, does not prevent us from paying due regard 

to a series of physical phenomena which accompany the former. To 

these the peculiar internal structure of glass-hard bars, the warping 

which frequently attends sudden cooling, etc., are to be referred. We 

conclude, therefore, that the cause chiefly influential in bringing about 

glasshardness in steel is chemical in its nature, and that, in consequence 

of the physical phenomena which invariably accompany it, the degree 

of glasshardness is more or less modified. On the latter ground the 

continual increase of the T. B. H. after the critical temperature above 

referred to has been reached is to be explained.

(d) The observed T. E. H. can, of course, only be assumed as directly 

expressive of its hardness when the rod under experiment is homogeneous throughout. In thick bars, which in the glass-hard state may 

be considered as made up of a series of concentric cylindrical shells, the 

hardness of which decreases rapidly as we pass from the exterior to the 

interior, the circumstances become more complicated.

Furthermore, suppose the ends of a thick glass-hard cylinder to be 

kept at temperatures Tand t (T>t). In this case, since each of the 

infinitely thin cylindrical shells has a particular T. E. H. corresponding 

to its hardness, we are led to infer that thermo-currents, closing themselves in the interior of the cylinder, are the result the direction of 

these in the outer harder parts being from t to T, in the inner from T to 

t. In figure 29 (vertical section) the hypothetical condition of the cylinder in this case is indicated. As will be seen, its 

/^ electrical state corresponds to that of a rod circularly 

magnetized.

For the purpose of studying this question experimentally, a steel cylinder, 30 millimeters in diameter 

and 50 millimeters long, was turned and glass-hardened. 

This was placed vertically directly before the needle of 

a magnetometer (the deflection of which could be read Pig. 29.-Thermo-cur- ~ \ Tjr

rents evolved in a on with telescope and scale) in such a manner that the 

no cy m er. . Of equiiibrium Of the needle was left unaltered.

The relative position of the needle and cylinder, in other words, was such 

that the axis of the former, if prolonged, would intersect the axis of 

the latter if prolonged at its middle point. Upon now cooling the

203 Magnus: Pogg. Ann., LXXXIII, p. 469, 1851; Sir W. Thomson, Phil. Trans.,111, 

p. 722, 1856.

204 Mousson: N. Denkschr. d. Schwz. Gesell., XIV, 8, p. 1-90; Chwolson: Carl's Rep., 

XIV, p. 15.

(812)
BAHUS AND STROUHAL.] APPENDIX. 221

upper end of the cylinder with a piece of ice, or warming by projecting a jet of steam against it, very decided deflections were observed 

toward the right or left, respectively, which increased with the difference 

of temperature T t, and vanished as this difference became nil.

As the cylinder was not magnetic, it is improbable that these phenomena can be referred to a change in the state of magnetic distribution. With reference to the direction of the currents, however, no simple results could be arrived at.

(e). Relative thermo-electric qualities of soft steel and soft iron. In § 7, 

c, we ascribed the very high value of the T. E. H. of a glass-hard steel 

rod to the large proportion of chemically combined carbon contained 

therein. If this be 'true, the thermo-electric difference between soft 

steel and soft iron, in both of which combined carbon is either wholly 

absent or exists only in traces, must be quite small. This inference is 

supported by the data actually found for soft iron. Making allowance 

for the difference of circumstances involved, the result to be derived 

from the experiments of Kohlrausch and Ammann also agrees sufficiently 

herewith.

On the other hand, Joule205 has long since shown that ordinary castiron is thermo-electrically negative towards copper, all the more, therefore, towards soft steel a result which I should be inclined to predict 

from the quantity of combined carbon contained.

The minimum values of T. E. H. (obtained by cooling the red-hot bar 

as slowly as possible) of different kinds of steel206 and of soft iron are 

approximately the same; whereas the maximum values of this constant 

(obtained by cooling the highly heated bar as rapidly as possible) differ 

enormously; this difference being a direct function of the quantity of 

carbon contained.

(/) Thermo-electric effect of magnetization. Sir William Thomson207 has 

shown that in a thermo element, consisting of magnetized and unrnagnetized steel of the same hardness and form, thermo-currents due only 

to magnetic difference are generated. The direction of these currents 

was found to be in one case from unmagnetized to longitudinally magnetized through warm, in another from transversely magnetized to unmagnetized through warm, therefore also from transversely to longitudinally magnetized through warm.

For the purpose of informing myself of the magnitude of the thermoelectric difference thus produced, the following experiment was made: 

A soft rod (I, Table II) was tested for its electro motive force when 

combined with copper (as described above, p. 348), and the locus of the

2°5 Joule: Phil. Mag. (4), XV, pp. 538-'39, 1857.

JW Steel is here used as distinguished from iron only by containing a greater proportion of carbon. No attention has been paid in this paper to the effects of P, S, Si, Mn, 

etc., so often present in both.

207 Thomson: Phil. Trans. Ill, pp. 722-'7, 1856.

(813)
222 IKON-CARBURETS. [BULL. 14.

equation Er=ar /3r2 constructed from fifteen very carefully made 

observations.

Hereupon a large magnetic battery, weighing 40 pounds, was so placed 

that each of the ends of the horseshoe touched a receiver. The distance 

between the poles of the magnet and the corresponding ends of the steel 

rod was thus about 50 millimeters. A second series of fifteen observations was now made. Upon comparing the locus of the latter with that 

that of the former, the two curves coincided so completely that no influence could be discerned.

Herefrom I conclude that the thermo-electric effect due to difference 

of magnetic state may, in comparison with that which can be produced 

by a difference of hardness, be completely neglected.

(g) Relation between T. E. H. and density of steel. A very curious analogy was found in comparing the results at which Fromme208 arrived, in 

studying the specific gravity of differently tempered steel, with the T. 

E. H. of similar rods as found in my experiments. Dr. Fromme, if I 

infer correctly, limited his experiments to rods whose diameter was 

greater than 2 millimeters, and less than 7 millimeters. His results are 

contained in the following table, the volume of the soft bar being put = 

unity.

TABLE IX.

Soft.................

Annealed blue ...... 

Anneaied yellow ....

Volume.

1.000

1.002 

3.005 

1. 010'

Volumeincrease.

0.000

0.002 

0.005 

0.010

T. E. H.

0. 000 OdO

0. 000 024 

0.000 042 

0.000 117

In the fourth column the T. E. H. of rods cited in Table III. (these, 

as I believe, corresponding very closely to those for which the data of 

Fromme apply) is added. If we take into consideration that the results were obtained from different material, the parallelism observable 

is striking. To tbe very large difference between glass-hard and yellow annealed, when compared with the much smaller difference between yellow and blue, blue and soft, as seen in both observations, 1 

would once more call attention. The fact that glass hard rods can be 

considerably annealed at comparatively low tempeartures must be regarded as an adequate indication of their unnatural (strained) condition.

A second result of Fromme, that the specific gravity of thin rods 

suffers greater loss by glass-hardening than that of thick rods, also 

harmonizes with the conclusions drawn in § 7 (b) with reference to the 

T. E. H. of such rods.

wFromme: Getting. Nachr. p. 165, 1876. 

(814)
BAUUS AND STROUHAL.l APPENDIX. 223

8. HARDNESS AND SPECIFIC RESISTANCE OF STEEL: DEDUCTIONS.

From the data for the specific resistance of rods of different hardness 

inferences analogous to the above may be deduced.

(a) The specific resistance of steel increases continuously with, its 

mechanical hardness.

(&) Eods like annealed differ but slightly, glass-hard rods considerably, with respect to their specific resistance.

(c) Relation between the thermo-electric hardness and the specific resistance 

of steel'. On comparing the values found for the ratio J $0 / T. E. H., we 

infer that the specific resistance of steel is approximately a linear function of its thermo-electric hardness. In Fig. 30 these results are graphically represented.

I Avill remark, however, that the assumption of proportionality as 

based on the above figures is to be regarded as a first approximation

!2

A"

7

FIG. 30. Kelation between thermo-electric power and specific resistance.

only, notwithstanding the fact that the discrepancies fall within the 

errors of experiment. A rigid discussion of the latter comes more appropriately within the scope of another paper soon to appear. In this 

place I would only call attention to the following: In the thick bars

(815)
224 IRON-CARBURETS. [BULL. 14.

experimented upon the value of A $0 /T. E. H. is usually too large 5 a 

fact which is easily accounted for, as the unavoidable resistances of 

contact above referred to will in this case have a relatively great effect, 

the resistances of the bars themselves being very small. In the rods 

included in Table VI it was impossible to secure uniform redness of 

ignition throughout; the ends invariably remained darker.. As T. E. H. 

depends principally on the warm end, A $ , however, on the mean hardness of the whole bar, we have thus a second cause for an overlarge 

ratio.

So much I think to have fully established, that T. E. H. and specific 

resistance throughout their variations are very simple functions .one of 

another. T. E. H. and specific resistance must therefore be .looked 

upon as effects of the same cause, as phenomena having some very intimate connection.

(d) Particular attention must here be called to the remarkable result, 

that the specific resistance of steel can by a process of glass-hardening 

be increased to nearly three times its value in soft steel.209 As this datum 

far exceeds that determined by Mousson (about 25 per cent.), it is not 

without some hesitation that 1 make it public. The care bestowed on 

the experiments, however, together with the regularity-observed in tbe 

variation of the results, I believe sufficiently insure their correctness. 

See, moreover, § 6, E.210

(e) As deserving special notice, I will further add that the thermocurrent always passes from the bar with greater to the bar with less 

resistance.211 The few exceptions to this fact in the tables were afterwards found to be referable to errors of experiment by direct observation.

(/.) Like T. E. H., so also the specific resistance of steel approximates 

to the value of this constant for soft iron, Upon the value found for

209 It is to be observed, however, that the difference between the specific resistance 

of steel in the soft and hard states is dependent on the composition, increasing with 

the quality of carbon contained from a very small value in soft iron to the very 

large value above announced for steel.

210 Chwolson reports the increase of resistance due to glass-hardening to be only 0.6 

per cent. This I can only explain by supposing the results of this observer to have 

been obtained with wires suddenly cooled at a temperature below that referred to in 

S7(o).

211 1 would here again refer to the fact that, according to Magnus, Thomson, and 

Mousson, drawn-steel wire and hard-tempered steel are on opposite sides of soft steel, 

both with respect to theirs thermo-electric properties and their specific resistance. 

Thomson furthermore finds transversely magnetized steel electro-negative towards 

soft steel, this again towards longitudinally magnetized steel. Auerbach' (Wiecl. 

Ann., V, p. 316, 1878), analogously, that the specific resistance of hard steel continuously increases as the rod passes from a condition of saturated longitudinal to a condition of saturated circular magnetization. The result above enunciated has therefore probably even a more general signification.

(816)
HABU8 AND BTBOUHAL.] APPENDIX. 225

the ratio A $0//T. E. H., however, not much reliance can be placed, the 

factors involved being too small to admit of accurate determination. 

With cast-iron no experiments were made.

9. REMARKS ON THE ABOVE, CONSIDERED AS AUXILIARY TO THE 

DETERMINATION OF THE RELATION BETWEEN HARDNESS AND MAGNETIC MOMENT.

In this place I will avail myself of the experiments of Ruths on the 

relation between hardness and magnetic moment, these being perhaps 

the most comprehensive. With sufficient approximation for the purpose I will put the T. E. H. of glass-hard rods = 120:106 ; that of the

yellow annealed, = 40 :106 ; of the blue, = 20 :106 ; and with these as 

abscissae and Ruths' values for the corresponding permanent magnetic 

moments ("in millions of absolute units," milligrammes-millimetersseconds) as ordinates, suppose the curves belonging to each of the bars 

to be constructed. These curves are given in figure 31, the attached 

number referring to the ratio between 

the length and the diameter of each 

rod.212

I will omit the interesting deductions which Ruths makes from his 

data, these going beyond our present 

purpose.

From an inspection of the curves 

we derive the following important 

results, viz: that, like the electrical 

properties of steel and its specific 

gravity, so also the maximum of permanent magnetism is largely modified by the different degrees of glasshardness of the bar (i. e., those lying 

above yellow annealed, and scarcely 

distinguishable mechanically). In 

the second place, the results of Ruths, being obtained from comparatively thick rods, are largely influenced by structure. In view of these 

facts, I deem the hope by no means too sanguine that if, to avoid ctfmplicatious from structure, we experiment on thin rods, ttfe maximum 

of permanent magnetism may be empirically expressed in terms of the 

dimensions and T. E. H. only; that, furthermore, from the parallelism 

discovered in the variation of specific gravity and the electrical prop212 The data employed are those obtained by Ruths for rods 120 millimeters long, and 

1.7,2.4, 2.9, 3.8, 4.9, 5.9 millimeters, respectively, in diameter, with very powerful 

magnetizing forces.

(817)

Fig: 31. Diagram of .Ruths' results.
226 IRON-CARBURETS. ' [Buu,.l4.

erties of steel, the T. B. H., the specific resistance, and the magnetic 

moment are in some very intimate way connected with the volume of 

a unit of mass. This would imply a connection of these phenomena 

with the intermolecular spaces of steel.

In conclusion, it gives me great pleasure to acknowledge my indebtedness to Professor Kohlraush for much kind assistance throughout the 

course of the experiments.

PHYSIOM. INSTITUTE, UNIVERSITY OF WURZBURG,

February, 1879.

(818)
IKDEX.

Page. 

Absolute thermo-electric data ............................ ............ .;... 71

Ackermann. (See Jarolimek.)

Addenda.... ............................................................. 6

"After-action," Certain effects of.................. ........................ 124

Alloys, Data for thermo-electric power of.................................. 82,84

Data for specific resistance of.............. T'.....................1.. 84,85

Digest of electrical behavior of...................................... 85,86

Discussion of general electrical properties of........................ 87

Electrical behavior of, explains certain phenomena in steel ......... 88

how prepared (fused, drawn)....................................... 80

Literature of electrical behavior of............................. ..I. 80

of German silver, Temperature-coefficient and resistance of.......... 17

of silver, Temperature-coefficient and resistance of.................. 16,85

Range of electrical variations and density of........................ 87,196

Ammann. (See Kohlrausch.)

Annealed rods influenced by lower temperature............................ 57

influenced by higher temperature........................... . 59

Annealing at 66°, Eesults of............................................... 47

at 100°, Results of.............................................. 43,49

at 185°. Results of.......................'....................... 51

at 330°, Results of.............................................. 53

at red heat, Results of.......................................... 60,94

Character of the phenomenon of ................................ 55

chemically interpreted.......................................... 94

Cotemporaueous magnetic and resistance effects of ...........162,164,199

Digest of mechanical results of.................................. 54

effect of temperature, Character of.............................. 55,195

effect of time of exposure ....................................... 43

General character of the phenomenon of......................... 71

in hot oil-baths, Method of ..................................... 40

in hot oil-baths, Results of...................................... 41,215

Magnetic effect of .............................................. 165,199

Magnetic effect of successive..................................... 161

Mechanical effect of successive.........................."........ 57

Method of, in magnetic work.................................... 123

physically interpreted.......................................... 95

Relation of, to viscous phenomena .............................. . 95

Slow and instantaneous, compared .............................. 59

Anomalies in iron and in steel at red heat............... ........ r ......... 99,197

Electrical, due to structure in hard steel......................... 66-68

Apparatus for hardening steel wire .............. ......... ........ .......... 29,204

Auerbach, Resistance-effect of magnetization found by..................... 104,224

Temperature-coefficient for iron found by........................ . 24

Ausgliihen, Meaning of.................................................... 94

Arenarius, Thermo-electric formula of.......... ..........................35,81,206

(839) 227
228 INDEX.

Page. 

Barlow on magnetism and carburation..... ................................ 112

Banr on disappearance of magnetism at red heat.......................... 99

Becker, G. F., indorsed research............. .............................. 5

Becquerel, Thermo-electric scale of ........................................ 7

Thermo-electric experiments of (strain)......................... 207

Beetz on resistance effect of magnetization ................................ 104,106

.Be"noit on temperature- coefficient of iron and of steel....................15,21,90,99

Biot, Magnetic distribution studied by..................................... 145

Bose, v. (See Matthiessen.)

Bosscha, Zero method of................................................... 208

Bulletin, Contents of supplementary ....................................... 8

Calibration, Galvanic ................................^...................^ 38

Method of...... .............................................. 72

Carbon, combined and uncombined, Electrical effect of..................... 186

Electrically active or neutral...................................... 79,196

Carburation, Effect of...................................................... 13,39

Magnetic effect of............................................. 112,148

Quality of................................................... 190

Caron on cause of hardness in steel........................................ 79

on composition of iron-carburets .................................... 77,79

Cast-iron, Digest of electrical behavior of ................................. 183,184

Electrical behavior of malleable................................. 101,1055

Electrical resistance of.......................................... 182

Peculiarities of electrical behavior of........................'.... 94,196

Properties of gray ............................................... 76,219

Properties of white ..........................:.................. 76,219

Temperature-coefficient and resistance of........'. ................ 22,23

Thermo-electric data for......................................... 179-182

Classification-diagram .................................................... 191

Synthetic methods for constructing.................. 8

Classification-function .................................................190,201,202

referred to magnetism or density..........._..'...... 193,202

Clarke, P. W., aided research ............................................. 5

ClausiuB on resistance and absolute temperature........................... 24

Chemical composition, Effect of, on glass-hardness.......................... 38

Chernoff on sudden cooling of hot steel...................... ...........'39,98,99,197

Chwolson on electrical behavior of iron.................................... 176

on electrical effect of temper..............................70,208,220,224

on minimum resistance of metals ............................... 93.

on resistance-effect'of volume-reduction......................... 91

Coercive force, how understood..........................................95,145,159

Cohn on thermo-electric effect of strains.................................... 106

Cold, Annealing effect of.................................................. 17,170

Magnetic effect of...... .............................................. 170

Cooling, Discussion of slow and rapid ..................................... 174

Nomenclature for slow and rapid ..............;.................. 175

Commutators, Description of .............................................. 35,36

Conductivity. (See Resistance.)

Constants, Electrical, of iron, Table 76 ..................................... 177

of steel, Table 77..................................... 178

of cast-iron, Table 81................................. 184

of iron-carburets, Table 82 ........................... 185

Mechanical (dimensions, mass, density of magnets), Tables 49,51. w 125,129,

152.155,160,164

(820)
INDEX. 229

Page. 

Contact, Electrical........................................................ 37,210

Cotemporaneous magnetic and resistance effects......................... 162,164,199

Coulomb, Magnetic experiments of........................................ 203

Criterion, Empirical, for steel .....^........................................ 177

Critical operations, slow and rapid cooling................................. 174

operations, Nomenclature for ...................................... 175

Camming on phenomenon of sudden expansion in iron...................... 99,197

Cylinder, Thermo-currents evolved in.'..................................... 220

Decarburation, Effect of................................................... 175

.Definition of steel...................................................... 188-192,201

Density and electrical variations in alloys.......................... ........ 87,19f

and diameter of steel rods ......................................... 15(

and dimensions of magnets, Tables 49, 51 .......................... 125,12t

and magnetism.................................................... 139,144

and thermo-electric hardness..............................:....... 19,222

and resistance of steel............................................. 69,92

Classification-function based on ................................... 202

effect of incipient annealing ....................................... 149

of steel..................................................... ....77,125,129

Depretz on measurement of heat-conductivity.............................. 25

Deville on cause of hardness in steel....................................... 89

Diameter, how measured .................................................. 37

Dimensions and hardness, Eolation between ............................ 150,217-219

and magnetizability, Relation between........................ 197,198

Effect of, as regards structure ................................. 14

Magnetic effect of............................................ 113

of magnets. (See Constants.)

Thermo-electric effect of...................................... 217,219

Dimension-ratio, Critical value of.... ............................ .......... 112,144

general effect of.......................................... Ill

hardness, magnetization of steel, Tables 50, 53 ..... 126-128,130-135

. ' hardness, etc., Digest of Tables 54-65.............. 136-138,140-142

with magnetic loss (per cents.) due to annealing .......... 163

Direct and indirect magnetic effect of temperature......................... 165

Drawn hardness, Effect of annealing in case of............................. 93,196

Distribution of magnetism................................................. 145

Dufour, Magnetic experiments of.......................................... 158

Durassier. (See Treve.)

Edelmanu, Bifilar magnetometer of........................................ 167

Eibiswalder Wolfrain-stahl, Magnet made of................................ 172

Electrical conductivity, Measurement of ...... ............................ 36,213

resistance. (See Resistance.)

contact, Degree of excellence of................................. 37

Energy released on annealing.............................................. 59

Errors of measurement, Magnitude of...................................... 68

Factor of galvanometer, how measured .................................... 34

Families of magnetic curves ..........................................14,139,142,162

Faraday and Stoddard, Silver-steel analyzed by............................ 178

Field, Magnetic, described ................................................. 107,118

Forquignon, Decarburation studied by..................................... 175

Malleable cast-iron studied by.............................101,103,186

Views of, regarding iron-carburets............................ 78

Frankenheim on methods of magnetization ................................ 120

(821)
230 INDEX.

Page 

Franz on currents due to loose contacts.................................... 2191

(See Wiedemann.) 

Freiberg, Magnet made by ................................................ 172

Frick, Table for annealing given by....................................... 217

Fromme on density of steel...... ..........................................90,93,97

on magnetism and hardness ...............................Ill, 146,147,203

on methods of magnetization by................................... 119

Funkler's magnetic battery...................I............................ 153

Galvanic calibration, Analogies of......................................... 74

Methodof........................................... 72

Galvanometer-factor, how measured ....................................... 33,34

Gaugain, Magnetic experiments of................................... ....111,151,203

on currents due to loose contacts................................. 21£

Gauss, Constants in magnetic forinulsB of .................................. 126,130

on methods of measuring magnetic moment. .........^............... 120

German silver annealed at 100°, Eesults for................................ 94

Glass-hardness, Apparatus for imparting.................................... 29,204

appears suddenly .......................................... 40,219

chemically interpreted. ..................................... 98

General character of....................................... 38

intensified by Cumming's phenomenon ..................... 99

physically interpreted ..................................... 99

Gordon on unique maximum of magnetizability............................ 145

Gore on disappearance of magnetization at redheat........................ 99,197

Gray, Experiments of, on magnetism and hardness.................. Ill, 147,148,203

Green's equation of linear magnetic distribution................ ............ 145

Hankel, Thermo-electric experiments of................................... 7,206

Hansteen, Magnetic experiments of .... .................'........ .......... 203

Hardness and dimensions (thickness)................................... 150,217-219

and magnetic constants of steel .......................... 126-128, 130-135

and magnetism, earlier results digested .................. ........ Ill

and resistance...............................................62-68,207,223

and thermo-electric behavior ................................ 62-68,205,217

attained, Maximum of............................................ 39,129

conditioned by carburation .......................... ............ 39,103

dimensions, etc., Digest of, Tables 54-65 .................. 136-138,140.-142

dimensions, magnetization of steel, Tables 50,53 .......... 126-128,130-135

how measured .................... ...........................65,121,205

in steel, Theories for............................................. 89

Kind of, discussed in this memoir................................ 13

Limiting degree of.............................................. 56

Original definition of (T. E. H.).................................. 207

Permanent, for a given temperature ............................. 8,56

Thermo-electric, defined .......................................65,189,201

" Hard" state, Properties of ............................................... 185

Hausmann on cause of hardness in steel.................................... 89

on density of steel.............................................. 77

Hautefeuille. ( See Troost.)

Heat-conductivity, Method of measurement of.............................. 25,27

Heat-expansion interferes with the strain of hardness ...................... 96

Helix, Data for .................................................. ......107,118,153

Heraeus. Platinum furnished by............................................ 80

Hezner on cause of hardness in steel .................. .................... 89

Holmgreu, Magnetic experiments of....................................... 154,167

(822)
INDEX. 231

Paga. 

Holz, Magnetic experiments of ...................................... ...... 205

Method of magnetization of.......................................... 11$

Holtzmann. (See Matthiessen.)

Homogeneity (longitudinal), Magnetic importance of................... ."... 117

Tests and data for..................38,122,125,129,130

Hot oil-bath, Use of, in annealing ...........................................40; 215

Ignition, Effect of temperature of, on hardness.......................39,194,211,219

gentle, Resistance and density effect of............................ 93,196

of iron in hydro-carbons, Effect of.......................... ...... 191

Impurities in iron and steel, Electrical effect of............................ 61,188

Incipient annealing, Anomalies during..................................... 66,150

Individuality of behavior of steel rods discussed .................... ....115,116,1391

Intersection of curves of classification...................................... 186"

of magnetic curves............................................ 144,198-

Iron, Electrical characteristics of........................................... 176

General electrical constants of, Table 76 ............................. 177

mechanically distinguished from steel.......................... 99,177,188,221

Temperature-coefficient of ........................................... 15,20,21

Thermo-electric behavior and resistance of, Table 32 .................. 61

Iron-carburets, General electrical characteristics of ...... ............ ...... 184,200

Series of............. ..............................188,191,200,201

Jarolimek, on methods of obtaining great hardness......................... 31

Jarolimek u. Ackermann, on tempering in hot liquids...................... 39

Jamin on magnetism and carburation...................................... 112

Jeans on criterion for steel ................................................ 177

on critical temperature in cementation............................... 99

on density of steel .................................................. 77

Jenkinon currentsdue to loose contacts.................................... 219

on thermo-electric aeries............................................ 7

jonle on deformations accompanying magnetization........................ 104

on electrical behavior of alloys ...................................... 80*

 on electrical behavior of cast-iron ............................103,178,186,221

on electrical behavior of iron........................................ 176

on electrical behavior of steel ........................................ 70,174

Jullien on cause of hardness in steel....................................... 891

Karsten, Criterion of, for steel.... ......................................... 177

Density of steel given by ....................................... 77

Distinction of, between white and gray cast-iron ................. 76,77

Hardness of steel explained by ................................!.. 89,173

Polycarburet theory of .......................................... 98

Kerlon causes of hardness in steel......................................... 89-

King, Clarence, aided research .................................. .......... 5

KirchhofPs form of Wheatstone's bridge.................................... 36,37

Kohlrausch, Form of bridge devised by ..............................26,121,122,130

Magnetic work proposed by................................... 203

Magnetometer devised by..................................... 120

Thermo-electric investigations of ........... .... .............. 206,221

Value of the unique magnetic maximum found by............. 145

Valuable assistance given by .................................7,210,226

Kohlrausch u. Ammann, Zero method used by ............................. ' 203

Lament, Magnetic experiments of........................................ 151,154,203

Limits of magnetic state for 100°, Tables 67-74 ................. 153,154,157,161,163

List of illustrations ........................................................ 12

Logarithmic interval, Importance of, in classifying iron-carburets...... .... 187

(823)
232 INDEX.

Logarithmic intervals in case of temper.................................... 142

Magnus, Thermo-electric experiments of............................ 110,207,220,224

Magnetic battery, Funkler's form of......................... .............. 153

"capacity varies largely between blue annealed and soft........... 124

constants of steel and hardness...........................126-128,130-135

effect of annealing, Direct....................................... 155,165

effect of annealing, Indirect..................................... 155,165

effect of hardness, Scheme for research........................... 71

effect of percussion.... .......................................... 169,170

effect of successive annealing.................................... 157

field, described .................. ............................107,118,119

functions too complex for classification-diagrams ................ 193,202

inductor, Weber's form of......... ...... ....................... 36,210

moment, Method of measurement of ............................. 120

results of Fromme, tabulated.................................... 147

results of Gray, tabulated....................................... 148

results of Ruths, Table 66 ....................................... 146

retentiveness and dimensions, Relation between.................. . 163

Magnetizability and dimensions, Relation between.......................... 142,198

and hardness, Relation between............................ 139,197

Maxima and minima of........................ ............ 198

Unique maximum of...................................... 145,198

Magnetizing force, Intensity of ....... ...... ................ ............ 107,118,153

Magnetism and carburation ............................................... 112

and density.................................................... 144

and dimension-ratio, Special discussion of....................... 142

and hardness ....... ..... ..............................112,136-139,197

and hardness (earlier work), Digest of.......................... lit

and resistance, Simultaneous variations of................... 155,161,164

and temperature, Temporary and permanent effects of........... 151

Magnets, How to temper and magnetize.................................... 171,200

Mechanical constants of, Tables 49,51............. 125,129,152,155,160,164

Magnetization, Apparatus for measuring electrical effect of................. 106

circular, Electrical effect of............I.................... 105,205

Classification-function bnsed on intensity of................. 202

hardness, dimensions of steel, Tables 50,53........... 126-128,130-135

hardness, etc., Digest of Tables 54-65........'......... 136-138,140-142

Method of.................................................. 118,119

Pre-existing, effects of...................................... lf>9

Resistance-effect of...................................-.'.... 105

Thermo-electric effect of......................... 104,108,109,197,221

Unique maximum of.....................................5,8,145,198

Malleable cast-iron, Electrical behavior of................................. 100-102

Hardness of, without electrical effect ............'..... 103,197

Hardness of, without volume effect.................... 103

Matthiessen on electrical behavior of alloys.... ...... ................ ...... 80,81,84

on general temperature-coefficients for metals.................. 24

on temperature-coefficients of alloys ........................... 16

Views of, on the constitution of iron-carburets................. 78,95

and Hockin on method of resistance-measurement.............. 17,121

and v. Bose on annealing effect in drawn wires................. 93

and Vogt on temperature-coefficients of alloys, &c ....... ......20,84,85

Maxima of magnetization ................ ............. 1.................... 140,198

of resistance of steel ............................................... 177f 195

. (824)
INDEX. 233

Maxima of thermo-electric power, etc....... .................... ..........40,44,195

Maximum density of steel ................................................. 6

of permanent hardness defined .......... ......... ...... .... ...... 56

of permanent magnetism for 100°. (See Limits.)

variation of electrical constants in iron-carburets ............ .... 186, 187

Maxwell, Thermo-electric series interpreted by. .......... ...... ...... ...... 7

Mayer on deformation accompanying magnetization ........................ 104

Metcalf, Magnetism, hardness, etc., discussed by ........................... Ill

Meyer on the coefficient of magnetization.. ................................ 114

Minima of magnetization...... ............................................ 139, 198

Moser and Riess, Magnetic researches of ................................ 154, 159, 167

on magnets successively annealed. ........................ 158

Mousson on magnetism and temperature. ............................ .1.... 151

on resistance-effect of temper, strains, etc .................. 70, 208, 220, 224

Structure of hard steel described by:... .......................... 96

on temperature-coefficient, iron and steel ......................... 15

Thermo-electric series given by ............ ...... ...... ...... .... 7

Milller, Magnetic experiments of ....................................... Ill, 112, 203

on resistance-effect of high temperature...... ...................... 90

Negative thermo-electrically denned ....................................... 6

Neutral point, thermo-electric defined...... ............. .*.... ....... ...... 40,44

Nomenclature referring to slow and rapid cooling .................... ...... 175

Obach, Tables of, for Wheatstone's bridge...... .................. .... ..1... 37

Ohm, Value of ...........;.... ............................................ 5

Oxide films, Temper value of, etc ........................... 8, 18, 19, 113, 139, 142, 203

Parallelopipedon, Magnetic behavior of .... .................. ...... ........ 152,163

Peltier's phenomena, Effect of. ............ ................ ............ .... 208

Percussion, Magnetic effect of.........................:................ 166, 169, 170

Permanent hardness, Maximum of, defined...... .... ....................... 8,56

magnetism defined ............................................. Ill

magnetism, Maximum of, at 100°. (See Limits.) 

Percy-Wedding on decarburafcion.. ...... ...... .... ...... ...... ...... ...... 175

oa irou -carburets.. ........................................ 76

on malleable cast-iron. ...... .... ...... ...... ...... ........ 101

on silver-steel. ............................................ 178

ou temper ................................................. 173

Piotet on magnetism and carburation ...................................... Ill, 112

Phenomena of annealing, General laws of .......... ...... .................. 55, 195

Pliicker, magnetic experiments of ......................................... 111,203

Poggendorff 'a mirror galvanometer ........................................ 120

Poloni on magnetism and temperature ..................................... 151, 154

Polycarburet, Karsten's theory regarding .................................. 98

Positive thermo-electrically defined. ....................................... 6

Pre-existing magnetization, Effect of, on magnetizability ................... 159, 199

Quality of carburation, Meaning of .............. ................ .......... 190

Ratio of dimensions, General, effect of ...... ................................ Ill

Hesistance a minimum after gentle ignition ............................... 93

a volume-function .... ..............................'........... 89, 196

and density of steel, Table 1 .................................... 19..92

and magnetism, Simultaneous variations of ..................... 162, 164

and magnetization, Simultaneous variations of, Tables 68, 71, 72, 

75..................... .................................. .155, 161, 164

and temperature, Equation of, for steel, etc ..................... 17

at points of contact, Importance of. ............................ 37

' (825)
234 INDEX.

Page, 

Resistance effect for variation of volume .................................90,92,19$

effect (maximum) of temper.............................. 71,177,195,224

Method of measurement of, etc............................36,70,210,215

Normals for comparison of ..................................... 37

ofalloys, Table40 ....................................f ........ 84

of cast-iron, Table 80 .......................................... 183

of malleable cast-iron, Table 43 ................................ 102.

of steel, Tables 7,33, IV-VIII.............................41,63,215,216

of wires annealed in oil.......................................41,43,216

Relation of, to thermo-electric hardness, Table 34 ............... 63

(See Thermo-electric behavior and power.)

Value of oxide-coats of steel in terms of......................... 19,142

Retentiveness, and dimensions, Relation between........................... 163-.

Magnetic................................................... 152

Riess. (/SeeMoser.)

Righi on magnetism and hardness ......................................... Ill

Rose, Joshua, on tempering ............................................... 39'

Rowland, Magnetic experiments of ........................................ 203

Rules'for tempering and magnetizing ...................................... 171,200>

Ruths, Magnetic experiments of ........................................... Ill, 203

Magnetic experiments of, discussed................................. 146, 225

Sauerwald, Galvanometer made by ........................................ 36

Scheme for researches with steel, General .................................. 71

Sections of wires how measured........................................... 122

Seebeck on thermo-electric scale ........................................... 7

Senguerd, Faucet devised by.............................................. 30

Sensitiveness of the electrical properties of iron-carbides ................... 192

Series of iron-carburets.............................................188,191,200,201

Siemens' mercury unit, Value of.....................................:..... 5

Silver-steel, Character of.................................................18,28,178

Soft iron, Electrical behavior of........................................... 61

Soft steel, Electrical behavior of................ 1.......................... 60

"Soft" state, Properties of ................................................ 185.

Softening, Method adopted for ............................................ 60,101

Specific magnetism defined ................................................ 121

Strain of drawn hardness, General character of............................. 110*

of temper, Electrical effect of, etc...................... 13,96,103,110,186,197

Magnetic effect of changes of....................................... 151,165-

Steel annealed at <2°, then exposed to <i° (successive annealing), Tables 29,30.57,58,59' 

Definition of.................... ..................................188-192,201

Density and resistance of, Table 1 .................................... 19,92:

Electrical characteristics of .......................................... 177

Electrical relation of, to iron.................;....................... 60,221.

General electrical constants of, Table 77 .............................. 178

kind used, described ............................................18,28,115,178

Resistance of. (See resistance.)

Temper and resistance of, Tables 47, 48...............;.. .............. 124

Temperature-coefficient of............................................ 15

Temperature-coefficient of, Tables 1, 2, 3.............................. 19

Thermo-electric behavior of, annealed in steam, Tables 9 to 15......... 43-46

Thermo-electric behavior and resistance of:

annealed at66°, Tables 16-18..................................... 47,48

annealed at 100°, Tables 19-21.................................... 49,50

annealed at 185°, Tables 22-24 ...................:................ 51,52

(826)
INDEX. 235

Page. 

Steel, thermo-electric behavior and resistance of Continued.

annealed at 330°, Table 25-27..................................... 53,54

anuealed in oil, Tables 7, VII...................................... 41,216

annealed soft, Table 31............................................. 60

Thermo-electric hardness and resistance of, Table 34 .................. 66

Thermo-electric power and resistance of, Table 8...................... 43,6ii'

Thermo-electric power and temper of, mean results, Table28 .......... 54

Structure, anomalies of, Electrical effect of................................. 66,68'

Definition of, etc ....................................8,14,96,114,113,194

Methods of studying ........................................... 114

Successive annealing. Magnetic effects of .................................. 157,161

Mechanical effects of ..........:..................... 57-59'

Sudden cooling, Character of the effects of................................. 38

Summary................................................................. 194

Sundellon electrical behavior of alloys ..................................... HOTable 1, on the temperature-coefficient, resistance, density, and dimensions

of steel rods...................................................... 191

2. on the temperature-coefficient, resistance, and temper (oxide-coats)

of steel rods...................................................... 19'

3. on the temperature-coefficient and resistance of steel rods, practical 

digest...... ..................................................... 19

4. on the temperature-coefficient and conductivity of iron............ 20

5. on the temperature-coefficient and resistance of iron, digest........ ' 21

6. on the temperature-coefficient, resistance, and dimensions of cast-iron 

rods............................................................. 23

7. on the therino-electrics and resistance of steel annealed in oil...... 41,42'

8. on the thermo-electric power and resistance of steel annealed in oil. 43-

9. 10, 11, 12, 13, 14, 15, on the thermo-electric behavior of steel annealed in steam for different lengths of time....................... 43,46

16, 17, 18, on the thermo-electric behavior and resistance of steel annealed at 66°............ ......................................... 47,48-

19, 20, 21, 011 the thermo-electric behavior and resistance of steel annealed at 100° ................................................... 49,50'

22, 23, 24, on the thermo-electric beliavior and resistance of steel annealed at 185° .................................................... 51,52

25, 26, 27, on the thermo-electric behavior and resistance of steel annealed at 330° .................................................... 53,54

28. on the thermo-electric power of steel annealed at 66°, 100°, 185°, 

330°, general digest............................................... 54

29. 30, on the electrical behavior of steel annealed at £2°, then exposed 

to ti°,ta ^tL.......................................J.............57,58,59-

31. on the thermo-electric behavior and resistance of soft steel........' 60

32. on the thermo-electric behavior and resistance of soft iron........ 61

33. on the observed and calculated specific resistance of steel......... 63

,34, comparison of the values of thermo-electric hardness and specific 

resistance of steel ................................................ 66

35. on the thermo-electric behavior of silver-platinum alloys.......... 82

36. 37, on the thermo-electric behavior of silver-gold alloys........... 82,83-

38. on the thermo-electric behavior of silver-copper alloys............ 83

39. on the thermo-electric behavior of silver-zinc alloys .............. 84

40. on the electrical resistance of certain alloys of silver.............. 84,86-

41. on the electrical resistance and temperature-coefficient of alloys of 

silver ............................................................ 85-

42. on the thermo-electric behavior of malleable cast-iron ............ 101,102,

(827)
236 INDEX.

Page 

Table 43, on the electrical resistance of malleable cast-iron ................. 102

44. on the thermo-electric power and specific resistance of malleable 

cast-iron................................!'.................... .... 102

45. 46, on the thermo-electric effect of magnetization of iron.......... 108,109

47, 48, on the temper and electrical resistance of annealed steel ...... 124

49. constants (dimensions, density, mass) of magnets................. 125

50. dimensions, magnetic moment, specific magnetism, specific resistance, and temper of permanently saturated steel rods.............. 126-128

51. constants (dimensions, density, mass) of magnets................. 129

52. data for the observed homogeneity of the steel wires used ........ 130

53. dimensions, magnetic moment, specific magnetism, specific resistance, and temper of permanently saturated steel rods.............. 130-135

54. 55, 56, 57, 58,59, 60, 61, 62, 63, dimensions, specific magnetism, specific resistance, and temper of permanently saturated steel rods, digest...... ............ ............................... ......136,137,138,140

64, 65, oxide-color (temper), dimensions, permanent magnetizability of 

steel ............................................................. 142

66. Ruths's magnetic results....... ...... ............................ 146

67. maxima of permanent magnetizability for 100°.................... 154

68. temper, resistance, magnetization, and magnetizability of steel in 

case of continued annealing at 100°............................... 155

69. 70, magnetizability of steel successively annealed at 100° ......... 157

71, 72, temper, resistance, magnetization, and maguetizability of steel 

in case of continued annealing at 100°............................. 161

73, 74, magnetizability and dimensions of steel rods thoroughly annealed at 100° .................................. ................. 163

75. simultaneous variations of magnetization and galvanic resistance

in case of continued annealing .............................. ..... 164

76. general electrical constants of wrought-iron............ ...... .... 177

77. general eletrical constants of steel................................ 178

78. 79, thermo-electric behavior of cast-iron.......................... 179-182

80. electrical resistance of cast-iron.................................. 183

81. general electrical constants of cast-iron .......................... 184

82. general electrical characteristics of the iron-carburets............ 185

I, thermo-electric hardness (T. E. H.) and temperature of ignition of 

steel........................ ...................................... 211

II, III, thermo-electric behavior (T.E. H.) of steel (older results)..... 212,213

IV, V, VII, electrical resistance of steel (older results)............... 215

VI, VII, thermo-electric hardness (T. E. H.) and resistence of steel (older 

results)...........................-......-. ....................... 215,216

IX, density and thermo-electric hardness (T. E. H.) of steel .......... 222

Tait on anomalous behavior of iron........................................ 99,197

Thermo-electric investigations of ..................................... 35,206

Temperature of ignition, Effect of, on hardness...........................39,211,219

Temperature-coefficient, a volume-function................................. . 24

for iron-carburets, Single series of.................. 94

for iron-carburets, Summary of .................... 194

Measurement of, for cast-iron...................... 22

Measurement of, for steel.......................... 17

of iron, earlier results............................. 15

of steel, earlier results............................. 15

related to electrical resistance..................... 16,24

and resistance of alloys, Table 41 .................. 16,85

of cast-iron, Table 6 ................ 23

(828)
INDEX.- 237

Page. 

Temperature-coefficient and resistance of iron, Tables 4, 5.................. 20,21

of steel, Tables 1,2,3................ 19

Temper chemically interpreted ............................................ 76,78

Decisive evidence as to the nature of the electrical effects of........ 103

due to simultaneous physical and chemical changes................ 100

Interpretation regarding, obtained from alloys'..................... 83

mechanically interpreted..........................................78,95,99

Summary of effects of ............................................. 194

Tempering analogous to magnetization.................................... 13,97

Apparatus for..................................................29-31,'204

Conception of an ideal process of...........:.................... 97

Difficulties of............................ ...................... 13

Physics of the process of........................................ 70,98

Theoretically perfect........................................... 13,14

Temper-value of oxide tints................................8,18,19,113,139,142,203

Temporary magnetism defined by Wiedemann...... ...................... ill

Terrestrial magnetism, Intensity of..................................... 120,126,130

Thermal expansion, Bearing of, on annealing.............................96,97,196

Thermo-currents evolved in a thick, hard, steel cylinder ................... 220

'Thermo-electric anomalies ..:............................................. 66

behavior of alloys, Tables 35-39 ..........................82,83,84

of'cast-iron, Tables 78, 79 ........................ 179-182

of malleable cast-iron, Table 42.................. 101

of soft iron, Table 32............................ 61

of steel. (tfeeSteeJ.) . 

effect of magnetization............................. ....109,110,221

effect of magnetization, Tables 45,46....................... 108,109

hardness and density of steel.:............................ 222

hardness and mechanical hardness compared............... 217

hardness defined ........................................65,189,201

hardness independent of magnetic state ................... 110

hardness, General interpretation of...... .................. 189,201

hardness, Zero of ........................................25,65,195

interval (maximum) for steel............................... 71,177

power and resistance of alloys, Table 42 ................... 85,86

of malleable cast-iron, Table 44 ...... 102

of steel. (See Steel.) 

power and specific resistance, Relation between........ 62,63,66,223

power, Maximum of....................................... 177,195

power, Method of calculation of........................... 36

power, Method of measurement of.................. 31,33,34, 58,208

series..................................................... 7

Thermo-eleotrics of steel wires annealed in oil............................ 41,43,216

Thermo-element, Forms of............ ..................................... 31,209

Thickness of steel rods, Magnetic effect of.................................. 113

Mechanical effect of..........................14,150,217-219

Thomson, Magnetic law of................................................. 113,115

on electrical behavior of iron....... .............................. 106,176

on thermo-electric effect of magnetization ....................... 104,221

Thermo-electric experiments of.............................. .207,220,224

Time of exposure, Effect of, in annealing................................... 43,195

Magnetic effect of....................................... 166

Magnetic limit independent of........................... 157

Treve et Durassier, Magnetic experiments of............................111,112,203

(829)
238 . INDEX.

Page. 

Troost on iron-carburets, Views of........................................... 78

Trowbridge, Magnetic effect of cold described by .......................... 151,170

Tunner on cause of hardness in steel...... ................................. 89

Uniformity of hardness, ho w tested, etc .....................38,117,122,125,129,130

Unique maximum of magnetization ..................................6,139,145,198

Viscosity defined .......................... ............................... 95

Bearing of, on annealing ........................................ 95,196

Vpgt. (See Matthiessen.)

Volt, Value of............................................................. 5

Volume-function.......................................................... 89

Volume-increase, Resistance effect of ...................................... 89,196

Wagner, on properties of iron-carburets ................................... 219

Tables for annealing given by ............................... .... 217

Waltenhofen, v., on magnetism and carburation ............................ 112

on magnetism and hardness .................................. Ill

Weber, Commutator of.................................................... 35

Magneto-inductor of................................................ 36,210

Wedding. (See Percy.)

Wertheim on deformation accompanying magnetization.................... 104

Wiedemann, G., digest of temperature-coefficients of iron and steel......... 15

Magnetic experiments of.................................. 111,203

on magnetism and temperature ........................... 151,154

on methods of magnetization .....:.......................

on resistance-effect of magnetization......................

on thermo-electric series..................................

Temporary and permanent magnetism defined by..........

Wiedemann u. Franz on measurement of heat-conductivity.................

Wild, on magnetic permanence............................................ 167,171

White cast-iron, Electrical behavior of .................................... 179,186

Wolfram-stahl............................................................ 172

Wrought-iron. (See Iron.)

Wtirzburg, Bifilar magnetometer of..... . ............ ........ . 168

Zero of thermo-electric hardness..........................................25,65,195

(830)
DEPARTMENT OF THE INTERIOR

BULLETINS

OP THK

UNITED STATES

GEOLOGICAL SURVEY

VOL. II.

WASHINGTON

GOVEBNMENT FEINTING OFFIOB

1886
CONTENTS.

BULLETIN NO. 7.

Paga.

A catalogue of geological maps of America (North and South), 1752-1881, in 

geographic and chronologic order, by Jules Marcou and John Belknap Marcou 1

BULLETIN NO, 8. 

On secondary enlargements of mineral fragments in .certain rocks, by R. D.

living and C. E. Van Hise*.............................. .............. 185

BULLETIN NO. 9.

A report of work done in the Washington Laboratory during the fiscal year 

1883-'84; F. W. Clarke, chief chemist; T. M. Chatard, assistant chemist... 241

BULLETIN NO. 10.

On the Cambrian faunas of North America;. preliminary studies; by Charles 

D. Walcott ......................................:l........................ 281

BULLETIN NO. 11.

On the Quaternary and recent mollusca of the Great Basin, with descriptions of 

new forms, by E. Ellsworth Call. Introduced by a sketch of the Quaternary 

lakes of the Great Basin, by G. K. Gilbert ................................. 355

BULLETIN NO. 12.

A crystallographic study of the thinolite of Lake Lahontan, by Edward S. 

Dana..................................................................... 421

BULLETIN NO. 13.

Boundaries of the United States and of the several States and Territories, with 

a historical sketch of the Territorial changes, by Henry Gannett, chief geographer. ............................................................ . 457

BULLETIN NO. 14.

On the electrical and magnetic properties of the iron carburets, by Carl Barns 

and Vincent Strouhal. . .............................................. 593

HI
ILLUSTRATIONS.

BULLETIN NO. 8.

PagePlate I. Huronian quartzite of East Neebieh Rapids, Saint Mary's River... 187

II. Crystal-faced enlargements of quartz fragments................... 197

HI. Thin sections of quartzites ....................................... 199

IV. Thin sections of red quartzite .................................... 207

V. Thin sections of sandstone and quartzite.......................... 209

VI. Thin sections of quurtzite, &c.................................... 213

Fig. 1. Portion of section of Eagle Harbor sandstone......................... 229

Fig.2. Enlarged fragment of triclinic feldspar .................... ....... 229

Fig. 3. Enlarged fragment of feldspar, including some quartz ................ 230

Fig.4. An enlarged fragment of orthoclase.................................. 231

BULLETIN NO. 10.

Plate I. Fossils of the Saint John formation ............................. 336

II. Fossils of the Saint John formation............................. 338

III. Fossils of the Saint John formation ............................. 340

IV. Fossils of the Saint John formation ............................. 342

V. Fossils of the Saint John formation ............................. 344

VI. Fossils of the Saint John formation ............................. 346

VII. Fossils of the Braintree argillites ............................... 348

VHI. Fossils of the Braintree argillites ............................... 350

IX. Fossils of the Braintree argillites ............................... 352

X. New Phylloid crustacean ....................................... 354

BULLETIN NO. 11.

Plate I. Sketch map of the Great Basin ................................... 357

II. Comparative dimensions of Pompholyx effusa ...................... 412

III. Comparative dimensions of shells................................. 414

IV. Comparative dimensions of shells from fresh and brackish stations. 416

V. Comparative dimensions of shells................................. 418

VI. New recent and Quaternary mollusca............................. 420

Fig. 1. Diagram showing superposition of tufas............................. 365

Fig. 2. Dentition of Amnioola dalli ........................ .....<,.,......... 400

Fig. 3. Articulation of intermediate teeth........................ .^......... 400

BULLETIN NO. 12.

Plate I. A characteristic specimen of thinolite ............................ 423

II. Illustrations of the structure of thinolite.......................... 452

III. Illustrations of the structure of thinoli te.......................... 454 r*

Fig. 1. Diagrammatic section, illustrating the relation of the tufas .......... 431

v
VI ILLUSTRATIONS.

BULLETIN NO. 14.

Page. 

Fig. 1. Electrical conductivity and temperature-coefficient of silver-platinum

alloys ........................................................... 608

Fig. 2. Diagram of the relation between specific electrical resistance and tern-.

 perature-coefficient for wrought iron, for steel, and for cast iron... 615 

Fig. 3. Diagram of a resistance apparatus for measuring heat conductivity.. 618 

Fig. 4. Apparatus for hardening steel rods ................................. . 621

Fig. 5. Form of thermo-element ........................................... 624

Fig. 6. Disposition of thermo-electric apparatus...................."........ 625

Fig. 7. Disposition of appartus for measuring the galvanometer-factor...... 625

Fig. 8. Details of thermo-electric apparatus................................ 626

Fig. 9. Hard wires annealed for six consecutive hours in steam, at 100°..... 638

Fig. 10. Hard wires' annealed continuously at 0°, 66°, 100°, 185°, 330°, and

1,000°, respectively............................................... 647

Fig. 11. Diagram of the relation between the thermo-electric power of steel in

different states of temper, and its specific resistance............... 656

Fig. 12. Disposition of apparatus for calibration ............................ 665

Fig..13. Specific resistance and thermo-electric constant; steel, silver-gold,

silver-platinum, silver-zinc........................................ 678

Fig. 14. Disposition of apparatus ........................................... 698

Fig. 15. Specific magnetism of rods annealed from 0° to 1,000°................ 709

Fig. 16. Disposition of apparatus for resistance measurement ................ 713

Figs. 17,18. Relation between specific magnetism and hardness of steel-for different dimension-ratios ........-............. .................... 733

Figs. 19,20. Relation between specific magnetism and dimension-ratio of steel

Tods, for different degrees of hardness ............................ 735

Fig. 21. Diminution of specific magnetism and specific resistance produced by

continued annealing (low temperatures).......................... 748

Fig. 22. Simultaneous variation of specific magnetism and specific resistance

in case of continued annealing (low temperatures)................ 754

Fig. 23. Simultaneous variation of specific magnetism and specific resistance

in case of continued annealing (high temperatures)............... 756

Fig. 24. Diagram of the mean variation of the thermo-electric hardness and of

the specific electric resistance of iron carburets3 with their degrees

of carburation ...........* ....................................... 777

Fig. 25. Classification diagram ............................................. 784

Fig. 26. Apparatus for hardening ............................................. 796

Fig. 27. Disposition of apparatus........................................... 800

Fig. 28. Original form of thermo element ................................... 801

Fig. 29. Thermo-currents evolved in a hard and thick cylinder .............. 812

Fig. 30. Relation between thermo-electric power and.specific resistance...... 815

Fig. 31. Diagram of Ruths' results.......................................... 817