DEPAKTMEHT OF THE JNTERIOK

BULLETIN

UNITED STATES

No. 26

30250

WASHINGTON

GOVEBNMENT PRINTING OFFICE 

 1885

UNITED STATES GEOLOGICAL SURVEY

J. W. POWELL, DIRECTOR

COPPER SMELTING

BY

HENRY M. HOWE

30250

WASHINGTON

GOVERNMENT PRINTING OFFICE.

[Bulletin No. 26.1

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 and economic geology and paleontology. The annual report of operations of the Geological 

Survey shall accompany the annual report of the Secretary of the Interior. All special memoirs and 

reports of said Survey shall bo issued in uniform quarto series if deemed necessary by the Director, 

but otherwise in ordinary octavos. Three thousand copies of each shall be published for scientific 

exchanges and for sale at the price of publication; and all literary and cartographic materials received 

in exchange shall be the property of the United States and form a part of the library of the organization : And the money resulting from the sale of such publications shall be covered into the Treasury »f the United States."

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

by Congress:

'' That whenever any document or report shall be ordered printed by Congress, there shall be printed, 

in addition to the number in each case stated, the' usual number' (1,000) of copies for binding and 

distribution among those entitled to receive them."

Under these general laws it will be seen that none of the Survey publications are furnished to it for 

gratuitous distribution. The 3,000 copiesof the Annual Report are distributed through the document 

rooms of Congress. The 1,900 copies of each of the publications are distributed to the officers of th« 

legislative and executive departments and to stated depositories throughout the United States.

Except, therefore, in those cases where an extra number of any publication is supplied to this office by 

special resolution of Congress, as has been done in the case of the Second, Third, Fourth, and Fifth Annual Reports, or where a number has been ordered for its use by the Secretary of the Interior, as in tha 

case of Mineral Resources and Dictionary of Altitudes, the Survey has no copies of any of its publications for gratuitous distribution.

ANNUAL REPORTS.

Of the Annual Reports there have been already published:

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

preliminary report desciibing plan of organization and publications, 

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

1882. 8°. Iv, 588 pp. 61 pi. 1 map. 

ILL 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-'88, by J. W. Powell.

1884. 8°. xii, 473 pp. 85 pi. and maps. 

The Fifth and Sixth Annual Reports are in press.

MONOGRAPHS.

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

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

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

HI. Geology of the Comstock Lode and the Washoe District, with atlas, by George F. Beoker. 1882.

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

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

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

29 pi. Price $1.85.

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

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

VLT. Silver-lead Deposits of Eureka, Nevada, by Joseph S. Curtis. 1884. 4°. xiii, 200 pp. 1C pL 

Price $1.20.

Vm. Paleontology of the Eureka District, by Charles D. "Walcott. 1884. 4°. xiii,298 pp. 24 L 

24 pi. Price $1.10.
ADVERTISEMENT.

The following are in press, viz:

IX. Brachiopoda and Lamellibranchiata of the Raritan Clays and Greensand Marls of New Jersey, 

0>y Robert P. Whitfield. 1885. 4°. is, 338 pp. 35 pi.

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

a885. 4°. , pp. 56 pi.

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

Cook Russell. 1885. 4°. xiv, 288pp. 46 pi.

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

The following are in preparation, viz:

I. The Precious Metals, by Clarence King.

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

 Lake Bonne ville, by G. K. Gilbert.

 Sauropoda, by Prof. 0. C. Marsh.

 Stegosauria, by Prof. 0. C. Marsh.

 Geology of the Quicksilver Deposits of the Pacific Slope, with atlas, by George F. Becker.

 The Penokee-Gogebic Iron-Bearing Series of North Wisconsin and Michigan, by Roland D. 

Erving.

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 head 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 sizes. 

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

Of this series of Bulletins Nos. 1 to 25 are already published, viz:

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

a Geological Sketch of Buffalo Peaks, Colorado, by S. F. Emmons. 1883. 8°. 42 pp. 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, 

3$
w York, to Bradford County, Pennsylvania, by Henry S. Williams. 1884. 8°. 36pp. Price 5 cents.

 4. On Mesozoio Fossils, by Charles A. AVhite. 1884. 8°. 36 pp. 9 pi. Price 5 cents. 

3L A Dictionary of Altitudes in the United States, compiled by Henry Gannett. 1884. 8°. 325 pp. 

IPrioe 20cents.

 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 Rocks, by R. D. Irving and C, R. 

VanHiae. 1884. 8°. 56pp. 6 pi. Price 10 cents.

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. 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 

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

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

H2. A Crystallographio Study of the Thinolite of Lake Lahontan, by Edward S. Dana. 1884. 8°. 

3ft j»p. 3 pi. Price 5 cents.

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

31885. 8°. 135pp. Price 10 cents.

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

'StrouaaS. 1885. 8°. 238 pp. Price 15 cents.

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

IPrice 5 cents.

J.6. On the higher Devonian Faunas of Ontario County, New York, by J. M. Clarke. 1885. 8°. 

i88lpp. 3 pi. Price 5 cents.

17. On the Development of Crystallization in the Igneous Rocks of Washoe, by Arnold Hague and 

J. P. Iddings. 1885. 8°. 44 pp. Price 5 cents.

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

by Dr..C. A. White. 1885. 8°. 26pp. 3 pi. Price 5 cents.

19. Notes on the Stratigraphy of California, by George F. Becker. 1885. 8°. 28 pp. Price 5 cents.

20. Contributions to the Mineralogy of the Rocky Mountains, by Whitman Cross and W. F. Hille- 

%rand. 1885. 8°. 114pp. Ipl. Price 10 cents.

21. The Lignites of the Great Sioux Reservation, by Bailey Willis. 1885. 8°. 16 pp. 5 pi. Price 5

cento.
ADVERTISEMENT.

22. On Now Cretaceous Fossils from California, by Charles A. White, M.D. 1885. 8°. 25pp. 5 pi. 

Price 5 cents.

23. The Junction between the Eastern Sandstone and the Kowoonaw Series on Keweenaw Point, by 

R. D. Irving and T. C. Chamberlin. 1885. 8°. 124 pp. 17 pi. Price 15 cents.

24. List of Marine Mollusca, comprising the Quaternary Fossils and recent forms from American 

localities between Cape Hatteras and Cape Roqne, including the Bermudas, by W. H. Ball. 1885. 8°. 

 336 pp. Price 25 cents.

25. The Present Technical Condition of the Steel Industry of the United States, by Phineas Barnea. 

1§85. 8°. 85 pp. Price 10 cents.

26. Copper Smelting, by Henry M. Howe. 1885. 8°. 107 pp. Price 10 cents. 

Numbers 1 to 6 of the Bulletins form Volume 1; Numbers 7 to 14, Volume IT; and Numbers 15 to 23, 

Volume III. Volume IV is not yet complete. 

The following are in press, viz:

27. Work done in the Division of Chemistry and Physics during the year 1884-'85.

28. Tho Gabbros and associated hornblende rocks occurring in the neighborhood of Baltimore, by 

George H. Williams.

STATISTICAL PAPERS.

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

States, has been undertaken. Of that series the following have been published, viz:

Mineral Resources of the United States [1882J, by Albert Williams, Jr. 1883. 8°. xvii, 813 pp. 

Price 50 cents.

The second volume of this series, Mineral Resources of the United States, 1883 and 1884, is in press.

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

POSTAL NOTE OR MONEY ORDER, should be addressed

To THE DIRECTOR OF THE

UNITED STATES GEOLOGICAL SUBVBT,

Washington, D. 0. 

WASHINGTON, D. C,, November 16,1885.

CONTENTS.

Page.

Letter of transmittal........................................................ 9

Introduction................................................................ 11

I.

Reverberatory method for sulphuretedores.................................... 15

1. Ore roasting ....................---..---......-...---..-..-..-....--. 16

Roasting in heaps or piles........................................... 16

Roasting in stalls ...... ............................................. 18

Kiln roasting ........-...................... .....:.................-. 18

Furnaces for fine ore ...... .................. ........................ 19

Hasenclever and Helbig's........................................ 19

Gerstenhofer's .................................................. 19

Maletra's ........................................................ 19

Spence's........................................................ 20

Revolving cylinders............................................. 21

The Stetefeldt furnace........................................... 21

Reverberatory furnaces.......... i............................... 21

Open reverberatories........................................ 21

Muffles ..................................................... 24

Mechanical reverberatories.................................. 24

Objects of the roasting.............................................. 25

a. Oxidation of the iron, and incidentally of the sulphur........ 25

. &.. The expulsion of arsenic and antimony....................... 25

Pile and stall roasting ......:...,........................... 26

Roasting in reverberatories.................................. 26

Comparison of heap and reverberatory roasting .............. 28

2. Smelting the roasted ore in reverberatories............................ 28

Furnace construction................................................ 28

Fire box........................................................ 28

Firebridge ..................................."'................. 29

Binding ........................................................ 30

Erection of binding............................................. 32

The masonry............. ................r...................... 32

The bottom or hearth............................................ 33

Size and shape of hearth ........................................ 34

Chimneys...................... ..................................... 35

Draft............................................................ 35

Separate chimneys............ ................!................. 35

Central chimneys ............................................... 36

Shape .......................................................... 37

Stability........................................................ 38

Iron vs. brick chimneys ......................................... 38

Linings..........r.............................................. 38

Batter.......................................................... 38

Gas furnaces........................................................ 39

Smelting operation.................................................. 44

(427)
6

Page. 

Reverberatory methods for sulphureted ores Continued.

The matte.............................f............................ 47

The slag...........................................;................ 47

In general...................................................... 47

Classification ................................................... 50

Fusibility, simple silicates....................................... 50

Multiple silicates.......................... ................... 50

Specific gravity................................................. 52

Corrosiveness .J................................................. 52

Liquidity....................................................... 52

Scorification ......J............................................. 52

Chemical reactions.................................................. 53

In general...................................................... 53

Arsenicand antimony ........................................... 54

3. Roasting the first matte (coarse metal)................................ 54

The aim .............................................................. 54

The operation....................................................... 56

4. Smelting roasted coarse metal for white metal......................... 58

The aim ............................................................ 58

The operation....................................................... 60

Chemical reactions................................................... 61

4 a. Smelting roasted coarse metal for blue metal......................... 62

The furnaces...............................I........................ 62

The operation....................................................... 63

4 6. Roasting-smelting the raw blue metal for regule and bottoms......... 63

The aim ............................................................. 63

The operation....................................................... 63

Chemical reactions ............ ...................................... 64

5. Roasting-smelting the raw white metal and regule for blistered copper... 66

The aim .................................. i......................... 66

The operation...............................^....................... 66

Classification of ores and slags........................................... 70

Ores...... .......................................................... 70

Slags............................................................... 72

II.

Reverberatory method for oxidized ores and native copper.................... 73

Reducing-smelting with carbon.......................................... 73

Smelting without carbon .............................. ...1.. ............ 74

Comparison of the two methods.......................................... 74

III.

Shaft furnace proces's for sulphureted ores ................................... 74

General plan................................................ ......... 74

* 1. Ore roasting.......................................................... 76

2. Ore smelting ...........t .................. .^.... ^.................... 76

In general ...........^.............................................. 76

The deoxidizing effect............................................... 80

The average temperature of the ore .............................. 80

The proportion of fuel to burden................................. 80

The porosity of the fuel .......................................... 80

The porosity of the ore ......................-----..---- -- --- 80

The intimacy of mixture ........................................ 80

The basicity of the mixture................... ................... 80

The infusibility of the mixture .................................. 80

(428)
CONTENTS. . 7

Pago. 

Shaft furnace process for sulphureted ores Continued.

The preponderance of iron oxide............. .................... 80

Height vs. width ................................................ 81

Sulphides....................................................... 82

Arsenic and antimony............................................... 82

Volume of furnace .................................................. 83

Raschette furnaces.................................................. 85

Disposition of crucible .............................................. 86

Internal crucibles............................................... 86

Crucibles, partly internal, partly external........................ 87

External crucibles ..............r............................... 87

Water-jacketed vs. brick walls....................................... 88

Gust vs. wrought-iron jackets .....................1.................. 90

Blast, tuyeres, etc................ ................................... 91

Hot blast........................................................... 92

Products............................................................ 92

Matte ............................i.............................. 92

Slag.*.......................................................... 93

Details of working ......................,...f . ...................... 94

Mechanical charging.................'........................... 94

Changing tuyeres ............................................... 95

Filter charging ................................................. 95

Fine ore ...... ................'..........................-......... 95

3. Roasting the first matte .............................................. 96

4. Smelting the roasted first matte ...................................... 96

Products ........................................................... 98

Black copper ............................. ... i ................... 98

Matte .......................................................... 98

Slags......................!.................................... 98

iv.

Shaft furnace process for oxidized ores and native copper..................... 99

V.

Comparison of the reverberatory and shaft furnace methods.................. 99

Composition of charge.................................'.................. 99

Labor and fuel...... .................................................... 99

Arsenic and antimony................................................... 100

Technical skill............... ............................................ 101

The first cost of construction ............................................ 101

Repairs ...................v............................................. 101

The loss of copper.....................................................1.. 101

Fines................................................................... 101

Salamanders .............................. a ............................. 101

Rapidity ............................................................... 101

Size of establishment.................................................... 102

Bringing forward ...................................,...'................ 102

-VI.

Re'sume'..................................................................... 102

ADDENDUM.

Matte roasting in reverberatory furnaces at the Orford Copper and Sulphur

Works.................................................................... 103

(429)

LETTER "OF TRANSMITTAL.

UNITED STATES GEOLOGICAL SURVEY,

DIVISION OF MINING STATISTICS,

Washington, J). C., July 25, 1885.

SIR: I have the honor to transmit herewith a paper by Mr. Henry 

M. Howe, on copper smelting, for publication as a bulletin of the United 

States Geological Survey. This paper is supplementary to-the contributions on the metallurgy of copper which have appeared in the reports 

of this division, and is of great interest as embodying a most complete 

review of present practice.

Very respectfully, your obedient servant,

ALBERT WILLIAMS, JR.,

Geologist in charge. 

Hon. J. W. POWELL, Director.

9

, (431)

COPPER SMELTING

By HENRY M. HOWE.

INTRODUCTION.

la the following paper, a somewhat detailed account is given of the 

methods and the apparatus employed iu smelting copper ores and in 

bringing forward the resulting products to the condition of crude metallic copper by the reverberatory or Welsh and by the cupola or 

shaft furnace method. Since the subject of roasting1 copper ores and 

inattes-is ably treated by Dr. B. D. Peters, jr., in the "Mineral Eesources of the United States, 1882," published by the United States 

Geological Survey, it is comparatively briefly passed over in the 

present paper. The reader is referred for details to that volume, while 

the valuable information there given is here supplemented by some 

remarks on the expulsion of arsenic and antimony iu roasting, since 

Dr. Peters does not dwell on this important point, and by several tables 

giving the more important economic and technical results of the roasting of ores and mattes as practiced in various places. These tables, as 

well as two showing the corresponding results of smelting in reverberatory and in cupola furnaces, have been compiled from a great number 

of sources, largely from private communications from the superintendents of copper smelling works,2 expressly for this work. The writer is 

not aware that so extensive a compilation of these features of copper 

metallurgy as is given in the tables has heretofore been published.

The chief problem which is presented in copper smelting is to separate the copper contained in the ore 

1. From the accompanying silicious or earthy gangue.

1 Iu copper metallurgy in Great Britain, and also in general in this country, true roastings (i. e., oxidizing, chloridiziug, and similar operations carried on at elevated temperatures without fusion or with at most incipient fusion) are spoken of as " calcinations," the word " roasting" being applied to a particular strongly oxidizing smelting 

of the Welsh reverberatory process. In. this paper the writer uses these words in their 

strict sense, designating the so-called " calcinations" by their true name, " roastings," 

and the oxidizing fusion of the Welsh process as a " roasting-smelting."

3 Where these figures have appeared improbable, the writer has called for corroboration and explanation of them, but he has not, in general, boeen able to verify them 

by personal observation.

11 

(433)
12 COPPER SMELTING. [BULL. 26,

2. From iron, lead, zinc, nickel, etc.

3. From arsenic and antimony.

4. From sulphur.

The general plan of the separation is the same in the reverberatory 

and the shaft furnace methods.

1. The gangue is removed by fusion, the copper, in the case of .oxidized ores, being previously reduced to the metallic state. On melting, 

the copper is collected in a matte or in the metallic state, the siliceous 

and earthy components of the ore uniting in a slag which is specifically lighter than the matte or copper, thus affording a ready means of 

separation.

2. In the case of sulphureted ores the separation of copper from 

iron and most of the other heavy metals is based on the fact that, while 

the affinity of these metals for sulphur is little if at all stronger than 

that of copper, they have a much stronger affinity for oxygen, so that 

by a series of oxidizing roastiugs, each followed by a fusion, the iron and 

the other heavy metals are gradually scorified and removed, while the 

copper unites with the remaining sulphur to form a matte, whose tenor 

in copper of course increases at each fusion with the expulsion of the 

iron, sulphur, etc.

In the case of oxidized ores and native copper the .greater affinity of 

iron and most of the other heavy metals for oxygen has to be relied on 

for their elimination. We may have a fusion in which the balance between the oxidizing and the reducing tendencies is such that all the iron 

arid a little of the copper remain oxidized and pass into the slag, -while 

most of the copper is reduced to the metallic state. That portion of 

the copper which passes into the slag may be recovered by precipitation on iron bars inserted into it, or by submitting the slag to a subsequent reducing smelting. Or this balance may be such that all the 

copper and part of the iron-are reduced to the metallic state, the latter 

element being subsequently removed by an oxidizing fusion (" roasting "-smelting and refining). Or we may expose oxidized ores to a 

mixture of reducing and oxidizing gases capable of reducing copper 

(but not iron) to the metallic state and, by a subsequent nearly neutral 

fusion, scorify the still oxidized iron.

3. The elimination of arsenic and antimony is chiefly based on the 

volatility of their sulphides, of metallic arsenic and of arseuious acid 

(As2O3 ) and trioxide of antimony (8b2O3 ).1 In each of the roastings, the

1 The volatilizing point of metallic arsenic is stated by some authorities as at a dull 

red heat and by others as at 180° C. Arsenious acid (As303 ) volatilizes at about 218° C. 

Arsenic acid (AsjOs) uncombined with bases is decomposed by heat alone at a full red 

heat into free oxygen and arsenious acid; but the metallic arseniates (compounds of 

arsenic acid with the oxides of the metals) do not in general appear to be decomposed 

by heat alone. The sulphides of arsenic, both realgar (AssSj) and orpiment (AsaSa), 

are readily volatile. But when arsenic is combined witli sulphur and a great excess 

of copper, iron, etc., in a matte, it is not volatilized by heat alone. The same ia true

(434)
HOWB.] INTRPDUCTION. 13

arsenic and antimony are partly oxidized. As they oxidize, part is expelled as they pass through the intermediate volatile state of ar.senious 

acid and trioxide of antimony; while part, becoming fully oxidized, combines with the metallic oxides to form arseniates and antimoniates, 

which are non-volatile. In the subsequent fusion, part of the still unoxidized arsenic and also (though to a smaller extent) of the antimony 

is expelled as sulphide; while the portions previously fully oxidized to 

the non-volatile condition of arseniate and antimoniate are again reduced : part to metallic arsenic and antimony, which combine with 

the resulting matte, while part is expelled while they are in the intermediate volatile state of arsenious acid and trioxide of antimony. Thus 

in the alternate oxidizing and deoxidizing operations, the roastings and 

fusions, much of these noxious elements passes alternately from the state 

of sulphide, in which they are quite strongly held by the matte, to the 

nou-volatile completely oxidized condition and back again, and on each 

of these passages a portion is expelled in the intermediate volatile state 

of arsenious acid and trioxide of antimony.

These elements are sometimes, when present in great quantity, eliminated in a speiss, and they are frequently concentrated in a small portion 

of the copper (in copper bottoms) by reducing a little of that metal to 

the metallic state, the rest remaining in a matte which is nearly free from 

arsenic and antimony.

In roasting pyritons ores a considerable amount of arsenic and even 

of antimony may be expelled as sulphide, in combination with the sulphur 

volatilized from the pyrites.

4. In the series of roastings and fusions whose aim is the expulsion 

of iron, of arsenic and antimony, and of the other heavy metals, much 

of the sulphur is inevitably expelled. By prolonging this series after 

the expulsion of the iron the last portions of the sulphur are finally 

expelled as sulphurous and sulphuric acids (anhydrides).

It is desirable to retain a considerable portion of the sulphur until 

the iron, arsenic, and antimony have been expelled; on account of the 

power which sulphur possesses of removing copper from its oxides without deoxidizing iron, its presence enables us to prolong and push further the oxidizing operations by which the iron, arsenic, and antimony 

are expelled, without incurring, in the subsequent smeltiugs, a heavy 

scorification of our copper. It is moreover much easier to expel these 

elements (iron, arsenic, and antimony) while they are combined with

of antimony. Metallic antimony volatilizes, though slowly, at a white heat. Its trioxide (Sb2 03) melts below a red heat and volatilizes when heated to a higher temperature. Autimonic acid (SbaOs), when uncombined with bases, is decomposed at a red 

heat into free oxygen and tetroxide of antimony (Sb-jC^), which appears to be unalterable by heat alone ; but it does not in general appear practicable to decompose the antimoniatea by heat alone. The trisulphide of antimony volatilizes at a white heat, but 

some other combination of antimony and sulphur appears to volatilize at a lower temperature, The sulphides of antimony are much less volatile than those of arsenic,

(435)
14 COPPEE SMELTING. LBULL. 26.

the sulphur in a matte than when, by the expulsion of the sulphur, they 

become alloyed with metallic copper.

Where sulphureted ores are to be treated with a large proportion of 

oxidized ores, the roastings. may advantageously be abridged or even 

dispensed with, the oxidized ores furnishing the oxygen required for 

the expulsion of the foreign elements.

Where oxidized ores alone are to be tieated the problem is much 

simplified; the iron being already oxidized and arseuic and antimony 

having been for the most part removed by processes of nature similar 

to those which have removed the sulphur and oxidized the iron, little 

remains to be done in general beyond submitting the'ore to a fusion, 

too mildly deoxidizing to reduce°any great amount of iron to the metallic 

state yet sufficing to reduce the copper, the iron passing into the slag.

Thus we may say that the reverberatory and the cupola methods each 

consist of a series of oxidations (roastings), in which iron, sulphur, arsenic, antimony, and to a smaller extent the copper itself are oxidized, 

alternated with smelting operations in which the copper thus oxidized 

is again deoxidized, be it by carbon or carbonic oxide, or at the expense 

of some remaining portion of hitherto unoxidized sulphur or iron, and 

in which the oxidized iron is removed in a slag. The oxidized arsenic, 

antimony, and sulphur escape in the gaseous state.

The roastings may take place in heaps, stalls, kilns, reverberatories, 

or shaft furnaces, according to the mechanical condition and chemical 

composition of the ore treated, the price of the fuel available, and its 

quality, the practicability and expediency of recovering the sulphur 

expelled as sulphuric acid, etc. The fusions may take place either in 

cupola (i. <?., shaft) furnaces or in reverberatories, the choice depending, 

primarily, on the relative prices of coke, anthracite, and suitable charcoal on the one hand, and of bituminous coal, wood, peat, sawdust, etc., 

on the other hand; and, secondarily, on the character of the gangue and 

the character, and cost of the available fltfxes, on the constancy of the 

quality of ore supplied, and to a certain extent on the class of workmen 

obtainable, the size of the establishment, etc. In some establishments 

all of the fusions are performed in cupola furnaces; in others they are 

all performed in reverberatories. Although under all ordinary circumstances it is more economical to use a mixed process -(performing the 

fusion of the ore in cupolas, and the last fusion of matte, whose product 

is mainly or wholly metallic copper, in reverberatories, the choice of 

furnace for the intermediate operations being dictated by considerations which will be given at length in a later paragraph), it is more 

convenient to consider and describe as two distinct and separate 

methods the smelting and bringing forward to metallic copper, employing on the one hand cupolas alone and on the other reverberatories alone for all the fusions. The relative advantages of the two 

methods &nd the cases in which each is specially Applicable can be 

more intelligently discussed after describing the processes themselves,

(436)
HOWE.] REVERBERATORY METHOD FOR SULPHURETED ORES. 15

REVERBERATORY METHOD FOR SULPHURETED ORES.

The procedure in this process varies endlessly, according to local conditions and traditions, not only as regards the details of the several 

operations, but as regards the number of operations employed. In general the number of operations depends chiefly upon 

1. The ratio of the copper to the sulphur, and especially to the sulphide of iron, in the ore. Where this ratio is high the matte obtained 

in the first smelting will be comparatively rich in copper, and hence 

may be brought forward to the metallic state in a small number of 

operations.

2. The importance attached to the expulsion of arsenic and antimony. These elements are expelled more completely by a large number of comparatively incomplete roastings (alternated, of course, with 

smeltings) than by a smaller number of extremely thorough roastings; 

and in order to increase the number of roastings, with a view to increase 

the expulsion of arsenic and antimony, it is sometimes desirable to add 

raw pyrites in a comparatively advanced stage of the process to throw 

the grade of the product back.

3. The cost of labor and fuel as compared with the value of the copper per pound at the smelting works. If each' of the roastings is extremely thorough, higher grade products will be obtained in each smelting, and consequently the copper will reach the metallic state in a smaller 

number of operations and at a considerably smaller cost than if the 

roastings had each been less thorough, but the loss of copper in the 

slags will also be greater. Where labor and fuel are dear and where 

the copper is of comparatively low value (either owing to long distance 

from.market or to depression of the price of the metal), it is naturally 

advisable to push the early roastings farther, so as to lessen the number 

of operations and thus the total cost of extraction, even if the loss of 

copper be thereby increased, than would be expedient if fuel and labor 

were cheap and the copper worth more per pound at the smelting works.

4. Finally, if oxidized ores of copper are to be had to mix with our 

sulphurets, their use may enable us to abridge the roasting operations 

or even to dispense with them altogether.

It would be not only tedious but useless to attempt to describe all 

the methods of procedure. To fix our ideas, let us select for description 

t^wo important methods followed at Swansea and sometimes designated 

as the "ordinary" and the "extra", or "selecting"process respectively. 

The first consists of six operations, the second of seven. As far as the 

first three and the last two operations are concerned the two processes 

are nearly identical, the chief difference being that the fourth operation 

of the ordinary process is in the extra process replaced by two operations.

The ordinary process is as follows:

(437)
16 COPPEK SMELTING. . [HULL. 26.

1. Roasting the ores of class I (ordinary sulphurets).1

2. Smelting the roasted ore of class I with the raw ore of class II 

(lean or impure oxidized ores), obtaining coarse metal (matte), which 

is roasted in (3), and a clean slag, which is thrown away.

3. Roasting the coarse metal.

4. Smelting the roasted coarse metal with ores of class III (chiefly 

rich pure oxidized ores), obtaining white metal.

5. Roasting-smelting the white metal for blister copper.

6. Refining the blister copper.

The extra or selecting process is as follows:

1. The same as in the ordinary process.

2. The same as in the ordinary process.

3. The same as in the ordinary process.

4a. Smelting the roasted coarse metal for blue metal.

4&. Roasting-smelting the raw blue metal for regule and bottoms.

5. Roasting-smelting the regule and bottoms for blister copper.

6. Refining the blister copper.

1. ORE BOASTING. 

ROASTING IN HEAPS OK PILES.

Where the ore contains enough sulphur or bituminous matter to keep 

up an active combustion after the wood employed for firing it has burnt 

out, this method is much the cheapest, requiring the minimum of handling and of plant. It, however, ties the ore up sometimes for many 

months, and certain precautions have to be taken to prevent loss of copper, as soluble sulphate of copper is formed which is liable to be washed 

out by the rain.

Nearly all the sulphur contained in the ore is inevitably lost in pile 

burning, though a very small fraction of it may be condensed as sulphur on the tops of the piles, as at Agordo, the Lower Harz, etc.2

Some examples of the economic features of heap or pile burning are 

given in the following table:

1 See classification of ores and slags, pp. 70-72.

2 Kerl, Grundriss der Metallhiittenkunde, I, p. 139.

(438)
TABLE I. Examples of heap roasting

W

fcO

rto

1

Composition of ore :

Boasted ore smelted, in cupola yields matte containing 

Pomt Shirley, 

Mass.

100 to 150

..........{

17 to 20 

10 to 15

0.15 

0.021 

9

32.5

31 

35.5 

R.,p.273

*a> s5 0.-S

flfc

 §£

&I ' «},§

210

50.0 

P e a-n d 

Zn 42. 0 

1.6 

Say 95.

0.147 

0.007 

40

R., p. 314

Mansfeld. Bituminous schists.

150

7

3 to 5

0.3 

0.04 

10

45.5 

R., p. 378

Mansfeld. Bitu- minous schists.

< 80 to 200 

I Fuder 

K., p. 13

co

CO

a Arsenions acid and sulphide of arsenic copiously evolved. 6 Roast preliminary to 

E. =T.Egleston, Transactions o_f the American Institute of Mining Engineers, X, p. 33. P.=E._D. P

G. ="W. Glenn, private communication. P. N". = Private 

K. Kerl, Grundrisa der Metallhuttenknnde, 1881. R. = Rivot, 
1*8 COPPER SMELTING. [BULL. 26.

ROASTING IN STALLS.

Boasting in stalls requires somewhat more labor than heap burning, 

and a considerable amount of plant. Except where fuel is very dear 

and labor comparatively cheap, these drawbacks will nearly or quite 

counterbalance the advantages it offers over heap burning in effecting a 

small economy of fuel and a somewhat more complete roasting. Beyond this, there is less mechanical loss in stall roasting than in heap 

burning, which becomes a matter of great moment in rich ores.

KILN ROASTING.

Kiln roasting gives a more complete control over the operation and 

more thorough oxidation than either pile or stall roasting, requires no 

fuel, permits the nearly complete recovery of the sulphur as sulphuric 

acid, and requires but as many hours as pile roasting requires weeks or 

even months. On the other hand, kiln roasting requires considerably 

more labor and an extensive and costly plant, so that, except where 

the recovery of the sulphur is aimed at for the manufacture of sulphuric acid or for the protection of the neighborhood from its fumes, 

kiln roasting is rarely as advantageous as pile or stall roasting. When 

ores lean in sulphur are treated the output of each kiln is very much 

greater and the first cost of the kilns per unit of daily capacity (their 

chief drawback) consequently very much less than in the case of ores 

rich in sulphur.

Only lump ore can be treated in the ordinary kilns, and it is not in 

general found practicable to have more than 8 per cent, of fine ore 

mixed with the lumps.

The following table gives some examples of the size and the output of 

kilns and of the expulsion of sulphur in them :

TABLE II. Size, output, <fc., of pyrites kilns.

Locality of ore.

Davis, Mass.... 

Westphalian . . . 

Norwegian .....

Capelton, Can . .

Per cent, of sulphur.

Before 

burning.

48 

40 to 42 

38 to 40 

49 

41 to 42 

41 to 42 

40 

40 

Very 

small.

After 

burning.

3

4.5

Grate.

Length.

< // 

5 8

(a)

4 6

Width.

/ // 

4 6

(a)

4 6

Thickness oforebars. grate on 

/ // 

2 3

......

16J 

2 6 

(6)

Pounds roasted orefoot ofper squae twenty- grate per

lour hors.

30 

35 

40 

32 

50 to 64 

38.3 

30.5 

49

Pounds roasted orekiln twen- per 

ty-four hours.

787 

000 

1,012 

800

1,000

Days of labor per 

of tonre.

......

0.41

Authority.

> Lunge.

Private notes. 

\ Bode.

BrJiuning. 

Private notes.

a Twenty-five square feet grate.

(440)

b About 7 feet.
HOWE.J REVERBEEATORY METHOD FOR SULPHURETED ORES. 19

FURNACES FOR FINE ORE.

Three of these, Gerstenhofer's,1 Hasenclever and Helbig's,2 and 

Maletra's,3 have corne into extensive use for roasting ores where the 

manufacture of sulphuric acid is aimed at. Each effects a thorough 

roasting with a considerable saving of fuel and labor as compared 

with roasting in reverberatories. The first two, however, are very 

costly in construction.

Hasenclever and Helbig's burner consists of a vertical series of zigzag 

shelves inclined at an angle of 38° ; on these the ore lies at its natural 

angle of repose, 33°, and gradually slides down from each shelf to the 

next lower as that on the lowest shelf is withdrawn. This burner, 

though capable of good work, apparently cannot compete with Maletra's 

or Gersteuhofer's under any ordinary conditions.

Gerstenhofer's beautiful furnace hardly needs description. Briefly, 

it consists of a vertical shaft, across which run a great many (say 100) 

parallel horizontal fireclay bars, staggered so that the ore falls from 

one to another as it passes from the feeding hopper at the top to the 

discharge at the bottom. This seems to be an excellent apparatus for 

treating ores and mattes lean in sulphur, especially where the manufacture of sulphuric acid is aimed at and where the material to be 

treated would be pulverized at any rate. Where the material is in 

lumps it will not often be expedient to pulverize or granulate it for 

this furnace. It is used in Freiberg for roasting* ores and in Swansea 

extensively for matte-roasting, the matte being granulated especially 

for the purpose. The first cost of the furnace and the cost of repairs 

are very heavy per unit of output, and it is stated that the ore must 

be reduced to a very uniform size, the largest grains not exceeding 0.04 

inch in diameter, a condition hard to comply with.

Maletra's (or Schaffner's) furnace is better adapted to ores very rich 

in sulphur, such as cupreous pyrites, but less applicable .to ores lean 

in sulphur than Gerstenhofer's. It consists of a rectangular firebrick 

chamber some 7 feet 6 inches high, 9 feet long, and 4 feet 6 inches wide, 

all inside measurements. In this chamber'are seven shelves, each extending the whole width of the chamber, but each 6 inches shorter than 

the inside length of the chamber, so that spaces are left between the 

ends of the shelves and the end walls of the chamber, and through these 

spaces the ore is transferred from shelf to shelf. The shelves are staggered so that these spaces come alternately at the front and rear ends 

of the chamber. The fine ore is charged on the upper shelf and after 

four hours moved to the next lower shelf, when a fresh charge of ore is 

introduced on the upper shelf. After four hours more each charge is

1 Sulphuric acid aud alkali, Lunge, I, p. 205, and Kerl's Grnndrisa der MetallMttenkuudo, I, p. 147.

2 Lunge, op. cit., p. 196. 

'Ibid.,p. 218.

(441)
20 COPPER SMELTING. [BULL. 20.

moved to the next lower shelf, and so on, each lot of ore remaining 

four hours on each of the seven shelves, and thus having a total exposure of twenty-eight hours. Here, as in the two furnaces last described, the compact arrangement allows so little radiation of heat 

that the heat generated by the combustion of the sulphur and iron of 

the ore suffices to keep the apparatus up to the proper temperature 

without the employment of any extraneous fuel; the removal of the 

ore from shelf to shelf exposes fresh surfaces to the air.

This burner has a great advantage over Gersteuhofer's in not requiring the ore to be either uniformly or very finely crushed. In some cases 

dust and pea size are roasted together, leaving it is said only 1 to 1.5. per 

cent, of sulphur in the ore. For fine ores, rich in sulphur, this is probably by far the best apparatus yet devised,whether for acid making or 

as merely preliminary to smelting simple in construction, repairs, and 

operation, and highly efficient. It is already extensively used in this 

country and in Europe for burning cupreous and other pyrites for acid 

making.

As compared with Gerstenhofer's, Hasenclever and Helbig's, and 

other automatic furnaces, it has the serious disadvantages that the doors 

must be frequently opened, allowing a great excess of air to pass into 

the acid chambers, with loss of acid and increased consumption of niter, 

and that considerable labor is required in charging and working the 

ore.

Spence appears to have removed both these drawbacks of the Maletra 

furnace by making it automatic. He attaches to it an ingenious arrangement of automatic traveling rakes 1 and an automatic charging and discharging apparatus, the rakes which stir the ore and transfer it from 

shelf to shelf passing through stuffing boxes and thus preventing the 

entrance of air. This modification of the Maletra furnace is coming 

into use in this country, and appears to the writer to be the most 

promising mechanical roaster yet proposed for cupreous pyrites. The 

corrosion of the iron moving parts by the acid fumes, a fatal stumbling 

block to many mechanical roasters, has certainly been here reduced to 

a minimum. Still, it can hardly be considered as fully established that 

the advantages which it offers more than compensate for its increased 

first cost and its probably heavy additional wear and tear.

1 The Spence furnace is described by W. H. Adams in Transactions of the American 

Institute of Mining Engineers, Vol. XIII, p. 345; also, in The Engineering and Mining 

Journal, April 11,1885.

(442)
UOWE.] REVERBERATORY METHOD FOR SULPHURETED ORES. 21

TABLE III. Showing some economic features of roasting pyrites in ffasendever and ITellig's, 

Girstenhb'fer's, Maletra?s, and ^pence's furnaces.

Name of furnace.

Hasenclever and Helbig.

......Do................

......Do................

Spence (mechanical) a . . .

Kind of ore.

C Pyrites ............

I Cupreous pyrites . . 

Cupreous pyrites . . .

....do..............

Cupreous pyrites. 

Capellon, Canada. 

Pyrites.' Charlemont, 

Mass. 

Pyrites. Louisa 

County, Virginia.

days Labor, per roasted. ton ore

0.66 

0.62 

0.56 

60.375

Output fur- per twenty- nace per four hos, in 000-pound 2,tons.

0.5 to 0.8 

0.75 to 1.0 

2.0 to 5.0

0.75 

1.00 

0.65 

3.6 to 4.75

Per cent, sulphur 

in ore.

Initial.

48 

40 

49 

46

Final.

3.7 to 6.5

1. to 1.5 

4 

4 

1.25 to 2.25

Authority.

> Lunge, op. cit. 

5 p. 100. 

Lunge, op. cit. 

p. 205. 

Lunge, op. cit. 

p. 215. 

Private communication. 

Do.

W. H. Adams, 

private communication.

a 1.25 horse power are used in working each furnace.

b When working only two furnaces. The labor per ton should be much less if a larger number of 

furnaces were used.

Revolving cylinders, such as Bruckner's, Oxland's, etc., have not hi 

general been successful in roasting copper ores. Ores rich in sulphur 

are so plastic during the early part of the roasting that the surfaces of 

the individual pellets of ore are closed, or, as it were, welded up by the 

series of impacts produced by their fall through the cylinder. This objection does not apply with as much force in the case of ores lean in 

sulphur, and further experience may show these furnaces to be desirable 

for such ores.

The Stetefeldt furnace, for the same reason, has generally been considered inapplicable to copper ores ; but it may yet be found applicable 

to ores containing little sulphur.

Reverberatory furnaces. 1. Open reverberatories employ at least as 

much labor per ton of ore treated for a given amount of oxidation as 

Maletra's shelf-burners and considerably more than heap, stall, or kiln 

burning; in addition, they involve a pretty heavy consumption of fuel, 

say 0.114 tons fuel and upward per ton of ore. They are therefore 

rarely desirable for ores rich in sulphur, which, if in lumps, are best 

roasted in piles, stalls, or kilns, and if fine in Maletra's (or perhaps 

Spence's) furnace. Reverberatories are, however, desirable, especially 

when fuel is cheap, for ores too lean in sulphur to furnish the heat needed 

for their own roasting and for ores containing much arsenic or antimony, 

since they afford special means for the expulsion of these elements.

One great advantage which reverberatory roasting furnaces offer as 

preparatory to other processes (viz, enabling the oxidation to be carried 

farther than is practicable in heaps and kilns) here in general counts for 

little, since an oxidation sufficiently thorough for the purposes of copper 

smelting can be obtained in heaps and kilns where the ore is rich enough 

in sulphur to be appropriately treated in them.

(443)
TABLE IV. Matte and ore roasting in rever

Authority. ........................

Dimensions of furnace :

^ Height of roof above hearth at

Work done : Weight of charge in 2,000- 

pound tons ..................

Thickness of charge on hearth .

Tons output per furnace per

Composition of material roasted :

Smelte'd in reverberatory yields 

matte containing 

and slag containing 

Conner ........................

. f

000 " i"

Ef

09

1.

L. P., p. 170 .

14' 1i"

4' ...........

3'...........

19 4

4' ...........

1' 4" ........

3' 2" ........

46'6 ........

3' 6" ........

3.8 .........

12...........

7.65.........

24 ..........

10. .........

20...........

30

30 to 33 .....

30 to 33 . ...

fin *,

0.5..........

Swansea, matte (coarse metal), 

1848.

2.

R., p. 217... 

17' 2J"

14' 1J"

3' ...........

19.4 ...... ..

4'.......-...

l'7f. ......

1' 4".. ......

3' 2" ........

46'..........

3

1 a/i

4.96.........

36...........

3

O

on c

oo *7

34.2.........

21.23........

5.9..........

65.72........

58...........

1 to 1. 7 .....

ffl 

g

cfoo

COO

09

3.

V. ........ 

28'.....-..

13'........

15.88......

J2. ........

30 to 35 ...

Swansea, matte 

1880.

4.

V,p.21...

4.5........

36.........

8..........

23.........

33.........

72 to 75 ...

Briglia, cupreous pyrite.

6.

C.,p. 320.. 

13'........

15* 5".....

~

5.88.......

K

0

4

4

6
Outlay of labor and fuel :

VDP] tons ^Per Auuu IDS. OI f

Brick, tons ::> terial roasted. £

< An. 72pts.

0.123.......

0.0036.......

Bit 28 pts. I

An.72pt8.J

0.70.........

0.41.........

Wood. ....

0

a Roasted matte, smelted in a cupola, yields two parts of black copper and on

6 Serves ten roasting furnaces.

C. = Capacci, Revue Universelle, 1881. X.

E. = Egleston, Transactions American Institute of Mining Engineers, iv, p. 421. 

"K. = Kerl, Grundriss der Metallhuttenknnde, 1881. I. 

L. P. = Le Play, Description des Proc6des M6taUurgiques, etc.

P. N. = 

R. = 

V. = 
"24 COPPEE SMELTING. [BULL.M.

Table IV gives the dimensions of several reverberatory roasting furnaces, the work done in them, and the outlay of fuel and labor, both in 

ore and matte roasting. A comparison of the first and second with the 

third and fourth columns shows how greatly the output, not only per 

furnace, but also per square foot of hearth area, has been increased in 

^ modern practice.

2. Muffles afford a somewhat more strongly oxidizing atmosphere 

than open reverberatories, and a more uniform temperature, and there 

is less loss from flue dust. This latter is not, however, a very weighty 

-consideration, except in the case of rich ores and those carrying considerable silver or gold besides copper, and the considerably greater 

consumption of fuel in muffles generally renders them less desirable for 

ordinary ores than open reverberatories. At Lambert's works,1 and at 

Polvereda, and many other points in Chili excellent and highly economical work is done in muffles heated with the waste heat from ore smelting reverberatories. As the fuel item is thus entirely eliminated, the 

muffle becomes under these conditions perhaps the best of appliances 

for fine ores lean in sulphur.

3. Of mechanical reverberatories, from lack of space, I can only mention 

Gibbs's2 mechanical furnace, in which the hearth revolves, the ore being 

stirred by fixed knives which plow through it as it travels around on 

the hearth. Though of great promise it is said to have been abandoned. 

A description of Park's,3 MacDougall's,4 and O'Harra's 5 furnaces would 

carry us beyond the limits of this paper.

The preceding figures of the consumption of fuel and labor in roasting a ton of ore are briefly summed up in the following table. While 

these figures are by no means strictly comparable, since different ores 

are treated in each case with different degrees of thoroughness and of 

skill and with somewhat different objects, yet they are so nearly comparable as to be instructive. It should be remembered that the roasting in reverberatories, which aims only at the partial oxidation needed 

as a preliminary to smelting, is intentionally less thorough than that 

in kilns and in maletra-burners, in which the most complete possible 

expulsion of the sulphur, for conversion into sulphuric acid, is sought.

1 Copper Smelting, its History and Processes, Henry Hussey Vivian, Scientific Publishing Company, New York, 1881, p. 17.

2 Lunge, op. cit., p. 208.

3 Koasting Gold and Silver Ores, G. Kustel, 1880, p. 81.

4 Lunge, op. cit., p. 222. 

6 Kustel, op. cit.; pp. 82-84.

(446)
IIOWB.] REVERBERATORY METHOD FOR SULPHURETED ORES. 25

TABLE V. Showing the consumption of fin I and labor in roasting one ton of ore by different

methods.

Mode of treatment.

Maletra's shelf burner . 

Keverberatory furnaces

Labor.

Days. 

0. 13 to 0. 30 

0. 25 to 0. 41 

0. 56 to 0. 67 

0. 30 to 0. 70

Fuel.

Quantity per ton of ore.'

...... do .................

Kind.

Wood. 

Coal.

OBJECTS OF THE ROASTING.

1. An oxidation of the iron and incidentally of the sulphur as complete 

<rs is possible without involving an undue loss of copper in the slags of the 

following smelting. If the oxidation be very imperfect, the resulting 

matte will contain so much iron that its bringing forward will be unduly costly. If the oxidation be too thorough, an undue loss of copper 

will occur on smelting the roasted ore, first, from the individual shots

 of the resulting matte carried out by the slag being very rich in copper; 

iind second,.sometimes from actual scorification of copper. Of course, 

what an undue loss of copper is depends on local conditions: if labor 

and fuel are dear, if heavy freight is to be paid on the copper produced, 

.and if the price of copper itself is low, as at present, we should aim in 

the first smelting for a product much richer in copper than when the

 opposite conditions prevail, since under the former supposition the saving of assumedly high-priced fuel and labor due to having a rich instead 

of a lean matte to "bring forward" to the condition of ingot copper 

would weigh more heavily against the increased loss in the slags of 

assumedly low priced copper.

It is rarely for the interest of the proprietors to produce the cleanest 

possible slags.

Thus, at Swansea,1 where fuel and labor are very cheap, and where 

copper is of great value, owing to the immediate neighborhood of the 

market, they aim at a matte with from 30 to 35 per cent, copper; in the 

Copiap6 district in Chili, however, where fuel and labor are costly and 

copper comparatively low in value, owing to the great distance from 

market, they aim at obtaining a 50 per cent, matte in the first smelting.

2. The expulsion of arsenic and antimony. As already stated, these 

elements may be volatilized as sulphides, and in the partially oxidized 

condition of arsenious acid and tridxide of antimony. Mildly oxidizing 

conditions, which will tend to form these imperfectly oxidized compounds, rather than non-volatile fully oxidized arseniates and antimoniates, and which may even allow the arsenic and antimony to be attacked 

by the volatilized sulphur, are thus more favorable to their expulsion 

than are strongly oxidizing conditions, which would hurry them through

'Vivian, op. cit., p. 14. 

(447) '
26 COPPEE SMELTING. [BULL. 26.

the intermediate volatile state to the stable condition of arseuiates and 

antimoniates, and would rapidly oxidize the volatilized sulphur, and 

thus prevent it from volatilizing the arsenic and antimony as sulphides.

(a) In pile and stall roasting, the exterior portions of the individual 

lumps in the middle and upper layers of the piles are indeed exposed for 

a long time to the passing sulphur, which is volatilized from the lower 

layers, and to air whose oxidizing power is greatly weakened, part of its 

oxygen having been absorbed and fixed by the oxidation of the iron and 

part having been converted into sulphurous acid. The interiors of the 

lumps, however, especially in compact oresf are not so fully exposed to 

these mildly oxidizing con'ditions and to contact with volatilized sulphur, 

both so favorable to the expulsion of arsenic and antimony. What sulphur volatilizes from the interior of the lumps generally escapes through 

a few fissures, from the immediate vicinity of whose walls it may indeed 

drag away a portion of these hurtful elements; but the arsenic and the 

antimony in the greater portion of the interior of the lumps are to a 

certain extent protected from removal. Hence we see that their expulsion is favored by having as large a proportion of exterior to interior 

as possible; that is, by having the lumps as small as is compatible 

with allowing regular burning and proper draft.

For the same reason, in matte roasting it is desirable to cast the 

matte in thin plates rather than in irregular thick lumps, since the 

proportion of surface is much greater in the former. The expulsion of 

arsenic and antimony as sulphides is favored by mixing pyrite with 

the ore as intimately as possible, so as to increase their exposure to the 

volatilizing sulphur; and Eivot1 recommends bricking pulverized 

arsenical ores and cupreous pyrite together in intimate mixture, so as 

to allow the sulphur volatilized by the pyrite to drag off the arsenic.

It is evident, also, that the expulsion of arsenic and antimony as sulphides is in pile roasting much more favored in ores where the minerals carrying these elements (such as mispickel, tetrahedrite, enargitc, 

etc.) are naturally intimately mixed with pyriie than when the reverse 

is the case.

(b) In roasting in reverberatories, during the intervals between the rabblings, and while the ore is lying still on the hearth, we may distinguish 

three horizontal zones: First, there is the upper surface, directly exposed 

to ihe atmosphere of the furnace whose oxidizing action is slightly weakened by the presence of sulphurous and sulphuric acids evolved from 

the underlying layers and of the products of the combustion of the 

fuel; second, the layers immediately underlying the surface, in which 

a small portion of free oxygen enters by diffusion, and in which sulphur 

and sulphurous acid evolved from the undermost layers oppose the 

oxidizing action of what free oxygen there is present; third, the undermost layers, to which little, if any, free oxygen can penetrate, and where

1 Op. cit., p. 142. 

(448)
HOWE.] REVERBERATORY METHOD FOR SULPHURETED ORES. 27

each pellet of ore is simply exposed to the action of the other pellets 

with which it is in contact, of volatilized sulphur and of sulphurous 

and sulphuric acids (anhydrides) generated by the action of sulphur'on 

previously formed metallic oxides.

The expulsion of arsenic and antimony as sulphides is favored in the 

middle and lower zones by the presence of volatilized sulphur, mixed 

with sulphurous acid and at most a very limited supply of free oxygen 

and sulphuric acid. In the upper part of the middle layer, to which a 

small amount of free oxygen penetrates, we have the gently oxidizing 

conditions favorable to the formation of arsenious acid and trioxide of 

antimony. In the upper zone the stronger oxidizing conditions rather 

favor the formation of fixed arseuiates and autimoniates, though even, 

here part of the arsenic and antimony may volatilize and escape while 

passing through their intermediate volatile condition of arsenious acid 

and trioxide of antimony.

Now, when we come to stir the mass up and to transfer particles, 

whose arsenic and antimony, while in the upper zone, had passed to the 

fixed acid condition, down into the middle and lower zones, it is probable that we afford these metals a fresh opportunity to volatilize by 

reducing them to the volatile conditions of arsenious acid and trioxide 

of antimony through contact with volatilized sulphur and with the still 

uuoxidized metallic sulphides of the surrounding ore pellets.1 The low 

oxides (protoxide of iron and suboxide of copper) of these ore pellets 

and the sulphurous acid present in the middle and lower zones also 

exert a reducing action on arsenic acid, with the formation of higher 

oxides of iron and copper and of sulphuric acid.2 Thus each individual 

atom of arsenic (and of antimony ?) may travel back and forth many times 

through the volatile condition, being oxidized to and perhaps past it 

at the upper surface, and again reduced back to if not past it as it is 

again drawn down below the surface, seesawing back and forth to and 

from the volatile state. And every time that it arrives at this volatile 

condition an opportunity is offered it to volatilize and escape. This 

opportunity for reduction from the fixed acid state is, of course, only 

offered to these noxious metals as long as a considerable amount of 

unoxidized sulphur and iron or of low oxides of iron or copper remains 

to effect their deoxidation. But, even after the nearly complete oxidation of the sulphur and iron, similar opportunities may be, and indeed 

often are, offered to the arsenic and the antimony to pass once more from 

the fixed acid state towards the metallic state and back again, by mixing a small quantity of coke or coal dust with the roasting ore, and 

then excluding the air as completely as possible so as to strengthen the 

reducing conditions. The carbon plays a role similar to that already 

ascribed to the sulphides and low oxides in reducing arsenic and anti1 The behavior of antimony under these conditions is not so clear as that of arsenic. 

4 Balling, Compendium dor metallurgischen Chemie, p. 51.

(449)
28 COPPEE SMELTING. [BULL. 26.

mony to and perhaps through the volatile state. By .prolonging the 

roasting after the combustion of the coal dust has been completed we 

reoxidize any arsenic and antimony which may haye been carried back 

past the volatile state, and we again pass them towards it.

Of course, the expulsion of arsenic and antimony is favored by the 

presence of a large proportion of pyrites, both because the sulphur distilled from the pyrites tends to drag them off as sulphides and because the presence of the pyrites prolongs the roasting, and thus increases the number of times which the arsenic and antimony pass back 

and forth past their volatile conditions; hence it is sometimes desirable 

to mix pyrites with impure ores to further the expulsion of their impurities.

(c) In comparing the heap and the reverberatory treatment, it may be 

said that this alternation of oxidizing with reducing conditions in the 

reverberatory should offset the advantage as regards the expulsion of 

arsenic and antimony which pile burning offers in its prolonged exposure to gentle oxidizing conditions. The further advantages in this 

regard which the reverberatory offers in the enormous surface exposure (owing to the fine state of division of the ore, which in piles is in 

large lumps, whose interior may be comparatively little acted on), in 

the uniformity of its action (pile roasting being necessarily very irregular), and in the power of reducing arsenic and antimonic acids with 

coal dust render it probably much more efficient for the expulsion of 

these metals than pile roasting is. Exact comparative tests are, of 

course, needed to enable ona to speak with absolute certainty on this 

head.

The advantage of the reverberatory over pile roasting as regards the 

expulsion of arsenic and antimony is probably considerably less in the 

case of ores in which the arsenical and antimonial minerals are intimately mixed with-pyrites than when the reverse is true, since in pile 

roasting in the former case the sulphur volatilized from the pyrites has 

a far better opportunity to drag off these metals as sulphides than 

when the antimonial and arsenical minerals are well separated from 

the pyritous portions. In the reverberatory, on the other hand, the 

whole is so mixed together that the original mechanical condition of 

the ore in this respect matters little.

2. SMELTING THE ROASTED ORE IN REVERBERATOREES.

FURNACE CONSTRUCTION.

Fire-box. The distance from the bars, which are of wrought iron, to 

the top of the fire-bridge is generally very great, often upwards of 3 

feet, to allow a thick bed of clinker on which the coal rests. The 

 clinker both preheats the air and prevents fine fuel from falling through 

the bars. The area of the grate is generally about one-fifth of that of 

the hearth, though it should be larger than this in case the fuel be either

(450)
HOWE.J EEVEEBEEATOEY METHOD. FOE SULPHUEETED ORES. 29

unusually bulky or of low calorific power, as in the case of wood, peat, 

lignite, etc. Grunerl gives the following proportions of hearth area to 

grate area:

Copper refining furnaces, 4:1.

Copper matte smelting furnaces, 5 or 6:1.

Black copper furnaees, 4.50:1.

For exceptionally refractory ores the area of the grate should be 

more than one-fifth that of the hearth; for exceptionally fusible ones, 

proportionally less.

If we base the area of the grate on the weight of fuel which is to be 

burnt on it, then we should allow about 25 pounds of coal per square 

foot of total grate surface per hour. The fuel consumption sometimes 

falls as low as 16 pounds of coal per square foot of grate per hour and 

sometimes rises to 36 pounds, but about 25 pounds appears to be the 

best practice. It should, of course, be influenced by peculiarities in 

the nature of the fuel, strength of draft available, etc.

Special varieties of coal may, of course, require special forms of 

grate, but the deep rectangular grate with a deep bed of clinker is 

nearly universally used, even for fine coal.

Mre-bridge. The longitudinal thrust of the hearth, due to its expansion on being heated, has to be met by inserting in the fire-bridge a 

very strong iron plate, or, better, a cast-iron box-girder, called a bridgeplate. The bridge-plate carries the stress either to the longitudinal 

walls of the fire-box, which in turn carry it to the buckstays at the rear 

end of the fire-box, which are held firmly to buckstays at the firont end 

of the furnace by longitudinal tie-rods; or, better, the bridge-plate rests 

directly on the buckstays at the rear of the main body of the furnace, 

which are also firmly held by longitudinal tie-rods. To protect the 

bridge-plate from the heat the fire-bridge must be very thick, and to 

the same end, as well as to retard its corrosion, a current of cold air 

should pass through it to cool it. An arrangement adopted by the 

writer is to make the arch on which the furnace bottom rests hollow, 

so that a current of air may pass through it and the bridge-plate and 

by means of a damper be either admitted beneath the grate-bars or, in 

case it is desired to increase the oxidizing action of the furnace, directly 

into the laboratory. This arrangement intercepts and utilizes the heat 

which would otherwise escape from the bottom of the furnace. The 

same thing can of course be effected in many other ways.1

The inwalls rest directly on the lower arch. They should be laid all 

headers.

The roof is also laid alhheaders, and in a very flat arch, whose generatrix is parallel with the major axis of the furnace. The arch is made as 

flat as is consistent with stability; for ordinary widths a rise of one-half 

inch for each foot of span suffices. The roof bricks are laid in courses

1 Trait6 de MStallurgie, I, p. 269, 1875. 

(451)
30 COPPEE SMELTING. TBOLL. 26.

2£ inches thick, the courses being parallel with the major axis of the 

furnace; that is to say, the length of the brick (9 inches) is normal to 

the soffit or intrados, the bed joints (the 4^-inch dimension of the brick) 

parallel with the major axis of the furnace, the side joints (the 2^-inch 

dimension of the brick) parallel with the minor axis, and consequently 

perpendicular to the major axis. The side joints break joint at each 

course. This manner of laying the roof gives such stability that it 

enables us to use extremely flat arches. It is no uncommon thing for 

the old thin roofs of copper-smelting reverberatories, when cooled down, 

to be actually lower in the middle than at the sides in certain places j 

that is, for large portions of the upper surface of the roof to be actually 

concave. When such a roof is again heated the strength of the bond 

just described is so great that when adjoining portions which had remained convex again become heated, expand, and rise, they raise the 

portion which had been concave.

The plan employed in puddling and heating furnaces of laying the 

roof bricks in 4£ inch courses parallel with the minor axis of the furnace, 

instead of in 2^-inch courses parallel with its major axis, while facilitating repairs, would, if used in the broad, flat arches of copper-smelting reverberatories, allow the separate courses to fall down, one by 

one, as has been shown by actual experience, since this manner of laying the roof does not give stability.

It is a usual rule to make the lower edge of the velvetry level with 

the upper front edge of the fire bridge.

Binding. The transverse stresses to be resisted by the binding are 

the thrust of the roof and the lower arch and their expansion, and 

more especially that of the bottom, on being heated. Of these the expansion of the bottom is the most serious, because its mass is very 

great, and because the stress due to its expansion comes in the middle 

of the length of the buckstays. These stresses are resisted by a set of 

vertical backstays at the sides of the furnace. Each buckstay is held 

in place by two tie rods extending from its top and bottom to a buekstay at the opposite side of the furnace. Each buckstay is thus a vertical beam supported at both ends (by the tie-rods) and loaded with 

an irregularly distributed load (the thrusts of the arches and the pressures due to the expansion of the arches and the bottom). The buckstays 

are rarely stiff enough for the stresses they encounter and generally 

bend a great deal, thus shortening the life of the furnace and greatly 

increasing the cost of repairs. Old rails are generally used, but the 

writer strongly recommends the use of light I beams. The buckstays 

should be of wrought, not of cast, iron, unless there is an unusual difference in cost in favor of the latter material. Cast-iron buckstays 

should be made of much greater strength than is required in case of 

wrought iron, since the latter material is so comparatively flexible that

1 Transactions of the American Institute of Mining Engineers, IX, p. 689.

(452)
IIOWB.] REVERBERATORY METHOD FOR SULPHURETED ORES. 31

if an undue stress comes on one buckstay it can safely yield enough to 

cause its excess of stress to be transferred to its neighbors, while if all 

are unduly strained their bending gives timely warning, and the tierods can be relaxed. With rigid cast iron, however, each buckstay has 

to uphold the load which happens to fall on it without bending, and 

its sudden snapping is the first intimation that it has been overloaded. 

This disadvantage of cast iron, however, may be met by having the tierods hold the ends of the buckstays not rigidly but through powerful 

spiral springs.

The load on the buckstays, of course, varies greatly in different furnaces, but it is probably safe to assume that, in furnaces of ordinary 

widths, the total transverse stress is equivalent to a load of 5,000 

pounds per running foot of the length of the furnace, concentrated at 

the middle of the length of the buckstays. From this may be calculated 

the dimensions of tie-rods and buckstays required to withstand it. The 

tie-rods beneath the furnace should be much thicker than this load requires, to allow for corrosion. They should be placed beneath the lower 

arch, so as to lessen their expansion from heat. Many engineers contend, and not without reason, that the lower ends of the buckstays 

should be held, not by tie-rods, which inevitably expand greatly from 

the heat, but by placing large flagstones against them bedded firmly in 

the ground. Expansion from heat becomes a still more serious thing in 

the case of the much longer longitudinal tie-rods which retain the lower 

ends of the buckstays at the ends of the furnace.

The side buckstays should be so long that the tie-rods at their upper 

ends may stand several inches above the roof when the latter is cold, 

as it rises greatly when heated, sometimes as much as 6 inches.

The chief longitudinal stress is that due to the expansion of the 

hearth or bottom. Like the transverse stresses, this is resisted by a 

system of tie-rods and buckstays, the stress at the fire-bridge end being carried from the hearth or bottom to the buckstays by the powerful bridge-plate already described.

These several stresses may be advantageously concentrated on the 

buckstaySj both side and end, by bedding 3" and 5" angle-irons in the 

brick-work horizontally, and bearing directly against the buckstays, the 

5-inch angle-irons opposite the bottom and the 3-inch ones opposite 

skewbacks of the roof and of the arch beneath the bottom. The 

thrust of the bottom at the front end is generally carried to the buckstays on either side of the skimming-door by means of a heavy castiron plate, greater stiffness for a given weight being sometimes obtained by making the plate very thick indeed, say 4 or 5 inches, but 

open-worked, like the cane bottom of a chair, the minimum of material 

thus being concentrated in a series of deep, stiff ribs.

The tie rods may either be threaded at the ends, passing through 

holes in the ends of the buckstays, or formed into a loop and passing 

around the ends of the buckstays. In the latter case the tie-rods should

(453)
32 COPPER SMELTING. [BULL. 26.

be tightened with turn-buckles in their middles rather than with wedges 

at their ends; the extra cost of the turn-buckles is trifling, and the 

wedges are at best slovenly and liable to slip. To make the threaded 

portion as strong as the unthreaded, the diameter of the rods at the 

bottom of the threads should be equal to (or better, slightly greater 

than) that of the unthreaded portion.

The furnace is much neater in appearance and probably considerably 

more durable if it be all encased in wrought or cast irou plates reaching down to the ground level. This plan enables us to place the buckstays farther apart, concentrating their strength in a smaller number 

of stiffer buckstays, with stronger tie-rods; the total weight of material 

required for the buckstays is considerably reduced by this condensation, and the cost of the system of buckstays and tie rods decreased in 

a still larger proportion, thus partly compensating for the extra cost of 

the binding plates.

Erection of binding. The rule should be to build the masonry against 

the iron work; and it should not be attempted to fit the iron work to 

the masonry. Thus, when the walls have reached the springing of the 

lower arches the buckstays and tie-rods should be put in their proper 

places and tightened up permanently. The angle-irons and the binding plates should be put in position as soon as the masonry reaches the 

level destined for their lower edges. In this way the masonry can be 

rammed firmly against the iron work and the greatest extent and uniformity of bearing obtained. All the iron work, but more especially 

the lower tie-rods, should be smeared with hot tar, and the tie-rods 

should be heated before applying the tar, so as to increase its adhesion.

The masonry. All the brick-work above and including the lower arch 

should be laid in fire-clay; it is a first rule to make all joints as thin as 

possible, since the clay joints are more fusible than the bricks themselves. For the roof and inwalls cutting of bricks should be avoided 

as far as possible; bricks molded to the proper shape (wedge, split, 

soap, jamb, etc.) being much cheaper and far more durable than chipped 

bricks, as the chipped surfaces are not, it is said, so refractory as the 

kiln-burnt surfaces.

The outer walls may be made of inferior fire-bricks, or even of red 

bricks. The roof should be of the most refractory bricks obtainable, 

such as the Diuas, Allentown, or Mount Savage. Many prefer to simply dip the roof bricks in thin fire-clay slurry on laying them, as the 

thinnest possible joints are thus obtained. Too great care cannot be 

bestowed on laying the roof. The key-bricks should be driven so tight 

as to raise the whole roof off the center on which it is built..

For the fire-box and the inwalls, at least for the portion of the inwalls 

which comes in contact with the charge, Dinas and similar silica bricks 

are not suited, since here it is not so much the heat as the corrosive 

action of the clinker and slag that is to be resisted. These parts should 

therefore be made of more basic or aluminous bricks. The Stourbridge

(454)
HOWH.] REVERBERATORY METHOD FOR SULPHURETED ORES. 33

bricks, which have as high as 45 per cent, of alumina, and the Garnkirk, are greatly esteemed for inwalls.

The brick-work of the roof, inwalls, fire-box, and bridge should be 

laid all headers. When laid in this way it lasts and holds together till 

the greater part of the length of the bricks has been worn away or 

incited off.

The bottom or hearth. Its preparation is a most difficult matter. It 

must be sufficiently refractory to resist the intense heat and it must be 

so solid that the matte or copper floating on it can find no crevice down 

which it can work. It is generally held that it cannot be made of brickwork; that no matter how tight its joints be nor how cunningly it be 

dovetailed together, the matte works down through the joints and 

gradually lifts the brick bottom up. It is therefore universally made 

inouolithically of more or less pure quartz sand alone.

In Swansea an only moderately refractory sand is (or was formerly) 

used for making the bottoms, having the following composition : 1

Silica........................................................................ 86.0

Lime........................................................................ 5.7

Magnesia.................................................................... 0.8

Alumina..................................................................... 1.6

Peroxide of iron.................. ............................................ 1.2

Carbonic acidjwith trace of water............................................ 4.5

99.8

At Bergen Point moderately refractory sand from Perkiomen is used 

with great success. From these instances it might be supposed that 

some degree of fusibility was necessary or desirable in bottom sand; 

but in the Copiap6 Valley in Chili, and elsewhere, the bottoms made 

of pure crushed glassy quartz stand three years and more. Thus excellent bottoms may be made from materials of widely varying properties; but each material requires different treatment. Highly skilled 

workmen brought to New York Harbor from Britain could not make 

durable bottoms with the Perkiomen sand, which was used in a neighboring establishment with perfect success; and the sand they were 

accustomed to using had to be imported from Britain for them.

In making these pure quartz bottoms in Chili about one-third of the 

quartz required for the bottom is charged at a time, each portion being 

brought up to a bright red throughout with repeated stirring before the 

next portion is introduced. When all has been heated to a fair red heat 

the bottom is patted into shape (it is slightly dish-shaped, and from 2 

to 3 inches lower at the tap hole to allow the furnace to drain) with a 

heavy flat dish-shaped tool. The doors are then closed, and the heat is 

raised to its utmost intensity; indeed a higher heat is needed in making 

the bottom than in the regular smelting work. Moderately fusible 

loam sand is piled against the exteriors of all the doors to keep the heat 

in, and the temperature is considered high enough when the sand on

1 Le Play, op. cit., p. 72. 

Bull. 26 3 (455)
34 COPPEE SMELTING. [BULL. 20.

the outside of the 3-inch thick tile doors has fused. This generally 

takes six to eight hours hard firing.

The doors are now opened, and the quartz (which is now quite plastic 

and viscid, being sintered for, say, one-half inch in depth) is beaten into 

shape in the tap hole. As soon as the bottom has cooled to a dull cherry 

red, a layer of three-fourths of an inch of loam sand is thrown on it, with 

the double object of preventing the charge from indenting it and of 

isintering the upper surface a little more completely. A light charge of 

:fusible ores and scrap matte is now introduced and melted. The matte 

iis mostly absorbed by the bottom. The charges are now rapidly increased in weight till the normal charge is reached. In making the 

ibottoms of roasting and refining furnaces the same course is followed, 

'but the seasoning, as it is termed, is done with slag and scrap copper 

instead of ore and matte. The matte or copper is at first rapidly and 

later slowly absorbed by the bottom, which is finally converted into a 

;solid monolith of matte or copper mixed porphyritically with quartz. 

"While the bottom is new care is taken not to indent it in charging, nor 

;to allow the heat to fall below a cherry red, as below this temperature 

the bottom is liable to crack if currents of cold air strike it. If it does

 crack it must be quarried out and the whole operation begun again.

Size and shape of hearth^ Since all parts of the hearth must be readily 

;accessible from the working doors for rabbling and fettling, its corners 

.are rounded off and filled in. The hearth must not be so wide that the 

furnaceman's tools cannot reach conveniently at least to its middle, nor 

.so long that the flame cannot reach with fall power to its farthest endIt may be that the greatest length attainable with direct firing has been 

:reached, and experience thus far seems to indicate that with the present 

ilength of hearth a width greater than that now used is not desirable. 

'To bring the temperature at the end farthest from the grate up to 

that of the remainder oi the furnace the hearth is narrowed there and 

the roof lowered; indeed, it is a general rule in reverberatory furnaces 

^that the temperature is locally raised by narrowing the furnace and 

ilowering the roof.

The flue is generally made narrow and short, and rises to the chimney

 with a steep inclination. The short and strongly inclined flue certainly

 favors strength of draft by diminishing the angle which the products

 of combustion have to turn on entering the chimney and by diminishing the friction of their passage through the flue. Narrowness of flue 

tends to check the draft, but it has the compensating advantage of 

.giving the products of combustion a high velocity in the flue itself, so 

that it. is kept hot for a long distance from the furnace and the radiation of heat from the laboratory into the flue is very small; but these 

;short narrow flues, with an independent chimney for each furnace, are 

liable to cause a heavy loss in flue-dust. 

. (456)
H.OWB.I . REVERBERATORY METHOD FOR SULPHURETED ORES. 35

. " CHIMNEYS.

Draft; In the draft of chimneys we may distinguish between intensity 

and volume. Yolume of draft is due mainly to area of cross-section, intensity to the height of the chimney and to the difference between the temperature of its contents and that of the external air. Of course these 

two factors influence each other. The friction in narrow chimneys checks 

the intensity, and intensity of draft, by increasing the speed of the 

gases, increases the volume passing a given cross-section in the unit of 

time. The quantity of air which a chimney is able to draw through the 

interstices between the fuel on the grate, which is, of course, proportional to the amount of fuel which can be burnt per minute by the 

draft of the chimney, is, neglecting friction 

1. Proportional to the sum of the areas of the interstices between 

the lumps of fuel (and hence proportional to the grate area), until this 

sum becomes as great as the area of the chimney itself or of the smallest 

aperture in the flues leading to it.

2. Directly proportional to the square root of the height of the 

chimney.

3. Nearly directly proportional to the temperature of the gases in 

the chimney. The weight of gas passed through the chimney, however, 

reaches its maximum when the hot gases in the chimney are at 604° F. 

(273° 0). When the gases become hotter than this they indeed travel 

more swiftly through the chimney, but they are so greatly expanded 

that the actual weight of the gases passed through the chimney per 

minute diminishes. Hence for the maximum draft the hot gases in the 

chimney should be nearly, but not quite, hot enough to melt lead.

According to Gruner, the velocity of the hot gases in the chimney 

should .not be over 10 to 16 feet per second.

If we base the area of the internal horizontal cross-section of the 

chimney on the weight of coal which is to be burnt in each hour by its 

draft collectively on all the grates which it serves, then it appears 

that wo should provide for chimneys in general not less than 1 square 

foot of this area for each 120. pounds of coal burnt per hour, and that 

in some cases we should provide as much as 1 square foot of this area 

for each 75 pounds of coal burnt per hour. For copper-smelting furnaces the weight of <coal to be burnt per each square foot of this area 

should not greatly exceed 75 pounds per hour, and in certain extreme 

cases (as, for instance, where the chimney is liable to become partly 

choked with accretions) as much as 1 square foot of this area is provided for each 50 pounds of fuel to be burnt per hour.

Further considerations on the dimensions of chimneys required for 

proper draft will be found in the immediately following paragraphs:

Separate chimneys. Each furnace is usually provided with an independent chimney, built as close as possible to the skimming door; indeed, this arrangement is often, though erroneously, considered absor

(457)
36 COPPER SMELTING. [BULL. 26.

lutely necessary. The chimneys have in general no damper, the draft 

through the furnace being regulated by the condition of the clinker in 

the grate, and being practically wholly suspended when the furnace 

is being charged or skimmed, by opening the skimming door, which 

allows a great volume of cold air to pass direct to the flue without 

entering the furnace farther than the velvetry, and to practically fully 

satisfy the dralt of the flue. But for this checking of the draft during 

charging, a considerable Joss in flue-dust would then occur; since at 

the moment of charging, the fine particles of ore while falling to the 

hearth would be much more liable to be carried off by the draft were 

it not thus checked than they are after they have come to rest on the 

hearth.

Chimneys serving each one furnace are usually from 50 to 60 feet high, 

and their inside area in a large number of cases which have come to the 

writer's notice varies from about one-fourth to one-half the total grate 

area. Their height is influenced by the contour of the immediately 

surrounding country, the "lay of the land," much higher chimneys 

being required when surrounded by hills or by very high buildings. The 

chimney should project several feet above the highest points of all buildings in its immediate vicinity.

Central chimneys, common to many furnaces, however, are desirable: 

First, when it is considered necessary to carry the products of combustion to a great height on account of the proximity of hills or very high 

buildings, or to avoid nuisance and injury to the neighborhood, the 

cost of a single very high chimney, of cross section large enough for 

ten furnaces, being not much greater than that of one of equal height 

but of internal diameter only large enough for one furnace, since stability requires large diameter; second, when very rich or argentiferous 

or auriferous ores or pulverized mattes are smelted, since here the 

value of a given weight of flue-dust is greatly increased, and long flues 

and settling chambers become desirable, their friction and cooling effect 

on the products of combustion making the employment of a quite high 

chimney indispensable for the sharp draft required. The experience 

at Bergen Point and elsewhere proves that the use of a common 

chimney for copper smelting reverberatories is not only wholly practicable but highly important as regards flue-dust. t

For common central chimneys flues should be provided of great 

height: First, that their walls may afford large settling surface for fluedust; second, that their large area of cross-section may cause the 

products of combustion to travel slowly and thus induce them to deposit their flue-dust; third, that much flue-dust may accumulate in them 

before reducing their effective cross-section to such a point as to unduly check the draft, so that it may only be necessary to clean them 

at long intervals ; fourth, to allow abundant standing room when cleaning them out, diminishing the cost of that operation. Where the flues 

are bent, curves of long radius should be used, and the flues should be

'(458)
HOWE.] REVERBERATORY METHOD FOR SULPHURETED ORES. 37

brought almost parallel before opening into each other, to avoid interference of cross currents, which seriously checks the draft; and 

where the separate flues discharge into the chimney they should be 

curved upwards strongly, and partition walls should be carried up 

inside the chimney to separate the currents of gas entering from the 

several flues till they become approximately parallel.

Copper-smelting reverberatories require very intense draft. Owing 

to the often very great length of the flues connecting the furnaces with 

common central chimneys, the gases reach, these chimneys much 

cooler than in the case of separate chimneys built close to each furnace, 

thus greatly diminishing the intensity of the draft. To compensate 

for this it is necessary to give common central chimneys much greater 

height than is required for separate chimneys serving only one furnace 

each. The writer recommends a height of from 100 to 140 feet above 

the grate level for common central chimneys. According to Gruner 

little is in general to be gained by making chimneys more than 150 feet 

high.

In designing common-central chimneys we should bear in mind that 

the doors of some of the furnaces are liable to stand open, allowing great 

volumes of cold air to pass directly to the chimney and thus greatly 

tax its capacity, just when other furnaces need the sharpest draught. 

On the other hand a greater volume of gas can pass through a square 

foot of area in wide common central than in narrow single-furnace 

chimneys, other things being equal, since in the former the friction is 

less, the ratio of wall surface to area of cross-section being smaller. 

Furthermore, in a common central chimney the gases are cooler, owing 

to their passage through long flues, than in chimneys serving single' 

furnaces, and hence are less bulky and require (other things being 

equal) smaller area of cross-section. All things considered, it is recommended that common central chimneys should have an area of crosssection somewhat larger than in the case of single-furnace chimneys, and 

that it should certainly not be less than one-fourth, but rather one-third 

of the total grate area of the smelting furnaces served. Kerl 1 recommends that the ratio of the least area of cross-section of chimneys in 

general to the effective grate area (i. e.r the openings between grate 

bars) should be from 1:1 to 1:2.

Shape. Square chimneys are cheaper than round ones per thousand of bricks contained in them, since they are laid more easily, it 

being easier to plumb the work from tjie corners and to keep these 

corners square than to build the work truly circular. Hence a square 

section is properly preferred for low chimneys. Round chimneys, however, not only require less brickwork per square foot of internal crosssection for equal thicknesses of walls (the ratio of periphery to area 

being smaller in the circle than in the square), but the circular shape

1 Kerl, Grundrisa der allgemeinen Hiittenkunde, 1879, p. 303. 

(459)
38 COPPER SMELTING: [BULL. 20.

 is considered more effective as regards draft than the square, since 

in the corners of the square the increased friction affects the draft.

Stability. The effective pressure of the wind, tending to overturn 

the chimney, is very much less on a round chimney than on a square 

one whose width is equal to the diameter of the round chimney, being, 

according to Rankine, only half as great. Hence stability requires that 

square chimneys shall have much thicker walls than are necessary for 

round chimneys of the same height and area of horizontal cross-section. 

These advantages make round high chimneys much cheaper than square 

high ones of equal intensity and volume of draft.

External buttresses on chimneys are not to be recommended. They, 

indeed, place material far from the neutral axis of the chimney, thus 

tending to increase its stability 5 but they increase the surface offered 

to the wind, and thus increase the wind stresses so much that stability 

is generally more cheaply obtained by using round chimneys of larger 

diameter.

The following rules should be observed to insure the stability of round 

chimneys:

(1) The outside diameter at the base should not be less than onetenth of the height of the chimney.

(2) The weight of the chimney, according to Rankine, should be such 

that a pressure of about 55 pouuds per square foot of a plane surface 

directly facing the wind, or 27.5 pounds per square foot of the plane 

projection of a cylindrical surface, shall not cause the center of pressure 

at any bed joint to deviate from the axis of the chimney more than onefourth of the outside diameter at that joint.

Iron vs. brick chimneys.1 Iron chimneys are very much more costly 

than brick ones and their draft is less powerful, other things being 

equal, since their walls are much thinner and the gases become consequently much cooler during their passage than they do in brick chimneys. Iron chimneys, however, are built much more quickly, require 

less care in drying, occupy less room and are much lighter, often a matter of importance in case of bad foundations.

Linings. To prevent the cracking of large brick chimneys they should 

have a lining of fire-brick 4£ inches thick separated from the main walls 

by an air space. The lining should not be bonded to the main walls, 

but should be at liberty to rise and fall freely as it expands and contracts with changes of temperature. A few bricks, however, should be 

allowed to project from the lining here and there, so as to touch the 

outer wall, and thus increase its stability.

Batter. Brick chimneys are generally of nearly the same size inside 

at top and bottom, being battered on the outside to correspond with the 

diminution of thickness of their walls in height. This diminution is 

generally effected by offsets of 4 inches each on the inside of the chim1 Transactions of the American Institute of Mining Engineers, IV, pp. 108,109.

 (460)
HOWE.J REVERBERATORY METHOD FOR SULPHURETED ORES. 39

iiey, to avoid cutting bricks, the thickness of the walls being everywhere 

a whole number of brick-widths. The batter should correspond with 

the rules for stability which are given above.

GAS FURNACES.

Gas furnaces, both regenerative (Siemens), as at Stora-Kopparberg, 

and non-regenerative, have been employed for copper smelting and refining, but in many if not most cases (as at Mansfeld, Ansonia, and 

elsewhere) they have been abandoned, as it is said that they increase 

the cost of repairs by an amount greater than that saved by their economy of fuel. In the case of regenerative furnaces the repairs are very 

.heavy, as the fine ore carried over into the regenerators while charging 

and the fine copper carried over during the boiling periods in " roasting-smelting" and refining furnaces rapidly corrode the regenerators. 

The present verdict against them is certainly surprising, and may yet 

be reversed. A regenerative gas furnace built by the writer for ore 

smelting in Caldera, Chili, effected a saving of about 30 per cent, in 

the cost of fuel. From a mathematical consideration of the subject the 

writer believes that while the Siemens system of reversing regeneration 

may for the very high temperatures required in steel smelting effect a 

considerably higher economy of fuel than systems of continuous regeneration, like those of Ponsard and Swindell, yet for the considerably 

lower temperatures required for copper smelting reverberatories these 

latter systems are likely to prove, under equally favorable conditions, 

more economical of fuel than the Siemens system.

(461)
40 COPPER SMELTING. fnuu,. 26.

TABLE VI. Examples of

Dimensions of furnace :

Width of hearth:

Depth of grate below top of bridge. . . 

Height of roof:

Height of bridge above hearth .....

Ratio of grate area : '

Work done:

"Weight of charge in 2,000-lb. tons. . . 

Composition of charge :

Copper ............ ............. 

Composition of product: 

Sulphur ........................

Copper .........................

Composition of slag :

Silica ..........................

Outlay of labor, fuel, etc. : 

Kind of fuel.. ................... ..5

"Weight of fuel per ton burden treated

For extra work, tons ........... 

Total, tons ...................

Days of labor per ton burden treated : 

Furnacemen ................... 

Helpers ........................

Total.........................

Bricks consumed, tons. J Per ton ( 

Fire-sand. 2. 000 Ib. tons > burden < 

Fire-clay, 2,000 Ib. tons. ) treated. ( 

Authority ..........................

Swansea, 1848. 1

Smelting 

roasted ore.

1.

13'............

2' 3J". ........

8' 11". ....... 7' 4?"

4' 8"..........

4' 3J". ........

3' 11" .........

1'7J».........

1'4" ..........

1' 4i"

46'74" ........

2' by 2' 4".....

1'byl'........

4.3 : 1........

1 : 6..........

4" 20»>. ........

1.43a......... 

14.6...........

22.26.........

11.36......... 

29.5...........

OA O

33.7........... 

28.5...........

0.5 ...........

2.9............

2.0............

60.5...........

32pts.bit. culm 

68 pts. ant. culm

0.624.........

0.153.........

0.777.........

0.35.......... 

0.24..........

0.59..........

0.016........ 

0.002......... 

0.003.......... 

L.P..........

Smelting 

roasted coarse 

metal for white 

metal.

2.

5>>55°.........

1.76d. ........ 

10.8d. ........

22.8d. ........

32.a ... ......

20.5........... 

6.2 ...........

73.2........... 

56. ...........

4.5............

1.0............

1.0............

33.0...........

26pts.bit. culm 

74 pts. ant. culm

0.654..........

0.300.........

0.954..........

0.32........... 

0.]?.. .........

0.49...........

0.0126........ 

0.062.......... 

0.012.......... 

L.P..........

Smelting 

roasted coarse 

metal for 

blue metal.

3.

2.26.......... 

16.1...........

32.6...........

32.6...........

23.3........... 

18.5...........

57.2........... 

54.4...........

2.8............

0.8............

1.2............

36.0...........

26pts.bit. culm 

74pt8.ant.cukn

0.231..........

0.706..........

0.230.......... 

0.131..........

0.361 .........

0.009.......... 

0.045.......... 

0.002.......... 

L.P..........

Eoastiugsmelting raw 

bluo metal for 

white metal.

4.

14' 1J"

2' 2". .........

10'............

C' 11". ........

4' 6" ..........

4' 4". .........

a/ -1 -lit

J/7J" .........

r *" ..........

1'4" ..........

46' 7^" ........

2' by 2' 4".....

4.2:1 .........

l:5(approx.).. 

11" 49m . .......

2.2c.... ...... 

23.3...........

18.5...........

57.2........... 

20.1...........

9 9

77.5........... 

51.6...........

6.3............

1.0............

2.0............

34.7...........

23pts.bit. culm 

77pts.ant.culm

0.712..........

0.108..........

0.820..........

0.22........... 

0.51..........

0.76...........

0.006.......... 

0.136.......... 

0.007.......... 

L.P..........

a Including slag and fluxes. 

6 Excluding slag and fluxes. 

c "No flux used.

P. = Private notes. (For columns relating to Caldera, direct from the books of the establishment. ) O = E. D. Peters, jr., private communication. 

L. P = Le Play, Description des Proc6d6s M6tallurgiques, etc.

(462)
HOWE.) REVERBERATORY METHOD FOR SULPHURETED ORES. 41

rfverl)era1ory smelting,

Swansea, 1848.

Roastingamelting white 

metal for 

regulo.

5.

................

................

3h 48"> ...... .. 

1.63...........

20.1...........

2.2............

77,5........... 

18.5...........

0.2............

81.1.. . ........ 

52.0...........

11.0...........

1.0............

1.0............

34.0...........

} bit and ant. ( 

5 culm. (

0.324..........

0.048..........

0.372..........

0.10.......... 

0.30...........

0.40 ..........

0.047..........

0.000..........

L.P..........

Roastingsmelting 

 white 

metal, &c., 

for hlister.

6.

-----------

24"........ 

4.Q8.......

18. ........

4.8........

75.4....... 

0.8........

0.9........

98.3....... 

49.0.......

20. ........

20.2.......

30 hit. culm. 

70 ant. culm

0.534......

0.060......

0.504......

0.15....... 

0.22.......

0.37.......

0.005......

0.010......

0.008......

L. P......

Caldera, Chili, 1877.

Ore-smelting.

7.

16' 6".....

11' 6" ..... 

5' 6" ......

5' 8"......

5' 3". ...... 

1'5" ......

1'4"......

1'2" ......

11 O//

3'hy3' ...

3.2 : 1....

1 : 5.2....

7.51-....... 

3.52.......

13.69cZ....

48.74......

0.83.......

> Bit. coal..

0. 52 ft .....

0.18....... 

0.36. .....

0.54.......

P. N......

Smelting 

for hlue 

metal.

8.

10' 6" .....

11' 6" ..... 

5'G" ......

V R"

5' 3" ......

1'5"......

I' 4" ......

1' 9"

1'2" ......

3' by 3'....

3.2 : 1....

1 : 5.2....

7.04h ...... 

3.536.....

29.6<S.....

66.5.......

1.78.......

Bit. coal . .

0.475......

0.166 ..... 

0.334......

0.500..-,..

P.N......

Roastingsmeltiug 

for Chilibars.

9.

16' 6" .....

11' 6".....

5,6" ...... 

5' 8"......

5' 3"...... 

1'5"......

1'4" ......

11 O//

1' 'i." ......

3' by 3'....

3.2 : 1....

1 : 5. 2....

24"........ 

6.3c ......

61. 83/....

? Chili \ 

I bars £

Bit. coal . .

0.748......

0.32....... 

0. 04 ......

0.96.......

P.N......

Chili oresmelting.

10.

14' 6"... 

2' 2" ...

9'

6' 6" ....

3' 2".... 1'8"....

1'8"....

I'l" ....

1' .......

1 : 5. 2 . .

..........

..........

..........

..........

P. N....

Butte oresmelting.

11,

14' 6" ....... 

T30" .......

H i f>n

6' 2" .......

At Rll

4' ...........

2' 4" ........

2' 2"........

1' 4" ........

50' . ........ 3' 2" by 3' 2"

1.8 : 1......

1 : 4.5......

5b ..... ...... 

3.3..........

11..........

91

21. o. ......

25...........

10. .........

65............

41.0.........

1.2 .........

4.0..........

48.0........

Bit. coal ....

0. 5 b ........

0.31.........

o. .....:....

Bergen 

Point, N.J., 

roastiugsmelting 

 whito metal 

and black 

copper for 

hlister, 1885.

12,

15' 4"......

9

1 <)ii

' A 1 '®1 '.'.'.'.'.'.'.

5' 9". ...... 

3' 4".......

1' 5". .......

241- ........ 

8 to 30" ....

Bit. coal . .

0.493......

0.28....... 

0.28.......

0.56.......

P.N. ......

d, e, f The charge in these three cases was as follows:

d.

Material.

Kind.

Sulphureted 

ores. 

Oxidized ore . .

Per cent, 

of copper.

14.11 

13.33

Per 

cent, of 

charge.

46.89 

53.11

100. 00

e.

Material.

Kind.

Sulphureted 

ores. 

Oxidized ores

Per cent, 

of copper.

48.75 

14.46

16.98

Per 

cent, of 

charge.

40.22 

1.62

58. 16 

100. 00

/.

Material.

Kind.

Oxidized ores

Per cent, 

of copper.

48.4 

66.6 

25.6

Per

cent, of 

charge.

4.87 

86.38 

8.75

100. 00

(463)
42 COPPEK SMELTING. [BULL. 26

TABLE VI. Examples of

Dimensions of furnace :

Width of hearth:

A 4- Una

Height of roof:

Height of chimney .................. 

Size of chimney inside ..............

Eatio of grate area :

W or k done,-

Weight of charge in 2,000-lb. tons 

Composition of charge :

Composition of product :

Composition of slag :

Outlay of labor, fuel, etc : 

Kind of fuel. ........................

Weight of fuel per ton burden

treated :

Total..........................

Days' labor per ton burden treated :

Total..........................

Bricks consumed, tonsVPer tone 

Fire-sand, 2,000-lb tons> burden ? 

Fire-clay, 2,000-lb. tons)treated.( 

Authority...........................

Boston and 

Colorado, ore 

sill citing.

13.

16' i" ......:..

10'. ...........

5'2" ..........

9' 7"

52' 6". ........

1 : 5.7........

K., p. 210. .....

Mansfeld, 

smelting burnt 

matte.

14.

1 Q' 11"

I'G" ..........

9' 10".........

3

1 nit

4'0" ..........

4'0" ..........

ill'..-:-......

2' 9" bv 2' fl" . .

1 : 3. 4 A .....

6*......'........

75.............

K.,p.l80......

Oker, smelting 

burnt matte.

15.

13' 1J" ........

8' 10J"

3' 11". ........

3' 3"..........

2'.............

1' 6"... .......

1' 3J".. .......

43'.... .. ...... 2' 4" by 2' 4"..

9tolO"........

2..............

K., p. 181......

Freiberg, 

smelting burnt 

matte.

16.

19' 1"

8'IOJ" ........

3' 81".. .......

3' 81". ........

2'2" ..........

187'...........-

5to6" ........

2.1............

1..............

0.52..........

K., p. 181......

a In eluding slag and fluxes.

(464)
flown.1 REVERBERATORY METHOD FOR SULPHURETED ORES. 43

rcvcrberatory smelting, <fc. Continued.

Smelting and refilling native copper. Cwm Avon, South Wales (1884 ?).

Hancock, 

Mich.

17.

..........

..........

24"......

9........

80.......

10.......

Bit. coal.

0,89.....

P.N....

Pittsburgh, 

Park Bros.

18.

12' 10"....

9' 9".. ...

0'9" .....

2' 3"...... 

]'3"S .....

10" by 1' 8"

1 : 3.63...

10.........

E. ........

Pittsburgh, 

Park Bros.

19.

n

/ O//

7'......... 

v in"

4'. ........

3'1J".-.-

2' 2" ...... 

0'9"1 .....

'i' io" "...

10" by 1' 8"

'1 : 5.5....

5..........

E.........

Pittsburgh, 

C.G-. Husscy & Co.

20,

10' 0" .....

4'.!!".".!.'

2' 10" ....

<)l (til

i' 6" by 1' 6"

5..........

E.. .......

Oresmelting.

21.

16'......

12'.....:

4'.......

4'.......

3' 6"....

3' 6" ....

20.......

27.5.....

0.44.....

6.58.....

4.0......

57.22 ...

4.16.....

L.......

Smelting 

for 

red metal.

22.

16'........

12'........

4'.....-....

3' 6" ......

3' 6"......

2 ffl

20.........

35.........

2.0........

L........

Smelting 

for 

blue metal.

23.

16' ........

12'........

4'.........

4' .........

3' 6"......

3' 6"......

JOh

2. a.......

35

50 to 60...

L.........

Smelting 

'or white 

metal.

24.

16'......

12'......

4'.......

4' .......

3' 6" ....

3' 6" ....

50 to 60 .

L. ......

Roastingfern el ting 

for 

blister 

copper.

25.

16'......

12'......

4'.......

4' .......

3' 6" ....

3' 6" ....

5........

75 to 85 .

no 4-fi on

L. ......

K = ICerl, Grrundriss der Metallhiittenkunde, 1881, 1. 

P. N= Private notes.

E = T. Egleston, Transactions of the American Institute of Mining Engineers, IX, p. 688. 

L = A. M. Levy, Kevue Universelle, Vol. 16, No. 2.

(465)
44 COPPER SMELTING. [BULL. 26.

SMELTING OPERATION.

The roasted ore, mixed with fluxes designed to form with the gangue 

and with the iron oxides produced in the preceding roasting a desirable 

slag, is introduced through a hole in the center of the roof, ordinarily 

closed with a tile, from a hopper which is sometimes fixed and sometimes 

on wheels running on an elevated track. Two workmen, one at the working door and one at the skimming door, now spread the charge as rapidly 

as possible. The doors are next closed and tightly luted, and the fire is 

urged. Three and a half to four and a half hours now elapse before the 

charge is again touched, the fire all the time being kept at its utmost 

intensity. About half an hour after closing the doors the upper surfaces of the more fusible portions of the charge have begun to melt; they 

filter across the still unmelted portions below, gradually reacting on 

them, and, collecting on the bottom, they leave fresh portions exposed 

to the flames. Soon black bubbles appear, from the formation of sulphurous acid by the action of the atmosphere of the furnace and of the 

metallic oxides on the undecomposed sulphides present. The ebullition 

increases in violence and then again decreases, till after three and a half 

to four and a half hours from the time of charging it has nearly ceased. 

The charge is now all melted except a few refractory lumps which adhere 

to the bottom and which are protected by the molten bath from the 

flames. To detach and expose them to the full heat of the furnace, the 

skimming door is now opened and the hearth diligently scraped with 

long rabbles, extending almost to the fire-bridge. This should detach 

all pieces adhering to the hearth, which should feel smooth and soapy 

under the rabble. If it feels rough and gritty, the door should be again 

closed and the bottom again rabbled after firing hard for half an hour 

or tin hour. The appearance of black bubbles in any part of the hearth 

is an indication that fusion is still incomplete there, and we cannot in 

general completely detach the ore from the bottom of the furnace in any 

portion of the hearth where the fusion is still so incomplete that the 

black bubbling is still strong there. For this reason it is in general 

unwise to attempt rabbling the bottom until the black bubbles have 

almost entirely disappeared from every portion of the hearth, since a 

second rabbling would still be needed to detach the last portions of ore 

from the bottom and since the additional rabbling thus introduced 

would waste fuel and time as well as labor. Time and fuel would be 

wasted, because opening the door to rabble the furnace cools it very 

rapidly, first, by almost .completely checking the draft, since the cold air 

rushing in-at the skimming door almost completely satisfies the capacity 

of the flue, and second, because much heat radiates from the furnace 

through the open doorway. This cooling down is a much more serious 

thing than might at first be supposed, since in these copper-ore smelting furnaces the highest temperature'we can possibly obtain is but 

slightly a.bove the melting point of the ore, and if the temperature be

(466)
HOWK.] REVERBERATORY METHOD FOR SULPHURETED ORES. 45

thus temporarily lowered, much time and consequently much fuel will 

be consumed in recovering it.

Two cases, however, occasionally arise in which it is best to rabble 

the charge while bubbling continues locally in certain portions of the 

hearth, or possibly even over the whole of it.

In the first place, if, owing to careless charging, the charge has been 

placed in too great quantity in one part of the hearth, or if one part of 

the furnace works considerably colder than the rest, the ore will remain 

incompletely melted there, and local bubbling will continue after the 

nearly complete disappearance of bubbles from the rest of the hearth has 

indicated the general completion of the fusion. Now, if in such a case as 

this wedeferred rabbling till this local bubbling had entirely ceased there 

would be great danger that in other portions of the furnace, where the 

charge had already been completely melted, the bottom would become so 

hot that the matte, which is very thin and penetrating, would work down 

into it, corrode it, and perhaps force up large lumps of it. If the working of the furnace proceeds normally, and the fusion of the charge is 

completed at about the same time in all the different portions of the 

hearth, there is little danger of the hearth becoming so hot as to be 

penetrated in this way by the matte to any injurious extent; for on introducing the cold charge into the furnace the bottom is greatly cooled, 

and the charge, when melted, is removed from the furnace shortly after 

its last cold portions have been scraped off the bottom, a new charge 

then being introduced which again cools the bottom before it has had 

a chance to get overheated.

In the second place, two rabblings may be desirable even when the 

ore is properly spread, if the furnace, and more especially if the bottom, 

has been unduly cooled. In this case the portions of the charge in 

contact with the bottom become heated only very slowly, and time and 

fuel may be saved by rabbling the bottom as soon as the upper portions 

of the charge have become thoroughly fused, scraping off as much ore 

as we can from the bottom, and then, an hour or so later, scraping off 

the remainder.

If, as nearly always happens, all adhering matter is removed at the 

first rabbling, the skimming^door is closed and the charge fired for 

thirty minutes to melt all yet unfused portions and to allow the matte 

to settle. The door is then opened again and the slag skimmed with 

long rabbles into the middle of a series of deep molds formed in 

slightly moistened sand on the floor immediately in front of the skirnming-door. Between these molds are sand partitions reaching nearly 

as high as the sides of the molds, and over these partitions the slag 

flows from each mold, as soon as it is filled, to its neighbor. This arrangement allows most of the buttons of matte mechanically drawn out 

with the slag to settle in the central block of'slag, called the plate slag, 

and few buttons pass beyond the two molds immediately adjoining it. 

Considerable skill is required to avoid drawing shots of matte out with

(467)
46 COPPER SMELTING. [BULL. 26.

the slag. The rabble must be dipped into it only very slightly and very 

gently, so as to avoid forming waves. Often the furnace is slightly 

cooled just before skimming, so as to stiffen the slag and make it easier 

to skiin. In the hearths of some ore-smelting furnaces there is a basin at 

the tap-hole large enough to contain all the matte, which accumulates 

there as fast as \i is released by the fusion of the lumps of ore. In this 

case the slag in the neighborhood of the skimming-door, where the 

skimming-rabble lays hold of it, rests directly on the bottom of the furnace, and the danger of drawing matte out with it is greatly diminished.

As soon as the slag is all skimmed the tap-hole is opened and the 

matte tapped into sand or iron molds, or, in case it is to be roasted in 

reverberatories or Gerstenhb'fers, it may be run in a thin stream into a 

deep basin of cold water to granulate it. The basin should be deep and 

the water supply copious to prevent explosions. Generally the matte is 

tapped only every second or, i ndeed, every third charge, the second charge 

of ore being dropped into the furnace immediately after skimming the 

slag. .

If the matte is tapped only once for every two charges the slag of the 

first charge is not skimmed very clean, and, in skimming the second 

charge, when the greater part of the slag has been removed, the working door is opened to cool and stiffen the remaining slag, so that it may 

be skimmed more completely. If the slag is slightly stiff the rabble 

takes hold of it firmly and drags it out; if it be too fluid the rabble slips 

through it. The difference is like that between skimming slightly viscid 

cream from milk and skimming petroleum from water. In skimming 

very liquid slags it is moreover very difficult to avoid propagating 

waves, which tend to mix up the matte and slag and thus to increase 

the mechanical loss of matte. The rabbling, skimming, and tapping 

must not be unduly delayed for fear of corroding the bottom, as 

already explained. After tapping the matte the fettling is repaired, 

if necessary, with a mixture of sand and clay, say of one part of fat clay 

to three parts by measure of pure quartz sand. The inwalls, for some 

4 or 5 inches above their contact with the hearth, should be protected 

by a thick layer of this fettling to prevent them from, being corroded by 

the slag. Every time the matte is tapped the fettling must be carefully 

examined and new fettling rammed firmly in where it has become corroded.

A new charge is now introduced and matters proceed as before. 

Much care must be paid to spreading the ore so that the fusion will be 

completed at about the same time throughout the furnace, and it must 

nowhere protrude so high as to interfere with the flame.

Should the hearth become too high in any part the ore is left very 

thin therein charging, so that it may melt quickly, and so that the accretions may be melted off while the fusion of the ore is being completed 

in other portions of the furnace. If this does not suffice, the accretion 

may be removed by leaving it quite bare when charging the ore and

(468)
HOWB.] REVERBERATORY METHOD FOE SULPHURETED OEES. 47

then placing some cast iron on it, which will cut it down while the charge 

is meltiug.

The slag is removed from its molds while hot, as it becomes extremely 

brittle on cooling. It is indeed preferable to remove all the blocks except the plate slag to the dump, while still liquid inside, and, by breaking off a corner of each block, to allow the still liquid contents to run 

out, leaving a shell, the bottom of which contains the greater portion 

of the total copper contents of the block, and is resmelted if rich enough.1

Iii viscid slags the top also often contains enough copper to pay for 

resinelting. The plate slag is usually so rich that the whole of it has 

to be resmelted.

Time occupied in smelting one charge of ore in reverl)eratori(8.

Total .......................................................................

Chill 

(private 

notes).

nl Oflm

5

on

17 1

10 [

8 \

0 0

4

Swansea, 

(LePJay).

0" 11"

3 38

10

1.3

The details of the charges and products, consumption of labor, fuel, 

supplies, etc., in many different instances will be found in Table VI, 

columns 1, 7,10,11,13, and 21.

The composition of the charge, as determining that of the resulting 

matte and slag, should be governed by the following considerations.

THE MATTE.

The proportions between (1) the unoxidized, (2) the oxidized copper, 

aud (3) the sulphur, more especially that existing as sulphide of iron, 

should be such that the resulting matte shall be neither so lean in copper as to render its subsequent bringing forward too costly nor so rich 

as to cause undue loss of copper in the slag.

THE SLAG.

In general the proportion between the silica, alumina, oxide of iron, 

lime, etc., in the charge should be such that the resulting slag shall be 

(1) specifically light, so as to separate readily from the matte; (2) at 

least moderately fusible, so as to economize fuel aud time in smelting 

it; (3) not excessively fluid when melted, so as to be readily skimmed, 

and (4) not so-excessively viscid that the. matte will not separate from 

it. The following are some examples of composition:

1 Vivian, Copper Smelting, its History and Processes, p. 14. 

(469)
48 COPPEE SMELTING. | BULL. 26.

TABLE VII. Composition of revcrberatory ore furnace slags. (See also Table VI.)

Silica:

Total....................

Total....................

slag Ore furnace 

Kaa- from 

flord. a

1,

52.00

8.90

17 64

16.22

5.45

(CujO?)0.40

1:1.83

Dillen- From 

Imrg. a

2.

47.54

3.90

28.98

15.59

3.26

(Cu2 0?)0.73

1: 1. 78

Bendorfer From 

Hiitte. a

3.

45.41

1.48

15.88

O.C7

1: 1. 76

30.0

30.50

60.5

2.9

28.5

2.0

0.6

5.0

CuO.5

100. 00

3.21

1:3.6

A

d ID

<a

s

t tn

1 '

4.

................... 100.00

Lime..................... ..................................

Total ................................................

From 'Montana, c

5.

48.0

30.0

19 e

Colo. From Argo, 

6.

39.7

si. 2

2.54

4.00

12.00

PbO 3.66

0.30

3.05

Parrot, ButteMontana.

7.

48.00

4.00

41. 00

2.00

1.5

SO. 8

1.2

3.35

C Awmvon, 

Wales, d

8.

57.22

6.58

27. 50

4.00

4.17

SO. 12

0.44

aKerl, Grnndriss der Metallhuttenknnde, 1881,1, p. 211.

b Le Play, Precedes M6tallurgiqnes Employ6es dans le Pays de Galles, etc, p. 216.

c Transactions of the American Institute oi' Mining Engineers, XI, p. 59.

d Levy, Kevue Universelle, Vol. XVI, No. 2, p. 286.

Of these the Swansea slag, which is even more acid than a trisilicate, 

is described by Le Play 1 as a sort of pudding, formed of fragments of 

quartz and silicious rocks, almost in contact with each other, suspended 

in a matrix, consisting of a silicate more or less compact. This porphyritic appearance is common in reverberatory ore furnace slags, the 

undissolved grains of quartz accumulating at the tops of the blocks of 

slag, the graiiis of matte toward the bottom. While these suspended 

quartz particles increase the loss of copper, first, by making the slag so

'LePlay, p. 204. 

(470)
HOWE.I REVERBERATOEY METHOD FOR SULPHURETED ORES. 49

pasty that it tends to retain shots of matte, and, second, by retaining 

small portions of copper in the interior of the individual unmelted 

grains themselves, it is quite possible to obtain economical results with 

slags containing even more unmelted silica than the Swansea slag above. 

Indeed, it is rarely advantageous to add fluxes to any great extent to 

even an extremely silicious ore for reverberatory smelting. To reduce 

the proportion of silica in this Swansea slag so low that it could all readily 

melt would require a great addition of flux, entailing expense for the 

flux itself, diminishing the quantity of ore which each furnace charge 

can contain, thereby increasing the outlay of labor and fuel per ton of 

ore, and, by augmenting the quantity of slag, tending to increase the 

loss from mechanically suspended matte probably much more that it 

would be lessened by the increased fluidity of the slag. Here lies the 

main advantage of the reverberatory over the cupola method, in that 

mixtures-which are practically infusible, taken as a whole, may yet be 

economically treated in the reverberatory by simply performing this 

partial fusion, portions of the different components combining together 

in some fusible ratio, the excess remaining unfused and floating in the 

fused portion as a sort of pasty pudding, which can be pulled out of 

the furnace in skimming. The completeness with which the copper can 

be recovered from highly silicious mixtures by this semi-fusion, is well 

illustrated by the above Swansea slag, which only contains on an average, year in and year out, 0.5 per cent, copper, while actually containing 30 per cent, of uucombined silica, part or even the whole of which 

may have remained completely unfused throughout the whole smelting 

operation. And from the fact that most of the small amount of copper 

contained in the slag is found not in the upper porphyritic portion, but 

in the lower completely fused layers, 1 we may infer that'the amount of 

undissolved quartz might be considerably increased without causing a 

more than proportionate loss of copper.

Of course, the amount of flux, if any, which it is profitable to add in 

any particular instance is a question of dollars and cents, which can 

often only be answered by calculations of profit based on actual tests on 

a large scale of the results of fluxing. But it is evident that excellent 

results, metallurgically considered, may be obtained in reverberatories 

with mixtures which could hardly be made to run at all in cupolas. 7

Basic mixtures may also be treated in the reverberatory. While it is 

likely that the heavy and very liquid sub-silicate of iron slags which can, 

though with difficulty, be treated in cupolas would corrode the sides and 

hearths so rapidly and carry off so much matte mechanically that their 

treatment in reverberatories could not be satisfactory, yet it is probable

1 In the mean of 18 samples from the top, 18 from the middle, and 18 from the bottom of blag blocks from six different fusions Le Play found (op. cit., p. 206) in the 

top O.G per cent, copper, in the middle 0.3 per cent., and in the bottom 1.3 per cent., 

or on an average O.b7 per cent.

Bull. 26 4 (471)
50 COPPER SMELTING. JBULI

that tbe viscid and refractory aluminous silicates and the comparatively 

basic silicates of lime.can be treated in reverberatories with fairly good 

results, metallurgically considered, when so infusible that they would 

not run at all in cupolas.

Classification. The more important reverberatory ore furnace slags 

may be classified as follows: .

Name of slag. Oxygen ratio of 

bases to silica.

2:1

1:1

1:1.5

1:2

1:3

Fusibility. I. Let us consider first the simple silicates. The order of 

fusibility among silicates with a single base appears to stand about iu 

the following order: Iron singulo- (most fusible), iron sub-; manganous 

singulo-, inanganous bi-, manganous tri-; ironbi-; lime tri-?, lime bi-?, 

lime singulo-?; iron tri-; magnesia bi-?, magnesia singulo-; alumina singulo-?; magnesia tri-?; alumina bi-?, alumina tri- 1? (leastfusible).

In regard to several of the above the evidence is quite contradictory. 

The exact position of those followed by ? seems especially doubtful. 

It seems pretty clear, however, that silicates of the protoxides of 

iron and manganese reach their maximum fusibility when the oxygen 

ratio of base to silica is approximately that of siugulo-silicate; that 

of magnesia when the oxygen ratio is about that of bi-silicate; with 

lime it is not clear whether the most fusible composition lies nearest 

the relation of bi- or that of tri-silicate; and with alumina whether it is 

nearest to that of singulo- or to that of bi-silicate. Experience appears 

to bear out the inference that the larger the proportion of protoxide of 

iron and of manganese to the lime and magnesia, the more basic should 

the slag be to secure the greatest fusibility; and the more acid the 

slag the larger should be the proportion of lime to the protoxide of iron 

and of manganese.

2. Multiple silicates ma.y next be considered. We can greatly increase 

the fusibility of the simple silicates of any one of the alkaline earths 

(baryta, lime, and magnesia), or of alumina, by adding to it the silicate 

of any other earth. Thus the simple silicates of alumina are much less 

fusible than those of lime; yet if we add silicate of alumina to silicate 

of lime in proper proportions we get a compound silicate more fusible 

than the simple silicate of lime is. Of course, if we add a fusible siiicate, 

such as that of protoxide of iron or of manganese, we increase the fusibility of the silicate of lime (or of any other alkaline earth) to a very 

much greater extent.

The fusibility of the "silicates of lime is increased more by adding to

them a silicate of baryta than by adding a silicate of magnesia or of

(472)
HOWK.J EEVEEBEEATOEY METHOD FOE SULPHUEETED OEES. 51

alumina, and it is increased more by adding a silicate of magnesia than 

by adding one of alumina.

According to Bodeinan, the most fusible'silicate of lime with alumina 

is the bi-silicate of the composition lime 30, alumina 14, and silica 56 

per cent., which corresponds to the formula 4 CaO,. A1 2G 3, 7 SiO2 . It is 

made less fusible by adding either silica or lime to it, and much less fusible by adding alumina to it. It is of course made much more fusible 

by adding oxide^f iron or of manganese to it, even without altering the 

oxygen ratio of the bases to the silica.

Among the compound singulo-silicates of lime with alumina, which 

are less fusible than the compound bi-silicates of these bases, those rich 

in the more fusible base lime (such as 12 CaO, 2 A12O3 ,9 SiO2 idocra'se) 

are more fusible than those richer in alumina. »

The order of fusibility among the compound silicates of lime with 

magnesia is not so clear. Here too the bi-silicates seem to be the most 

fusible. Among them the bi-silicate whose composition is expressed by 

the formula GlaO, MgO, 2 SiO2 (pyroxene), which contains one equivalent of lime to one of magnesia, appears to be more fusible than the other 

bi-silicates richer in the more fusible base lime. An increase in the proportion of magnesia in this compound (the oxygen ratio of the combined 

bases to the silica remaining unaltered) appears to diminish its fusibility more than an increase in the proportion of lime does.

The silicates in each of the following groups are placed in the order 

of their fusibility, as far as it can be made out from the altogether unsatisfactory data at present available. Where the relative fusibility of 

two or more silicates is altogether uncertain they are grouped together 

with a brace. Each such group taken collectively is to be understood 

as less fusible than the silicates above it, and more fusible than those 

below it in its own column:

TABLE VIII. Order of fusibility of certain silicates.

*

Approximate order of 

fusibility.

Most fusible ...............

- _ Bases of silicate.

Lime and alumina.

4 CaO, AbOs, 7 Si02 ..... 

3 CaO, AbO,, 0 SiOa ..... 

12 CaO, 2 Ab03 , 9 SiOj ... 

3 CaO, AbO,, :.! SiO*.... .. 

. 6 CaO, 4 Abba, 9 SiO* .... 

3 CaO, AbOa, OSiOa......

Lime and magnesia.

CaO, MgO, 2Si02 ....

(CaO, MgO, SiOa ..... 

{Z CaO, MgO, 3 SiOa.. 

( CaO, 2 MgO, 3 SiOz.. 

(CaO, Mt;0, 3Si02 .... 

}CaO, MgO, 4SiOz....

Lime and protoxide 

of iron.

CaO, 3 FeO, 2 SiOa. 

2 CaO, 4 FeO, 3 SiOa. 

CaO, FeO, SiOz. 

4 CaO, 4 FeO. 5 SiOz. 

CaO, FeO, 2 SiOz.

Of these compounds the silicates of lime with magnesia appear to be 

as a whole somewhat more fusible than those of lime with alumina, while 

those of lime with protoxide of iron are very much more fusible still. 

But the present state of our knowledge hardly warrants us in comparing the fusibility of the individual members of the lime^alumiria group

. (473)
52 COPPER SMELTING. [BULL..26.

with those of the lime-magnesia group. Oxide of zinc appears in general to make the mlicates less fusible.

Specific gravity. The presence of an excessive amount of protoxide of 

iron or of manganese in the slag is to be avoided, since these bases make 

the slag very heavy, thus interfering with the separation of slag from 

matte by gravity.

The corrosiveness of slag is a point which requires much attention 

in the reverberatory smelting, since the bottom and imjre especially the 

sides of the furnace are exposed for a long time and at an exceedingly 

high temperature to the action of the slag.

With a given oxygen ratio between the bases and silica, slags whose 

principal bases are protoxide of iron and manganese are far more corrosive than those in which lime, magnesia, and alumina, or any one of 

them, predominates. Potash and soda also make slags highly corrosive. 

In general, for a given relation between the different bases, the more 

basic the slag the more corrosive it is.

Liquidity. Basic slags whose chief bases are protoxide of iron or 

of manganese are so extremely liquid that they cannot be cleanly and 

satisfactorily skimmed, and are hence much dreaded in the reverberatory. In the shaft furnace their liquidity is rather an advantage and 

partly compensates for their corrosiveness, heaviness, and tendency to 

form salamanders. Oxide of zinc in general tends to stiffen the slag, 

hence a larger proportion of this base is permissible in reverberatory 

than in cupola work and in ferruginous and manganiferous than in 

earthy slags.

Scarification. The loss of copper in the slag has been spoken of up 

to this point as if it were wholly mechanical. In general the copper 

tends to scorify, that is to actually chemically combine with" the silica 

of the slag, more strongly when acid slags are produced than when the 

slag is basic, the affinities of the silica in basic slags being more completely satisfied than in acid ones. The tendency to scoriflcatiou, other 

things being equal, appears to be much greater when lime,«alumina, and 

magnesia preponderate among the bases than when protoxide'of iron 

or of manganese does. In sulphureted and especially in pyritous ores 

this tendency is strongly held in check by the action of the sulphide of 

iron; but when the copper exists in the ore mainly or wholly in the oxidized condition, scoritication becomes a serious matter, and the power 

 of ferruginous and inangauiferous slags to check it should .weigh 

strongly in deciding what slag is on the whole the most profitable.

To sum up, while the most advantageous slag for the reverberatory 

js probably about a sesqui-silicate of lime and protoxide of iron, with 

rather more protoxide of iron than lime, ore mixtures may be successfully smelted which yield slags of a very great range of composition, from 

snbsilicates to tri- and even quadri- silicates. Very acid slags, if rich in 

alumina, should contain also protoxide of iron or o*f manganese, since if 

they contained only liine or magnesia, together with their silica and

(474)
HOWE.I REVERBERATOR? METHOD FOR SULPHURETEB ORES. 53

alumina, they would be too infusible. Highly basic slags, on the one 

hand, require a certain amount of protoxide of iron or manganese to 

make them fusible; but, on the other hand, these oxides must not preponderate too strongly among the bases, as they make the slag corrosive, heavy, and hard to skim.

CHEMICAL REACTIONS.

In general. The roasted ore contains silica, oxides and sulphides of 

iron and copper, and earthy bases (lime, magnesia, alumina), etc. The 

oxides of iron, reduced to protoxide by the sulphides and partially also 

by the flames, eventually combine with the silica, as do also the earthy 

bases.

The oxidized copper, some of which is probably taken up by the silica 

at first, is deoxidized, chiefly if not almost wholly, by the protosulphide 

of iron (Fe S), whicti plays a most important part in copper smelting. 

The reactions of these different substances on each other is promoted (1) 

by the gradual trickling and filtering of the uppermost and first fused 

portions over and through the lower and as yet only pasty portions; (2) 

by the incessant ebullition of the enormous volumes of sulphurous acid 

evolved (estimated by Le Play at four hundred times the volume of the 

charge itself, and stated by Vivian 1 to contain 13 per cent, of the sulphur originally contained in the ore), which automatically causes a most 

thorough stirring uj> and mixture of the different portions of the charge, 

constantly .bringing fresh portions of the already liquified parts into 

contact with the still unfused surfaces and ever altering the surfaces of 

contact of the already melted matte and slag; (3) by the remarkable 

power possessed by protosulphide of iron of dissolving in the slag. Le 

Play 2 pointed out that the proportion of sulphur to copper in the slag 

was always much higher than in the matte (he found it 40 per cent, 

higher), whence it is inferred that in addition to the shots of matte 

mechanically suspended in theslagand wholly distinct from them there 

exists a considerable quantity of sulphide of iron. The absence of scorified copper in slags resulting from the fusion in a comparatively oxidizing atmosphere of mixtures containing at once large quantities of 

copper oxides and an immense excess of silica, whose powerful affinities 

for each other seem to offer conditions most favorable to scorification, 

is explained by the presence of protosulphide of iron in the slag itself, 

not in isolated buttons, which might not come in contact with the 

scorified copper, but apparently actually dissolved in it, and thus in 

the most favorable position for reducing by double decomposition what 

silicate of copper is formed during the fusion. FeS + Cu2SiO3 = Cu2S + 

FeSiO3 . The fact which underlies this reaction, that iron has a vastly 

greater affinity for oxygen but only a slightly stronger affinity for sul1 Copper smelting, etc., p. 19.

2 Le Play, Description dea Proce"de"s M6tallurgiques, etc., p. 212.

(475)
54 COPPER SMELTING. ^ [BULL. 26.

phur than copper has, is the foundation on which are based all processes - 

for smelting sulphureted copper ores.

Arsenic and antimony exist in the roasted ore partly as sulphides, arsenides, and autimonides, partly as arsenic and antimonic acids, free or 

combined with metallic oxides. The large quantity of sulphur and iron 

with which they are initially associated, and which have so much 

stronger affinity for oxygen than arsenic and antimony have, prevents 

tbat portion of these noxious metals which is present in an unoxidized 

condition ID the roasted ore from being oxidized during the smelting to 

any considerable extent, so that this part of the arsenic and antimony 

passes directly into the matte. The arseniates and antimoniates, however, are decomposed by the silica, which tends to combine with their 

bases, setting arsenic and antimonic acids free. Were, they isolated 

when set free, all the arsenic acid would be split- up by the heat into 

free oxygen and arsenious acid which would volatilize, antimonic acid 

being reduced to tetroxide of antimony (8b204 ), which is not volatile. 

But in .the pasty mass in which the arseniates and antimoniates are 

split up by the silica, the presence of sulphur and iron in large quantities interferes with the simple action of the heat. While it is probable 

that a certain amount of arsenic is driven out as arsenious acid, most of 

the arsenic and probably nearly all the antimony are deoxidized and 

combine with the sulphur, part of the sulphides of arsenic and antimony thus formed probably volatilizing, the remainder and probably 

by far the largest part entering the matte.

The net result of the smelting on the arsenic and antimony contained 

in the roasted ore is to volatilize part of these metals, the remainder 

combining with the copper in the resulting matte.

3. ROASTING THE FIRST MATTE (COARSE METAL). 

THE AIM.

The aim of this operation is to oxidize the iron, with a view to scorifying it in the following smelting operation, to a smaller extent to 

oxidize and thus volatilize the sulphur, and, at least in certain cases, to 

oxidize and volatilize the arsenic and antimony.

The extent to which the roasting is pushed depends (1) on whether 

the expulsion of arsenic and antimony receives special attention; (2) 

on whether oxidized ores are available for the subsequent smelting; (3) 

on whether rich sulphides nearly free from iron, arsenic, and antimony 

are to be had; (4) on the cost of labor and fuel.

These four considerations should determine whether it is best to push 

this roasting so far that the roasted matte shall reach the state of metallic copper in two operations (see p. 16), as in the "ordinary process" 

(4) smelting for white metal and (5) roasting-smelting for blister copper, 

the Welsh " roasting" or to limit it so that the metallic state shall only 

be reached after three operations, as in the u extra process" (4 a) smelt-

(476)
HOWE.] REVERBERATORY METHOD FOR SULPHURETED ORES. 55

ing for blue metal, (4 6) roasting-smelting for regule and bottoms, and 

(5) roasting-smelting for blister copper.

1. If the expulsion of arsenic and antimony is not especially aimed 

at, as has generally been the case in this country, the roasting of the 

first matte may be pushed very far, so that on smelting this matte we 

may obtain a second matte which is very rich in copper, and which may 

therefore be brought forward to the condition of metallic copper with, 

a small number of operations, and hence cheaply.

If, however, the expulsion of arsenic and antimony is especially aimed 

at (as is the case, 1st, when even fairly good copper is to be extracted 

from impure ores; 2d, when exceptionally pure copper is to be obtained 

from any but very exceptionally pure ores), enough sulphur and unoxidized iron must be left after smelting the roasted matte to allow three 

subsequent operations to be performed before reaching the stage of 

blister copper; for, the metallic state once reached, the expulsion of 

arsenic and antimony becomes far more difficult. Though an incomplete roasting doubtless expels less arsenic and antimony in itself than 

a thorough one does, yet, by leaving more sulphur and unoxidized 

iron in the roasted matte, it compels us to submit it to one more oxidizing operation than it would receive were the roasting thorough; and 

this additional operation increases the expulsion of these elements to 

an extent which far more than compensates for their being less fully 

expelled in the incomplete than in the thorough roasting.

2. Oxidized copper ores mixed with the roasted matte in the following smelting operation raise the grade of the resulting matte by oxidation and removal of part of the iron and sulphur; so that if such ores 

can be had at advantageous prices the roasting of the matte need not 

be so thorough, and hence not so costly, as would otherwise be desirable. Indeed, where oxidized ores are abundant, as in the desert of Atacarna, in Chill, the roasting of the matte is generally wholly dispensed 

with if only fair copper (G-. O. B.) is aimed-at.

3. If rich sulphureted copper ores free from arsenic and antimony 

are available for the subsequent smelting, we may push, our roasting 

further, and thus favor the expulsion of arsenic and antimony, and yet 

obtain on smelting a product containing enough iron and sulphur to 

enable us to submit it to the three operations of the extra process before reaching the metallic state. Indeed, if the original materials be 

very impure, or if the most complete possible expulsion of arsenic and 

antimony be desired, it may be advantageous to add enough pure sulphurets on smelting the thoroughly roasted matte to produce a new 

matte so rich in sulphur and iron that it may be submitted to an extra 

roasting and smelting in addition even to those of the "extra process."

4. If the prices of labor and fuel were high, that would incline us to 

limit the number of operations, and hence to push the roasting far, so 

that on smelting the roasted matte we would obtain a matte rich in copper and therefore cheaply " brought forward " to the metallic state.

(477)
56 COPPER SMELTING. [BULL. 26.

In point of fact, variations in the four conditions just mentioned, combined with local traditions, prejudices,'and whims, do endlessly modify 

the methods practiced. But the complexity and the great number of 

operations of the re verberatory process, so often complained of as senseless, really have at least a partial justification in the fact that the expulsion 

of arsenic and antimony, unlike that of sulphur and iron, is not favored 

by a small number of oxidations, each pushed very far, so much as by a 

greater number of less costly and less'thorough oxidations and reductions 5 for while the fullest state of oxidation of sulphur and iron is not 

unfavorable to their expulsion (sulphates of iron and copper are readily 

decomposed with expulsion of their sulphur in re verberatory roastingand smelting), the complete oxidation of arsenic and antimony prevents 

their expulsion, since it is the partially not the completely oxidized 

compounds of these elements that are volatile. Furthermore, the total 

cost of a long series of operations may exceed but slightly that of a 

smaller number of more costly ones.

Matte roasting, unlike that of ore, is rarely limited by fear of loss of 

copper in the slag produced in the subsequent smelting, since this slag 

is almost always resmelted at any rate. This idea could not, of course, 

be pushed so far as to slag an important proportion of the total copper, 

as the cost of recovering a unit of copper from the slag is considerably 

greater than from the matte produced with it; since the slagged copper, 

after the slag containing it is smelted in the first fusion operation (2), 

has to undergo two operations (3 and either 4 or 4 a) before reaching 

the condition it would have been in had it passed originally into the 

matte instead of into the slag. But the roasting is generally limited 

by other considerations before proceeding so far as to slag an amount 

of copper so large that any considerable expense is caused by its extra 

treatment.

THE OPERATION. 1

If in lumps the matte may be roasted in heaps, or, far better, in 

stalls or kilns; in either case repeated firings are needed. If in powder, 

reverberatories (either open or muffles, or Gerstenhofer furnaces) may 

be employed. The use of revolving cylinders has not been successful, 

so far as the writer knows, but the difficulty found in roasting ore in 

these furnaces on account of its great plasticity would be greatly diminished in the case of mattes. Several attempts lately made in this 

country to roast mattes in Maletra's shelf-burners seem to have had 

indifferent results. Where the recovery of the sulphur of the matte as 

sulphuric acid is aimed at kilns 2 will probably be preferred for lump

1 Mineral Resources of the United States, 1883, p. 280.

2 It is thought by many smelters in this country that matte cannot be successfully 

roasted in kilns. This is not correct; matte has been successfully roasted in kilns in 

several places in Europe, even for acid making. (Kerl, Grundriss der Metallhiitten-

(478)
HOWB.] REVERBERATOR! METHOD FOE SULPHUEETED OEES. 57

matte, muffles or better Gerstenhofer furnaces for pulverized matte. 

Where the sulphur is allowed to escape, choice will generally lie between roasting lump matte in stalls and pulverizing it and treating in 

open reverberatories or Gerstenhofers. 'At Mansfeld (see Table IX, 

below) 12 to 14 per cent, of sulphur from a matte containing 25 to 29 per 

cent, was recovered as sulphuric acid by the use of Gerstenhofer furnaces, yet this course has been abandoned there, and the matte is now, 

or was lately, roasted in stalls in lump form, and this although .the cost 

of pulverizing was greatly diminished by granulating the matte in 

water as it ran from the furnace. The experience at Bergen Point, however, seems to be that it is more economical to pulverize the matte 

with Blake or Sturtevant pulverizers, roast it in reverberatories, and 

grout it than to roast in stalls. Vivian, as late as December, 18SO, 

speaks very favorably of the Gerstenhofer, which I believe is still extensively used in Swansea for matte, burning.

The roasting of matte is conducted in much the same way as that of 

ore, whatever be the mode adopted, except that a higher temperature 

can be used, and that much more fuel is required, since little available 

heat is developed by the combustion of the comparatively small amount 

of sulphur and iron in the matte.

The employment of coal or coke dust for the expulsion of arsenic and 

antimony in matte roasting as explained in considering ore roasting, 

is especially recommended.

The most marked difference between the roasting of ores and mattes 

is that in the latter no sulphur can be volatilized as such (unless pyritous ores be added). This deprives us of a potent means of expelling arsenic and antimony as sulphides. The economic features of the roasting 

of mattes as performed in stalls and heaps in several places are given 

in the accompanying table (Table IX), and several examples of matte 

roasting in open reverberatories may be found in Table IV.

TABLE IX. Matte roasting in stalls, open piles, and GerstenMfer furnaces.

With or without grate ......

Weight of matte per charge,

tons of 2,000 pounds.

number or burnings.

twenty-four hours, tons.

00 -9 I«"

i!.

Ill

4$ o a>

PM

1.

With....... 

With.......

6.6

2

5

1.5 A

o 

cj 1 *

°"p-T

2.

Without ....

11

5

 2

01

es'1

3.

5'by6'by4'8"

With.......

5 '

3

12

0.5

N. Knob, Ore C., metal, in coarse 

piles.

4.

14' by 14' by

5'

32

6

30

Mansfelcl, matte, '.Gersteuhofer. 

6.

..........

10 to 15

Swansea, coarse Ger- mtal, 1880, 

stenhofer. i

6.

......

(479)
58 COFFER SMELTING. [BULL. 26. 

TABLE IX. -Matte roasting in stalls, open piles, and Gerstenliofer furnaces Continued.

Composition of material 

treated :

matte or ore.

Yields matte carrying:

Productof smelting consists 

of:

per.

used per ton matte roasted.

Shirley,Mass., Pt. metal, in coarse 

stalls.

1.

32.5

31.0

35.5

=65

tons.

0.22

R., p. 285

Agordo, coarse metal, in stalls.

2.

25

8 to 12

362 .

71 *\

28 5

tons; charcoal, 0. 085 

. tons. 

0.28

R., p. 344

Imaginary, white metal, stalls. in 

3.

72?

cords.

P.

Ore Knob, S". C,metal, in coarse

piles.

4.

22.08

47.00

23.41

3.38

355

54

46

cords; 

charcoal, 

15 bushels. 

0.56

E.

Mansfeld, matte 

Gerstenhofer.

5.

25 to 29.

17 to 24?

atory.

65 to 66

K.

Swansea, coarse metal, Ger- 1880, 

stenhofer.

6.

00

12

V.

A. =- Approximately.

E.=T. Eglestou, TraDsaotioiis of the American Institute of Mining Engineers, X, p. 32.

P. = E.D. Peters, jr., in Mineral Resources of the United States, 1882, p. 293.

R.=Rivot, Principcs G-eu6raux du Traiteruent des Minerals Metalliques, 1871,1.

K.=Kerl, Grundms der Metallhiittenkuude, 1881, p. 175.

V.=Vivian, Copper Smelting, etc., p. 21.

4. SMELTING FOR WHITE METAL. *

THE AIM.

In smelting the roasted coarse metal (the first matte) for the rich 

white metal of the "ordinary" process rather than for the comparatively lean blue metal of the ".extra" process, we do not so much aim 

at the expulsion of arsenic and antimony as at bringing our copper 

forward to the metallic state rapidly and cheaply. To effect this most 

advantageously we endeavor to completely scorify the iron, to remove all 

sulphur in excess of that needed to combine with the copper present as 

disulphide of copper (Cu2S), and at the same time to reduce all oxidized 

copper chiefly by means of the sulphide of iron undecornposed in the 

preceding operation! Practically this end cannot be accurately attained, and in fact we are compelled to leave some 4 to 8 per cent, of 

iron in the resulting matte, while the slag contains from 3 to 5 percent, 

of copper.

We aim at a product approximating the composition of disulphide of 

copper with, say, 71 to 75 per cent, copper. If it were much leaner in 

.copper it would be difficult to bring it forward to the condition of blister 

copper in the succeeding operation. It should not be much richer than

(480)
REVERBERATOEY METHOD FOR SULPHTJRETED ORES. 59

75 per cent, copper, since any excess of copper above that required to 

combine with the available sulphur present (part of the sulphur is 

appropriated by the iron and other metals present) to form disulphide 

of copper (Ou2S) would precipitate out in the metallic state, carrying 

with it most of the arsenic, antimony, and gold, creating thus an additional product whose treatment complicates the process, and a considerable part of which works down into the sand hearth, causing a heavy 

locking up of very impure copper. That part of the metallic copper 

thus precipitated which is not absorbed by the hearth will, on tapping 

the charge, accumulate in the bottoms of the molds nearest the furnace, through which the matte passes on its way to those farther off, 

the molds communicating with each other by slight depressions in the 

tops of the sand partitions which separate them. It is hence called copper bottoms. If it be desired to thus eliminate the arsenic, antimony, 

and gold in bottoms it is in general better to do so after performing the 

additional fusion of the extra process, since this additional fusion itself 

expels a large amount of arsenic and antimony, so that both the resulting matte and the bottoms accompanying it are freer from these noxious elements. It is sometimes, however, considered desirable to separate bottoms in the first fusion of the roasted "coarse metal,"eliminating arsenic and antimony at less cost, if less completely.

The silica for the scorification of the oxides of iron formed in roasting the coarse metal is furnished by the sand taken up mechanically by 

the coarse metal from the molds into which it is tapped in operation (2); 

by the fettling and bottom of the furnace; and very advantageously by 

the addition of silicious ores nearly free from iron sulphides, preferably 

containing the copper in an oxidized state, or of ore-furnace slags.

From the following examples it will be seen that the resulting slag 

is essentially a silicate of protoxide of iron, far more basic and ferruginous than the ore-furnace slag, and hence so heavy as to necessarily 

retain shots of matte,, While this does little harm, as the slag generally carries so much scorified copper that it has to be resmelted at any 

rate, it should not, on the one hand, be so ferruginous as to corrode the 

furnace too rapidly, yet it should be sufficiently ferruginous to subsequently act as a desirable flux for the usually acid ore-furnace charge, 

with which it is generally resmelted.

Miscellaneous oxides. . . .

Welsh white 

metal slag, a

33.8

5G. 0

0.9

1.5

0.3

1.4

2.1 

4.0

3.7

Kaafjord white 

metal slag. 6

31.0

56.0

6.9

0.6

3.5

0.3 

1.67

a Le Play oj>. cit., p. 254.

b Kerl, Grundriss der Metallhiittenkunde, I, p. 214.

(481)
60 COPPER SMELTING. ' [BULL. 26.

The furnace in which this operation is performed, called a "metal" 

furnace, is almost identical with that employed in ore smelting. There 

are generally, however, two air ports, horizontal passages, about 7 

inches square and nearly parallel with the longer axis of the furnace, 

extending from the back of the furnace to the laboratory, and thus admitting a large volume of cold air into the laboratory beneath the 

flames. This cold and therefore heavy air passes over the melted or 

melting charge underneath the flames, so that when these air ports are 

open the^ charge is exposed to a strongly oxidizing atmosphere, the 

flame heating it by radiation but not coming in contact with it, and, 

therefore, exerting no reducing action on it. It appears better to the 

writer to heat the air thus admitted by passing it through the walls or 

bottom or roof of the furnace, since it thus intercepts and returns to 

the furnace heat which would otherwise be lost, and since by using hot 

air instead of cold a greater quantity of air can be admitted into the 

laboratory without undesirably cooling the furnace, and more strongly 

oxidizing conditions can thus be obtained.

The metal furnaces are not provided with wells for granulating the 

matte. The principal dimensions of some metal furnaces are given in 

Table VI.

THE OPERATION. 1

The operation (see second column of Table VI) is performed very much 

as the ore smelting is. If part of the mixture is in powder and part in 

lumps, the lumps should be charged first and the fines placed on top of 

them. This arrangement places in the hottest position the fines, which 

are, from their structure, the least pervious to the heat, and the lumps, the 

easiest to melt, are most protected from, the heat. As the fine matte 

melts it can readily trickle down past the lumps to the bottom, reacting on 

them, absorbing their silica in passing, and leaving them protruding 

and exposed to the heat. If the fines were at the bottom they would 

lie there unacted on, since when the lumps charged above were melted 

they would simply lie as a liquid layer above the fines, protecting them 

from the heat. Again, by placing the lumps below, when the upper 

portion of the charge melts and falls to the bottom it will arrange itself in the interstices between the lumps, in level layers, matte below 

and slag above, the hearth being thus protected by the matte from 

the corrosive action of the basic slag. But if fines were charged direct 

on the hearth the iron oxides in which they are so rich would lie for 

a long while in actual contact with the hearth under conditions most 

favorable for corroding it, satisfying their affinity for silica by dissolving it from the hearth instead of by combining with the silica contained 

in the charge.

The amount of sulphur given off in this operation is so much less 

than in ore smelting that there is much less ebullition. About five

' l Le Play, op. cit., pp. 243 and 254. 

(482)
HOWE.] EEVEEBEEATOEY METHOD FOE SULPHUEETED OEES. 61

hours after charging, the bath is rabbled to remove any matter adhering to the bottom. After another half hour the slag is skimmed, the 

matte tapped, the fettling repaired, and a new charge introduced, much 

the same as in ore smelting. The whole operation generally occupies 

about six hours, though the length of this as well as of the other reverberatory smelting operations varies considerably.

CHEMICAL REACTIONS.

At the end of some three hours after charging the furnace we may 

distinguish three fairly well defined horizontal layers: below, the matte; 

next, a well fused slag; and above all, a layer of semi-fused slag, containing the original elements of the charge, quartz, metallic oxides, and 

sulphides, exposed to the most intense heat and gradually melting and 

passing to the lower layers. But these layers when first formed differ 

greatly from the final products, the matte at first being much leaner and 

the slag much richer in copper than at the end of the operation. Le 

Play found the following proportions of copper in the matte and slag 

at different stages:

Hours after charging. 

\

Three hours ten minutes. . . .

Five hours fifty minutes ....

Copper in 

matte.

Per cent. 

54 

52

65

74

Copper in

slag.

Per cent. 

9

8

5

3.5

As the fusion takes place in a strongly oxidizing atmosphere we 

should expect that the matte would grow richer in copper, owing to 

the expulsion of its sulphur as sulphurous acid and the scorification of 

its iron, and that the slag would at the same time grotv richer in copper by the oxidation and scorification of that metal. But in point of 

fact the slag grows leaner in copper as the operation progresses; that 

is to say in the latter part of this strongly oxidizing fusion there is an 

actual deoxidatiou of the copper scorified in the beginning of the operation. It is evident that this reduction of copper from the slag is 

effected mainly by the sulphide of iron present, as explained in considering the ore smelting. That this reduction is effected mainly by sulphide of iron and not by sulphide of copper is indicated by the fact that 

so little ebullition occurs during the operation. If the oxide of copper 

were reduced by sulphide of copper we should have, first, a-lively ebullition of sulphurous acid, and, second, the formation of a considerable 

amount of metallic copper, 2 Cu2OSiO2 + Cu2S = 6 Cu + 2 SiO2 + SO2 .

But as little ebullition takes place and as metallic copper is not 

separated, we must conclude that the reduction takes place thus: 

FeS + Cu2OSiO2 = FeOSiO2 + Cu2S.

The reaction of the matte and slag is promoted by the constant re-

(483)
'6'; COPPER SMELTING. [BULL. 26.

newal of their surfaces of contact after fusion; first, by the subsidence 

of the richer and heavier matte from the plane of contact of matte and 

slag as fast as it becomes enriched, portions still comparatively lean in 

copper taking its place from below;'second, by the sinking, from the uppermost and still incompletely fused pasty layer of slag, of drops of 

matte as they are released by progress of the fusion, not only reacting 

on the slag as they pass through it, but by their passage stirring it up. 

The mutual reaction of the matte and slag is further promoted by the 

great extent of the surface of their contact, due to the fact that they 

are spread out in two very thin layers extending across the whole area 

of the hearth.

4 a. SMELTING ROASTED COARSE METAL FOR BLUE METAL.

Since in smelting the roasted coarse metal for blue instead of for 

white metal we seek to produce a matte with less copper and consequently more sulphur and iron than white metal has, the oxygen in 

the metallic oxides in the charge must be in smaller proportion to the 

sulphide of iron present than in the operation last discussed, so that 

the sulphur and iron may not be oxidized to so great an extent as they 

there are. This should incline us to add sulphureted rather than oxidized fluxes. Since the extra process of which this operation is a part 

aims especially at the expulsion of arsenic and antimony, particularly 

pure ores are generally selected to furnish the silica needed for fluxing 

the oxides of iron, and the addition of the necessarily impure slags 

from the succeeding operations is avoided.

THE FURNACES (SEE TABLE Vl).

For the same reason special furnaces are used, which, though identical in construction with those employed for the other fusions, avoid 

.contaminating the products with impure materials left in the furnace 

from previous charges. Indeed, it is a general rule in the reverberatory 

process to avoid, as far as possible, performing any of the fusion operations of the extra process in furnaces in which impure materials are 

treated. The impurities absorbed by the hearth are liable to come up 

and contaminate the pure materials when least expected, even weeks 

and mouths after their absorption. So, also, special furnaces should, if 

possible, be reserved for each of the fusion operations, of both the 

 ordinary" and the "extra" process, lest low-grade material absorbed 

by the hearth should mix with the high-grade product resulting from a 

more advanced operation performed in a furnace in which a less advanced operation had previously been carried on. So, again, when the 

extra process is used, not to obtain exceptionally pure copper from very 

pure materials, but for producing perhaps merely a barely merchantable copper from impure materials, special furnaces should be employed, 

lest the impurities given off in great quantities and absorbed by the

(484)
HOWE.] KEVERBERATOEY METHOD FOR SULPHURETED ORES. 63

hearth in treating impure materials should later on contaminate the 

products of pure materials. 

This great differentiation in the functions of the various furnaces 

renders the reverberatory process more applicable to very large establishments, where the many classes of furnaces, each reserved for a special 

work, and each with its special workmen highly expert in their special 

operation, may be kept fully occupied.

THE OPERATION, ETC.

With the exceptions stated above, the details of the operation, its 

aims and chemical reactions, are the same as in operation (4) smelting 

for white metal, already described, to which the reader is referred, p. 58. 

(See, also, the third and eighth columns of Table VI.)

4 1). BOASTING-SMELTING BLUE METAL FOB BEGULE AND BOTTOMS.

THE AIM.

The aim of this operation is to scorify the small amount of iron 

which remains in the. blue metal as completely as possible and to bring 

the percentage of sulphur slightly below that required to form disulphide of copper (Cu2S) with the copper present; this causes the precipitation of metallic copper (bottoms) which has already been referred to.

The reason of this precipitation is that we cannot have a sulphide 

of copper, at .least in the molten state, containing less sulphur than 

disulphide of copper has. Consequently, if, as in this operation, we 

expose molten disulphide of copper to the air and oxidize a portion of 

its sulphur, a corresponding quantity of copper at once separates in 

the metallic state, so that the remaining matte is still of the composition of disulphide of copper. The copper thus separated sinks to 

the bottom of the furnace and thus separates from the matte by gravity. 

The important feature of this is that nearly all the arsenic, antimony, 

and gold (on account of their having a weaker affinity for sulphur than 

copper has), will separate out from the matte with this first portion 

of copper which is thus separated; so that this affords us a ready way 

of removing arsenic, antimony, and gold from the bulk of the matte 

and concentrating these metals in a small quantity of metallic copper 

which can be specially treated.

The oxidation of the iron and sulphur, and incidentally of the copper is effected by very slowly melting down the large blocks of blue 

metal in a strongly oxidizing atmosphere.

THE OPERATION.

The operation (see Table VI, column 4) is performed in furnaces similar 

to the ore-smelting furnaces, but provided with air ports. As the material is much denser far heavier charges can be made than in ore smelting. 

The blue metal, cnst in very large cakes and with much sand adhering

(485)
64 COPPEE SMELTING. (BULL. 26.

to it, is piled on the hearth, nearly filling the laboratory and reaching 

almost to the roof. Care is taken to leave large interstices through 

which the flames and air can draw, both among the cakes of matte 

and along the sides and roof of the laboratory. The air ports being 

left wide open, the temperature rises very gradually and the matte melts 

very slowly, the current of air oxidizing the drops of matte as they 

trickle down. This is kept up till the cakes have been melted down to 

a pasty mass, when the air ports are closed, increasing the draft, and 

the temperature is raised till the fusion is complete. If the oxides of 

the charge have been in proper proportion to the sulphides, and if the 

operation has been properly timed, a small amount of metallic copper 

will now have been formed. The workman learns whether this has occurred or not by dexterously exposing the bottom of the furnace by 

suddenly pushing aside the hath of molten matte with his rabble, when, 

if any metallic copper has been formed, it may be recognized as it lies 

on the bottom of the furnace by its beautiful sea-green color and metallic 

luster. If none is found, the oxidizing action is prolonged by keeping 

the doors open and allowing the air to strike on the molten matte, its 

surface being kept free from slag, the oxidation of the sulphur which is 

thus effected eventually causing the precipitation of metallic copper. 

As soon as this has occurred the charge is tapped out of the furnace 

into a row of sand molds. The metallic copper which has been formed 

will be found in the bottoms of the moulds nearest the furnace; hence 

the name " bottoms." Above it, and filling the rest of the molds will 

be found the very rich matte known as regule.

CHEMICAL REACTIONS.

During the slow fusion arsenic and antimony appear to be partly 

driven off as arsenious acid and trioxide of antimony (As2O3 and Sb2O3 ); 

the gentle oxidizing action to which each particle is exposed as, by the 

gradual melting away of the outer portions, it approaches the surface of 

the lump which contains it, favors the formation of these imperfectly 

oxidized compounds, the tendency in any one layer to form them rather 

than the non-volatile completely oxidized combinations (the arseniates 

and antimoniates) being probably at its strongest just before that layer 

becomes fully exposed to the strong oxidizing action of the atmosphere 

of the furnace and while that action is still weakened by the interposition of a thin film of partly oxidized matte.

The surfaces of these cakes of matte, exposed as they are to the 

strongly oxidizing atmosphere of the furnace at this high temperature, 

apparently contain a considerable amount of oxide of iron and of copper. Kow as the matte melts drop by drop, and as the drops trickle 

down one by one over these oxidized surfaces, each drop is exposed to 

the oxidizing action not only of the atmosphere of the furnace, but also 

of the pasty oxides over which it trickles; and these conditions, this

(486)
HOWB.] REVERBERATORY METHOD FOR SULPHURATED ORES. OO

intimate contact of drops of molten matte with semi-fused oxides, appear to effect the oxidation of the sulphur and iron of these mattes, 

containing as they do but little of these elements, much more energetically than the ordinary methods of roasting do, such as roasting in 

heaps, kilos, or reverberaf ory furnaces without fusion; arid yet there can 

be no doubt that the oxidation of the sulphur and iron of mattes and 

ores rich in sulphur and iron, but lean in copper, is performed much more 

economically by the ordinary methods of roasting without fusion than 

by this roasting-smelting of the Welsh process. Just where the line 

should be drawn between mattes w.hich are most economically roasted 

without fusion and those for which a roasting-smeltiug is most desirable 

it is hard to say, but it probably lies somewhere about blue metal containing say 57 per cent, of copper. At Bergen Point it is considered 

advisable in treating blue metal to roast part of it, which is then charged 

with large blocks of raw blue metal and subjected to a brief roasting 

fusion. At Swansea, I believe that nothing as rich as blue metal is 

roasted. At the time of the last information [ have from Baltimore no 

roasting proper whatever was done, mattes even much leaner in copper 

than blue metal being oxidized partly by-the Welsh roasting smelting 

and partly by the use of the scanty supply of oxidized ores. The same 

course was formerly followed at Phosnixville, where the later introduction of reverberatory roasting furnaces effected a great saving, and few 

metallurgists will probably to-day advise relying solely on the Welsh 

roasting smelting where compounds containing much below 50 per cent, 

of copper are to be treated, especially if the ratio of iron, to sulphur in 

them be large. ~ \

That portion of the copper which is oxidized during the roastingsmeltiug is again reduced for the most part when the mass unites on 

the hearth, partly by the sulphide of iron which has escaped oxidation, 

with formation of disulphide of copper and oxide or silicate of iron, 

but also in part by the disulphi.de of .copper with the evolution of snlphurous acid and formation of metallic copper. The enrichment and 

purification of the matte is thus effected: .First, by the direct oxidation 

of its impurities during the tusion ; second, by the oxidizing action of 

the oxides and silicates of copper formed in the fusion and later reduced at the expense of the iron and sulphur; and third, by the elimination of the foreign metals and of arsenic and antimony in bottoms.

The products of the operation are (1) a slag which may be.returned 

to the ore smelting, though it is generally so impure" that it is better to 

treat it with impure materials for an inferior grade of copper. Though 

far more basic than the ore furnace slag, the sand adhering to the blue 

metal and the silica greedily absorbed from the hearth and fettling by 

the oxides of iron formed in the roasting generally make it rather more 

acid than a singulo-silicate; (2) a generally spongy matte called "regule," with more,or less moss copper; (3) copper bottoms, generally 

very impure, and reserved till a sufficient amount has accumulated to 

Bull. 26 5 (487)
66 COPPEE SMELTING. I BULL. 20.

make a special refining charge for copper of inferior quality. In treating auriferous materials most of the gold concentrates in these bottoms, 

which are specially treated for that metal. 

Le Play gives the following analyses :

Tin................................

Bottoms.

92 5

Fe.Ni, Mn, ].6

4.8

.4

.2

99.5

Regule.

81.1

0 2

18.5

99.8

Slag.

34

1.

1.

12.

52.

100.

5. BOASTING-SMELTING THE RAW WHITE METAL AND REGULE FOR

BLISTERED COPPER.

The aim of this operation is to expel as sulphurous acid the sulphur 

which up to this point has been retained to effect the reduction of the 

oxides and silicates of copper inevitably formed while oxidizing the 

iron. The conditions at the same time favor the expulsion of arsenic 

and antimony, and the scorification of the heavy metals (Su, Ni, Co, 

Mn; Fe, etc.) present in small amount.

THE OPEKATION.

The operation (see Table VI, columns 6,9, and 25} is performed in furnaces similar to the smelting furnaces already described, and provided 

with air ports. The present tendency is to greatly increase the size of 

the "roasters," as these, furnaces are called, and one has lately been 

constructed with a capacity, of 35,000 to 50,000 pounds at each charge. 

Both labor and fuel are greatly economized by increasing the size of 

these furnaces. The labor, after the furnace is charged, consists almost 

wholly in overseeing the operation and managing the fire, the work of 

skimming the slag being short. As far as the supervision goes the furnacemen can nearly or quite as efficiently oversee 10 tons as an ounce. 

And since the exterior surface of the furnace is augmented by increments of its size in a much smaller ratio than its cubic contents are, 

the radiating surface and hence the loss of heat by radiation are 

smaller per unit of contents in large than in small furnaces. For very 

large furnaces several doors may be needed to enable the workmen to 

stow the large pigs of matte advantageously. These are charged by 

means of strong heavy peels, and piled almost to the roof, care being 

taken to leave interstices through which the flame and air can readily 

pass. On first charging, the air ports are closed for some ten minutes 

to raise the temperature of the furnace to the point at which the oxidation can take place. They are then opened and the temperature is gradually raised till the matte begins to melt and trickle down drop by drop,

(488)
HOWK.] REVERBERATORY METHOD FOR SULPHURETED ORES. 67

eacli particle as it melts and runs down being thus exposed in turn to 

the oxidizing action of the metallic oxides on the surfaces of the cakes 

of matte over which it runs and of the air which pours in through the 

air ports, the hob and light products of combustion passing in a thin 

layer close to the roof and heating the charge almost wholly by radiation. The first, drops begin.to run some thirty minutes after the furnace 

has been charged, and this gradual fusion is continued till, after from 

five to six hours, the whole has united on the hearth as a semi-liquid 

mass.

During this period the oxides of copper formed by the direct action 

of the air on the disulphide of copper react on adjoining particles 

of disulphide of copper with evolution of sulphurous acid and formation of metallic copper (Cu2S + 2 Cu2O = 6 Cu + SO2 ), which, from its 

greater specific gravity, collects on the hearth beneath the remainder 

of the charge, and thus at once is itself protected from further oxidation and separates the abundantly formed oxides of copper from the 

hearth, whose corrosion is thus prevented, while the copper oxides are 

restrained from passing into the condition of silicates, from .which the 

subsequent reduction of the copper would be very difficult. As in the 

roasting-smelting of blue metal the mildly oxidizing conditions presented to the different particles as, by the fusion and removal of the 

exterior portions, they in turn acquire a position immediately beneath 

the surfaces of their several cakes, should strongly favor the expulsion 

of arsenic and antimony as arsenious acid and trioxide of antimony, 

the oxidizing tendencies passing, by insensible steps, through every 

possible degree of strength as the thickness of the exterior shell of 

matte gradually decreases, till ife finally vanishes, and we have the 

direct action of the current of air untempered. While a portion of the 

arsenic and antimony is expelled in this way, other portions become 

completely oxidized and form the non-volatile arseniates and antimoniates. During this oxidizing period a considerable portion of whatever zinc, tin, nickel, cobalt, and other heavy metals there may be present is oxidized, to be scorified and removed in the crasses in the 

following period. When this semi-fusion or sloughing off has progressed 

so far that but little of the still unmelted portion of the charge protrudes above the surface of the pasty mass gathered on the hearth, so 

that the oxidizing effect of the current of air is greatly lessened, the first 

period is brought to a close, the air ports are closed, the temperature is 

raised, and the whole charge thoroughly melted. During this (the second) 

period the reaction of the disulphide of copper, Cu2S, on the previously 

formed copper oxides continues, with reduction of both sulphide and 

oxide to metallic copper and expulsion of sulphurous acid. The arsenic 

and the antimony of the previously formed arseniates and autimoniates 

are apparently also deoxidized by the disulphide of copper as well as by 

the escaping sulphurous acid, portions of them being completely deoxidized and uniting, with the copper and the remaining sulphur, other

(489)
68 COPPER SMELTING. [BULL. 26.

«r

portions being probably only partially deoxidfzed and brought to the 

condition of arsenious acid and trioxide of antimony, which are volatilized. The iron, which has been nearly all oxidized, rises to the surface 

a* fusion progresses, and when all has become liquefied the iron crasses, 

very rich in copper and quite impure, are skimmed off. If the charge 

contains much iron its scorification may be promoted by charging a small 

quantity of very pure silicious oxidized ores at the end of the first period 

(say 1,200.pounds of ore of 27 per cent, copper to a charge of 5£ tons 

of matte). The third period now begins, in which the charge is gradually cooled down under the strong oxidizing action of currents of air 

pouring iu through the air ports, which are again opened. The upper 

surface soon becomes so viscid that the escape of the sulphurous acid 

from beneath throws it up into little craters, thus enormously increasing 

the amount of surface exposed to the air and affording passages through 

which the air can descend to oxidize the sulphur and copper beneath. 

This is kept up till the whole mass is quite hard, except perhaps a small 

portion next to the bridge, unless the careful examination of the quantity of matte remaining undecomposed shows the ftimaceman earlier 

that the oxidation has progressed far enough.

When the mass has become so hard that the reactions between diuoxide and distilphide of copper no longer take place, the third period is 

terminated and the temperature is again raised, the oxidizing action 

being continued by leaving the air ports open except for short intervals 

when they are closed to increase the draft of the fire. The furnaceman must now .attentively watch the progress of operations and close 

the ports when the oxidation and removal of the sulphur have progressed so far that all the copper will have passed to the metallic state 

by the time the fusion has been completed. When all is liquefied the 

crasses are skimmed and the copper is tapped out into large sand molds. 

If the operations have been properly timed its surface will be covered 

with large smooth blisters; hence the name blistered copper.

In Chili, where the metallic copper produced is in general intended 

for the European market,.and where consequently great care is bestowed 

on the appearance of the bftrs, a smooth surface being above all things 

desired, a small quantity of 50 percent, matte, say 400 pounds toa charge 

of 5J tons, is charged a short while before tapping. After most of the 

copper has run from the furnace this matte begins to run out with it, 

and, being much lighter, forms a thin coating on the top of each mold, 

protecting the copper in setting from the action of the air, which but 

for this would tend to cause little craters or pimples from the evolution 

of sulphurous acid. When the bars thus-cast are quite cold this matte 

is chipped off with great care. The aim is to have the bars very smooth, 

from the belief that if they are rough a considerable amount of dirt 

may be caught on their rough surfaces, and that when the bars are 

sampled on their arrival in Europe by their purchasers an undue proportion of dirt will get into the samples.

(490)
MOWS.] REVERBERATORY* METHOD FOR 'SULPHURETED ORES. 60

For the same reason great care is bestowed on the preparation of the 

sand molds, the equivalent of six hours' labor being occupied in preparing them. Before tapping they are heated by burning wood on them.

The details of this roasting-smelting process differ greatly in different 

places. In some places the second period (the complete fusion after 

the slow oxidizing semi-fusion and the skimmingof the crasses) is wholly 

omitted, the cooling down and setting commencing as soon as the first 

period of semi-fusion is complete. This was formerly the practice at 

Swansea. In others, as at Bergen.Point and elsewhere in this country 

(and formerly at Phcenixville), the setting is wholly dispensed with, 

the charge being slowly melted down and then exposed, as it lies fully 

melted, to the action of the air admitted through the air ports and the 

side door, the crasses being frequently skimmed, until the whole is converted into metallic copper. As long as any sulphur remains the melted 

mass bubbles with a peculiar hissing noise from the evolution of sulphurous acid. When this ebullition ceases it is well to flap the metal 

for a short while to form a little dinoxide of copper, which dissolves in 

the metallic copper and completes the expulsion of the sulphur.

The following are examples of the time occupied in the several periods 

of this roasting-smelting process:

Chilian and Swansea practice. Time.

Chilian practice (private notes). 

1. Slow semi-fusion:

Charge 5 0 tons white metal of 70 per cent, copper:

Charging finished at. 

Ports closed I ill ......

Roast with open ports till.

2. Fusion completed at higher temperature:

Charge 1,200 pounds carbonates of 27 per cent, copper:

Close ports at.

Fire hard to melt lill .......

Skim slag'from 11 hours till.

3. Gradual setting

Open ports, cool down, and solidify from 12 hours till.

4. Pemelt ;ind tap :

Temporalnro raised till 

Skim crasses at ........

Tap at .................

Charging:

After fettling commence charging at. 

.Finish charging at ...............".....

Sivansea practice (after Le Play). 

1. Slow semi-fusion:

Charge finished at. ........

Ports closed till ..........

"Roast with open ports till

2. Gradual setting:

Open ports and cool down from 5 lira, and 30 ruin. till.

3. licmelc and tap:

Slow semi-fusion from 11 hours till

Chargiu

Fusion completed from 17 hours till tap at.

Commence charging at. 

Finish charging at .....

O h 0" 

0 30 

5 23

5 23

11 0

12 0

19 0

22 47

22 47

23 10

28 35

24 0

0 0

0 10

5 30

11 0

37 0

23 0

23 0

24 0

The products of this operation are, first, crude metallic copper, from 

which nearly all the impurities have been eliminated and which becomes 

merchantable after -One more operation (refining); second, slags and 

crasses of varying degrees of acidity, according to the amount of iron

(491)
70 COPPER SMELTING. [BULL. 26.

contained in the matte treated, to the care which has been taken to 

prevent the scorification of the copper, and especially to the extent to 

which the oxidation has been carried in the final slow fusion of the 

charge after setting it. If mattes of high grade and consequently 

very free from iron, such as regale and pimpled metal, have been 

treated, the slags will be essentially silicates of copper. As they are 

practically equivalent to rich oxidized copper ores, usually so hard to 

obtain, it is very convenient to use them in operation (4) smelting for 

white metal, as their use enables us to obtain a product of a given 

grade in that operation, with a less thorough preceding roasting. As, 

however, they are generally very impure, it is often preferred to treat 

them separately for copper of an inferior grade 1 , rather than to return 

to the regular process impurities which have been eliminated at such 

cost, and which, if thus returned, tend to accumulate, and have at any 

rate to be separated from the copper again and again.

The following are examples of the composition of the slag and copper 

produced by this roasting-smelting for blister copper:

TABLE X.

Oxide of tin ...............:......

Oxide of zinc.....................

1« a

 ?S? i'S

"3 

£

47.5

28.0

3

n

Ifi O

0.9

0.3

2.0

is?J 

||

03 O 

: *

36.0

7.0

6.0

4.Q 9

2 7

O Q

4.9

0.6

3.2

Tin........................

Welsh blistered 

copper.

0

7 n o

0309

0007

0.4 1.8

0. 1-6. 9

Blistered copper, from Kaafiord. b

99.2-99.4

0. 1- 0. 2

0.2 0.3

0. 0- 0. 02

0. 1- 0. 12

aLe Play, op. cit., p. 318. 6Kerl, Gmndriss der Metallhiittenkunde, I, p. 215.

CLASSIFICATION OF ORES AND SLAGS. 

ORES.

Having considered the various operations of the reverberatory process, we can more intelligently consider the reasons for the classification 

of ores adopted and for assigning the several classes of ores and the 

slags produced in the several fusions to the operations in which they 

are respectively treated. . . Class I. In the ores of Class I, which is treated in the first roasting, 

may be included:

1. Impure sulphureted ores rich or poor in copper, because to eliminate their impurities as fully as possible they should undergo as many 

operations as possible. They should not be added to any of the later

Vivian (op. cit., p. 28) strongly recommends this course. 

(492)
noWE.1 REVERBERATORY METHOD FOR SOLPHURETED ORES. 71

operations, because we mu^t not contaminate with impurities the furnace products which have already had their impurities at least partly 

removed in the earlier operations.

2. Impure oxidized ores, rich or poor, if they contain impurities 

(arsenic-antimony) in a condition in which they may be eliminated as 

sulphides by being roasted with pyritous ores in the first operation.

3. Sulphureted ores, pure or impure, rich or poor, containing much 

sulphureted iron. Of course, they must be roasted before smelting, 

that their iron may be scorified. If very rich in sulphureted iron they 

will yield even afrer roasting much sulphide of iron on smelting, so that, 

if charged in the second instead of the first smelting operation, they 

would contaminate with sulphide of iron the product of the roasted 

matte charged with them, which has already undergone three operations for the express purpose of removing that compound.

Class IL> In Class II, treated in the ore smelting without previous 

roasting, may be included:

4. Impure oxidized ores, except those containing impurities (arsenic 

and antimony), which would be removed by roasting with pyrites. They 

are treated in the first rather than in a subsequent smelting, lest their impurities should contaminate products which have already been at least 

partly purified in the early operations, and that their impurities may 

be expelled as fully as possible by undergoing the full number of operations.

5. Low-grade oxidized ores, both pure and impure (except those 

coming under subclasses 2 and 7) should be passed first through the 

regular ore-smelting rather than through one of the later operations, 

since they yield a large proportion of slag, and since it is only in this 

operation that slags clean enough to be rejected can in general be produced. If smelted in a later fusion they would greatly and uselessly 

augment the .quantity of slag to be resmelted.

Class IIL In Class III, which is treated in the second smelting 

(operation 4, smelting for white metal), may be included:

6. Rich, pure ores, both oxidized and sulphureted, if not containing much sulphureted iron. If oxidized their use enables us to obtain 

in this smelting a given product with less thoroughness, and hence less 

expense, in the immediately preceding calcination. If sulphureted, the 

proportion of sulphureted iron to copper is so small that they may practically be regarded as rich mattes mixed with gangue, from which they 

can be advantageously separated in this smelting, while if treated in 

the ore smelting (operation 2) we should contaminate their copper 

with sulphide of iron, which would have to be subsequently removed 

at great and useless expense.

7. Lean pure ores, oxidized or sulphureted, which do not contain any 

considerable quantity of sulphureted iron, but with a strongly silicious 

gangue, which forms an excellent flux for the oxide of iron whose scori-

(493)
72 COPPER SMELTING. [DULL. 20.

fication and removal is the aim of the smelting for white metal. These 

ores, if of extreme purity and available in larger quantity than that required for operation (4) smelting for white metal, may be also advantageously used" in (4 a) smelting for blue metal, and in (4 It) roastiug-smelting for regule and bottoms; and even as in Chili, for operation (5) 

roasting-smelting for blister, if the-matte treated in that operation contains iron. The preceding classification is summed up in the following 

table:

TABLE XI. Classification of ores..

Purity.

Impure . .

T> n

Jr lirG .....

Sulphureted or 

oxidized.

( Sulplrureted . . .

' Oxidized. ......

Sulphureted...

Oxidized.......

Eichness 

in copper.

Kich or

poor.

Rich or

poor.

1

Rich . . .

Poor . . .

I 

( Eich

) Poor . . .

Miscellaneous.

If impurities are removable by roasting with 

pyrites.

If impurities are not removable by roasting

with pyrites.

(If containing much iron

1 sulphide.

1 If not containing much

[ iron sulphide.

(If containing much iron

sulphide.

-J If not containing much

1 iron sulphide, but sili-

( cious.

C If silicious ...............

< If not silicious ............

Class.

I.

I.

II.

I.

III.

I.

III.

III.

III.

II.

Subclass.

1 and 3.

2.

4 and 5.

3.

6.

3.

7.

6.

7.

5.

Operation in 

which treated.

Ore roasting.

Ore roasting.

Ore smelting.

Ore roasting.

Smelting for

white metal.

Ore roasting.

Smelting for

white metal.

Ore smelting.

This classification does not, of course, aim to be complete; it is merely 

intended to illustrate the principles which guide one in assigning different varieties of ores to different operations.

SLAGS.

If the ore-fnrnace mixture be acid those portions of the resulting 

acid slags which have to be resrnelted on account of containing shots 

of matte form a desirable flux for the iron oxides scorified in the second 

fusion (smelting for white and for blue metal). These acid ore-furnace 

slags are generally so free from injurious impurities (arsenic and antimony, etc.) that they will not contaminate the advanced products of the 

second fusion.

The more basic slags of the later fusions are generally more impure 

than the ore furnace slags. Owing to the opportunity the iron oxides 

have for absorbing silica from the fettling these slags are rarely basic 

enough to be of great advantage in the ore smelting for fluxing the 

silica of the ore; and owing to their impurity it is generally desirable 

to treat them separately for an inferior grade of copper, purified perhaps by the separation of bottoms, rather than to return them with 

their impurities to the regular course of operations. "Roaster" slag,

' (494)
MOWE.] .REVERBERATORY METHOD FOR OXIDIZED ORES. 73

Lowcvor, from the roasting-smeltiug for blister copper, being very rich 

indeed in silicate of copper may, if not too impure, be advantageously 

used in the second smelting operation (4), its oxidized copper being 

very efficient in scorifying the sulphide of iron which we aim to eliminate in this operation.

The resmeltiug of slags, formerly carried out in rcverberatories, is 

now almost universally done in cupolas, except in so far as they are 

used as fluxes in the various revcrberatory. operations.

REVERBERATORY METHOD FOR OXIDIZED ORES AND NATIVE

COPPER.

In the comparatively rare cases in which oxidized ores are treated in 

the revcrberatory who.lly without sulphurets, the reduction of the copper has to be effected by the addition of some reducing matter, such as 

coal. In treating native copper we have to choose between (1) reducing 

in the operation itself the oxides of copper, which are necessarily 

largely formed during the inevitably oxidizing fusion, with coal or so'me 

similar reducing substance, and (2) subsequently recovering the scorified copper oxides from the slags by a separate reducing'fusion or by 

treatment with iron bars (Bivot and Phillips).

REDUCING-SMELTING WITH CARBON.

The operation, whether for oxidized ores or for native copper, is performed in very much the same way as iu smelting sulphureted ores, the 

fluxes needed to form with the gangue a desirable slag, together with 

ttift amount of coal or charcoal needed for the reduction, being mixed 

^ ith the ore or native copper before charging. The furnaces employed 

are very similar to the ore-smelting reverberatories already described, 

and should have a.deep.fire-box, so that the atmosphere of the furnace 

shall be as little oxidizing as possible. As a reducing agent, bituminous coal is much better than charcoal, since the hydrocarbon gases 

copiously evolved by the former efficiently stir up the melting mass, 

constantly exposing fresh portions of it to the reducing action of the 

coal, and themselves offering great reducing surface as they bubble 

through the overlying slag. When fusion commences, we have, besides 

the ganguo, the oxides and silicates of iron and copper, together with 

considerable metallic iron and copper reduced by contact with the coal 

and by the passage of the reducing gases. As fusion progresses the 

oxides and silicates of copper are reduced as they trickle down over 

the coal, and by the already reduced iron. Even after fusion is complete, the coal swimming in the slag will reduce scorified copper. Since 

iron is rapidly reduced at temperatures far below that of incipient 

fusion, much of this metal is inevitably brought to the metallic state 

unless the amount of coal charged is so small that much copper esca.pes 

reduction.

(495)
74 COPPER SMELTING. [BULL. 20.

When" melted, the charge is rabbled, skimmed, and tapped, jnst as 

in t he case of sulphureted ores. When, however, rich native copper concentrates are treated, the quantity of metallic copper produced in each 

fusion is so great that it may be advantageously refined, after skimming 

the slag, without removing it from the furnace in which it is smelted.

The products will be a slag and either refined or crude metallic copper. The slag can probably be rarely brought below a tenor of 1 per 

cent, copper without reducing so much iron as to make the refining 

very difficult.

SMELTING WITHOUT CARBON.1

This method is employed at Lake Superior for treating the mass copper 

and (native copper) concentrates, which are so rich in copper that the 

metal is refined in the smelting furnace itself after fusion is completed 

at the same operation in which it is smelted. The details of the fusion 

are the same as when carbon .is used for reducing. The slags are rich 

in -copper and are resmelted in cupolas.

COMPARISON OF THE TWO METHODS.

By smelting wjth reducing agents we obtain clean slags, but, in case 

of ferruginous materials, a copper alloyed with so much iron that its refining is costly. By smelting without reducing agents we obtain pure 

and easily refined copper, but a slag so rich that it has to be resrnelted. 

Evidently the former course is best suited to lean, the latter to rich ores 

and native copper. With lean ores, yielding much slag and little copper, it is more important to obtain a slag clean enough to be thrown 

away, even if this implies obtaining an impure and difficultly refined 

copper, than to obtain pure and readily refined copper together with 

slags so rich in copper that they have to be resmelted. On the other 

hand the plan of. smelting without reducing agents is especially suited 

to rich ores, since with them the advantage of obtaining the large yield 

of copper in a condition in which it is easily refined greatly outweighs 

the disadvantage of having to resmelt the small quantity of slag produced.

SHAFT FURNACE PROCESS FOR SULPHURETED ORES. 

GENERAL PLAN.

The general plan of operations, resembling that of the reverberatory 

process in its main features, is as follows :

1. Eoasting the ore.

2. Smelting the roasted ore in cupolas, obtaining a clean slag, which 

is thrown away, and a matte A.

3. Roasting the matte A.

'See columns 17, 18, 19, and 20 of Table VI. 

(496)
MOWB.J SHAFT-FURNACE PROCESS FOR SULPHURETED ORES. 75

4. Smelting the roasted matte A in smaller cupolas for black copper, 

obtaining 

(B) A slag, usually returned to the ore smelting, but sometimes clean enough to be thrown away.

(G) A rich matte, which is roasted and then resmelted in (4) 

again (either by itself or with the matte A). 

(D) Black copper.

5. Refining the black copper in reverberatories.

In many if not most cases, the second matte 0, after being roasted, is 

resmelted together with the first matte Aj so that the products obtained 

from C blend with those of A. In other cases the second matte C is 

smelted by itself, when we in general obtain still a third matte D with 

black copper.

On resmeltiug the roasted matte D we may again obtain both black 

copper and another matte E; on rcroasting and resmelting E, we may 

obtain again more black copper and a matte JF7, and so on, the proportion 

of matte to black copper obtained depending on the richness of the matte 

and the thoroughness of the roasting. Thus different portions of the 

copper contained in one and the same original charge of ore will reach 

the condition of ingot copper by means of greatly differing numbers of 

operations. Some, precipitating as black copper when the matte A is 

smelted, will undergo in all but the five operations above given; others 

will remain with the constantly decreasing quantity of matte till this has 

been reroasted and resmelted even five or six times, bringing the total 

number of operations up to thirteen, fifteen, or even more. The quality 

of the ingot copper produced from these different portions of one initial 

charge of ore will vary much. The arsenic, antimony, gold, and, to a 

smaller extent, silver will concentrate in the portions of black copper 

first produced, while that produced last, from matte which has been 

repeatedly roasted and smelted, will be much purer, first, because of 

the elimination of impurities in the first portions of black copper, and 

secondly, from their further expulsion in the repeated roastings and 

sineltiugs. By limiting the thoroughness of the several roastiugs, and 

by the addition of pure unroasted sulphureted ores or furnace products, 

we increase the proportion of matte to black copper which will be produced in the several smeltings and hence the proportion of pure to 

impure ingot copper finally produced, the average number of operations which the copper, taken as a whole, undergoes, and hence the 

total quantity of arsenic, antimony, etc., expelled, and at the same 

time the expense of the process.

By increasing the thoroughness of the roastings and by the addition 

of oxidized ores and products wo lower the average number of operations, the total expense of the process, the purity of the copper taken 

as a whole, and the proportion of pure to impure copper obtained. 

Though some black copper is generally produced in the first smelting of 

the roasted matte A, by limiting the thoroughness of the first two roast-

(497)
76 COPPER SMELTING. [BULL. 20.

ings, by the additioD of pyritous ores, etc., we may defer producing black 

copper till the third or eveu the fourth smelting, and thereby increase the 

total expulsion of arsenic and antimony. Since those portions of these 

elements which are precipitated out with the black copper can be less 

perfectly removed than if they had remained in matte, the greater 

the number of operations before the precipitation of the first black 

copper the purer will it be. It is much easier to expel arsenic and 

antimony from a matte than from metallic copper.

The black copper produced in the several different operations'may 

be refined separately for ingot copper of varying grades of purity, or, 

as is generally the case in this country, it may be mixed together. The 

same is true of the different grades of the rich matte produced with the 

black copper.

The black copper frequently contains so much iron that it is desirable to divide the refining into two distinct operations.

1. ORE ROASTING.

The roasting is performed exactly as in the reverberatory process, 

except that, where the expulsion of arsenic and antimony is not especially aimed at and we simply strive to reach the condition of ingot 

copper as rapidly as possible, the roasting may be pushed to an extent 

which, in reverberatory smelting, would entail serious loss of copper 

both mechanically and from scorification, since in cupola smelting the 

tendency to scorification is very much less and the mechanical loss 

in the slag considerably less than in the reverberatory.

If tbe ore is roasted in reverberatory furnaces and if the retention 

of sulphur is aimed at (to favor the expulsion of arsenic and antimony), 

we should avoid raising the temperature very high towards the end. of 

the roasting, as a high temperature decomposes the sulphates of iron 

and copper with the expulsion of their sulphuric acid j while if uudecomposed in the roasting, they would in the following smelting be 

largely'reduced to sulphides. If the retention of sulphur is not desired, our aim being simply to reach the condition of ingot copper as 

rapidly as possible, the temperature should be raised at the end of the 

roasting to decompose the sulphates. This is in shaft-furnace treatment a more important matter than in the reverberatory. since in the 

latter, with its comparatively violently oxidizing conditions, the reduction of sulphates to sulphides is hardly to be looked for.

2. ORE SMELTING. 

IN GENERAL.

The-roasted ore, mixed with appropriate fluxes, charged in more or 

less intimate contact with the fuel and traversed during the whole of 

its gradual descent by the inevitably rather strongly reducing gases, 

a reducing action from the time it enters the furnace till it is 

' (498)
HOWB.] SHAFT-FURNACE PROCESS FOR SULPHURETED ORES. 77

completely melted before the tuyeres. And even after melting, the reducing action is very strong, since the melted slag trickles down over 

the solid fuel, which reaches down to the bottom of the furnace. In addition to these powerful reducing factors, which we do not have in the reverberatory, we have the deoxidizing tendencies of the reverbcratory as 

well, the melted slag being traversed by the matte, which gradually 

falls through it, energetically deoxidizing any scorified copper; and we 

have the same suspension and solution in the slag of that powerful rcducing >agent, sulphide of iron. Not only does the shaft furnace thus 

offer much more energetic deoxidizing tendencies than the reverberatory, but its sulphidiziug tendencies are also much stronger than those 

of the reverberatory. The contact of the ore with the solid fuel and 

the reducing gases in the shaft furnace protects the sulphur from the 

oxides of the charge and from the free oxygen of the atmosphere of the 

furnace, and thus preserves it for union with the metals. .It moreover 

reduces the sulphates of copper, iron, lime, and baryta to sulphides, 

the sulphides of baryta and lime playing a role similar to.that of sulphide of iron, though weaker, in deoxidizing and sulphidizing scorified 

copper. The strength of the reducing and sulphidizing tendencies should 

be such that no copper should be scorified, and yet that no iron should 

be precipitated in the metallic state, enough sulphur being present to 

absorb any iron which is deoxidized. Where the expulsion of arsenic 

and antimony is not aimed at, the reducing action should be simply 

strong enough to prevent the scorification of copper, the deoxidation 

and sulphidizing of iron being avoided as far as possible, so that wo 

may obtain a matte as rich as possible in copper.

In zinc-bearing ores the zinc, reduced to the metallic state in the lower 

part of the furnace and volatilized, is again oxidized higher, up by the 

carbonic and sulphurous acids, attaching itself to the walls in hard 

crusts called caclmies.

Many examples of furnace construction and output, fuel and labor 

requirements, etc., in ore smelting are given in Table XII. The figures 

in columns G, 10, 11,14, 15, and 16 fairly represent the best American 

practice.

(499)
78 COPPEK SMELTING. [BULL. 26. 

TABLE ~£1I. Examples

Dimensions, &c., of furnace : 

Shape of furnace at bottom.

Water jacketed'or not ... 

Height from bottom : 

(1) To slag notch ....

(3) To throat ........

Inside dimensions:

Area of cross-section at 

tuyeres, por tuyere, in 

square feet.

Blast pressure, ounces 

per square inch.

Total burden smelted per 

twenty -four hours, 2,000 

pound tons. 

Outlay of labor ard fuel: 

Ratio of burden to fuel . . 

Kind of fuel .... ...... 

Days of labor per 2,000 

pounds burden smelted. 

Men employed at furnace 

per twenty-four hours. 

Composition of slag :

Copper ..................

Composition of product :

Aul hority ...................

Mansfeld, pile-burnt 

schists.

1.

Round . . .

Internal . 

Not......

2' 9" ..... 

3' 4" .....

26' 3" ....

6' 2" diam.

7'2J"diam 

4' 9" .....

2"

6 ........

32.4......

3000 Cent. 

132 <o 165.

6......... 

Coke ....

0. 6 to 0. 7

36

K., p. 168.

I

2.

Round . . . 

(a)

4. ........

7.72......

iito'ii.'e' 

i.........

25

40

0.3 to 0.5

K.,p.l68.

Panulcillo, Chilivery 

fusible ores.

3.

Round '. . .

..........

..........

8.........

Cold..... 

50.7......

7.5to9...

o.etoo.e

K.,p.l68.

Oker, burnt matte.

4,

..........

..........

..... .V ...

3.5.......

..........

K.,p. 177.

Hancock, Mich. slags,

1881.

5. 

Oval.....

Internal . 

Partly . . .

I'.IO" (?) . 

2' 6" .....

10' 4"....

7' by 4' 9".

11.2...... 

Cold.....

3. 5 (?).... 

Anth .... 

0.407(?)..

37 

10 

24 

27

0.5 

3.25

Say 98

P. N .....

Bisbee, Ariz.oxidized 

1885. ores, 

6.

Round . . .

Internal . Yes......

I'lO"...

O/ ft//

9' 0" . : . . .

3' 6" diam. 

4' 6" diam. 

I 17'

6.........

8......... 

Cold.....

6.6....... 

joke.. ...

0. 40 k . . . .

28 

27 

29

1.32 

3.8

Say 90

W. ......

Laurel Hil, N.Y., kiln- burnt pyritea, 1864.

7.

Round. ..

External.

Yes......

0" .......

o;

10'.......

4' diam . . 

4' 4" diam 

5' 6" diam

2 11

10........

18......... 

Cold.....

7.5 ......

Gas coke. 

0. 2 (?)...

is

31.12 

1.60 

51. 84 

2.96 

ZnO 3. 45 

0.55

40 to 50 

29 

24 

H. .......

a Partly internal, partly external (Sumpfofen).

6 An open slit extending completely around the furnace.

c Runs only 12 hours at a time.

d Including slag and fluxes. .

e This figure, given by the superintendent, seems almost incredible.

/ Excluding slag and flaxes.

(/Including fluxes but not slag.

h 54.3 bushels per ton of burden.

i Connellsville coke.

j Suowshoe coke.

k KIncludes inciuiies engineer, eugmeei, blacksmith, UHIUK.SIUIIII, etc.uc

I This slag is hiilily forrruginoii<», and usually a singulo-silicate or even somewhat more basic.

7i This sing, while highly ferruginous, contains usually a considerable amount of lime, and is more

basic las»ai/> tlio,i thanb a o singulo-silicaie. ci iirriilrt-aiKf'1.1 A

n For every 54 paita of black copper,.46 parts of matte are produced, containing 55 per cent, copper, 

o Charge, 06 por cent, roasted and 17 per cent, raw matte (each containing 40 to 50 per cent, copper), 

with 17 per cent, slag; product, two-thirds black copper, one-third white metal.

(500)
IIOWB.] SHAFT-FURNACE PEOCESS FOR SULPHURETED ORES. 79

of (.npola (.melting.

Ore Knob, C. N. pileburnt 1881. ore, 

8.

Square . . .

Internal . . 

Not.......

1' 0" ......

3' 10" sq ..

2.71'...... 

2J"

Ore Knob, C. N pileburnt 1881. raatte, 

9.

Square . . .

[nte'rnal .. 

Not.......

3' 10" sq . . 

2' 4" sq . . .

2. 71' (?)...

2 |a/?Y

Cold...... is/. ......

2.0/Ti.... 

Charcoal.. 

0. 69. ......

27.56 

4.29 

52.49 

9.59 

MgOl. 11 

0.57

23.41 

47.00 

22.08 E. ....:...

6 (?)...-...

Cold...... 

13.5/.....

2/A...... 

CharcoaU. 

0.59.......

94.24)

0.74) 

E. .......

South Strafford, Vt. pile-burnt pyrrhotite, 1884.

10.

Round ....

fnternal .. 

Yes ......

9".........

1' 9" .....

9' 6" ......

3' 8" diam. 

3' 9" diam. 

4' 0" diam. 

i: 84' ......

Q

7.25.......

Cold....!. 

44. 5 d.....

9. 3 d. ..... 

3okei ....

0

32.25

46.79

0.42 

3.54

( 22 to 33

i:::::::::

Arizona (locality with- held), oxidized ors, 

1884.

11.

Round ....

Internal . Yes.......

1' 2" ......

10' 4" .....

10' 4" .....

3' 1" diam. 

4' 6" diam . 

1. 2' .......

3" ........

6..........

8.8........

Cold...... 

37gr. ......

7.......... 

Coke ..... 

0.56^.....

91 I29 

12 

35 

13.6 

2.7 

2.0 

1

Say 96

J.H ......

t>

00

<D 

g

12.

Round . . .

2' 2V'

IV 'A" .....

2' 11" diam

3' ] I" diam 

1. 04' ......

4 .........

7.72....... 

5..........

C.........

Accessa, 1879.

13.

Round ....

.........

2' 04"

10' 11" ....

4' 3" diam.

4' 11" diam 

2.27'......

6..........

Milan, N". H 1884, kiln burnt pyrite.

14.

Round .'....

External .. 

Yes........

0" .........

I' and!' 6" . 9'

Bergen Point, N. J.,kiln burt cupreous 

pyrite, 1885.

15.

Rectangular. 

External.. 

Not......

O'O" ......

0' 9" ......

7' . . . <i' fi"

V 6" diam 

3'8"diain..

2J" and 2"..

16 to 24.....

Cold...... 

30 to 45.....

7.06........ 

Jascoke.. . 

0.214.......

8...........

.......1...

0.2to0.5

29

B. .........

4' by 11' .. 

4' by 11'... 

6' by 13'... 

5. 5'

6".... ....

12.........

Cold...... 

120........

7.......... 

Coke .? .... 

0.20.......

24 ........

(D

0. 34 to 0. 88

40 to 50

P.N......

Bergen Point, N. J.,roasted andgrouted inatte yielding black 1885. copper, 

16.

R e ctangiilar. 

External. 

Not.

0' 0". 

)' 9". 

5' G". 

4' 6".

4' by 11'. 

4' by 11'. 

6' by 13'. 

5.5'.

i". 

8. 

12.

Cold. 

90 d.

5.5. 

Coke?. 

0. 267.

24.

(m) 

0.75 to 2. 66 

(o) 

P.N.

B. = F. L. Bartlett, superintendent. 

C. = Capacci, Revue Univcrsello, 1881, X, p. 315.

E. = Eglestou, Transactions of the American Institute of Mining Engineers, X, p. 34. 

Gr. t=W. Gleun, superintendent. 

H. = J. H. Hcrreschoff, superintendent. 

J. H. = S. James, jr., and Carl Henrich, superintendent.

K. = Kei 1, Grundriss der Metallhiittenkunde. 

P. N. = Private notes.

"W. = Ben Williams, superintendent.

NOTE. The information in columns 15 and 16, received while this bulletin is in press, represents 

the very latest practice at the Orford Company's works, one of the most progressive in the country. 

In some points it does not agree accurately with certain remarks on shaft furnace practice made elaowhere in. this paper, which was written more than a year earlier^

(501)
80 ' COPPEB SMELTING. [BULL. 26.

THE DEOXIDIZING EFFECT.

The deoxidizing effect of shaft-furnace smelting depends, first, on the 

length of exposure to the deoxidizing action of the furnace ; second, on 

the strength of that deoxidizing action. The former is direct!j.proportional to the cubic capacity of the furnace and inversely to the rapidity 

of smelting. The latter is increased by increasing 

1. The average temperature of the ore, since deoxidation takes place 

much faster at high than at low temperatures.

2. The proportion of fuel to burden.

3. The porosity of the fuel, since porous fuel reduces carbonic acid to 

carbonic oxide faster than dense fuel does.

4. The porosity of the ore, porous ore being more readily penetrated 

by the carbonic oxide.

5. The intimacy of mixture of fuel and burden.

6. The basicity of the mixture, since the more completely the silica 

is saturated with bases the less resistance does its affinity offer to the 

reduction of such, weak bases as the oxides of copper and iron.

7. The infusibility of the mixture. This increases both the strength 

and the length of the deoxidizing 'action ; the former because a larger 

proportion of the deoxidizing agent, the fuel, is required to raise a 

comparatively infusible mixture to its higher melting point j the latter 

because a longer time also is required to raise it to that point, so, that 

the smelting proceeds more slowly.

8. The preponderance of oxide of iron among the bases, since this 

base, readily reduced at very low temperatures, seems to carry oxygen 

from the copper oxides to the carbon and carbonic oxide.

The deoxidizing action is weakened by increasing the quantity of 

blast, whether by increasing its pressure or the number or size of the 

tuyeres within certain limits; this hastens the rate of smelting, and if 

.carried beyond a certain point increases the proportion of air to fuel 

entering the furnace per minute, and hence the ratio of the free oxygen, 

and carBonic acid to the carbon and carbonic oxide to which the ore is 

exposed.

The deoxidizing action is probably also indirectly weakened by raising the temperature of the blast, 1 which, by increasing' the supply of 

sensible heat, enables us to smelt the ore with a smaller proportion of 

the deoxidizing agent, the fuel. Of course if. the proportion of fuel is 

not diminished, heating the blast may merely strengthen the deoxidizing action by raising the average temperature. Thus in certain cases 

it is said to have increased the tendency to form salamanders by the 

reduction of iron.

Intimacy of mixture of ore and fuel is promoted by distributing ore 

and fuel in uniform layers over the surface of the charge. It is diminished by charging the ore in one part of the furnace and the fuel in

'Kerl, Grundriss der allgemeinen Huttenkn, :<le ? 1879, p. SJ'.W. 

(502)
HOWB.I SHAFT-FURNACE PROCESS FOR SULPHURETED ORES. 81

another, so that they descend as two somewhat separate columns. This, 

is frequently effected, by charging the fuel in the middle of the furnace 

and the burden against the sides. * It weakens the deoxidizing action, 

directly by diminishing the extent of contact between fuel and ore and. 

indirectly by diminishing that between the ore and the reducing gases, 

since the latter pass in greater proportion through the comparatively 

open column of fuel than through the more compact column of ore.

The deoxidizing tendencies are stronger with internal and partly internal crucibles than when the crucible is wholly external, since in the 

former the slag, as long as it remains in the furnace, is in intimate contact with the column of fuel, which extends through it and rests on the 

bottom of the furnace.

9. If we have two furnaces of equal cubic capacities, so that the ore 

remains for the same length of time in each of them, one of them being 

narrow and high, and the other broad and low, it is probable that the 

latter will on the whole exert a more powerful deoxidizing influence than 

the former, because it will probably be necessary to use a larger proportion of the deoxidizing agent, the fuel, in the latter, in order to attain 

a given temperature in the hearth. This is because in the low broad 

furnace the gases have a shorter distance to travel from the tuyeres to 

the top of the charge and consequently arrive there hotter. Escaping 

from the top of the furnace hotter they carry away with them more sensible heat, and consequently.a larger proportion of fuel has to be burnt 

to generate the temperature required in the crucible of the furnace. 

Moreover, as the gases in this case reach the top of the furnace so hot, 

there is a greater tendency for the carbonic acid which they contiin to 

be reduced to carbonic oxide 1 by the surrounding fuel than in the comparatively cool-mouthed higher furnace. This reduction of carbonic 

acid to carbonic oxide of course absorbs a great-amount of heat; to 

compensate for this we have to use more fuel in order to attain the temperature needed in the crucible of the furnace, and an increase in the 

proportion of fuel means an increase in the strength of the deoxidizing 

action.

It is possible that in the low, broad furnace the average temperature 

of the ore may be higher than in the narrow high furnace, for two reasons : First, as the gases escape hotter from the toff*of the low furnace 

they may more quickly heat the descending ore to the temperature at 

which deoxidatiou commences; secondly, in the low broad furnace 

it may well be that there is a larger region which is intensely heated 

by direct radiation from the region of active combustion at the tuyeres 

than in the high narrow furnace. This, too, would tend to raise the average temperature of the ore, and of course the higher the average 

temperature of the ore the greater will be the average strength of the 

reducing action. This is, however, a mere conjecture.

'Transactions of the Anjevicau Institute of Mining Engineers, IH, .]> ^47, 

Bull. 26 6 (503)
82 COPPER SMELTING. . [BULL. 2s.

Both these considerations point to the low furnace as a more powerful 

deoxidizer thau the high one of equal cubic capacity, supposing the ore 

and fuel to be mixed with equal intimacy in both. But wo can more 

completely separate the ore and fuel in the low furnace than in the high 

one, by charging them ia separate columns, and we may thus offset the 

stronger deoxidizing tendencies of the low furnace largely and perhaps 

completely. Hence, while the low broad furnace is probably a stronger 

deoxidizer than the high narrow one of the same cubic capacity when 

burden and fuel are charged in horizontal layers, the reverse may be 

true when fuel and ore are charged in separate columns.

10. Sulphides in general, and pyrites especially, play a most important double part in the smelting operation, warding off the troubles 

which are caused both by too strong and by too weak deoxidizing action.

If the deoxidizing action be too weak, the tendency is, of course, for 

oxidized copper to become actually scorified; this is checked by the 

powerful affinity of the sulphur of the sulphides for copper.

If, on the other hand, the deoxidizing action be too strong, the tendency is for iron to pass to the metallic state and form salamanders; 

this, too, is checked by the powerful affinity of the sulphur for iron, the 

iron combining with the sulphur to form a matte instead of separating 

out in the metallic state.

The large amount of heat sometimes developed by the combustion of 

the sulphur and iron of the pyrites at the tuyeres in certain cases enables us to diminish the quantity of the fuel employed and thus to 

weaken the deoxidizing action.

Copper actually scorified may be deoxidized thus:

FeS + Cu2O, SiO2 == FeO, SiO2 + Cu2S 

Cu2 S + 2 Cu2O, SiO2 = 6 Cu + 2 SiO2 + SO2

ARSENIC AND ANTIMONY.

Arsenic and antimony may be expelled 

(1) By volatilizing as arsenious acid and trioxide of antimony (AsaO3 

and Sb2O3 ).

(2) By volatilizing as sulphides.

(3) By concentrating them in a speise.1

(4) By producing a small quantity of black copper, in which the 

greater part of these elements will be found concentrated.

They probably exist in the calcined ore largely, if not mainly, as arseniates and autimoniates. In the shaft furnace these compounds are 

in part reduced to arsenious acid and trioxide of antimony, which volatilize, and in part completely deoxidized, entering the matte, or the 

metallic copper if any is formed. Arsenic and antimony are expelled 

more fully by a gentle and prolonged than by a powerful and brief reducing action. To volatilize and expel them as completely as possible,

1 Kerl, Grundriss dor Metallhiitteuktmde, 1881, p. 134. 

(504)
HOWE.I SHAFT-FURNACE PROCESS FOR SULPHURETED ORES. OO

the length of their exposure to the deoxidizing conditions should be 

increased, either by enlarging the furnace or by running it slowly; 

while, to weaken the net deoxidizing action, both'so that the arsenic 

and antimony may be reduced only to the volatile condition of arsenious 

acid and trioxide of antimony and to prevent the increased length of 

the deoxidizing exposure from reducing an excessive amount of iron 

with the formation of salamanders, the deoxidizing tendencies should be 

weakened by the means already set forth, such as (I) using the minimum 

of fuel; (2) using dense compact fuel ; (3) charging ore and fuel in separate columns; (4) running on slags low in iron and not too basic; (5) 

adding pyritous ores, which also favor the expulsion of arsenic and antimony as sulphides.

By an extremely thorough roasting of ores rather rich in copper and 

comparatively lean in sulphur, followed by a strongly reducing fusion, 

we may produce with the matte a small quantity of black copper which 

will contain most of the arsenic and antimony ; this product may be 

so exceedingly impure that it should be separately treated lor an inferior grade of copper.

In ore smelting the shaft furnace appears to the writer to favor the 

expulsion of arsenic and antimony more than the reverberatory furnace does. That portion of these metals which exists in the roasted 

ore as sulpharsenide or sulphantinionide of the other metals, is probably expelled to but a very slight extent in either furnace. That poriiou 

which exists in the condition of arseniate and of antimoniate, however, may probably be expelled to a considerable extent in the shaft 

furnace, where these compounds are reduced by the solid fuel and the 

reducing gases, with the formation of the/volatile arsenious acid and 

trioxide of antimony at temperatures below the melting point of the 

charge, and the actual escape of these volatile compounds may therefore 

be looked for. In the reverberatory smelting, however, the arseniates 

and antiinoniates are reduced, not by the fuel, but by being decomposed 

with liberation of arsenic and antimonic .acids, by the silica of the 

charge, and by then being deoxidized by the sulphides of the charge. 

But as these reactions will only take place after fusion has set in, and 

as the deoxidation is effected- by actual 'contact with the melted sulphides, for whose sulphur both arsenic and antimony have a strong 

affinity and which are present in so great excess, there appears to 

be comparatively little chance foi'othe expulsion of arsenious acid and 

trioxide of antimony, the conditions powerfully favoring the complete 

deoxidation of the arsenic and antimony and their combination with the 

Diatte.

VOLUME OF FUKNACE.

The greater the cubic capacity of the furnace the more completely 

does the descending column of burden and fuel abstract from the escaping gases their heat, and consequently the more economical of fuel is 

the furnace. At the same time the output of the furnace increases with

(505)
84 COPPER SMELTING. [BULL. 26.

its cubic capacity. We must not, however, make the cubic capacity 

of the furnace so great that the ore will remain in it so long that 

an excessive deoxielation of iron will occur with formation of salamanders or of undesirably ferruginous matte. Thus the desire to economize 

fuel and to increase our output impels us to enlarge our furnaces; fear 

of deoxidizing iron restrains us.

Could we increase the output of the furnace proportionally to its 

increase of volume, so as not to lengthen the sojourn of the ore in the 

furnace, we might perhaps increase its volume indefinitely without 

undue deoxidation of iron, but beyond a certain point it appears to be 

impracticable to cause the output to keep pace with increased volume, 

so that the fear of deoxidizing iron actually limits the size of the furnace. Thus for ordinary ores it is generally believed that furnaces 

should not be over 13 feet high nor over 4 feet 6 inches wide at the 

tuyeres. (See dimensions of cupola furnaces in Table No. 12.)

Anything which lessens the tendency to form salamanders through 

the reduction of iron to the metallic state enables us to enlarge our 

furnaces with corresponding economy of fuel. Among other things 

which diminish this tendency may be mentioned fusibility of mixture, 

large proportion of sulphur to iron oxide, charging fuel and burden in 

separate columns, and more especially freedom from iron oxides. 

Thus at Mansfeld, where the ores are nearly free from iron, furnaces 

even 22 feet 7 inches high are successfully used.

In copper smelting comparatively high narrow furnaces, somewhat 

widened at the top, are preferred to lower wide furnaces for the following reasons: In a high narrow furnace the fuel is better economized, 

and, as already stated, there is probably less tendency to reduce iron 

than in low broad furnaces of the same cubic capacity; so that as far 

as the formation of salamanders is concerned we can give a narrow 

furnace larger volume than we can a broad furnace. We thus get 

better economy of fuel in narrow high furnaces, both because we can 

give them greater volume without reducing iron, and because even 

for equal volumes they economize fuel better than low broad furnaces. 

The furnace may, however, be advantageously widened toward the 

top for the following reasons among others: A wide throat gives us a 

larger area over which we can scatter file ore, and thus lessens the 

troubles due to its sifting down to the tuyeres. The ga.ses escape with 

lower velocity from the top of the charge and thus carry off less fineore and fuel. With zinciferous ores there is less clanger of the throat 

becoming choked with cadmies 1 (Gruner 2 considered that cadmies deposit less easily in narrow than in wide throated furnaces, owing to the 

more rapid passage of the gases; but even admitting this, a small deposit of cadinie will cause more inconvenience in blocking up a narrow

_» .__________________________________,_____________. .._______

Uteri, Grundriss cler uligerneiueu Metallhiitteiikunde, 1879, p. 247. 

8 Gruiier, Traitd dc M6tallurgie, I, p. 250.
HOWB.I SHAFT-FURNACE PROCESS FOR SULPHURETED ORES. 85

throat than a large one will in a wide throat). The wide throat gives 

us a chance to separate burden and fuel by charging them in columns.

RASCHETTK FUKNACES.

As has been already stated, it has not been found practicable to increase the output of shaft furnaces proportionally to their increase of 

size, so that if, by enlarging the width or height of a furnace, we carry 

the cubic capacity beyond a certain point, the sojourn of the ore in the 

furnace becomes so long that an excessive deoxidation of iron occurs, 

with the formation of salamanders or of undesirably ferruginous matte.

By keeping the height and width of the furnace small, however, and 

increasing its cubic capacity by making it oval or oblong in horizontal 

cross-section, as in the Raschet.e furnace, the increase of output so 

nearly keeps pace with the increased cubic capacity that practically 

the tendency to reduce iron does not appear to be materially increased. 

Furnaces of this shape, with tuyeres in both of the long walls and in 

the ends, have been very successfully used for both lead and copper 

smelting in Europe and .in this country. Those at Bergen Point, N. J., 

are 4 by 11 feet inside at the tuyeres, and smelt much greater quantities of burden than any other furnaces in the country. Their use is 

more general here than in Europe, where the round Pilz furnace is 

preferred. While the Raschette furnaces offer a certain advantage in 

saving labor (owing to the greater output per furnace), and in savingfuel, owing to the smaller proportion of heat radiated from their walls 

(the ratio of whose external surface to the volume of the furnace is 

much smaller than in a round furnace of a diameter equal to the width 

of the Raschette furnace), their main advantage is considered at Bergen 

Point to lie in the fact that they are less susceptible to serious derangements from irregular working. .Where fine ore forms a large proportion 

of the burden it is liable to run down to the tuyeres irregularly and 

sometimes in large quantities. This in a round furnace may cause very 

serious derangement or even necessitate drawing the furnace out. In 

the Raschette furnace, however, should one end become deranged the 

furnace may be quickly brought into good order by carefully keeping 

'the other end free from obstructions, and charging a little extra fuel, 

so as to raise the temperature there, and thus melt out the obstructions 

in the deranged end. Owing to this a much greater proportion of fine 

ore can be smelted in Raschette than in round furnaces. At Bergeii 

Point as much as 75 to 85 per cent, of the total burden is sometimes fine 

ore, and frequently the whole burden consists of grouted fines.

The shape and size of the vertical transverse section of these furnaces 

are governed by the same considerations as in the case of round or 

square furnaces.

(507) 
86 ' COPPER SMELTING. [BOM,. 20.

DISPOSITION OF CRUCIBLE.

With regard to the disposition of the crucible, we may divide shaft 

furnaces into those with 

1. Internal crucible (Tiegelofen).

2. Crucible partly internal and partly external (Sumpfofen).

3. External crucible, if any (Spurofen).

1. Internal crucibles. With these the separation of matte from slag 

takes place inside the furnace, where a very high temperature prevails, 

and where, consequently, the liquidity of the slag is at its highest. 

The matte gradually accumulates and is tapped at intervals; the slag 

floating above it is removed continuously or at very short intervals. 

As the slag remains for some time within the crucible, where it is penetrated by the column of fuel, and by the matte, which falls into it as 

fast as it melts before the tuyeres, the conditions are very favorable for 

the reduction of any scorified copper, and for that of iron with formation of salamanders. At the same time the matte or black copper and 

slag are kept so hot that they separate better than when the separation takes place outside the furnace. On the other hand, accretions in 

the crucible are liable to form, since every time it is tapped fine pieces 

of coke fall down into the space thus left empty, tending to choke it 

up. Moreover, accretions which form can only be removed with difficulty, even though a temporarily closed aperture be left, which can be 

opened for removing them. Should they 'become excessive the furnace 

must be drawn out.

Hence these furnaces are especially desirable where the production 

of black copper, or of a viscid refractory slag requires that the sepation of metal and slag shall take place at a high temperature, and 

they are to be avoided when the formation of accretions, such as iron 

salamanders, is to be expected (e. g., in case of ferruginous ores). Thus 

furnaces of this class, such as are made by Fraser & Chalmers, and by 

Rankin & Brayton, are admirably adapted to most of'the silicious oxidized ores of Arizona and New Mexico, which yield not only black copper but frequently very infusible slags, both of which would tend to chill 

if we attempted to separate them in external crucibles. On the other 

hand, for the ferruginous ores of the Eastern coast, with their very fusible slags and strong tendency to form salamanders, these furnaces are, 

in the writer's opinion, much less desirable than those with wholly external crucibles.

The slag is generally tapped from these furnaces intermittently, since 

if it flows continuously it not only cuts away the opening through 

which it escapes, but it is very difficult to adjust the size of the slag 

notch to that of the stream of slag closely enough to prevent the gas 

from blowing out of the furnace along with the slag. This may, however, be prevented by providing a water-cooled bronze cinder notch 

inclined upward, so that the column of slag flowing through it seals

(508)
HOWB.J SHAFT-FURNACE PROCESS FOR SULPHURETED ORES. 87

it and prevents the blast from blowing through it. When the slag 

flows in a continuous stream its velocity is much less than when it 

flows intermittently, and it consequently flows more quietly from the 

crucible, and thus deposits more fully any mechanically suspended 

shots of metal.

These furnaces with internal crucibles may advantageously be provided with external settling basins as well, to catch any shots? of metal 

mechanically carried out with the slag, and they should be so arranged 

thai, in case accretions form on the bottom, they can be worked temporarily as external-crucible furnaces, the melted matte and slag being 

allowed to run across the bottom and out of the furnace as fast as they 

melt, so as to cut down the accretions.

2. Crucibles partly internal, partly external. In these furnaces the internal crucible is continued outside of the front wall of the furnace as 

a sort of fixed forehearth. This arrangement permits the easy introduction of tools to remove accretions in the lower part of the iurnace, 

and pasty slag inay be pulled out of the furnace. Here, as in furnaces 

with internal crucibles, the matte is tapped intermittently, the slag running constantly or at short intervals. These furnaces, now little used for 

copper smelting, are chiefly applicable where the slag is necessarily so 

refractory that the shots of metal would not settle out of it if it were 

cooled by running into an external crucible, and where at the same 

time there is a strong tendency to form accretions, which are very difficult to cope with in furnaces with wholly internal crucibles.

3. External crucibles (fixed or moveable forehearths, steep boxes, settling 

basins, etc.}. The bottom of the furnace is strongly inclined, and all 

slag and metal run out of it as soon as melted into an external basin 

in which their separation by gravity occurs. Except when black copper or a very refractory slag is produced this arrangement is the 

most convenient, as the formation of accretions is reduced to a minimum by the constant flow of the molten matter over the bottom itself, 

the tendency being in general not so much to deposit salamanders as 

to cut the bottom down. This in turn is prevented by keeping the 

level at which the molten matte issues from the furnace constant by 

means of a water cooled block (generally of iron, but better of bronze, 

since iron is readily cut by the stream of matte) set in the masonry, 

over which the matte flows. Where a large quantity of fusible matte 

is produced both matte and slag may be made to flow continuously 

from the external settling basin, which, to this end, is divided into two 

compartments by a transverse diaphragm extending down neaily to its 

bottom.1 The matte and slag enter the compartment nearest the furnace. 

The matte accumulates at the bottom till its upper surface reaches the 

lower edge of the diaphragm, thus sealing it and preventing the lighter 

slag from passing it. As the rnatte accumulates it will rise on the out1 The employment of this plan by the writer at Capleton in 1879 ie tho earliest of 

which he ie aware.

(609)
88 \ COPPER SMELTING.

side of tbe diaphragm so that we will have on its outside a column of 

matte alone, on its inside a column below of matte and above of slag. 

The slag may be drawn continuously from the upper portion of the 

inside column, the matte from the outside column, though of course at a 

little lower level than the slag. 

As these settling basins are liable to become choked by chilling, especially with refractory slags, they should be made readily removable, 

so that the working of the furnace need be interrupted but a few rniuutes when it becomes necessary to provide it with a fresh basiu. 1

If the slag contains scorified copper (chemically combined) it may be 

advantageously deoxidized, precipitated, and collected by placing a 

large number of wrought-iron bars (old rails, etc.) across the settling 

basin, so that the slag must pass over and between them, the copper 

beiug precipitated by the iron exactly as in the wet way.

To mitigate the disadvantage under which these furnaces suffer (the 

cooling of the melted matter before its separation takes place), the settling basins are sometimes roofed over, as at Cbanaral, Chili, and a 

large aperture is left in. th e breast of the furnace, so that a quantity of gas 

is blown from the furnace into the settling basiu above the settling 

slag. By making these basins very wide and providing against undue 

cooling the speed of travel of the matte and slag may be made so low 

that a. very complete separation takes place.

WATEK-.TACKKTED VS. BRICK WALLS.

On account of the difficulty of protecting brick walls against the corrosive action of the slag,' water-jacketed walls are coming constantly 

into greater use. Brick walls may last for many months (or even, as at 

Mansfield, for years), first, when the slag is nearly free from the protoxides of iron and of manganese, since it is these bases which corrode 

the brick-work 5 second, where skill is attained in "sticking up" the 

walls, i. e., in coating them while the furnace is running with a refractory ferruginous coating (probably consisting mainly of magnetic oxide 

of iron). This is effected by charging against the walls fine and thoroughly burnt pyrites or other form of oxide of iron. It is carried to. 

great perfection at Bergen Point, where, with highly ferruginous and 

extremely corrosive slags, campaigns of many mouths are made. Probably the enormous volumes of cold air blown in at low pressure through 

very large tuyeres facilitate this, the blast, owing to its excess and low 

pressure, passing in large quantity along the walls and both cooling 

them and preventing the reduction of the magnetic oxide.

Brick walls, when thus protected, effect a certain saving in fuel. 

They may be thus kept so cool that fhe radiation from them will hardly 

exceed that from the outer wall of a water-jacket, while in the latter 

the circulating water abstracts a large amount of heat from the furnace,

1 See description by F. H. McDowell of a furnace built by J. B. Tlerreshoff, at Laurel 

Hill, N. Y., in Transactions of the American Institute of Mining Engineers, Vol. XIII.

(510)
MOWKJ SHAFT-FURNACE PROCESS FOR SULPHURETED ORES. '89

which has to be met by burning more fuel. If the brick walls are allowed to get very thin, however, the loss of heat by transmission 

through them may become nearly equal to that carried off in the water 

of a-water-jacket. The saving in fuel is offset to an extent which varies 

very greatly by the extra cost of repairs in brick furnace's, due to the 

corrosion of the brick-work by the slag.

The actual outlay for repairs and relining brick furnaces at Bergen 

Point, excluding repairs to the settling basins, is less than two bricks 

per ton of burden smelted, or, say, 5 cents. The extra fuel consumption due to abstraction of heat by the jacket-water is in two instances 

as follows:

Heat abstracted by jacket-water.

Furnace at which observations were made.

Pounds of coke required per 24 hours to heut jacket-water,. assuming that

Percentage of total coke consumption required tor heating jacket-water...

South Striifford.Vt.

10

30° C.

07° C.

3,228

1,322

30

$0. 075

14

Laurel Hill, 

N. Y.

7

]5. 5°C.

77° C.

 2, OOU

1,328

14.7(?)

0. 03!) (?)

5.5

While these figures are not based on sufficiently extensive observations to allow us to generalize much from them, they certainly indicate 

that, even with the exceptional skill attained at Bergen Point, the cost 

of repairing the brick walls is nearly .equal to the value of the coke 

consumed in heating the jacket-water at South Strafiord, where the 

abstraction of heat in the jacket-water is not unusually low. But.beyond the fuel consumption necessitated by the abstraction of heat in the 

jacket-water, water-jacketed furnaces in many cases require expensive 

repairs. In careless hands the jackets are liable to burn out from .deposition of scale by the water, and they are apparently even in careful 

hands often eaten through by the matte.

While in central places, and extremely skillful and careful hands, the 

cost of repairing brick furnaces is probably considerably less than Maat 

of the combined cost of repairs and extra fuel consumption of wa,:rjacketed furnaces, in remote places the reverse is probably true, as in 

them the cost of repairs weighs heavily against the brick furnace, because 

the freight charges on our two bricks consumed per ton of burden 

smelted are much heavier than those on the extra fuel needed by the 

water-jacketed furnace. Further, where the greatest care and skill are 

not exercised the consumption of bricks for repairing brick furnaces becomes vastly greater than two bricks per ton of burden; and, even in 

the most careful hands, where the slag is ferruginous, the burning out 

of the brickwork causes constant annoyance, frequent stoppages for 

repairs, and, by altering the internal shape of the furnace, serious derangement of ita working.

(511)
90 COPPEE SMELLING. [BULL.28.

All things considered, it is believed that, except under altogether 

unusual conditions, brick furnaces are destined to give way to waterjacketed ones. Three sets of conditions, however, suggest themselves, 

under which brick walls may be the most desirable: First, when the 

slag is nearly free from oxides of iron and of manganese, jso that corrosion of the brick-work is not likely to occur; second, where, as in parts 

of Arizona, the water supply is too scanty to permit the use of waterjackets (here abundant blast should be provided find the, mixtures 

should be as free as possible from iron); third, in extremely cold climates, 

where the freezing of the water connections may become a serious annoyance.

The lining of brick furnaces should be of the most basic bricks attainable. Bauxite, graphite, and the basic linings used for Bessemer 

converters have been suggested. The lining should be laid in headers, 

and it should not be bonded to the outer wall except above the zone of 

fusion, since this bonding implies the use of stretchers, which are liable 

to fall out and expose the adjoining courses when only a few inches of 

their width has been melted off, while headers are much more stable.

In furnaces with internal crucibles the water-jacket should not be 

carried down to the upper level of the bath of melted slag and matte, 

since there would be danger both of its chilling them and of the matte's 

corroding it. With impure water scale rapidly collects in the jacket 

and must be frequently removed to prevent the jacket from burning.

CAST VS. WROUGHT-IRON JACKETS.

Cast-iron jackets are much cheaper than wrought, and if injured the 

old ca.stmg is worth, if in the immediate neighborhood of a foundry, a 

considerable part of the cost of a new one. Cast-iron jackets are, however, more liable to accident, both from blows of the workmen's tools 

and from cracking owing to cooling strains in the castings, and they 

cannot be repaired as easily or as well as wrought-iroii ones. Hence in 

the immediate neighborhood of a foundry cast jackets may be preferred j 

in remote places wrought-iron ones are more desirable.

To diminish the abstraction of heat by the jacket-water it should be 

hot when fed in and nearly boiling when drawn out; to utilize the heat 

which it abstracts it may be used to feed the boilers. If, as is'generally the case, the jacket is closed at the top, the water connections must 

be so arranged that the water may be forced into the jacket under strong 

pressure, since if steam forms in the jacket considerable pressure is 

often required to force water into it.

Instead of the ordinary water-jacket, a simple iron or copper shell, 

cooled by sprays of water, has been successfully employed. This is a 

much cheaper construction, and any cracking or undue heating of the 

shell is more easily detected than in the inner walls of ordinary jackets. 

It requires, however, rather more vigilance to prevent overheating and

(512)
HOWB.J SHAFT-FURNACE PROCESS FOR SULPHURETED ORES. 91

probably a larger water supply than the double-walled jacket, and has 

met with little favor.

BLAST, TUYERES, ETC.

The width (and through it the output) of the furnace is in one sense 

limited by the penetrating power of the blast, which depends on its 

pressure,, or, to speak more accurately, the velocity at which it enters 

the furnace, which, in turn, depends on its pressure, the size of the tuyeres, and the resistance, offered to its passage by the solid materials in 

the furnace. It is evident that for a given volume of blast per tuyere 

the smaller the tuyere the greater will be the velocity at which the blast 

issues from it, and the farther consequently will its momentum carry it 

into the furnace. If, however, the diameter of the stream of air becomes 

very small it is more easily turned aside, so that to get the farthest penetjration into the furnace for a given set of conditions our tuyeres must be 

so small as to give the blast high velocity, yet not so small that the 

stream of air is too easily diverted and that the friction in the tuyere 

becomes excessive. With the pressures ordinarily used the maximum 

penetration is probably attained with a tuyere diameter of from 2.75 to 

3.5 inches. Very large tuyeres, with low velocity of blast and small 

penetration, may be desirable in the case of brick furnaces, since here 

we may wish a large quantity of air to ascend along the walls to prevent their corrosion.

The conditions will evidently be much more uniform across the furnace at the tuyere level if the blast is introduced at a large number of 

points than if it all enters through a single tuyere; the area of the 

horizontal cross section of the furnace at the tuyere level, formerly iu 

the old-i'ashioned single-tuyered furnaces as high as 5 square feet per 

tuyere, in modern poly-tuyered furnaces rarely exceeds 2.25 square feet, 

and in this country is generally from 1.2 to 2 square feet per tuyere. 

This spreading out of the blast is carried to its extreme limit in the 

Hancock cupola (No. 5, Table 12), where the blast enters through a 

slit extending completely around the furnace. We may surmise that 

the tendency at Hancock to form iron salamanders (which is said to be 

so strong that the furnace has to be drawn out every day, bringing the 

reported i'uel consumption per ton of burden to nearly double that of any 

other well-managed American furnace within the writer's knowledge) 

may be due to the blast being so weakened by this extreme spreading 

out that it penetrates but a little way into the furnace, leaving a dead 

core in the center, a most potent cause of salamanders. There appears 

to be nothing iu the composition of the charge at Hancock to cause 

precipitation of iron, unless it be the enormous proportion of fuel employed.

The employment of two rows of tuyeres, one above another, as in 

Ireland's foundry cupola and iu the Milan copper furnace (No. 14,

(513)
92 COPPEE SMELTING. . [Butt. 28.

XII), seems to have little to recommend it, since, instead of concentrating the heat, so that with the minimum consumption of fuel we 

may obtain the maximum temperature before the tuyeres, it scatters it.

With very refractory ores an upper row of tuyeres, ordinarily closed, 

but used in cas,e accretions on the bottom of the furnace obstruct the 

lower tuyeres, might, however, be desirable.

The tuyeres should be so placed that the streams of air issuing from 

them will not interfere with each other. Thus in Haschette furnaces 

the tuyeres on the opposite sides should be placed staggering; in round 

furnaces they should not be diametrically opposite each other. They 

may each point a little to one side of the center of the tuyere horizon. 

The tuyeres often point downwards a little. This lowers the region 

of intense heat relatively to the tuyere level, enabling us to place the 

tuyeres a little farther above the bottom of the furnace without unduly 

lowering its temperature, and this in turn allows the accumulation of 

a greater quantity of molten matter in the furnace without interfering 

with the entrance of the blast. With internal-crucible furnaces this 

may be quite an advantage.

HOT BLAST.

Hot blast, heated in cast iron pipes in the upper part of the furnace 

and above the top of the charge, as well as in separate stoves, is successfully used in several places in Europe in smelting copper ores, and 

is said to have been lately introduced at an Arizona copper smelting 

establishment. It has been found to reduce the fuel consumption very 

considerably.

PRODUCTS.

1. Matte. Since the slag is more perfectly fused in the shaft furnace 

than in the.reverberatory, and since the tranquil settling in the crucible, 

whether internal or external, favors the complete separation from the 

slag of shots of matte more than does the skimming of the reverberatory, the matte may be richer in shaft furnace than in reverberatory 

smelting without causing an undue mechanical loss of copper in the slag. 

For this reason and because there is far less tendency in the shaft furnace to scorify copper, owing to its strong reducing action, we may aim 

at producing a much richer matte (by more thorough preliminary roasting, by adding oxidized ores or rich slags, etc.) than in reverberatory 

smelting. The writer can vouch for cases where, when producing very 

lean mattes with slags of favorable composition, the slag has contained 

only traces of copper.

(614) '
HOWK.J SHAFT-FURNACE PROCESS FOR SULPHURETED ORES. 93 

TABLE XIII. Examples of coniposiiidn of slia'ft-furnace matte. (Sec, also, Table XII.)

Copper ........

Nickel and coSilver..........

Maiisfeld.

1.

34.1-51.2

17. 0-24. 7

2. 4- 9. 6

0. 9- 2. 5

0. 1- 0. 3

Oker.

2.

57. 0-61.9

11.1-10.9

1. 1- 2. 1

0. - 1. 4

0.00

Biecbolsilurf.

3.

42. 9-4H. 8

25. 1 27. 1

0. 0- 1. 1

0.9- 1.2

0. 2. 33

OR P»_9D Q

ITablun.

4,

8. 3-12. 0

1. 2- 2. 9

0. 6- 3. 9

24. C 27. 2

Stefiuishiitte from

tetrabedvito, 

speiso being formed

with it.

5.

22. 1

47.0

0.08

Eoraas.

6.

22.03

52. 14

25 15

PhouixhUtte.

7.

33.03

1.04

25. 49

Oker.

8.

41.30

9*1 ^d

4.82

' 3.87

21.70

The above ia from Tlerl, Gruudriss dor Metallhiittcukundo, It'81, I, p. 109.

2. Slag. The composition of slags has been so fully discussed in 

considering reverberatory smelting that little remains to be added here. 

While the highly acid and aluminous slags which are permissible in 

the reverberatory could not be made to run in cupolas (and even those 

which can be smelted smelt so slowly and at so high a temperature that 

there is great danger of forming salamanders), we can in the cupola, 

especially if it be water-jacketed, run successfully on highly basic.ferruginous and manganiferous slags which in the reverberatory would 

cause great annoyance and expense by their corrosiveness and by the 

difficulty of skimming them, on account of their fluidity, which in the 

cupola is rather an advantage. With these slags the use of external 

crucibles (Spurofen) is desirable to prevent the formation of salamanders, 

and even then much care must be taken and the deoxidizing tendencies diminished as far as possible (by rapid running, excess of blast, 

charging fuel and burden in separate columns, low and narrow furnaces, 

etc.) to avoid forming them.

In zinciferous ores the sulphide of zinc remaining in the roasted ore 

and that formed in smelting by the deoxidation of oxide and sulphate 

of zinc in contact with the fuel and the metallic sulphides, tends strongly 

to entei the slag and to drag disulphide of copper with it; and this 

tendency appears to be stronger the richer the matte is in sulphur, perhaps because mattes rich in sulphur and consequently lean in copper 

are comparatively light and hence separate less readily from the slag.

The most desirable slag is probably between a singnlo- and a bi-silicate, 

mainly of lime and iron oxide, the latter base predominating, and with 

a little alumina, but only a little. If too rich in iron oxide, the slag becomes so heavy that the matte does not sepurato, readily. If there is not 

enough iron oxide the slag becomes refractory and a tendency to scorify 

copper arises. In smelting oxidized ores and native copper the presence of a considerable amount of oxide of iroa is especially desirable

(515)
COPPER SMELTING. [BULL. 26.

to prevent scorification of copper. The oxygen ratio of base to silica 

may vary at least from 1: 2.5, when lime predominates among the bases, 

to 1: 0.7, when oxide of iron predominates. The following are examples.

TABLE XIV. Composition of ore cupola slays. 1 (See, also, Table XII.)

Pro ox.de of manganese. . . .

Sulphur.. ............

Oxy gen ratio of base to acid .

Magnesia ..........

Protoxide of manganese .

Oxide of copper... .......

Oxygen ratio of base to

1.

47.91 

7.51 

1. 11 

0.35

39.3 

1.22

0.38

0.49

0.70 

1:1.94

9.

56.51 

9.42 

20.05

6.40 

6.21

2.

34.67 

4.38 

3.53

48.25

2.00 

2.89

1.07

1.85 

1:1.2

10.

31.44 

7. 80

4.46 

53. 2 L

3.

36.39 

11.06 

4.03 

0.54 

44.14

PbS 2.71

FeS 1. 05

11.

28. 5-29. 2 

8. 9- 9. 6 

1. 2- 3. 0 

5.1-11.6 

51. 0-52. 8

trace 0. 4

4.

50.00 

15.67 

20.29 

4.37 

8.73 

CusO 0.67

1.11

1:1.5

12,

21.62 

5. 15 

2 57

"'65.' 62

2.26 

2.08

1:0.7

5.

45. 20.

"""6.28 

2.40 

42.69

Cu 0.63

2.61

13.

22. 55 

5. 10 

2.95 

1.33 

38.31

5.22

6.

54.13 

10 53 

19.41 

1.79 

10.83

2.03

1:2.5

14.

7.

57.43 

7.83 

23.40 

0.87

7.47

0.30

1:2.1

15.

25. 24 50. 20 

14. 00 1 9. 10 

4.86 19.72 

ZnO 6.40, 6.63 

45. 96 29. 18

Cu 0.3-0.5

16.

44.00 

8.31 

6. 17 

2.50 

35.43

0.52

8,

56.5 

6.0 

G. 3 

14.3 

14.9

17.

47.50 

4.61 

13.72 

3 80 

26.68

0.16

1 Nos. 1 to 14 from Kerl, Gnindriss cler Metallhiittenlmude, 1881, p. 157; !N"os. 15 to 17, inclusive, are 

made at Ahrn, JocUbenr, and Brixlogg, respectively, all three being in the Tyrol. See Balling, Compendium tier metallurgiscuen Chemie, 188;!, p. 134.

Of these the 2d, 3d, and 5th are probably metallurgically the most 

desirable, while slags more acid than 7 'and 9, or more basic than 12 

and 13, will probably rarely be found advantageous.

The slags are generally so free from copper that they are rejected. 

Those portions carrying shots of matte may, if acid, be advantageously 

used to flux the ferruginous charge in the second smelting (operation 

4). If basic, they are returned to the ore smelting.

DETAILS OF WORKING.

1. Mechanical charging, which effects an important saving in labor, has 

been introduced in Europe, but not yet iir this country. Tne ordinary 

form of cup and cone charger is hardly applicable to copper smelting 

shaft furnaces, since it delivers the charge always in the same place, 

while in copper smelling it appears to be necessary to be able to place 

the charge in the middle or against the walls of the furnace at will, 

according to the working of the furnace. In many cases too, it is desir-

(516)
nowB.I SHAFT-FURNACE PROCESS FOR SULPHURETED ORES. 95

able to be able to charge the fuel in the middle of the furnace and the 

burden against the walls habitually.

This may be effected by using the double cup and cone, or by the 

common single cup and cone provided that the base of the cone is of 

the same diameter as the base of the cup, so that the cone can be lifted 

up above the cup. Then when the cone is lowered iu the ordinary way 

the charge is thrown towards the walls of the furnace. But if the cone 

be raised above the cup the charge will slide directly from the surface 

of the cup towards the center of the furnace.

The practice of charging the fuel in the middle of the furnace, the 

burden against the periphery, is largely followed in this country, espcially where there is danger of forming salamanders.

It is much to be regretted that the plan, widely adopted among 

American lead smelters with admirable results, of preparing the charge 

by systematically and uniformly mixing in horizontal layers great quantities of the ores and fluxes, whose composivion has been previously accurately determined, in proportions designed to give a slag of predetermined composition,is not ofteu followed among our copper smelters, 

who often charge flux and ore by the shovelful, or, if .by weight, without precautions which insure uniformity of charge, and rarely with a 

view to producing slag of predetermined composition. Indeed, with a 

few notable exceptions, our copper smelting is iu a much more crude 

condition than is the metallurgy of iron, of lead, and of the precious 

metals.

2. Changing tuyeres. It is a very common practice, especially with refractory ores, to have an excessive number of tuyeres, not using them 

all at once, but changing them off. If a tuyere becomes dark and the 

slag appears to be chilling in front of it, it is closed for, say, thirty to 

sixty minutes. During this time the chilled slag will have melted, and 

when the tuyere is again opened it will be found bright. This plan 

gives admirable results.

3. Filter charging. To prevent the fine ore from sintering around the 

lumps of coke, and thus hindering their combustion, Gleun 1 (who 

charges fuel and burden iu uniform horizontal layers) recommends 

charging the lump ore on top of the coke, and then the fine ore on the 

lumps, the lump ore serving as a 'filter for the fines. Part at least of 

the resulting advantage may be due to its preventing the fine ore from 

trickling down to the tuyeres, and part of the apparent saving in fuel 

and increase in rate of smelting may arise from the fact that the escaping gases draw the fine ore out of the furnace to a greater extent on 

account of its being placed on the top of the charge, so that the quantity 

of ore actually smelted is less than that charged into the furnace.

4. Fine ore. If a large proportion of the ore be tine, and especially if 

it be very valuable, from being rich in copper, or from carrying gold or

1 Engineering and Mining Journal, 1884, tl, p. 34.

(517) -
96 COPPEK SMELTING. lBULL.26.

silver, the fine ore must be grouted, or we must provide large settling 

flues or dust chambers, to prevent excessive loss from the ore being mechanically dragged off by the gases which escape from the top of the 

furnace, as well as to prevent it from sifting down to the tuyeres irregularly, and'deranging the furnace, though this may sometimes be more 

economically prevented by charging lumps of slag along with the ore.

For grouting ores we may use either lime or clay, adopting whichever 

will form the most desirable slag with the other slag-making components of the charge. In grouting roasted matte or exceedingly ferruginous roasted ores clay has a great advantage over lime, since it lessens 

the quantity of silicious matter which is needed to flux the oxides of 

iron produced in the roasting, while the use of lime for grouting would 

necessitate increasing the quantity of silicions flux.

In rare cases tar or petroleum residues may be used for grouting. 

The grouting may be advantageously done in a pug-mill, the grout 

being dried by the waste heat of the smelting or roasting furnaces.

The grouted ore is sometimes bricked under strong pressure, and some 

fine ores may be bricked by very strong pressure without grouting. -

3. BOASTING THE FIRST MATTE. ,

The aim and the details of working are substantially the same as in 

roasting the first matte (coarse metal) in the reverberatory smelting 

process, to which the reader is referred.

4. SMELTING THE ROASTED FIRST MATTE. (SEE TABLE XII.)

. The conditions are much the same as when smelting very rich ferruginous ores. To make the weight of slag as small as possible, only 

enough silicious flux (oxidized.ores, silicious slags, etc.) is added to form 

a slag of about a singulo-silicate or even a somewhat more basic composition with the iron oxides so largely produced in roasting the matte. 

If the roasting has been thorough, little matte will form, and our products will thus be mainly a ferruginous slag and impure black copper. 

On account of the excess of oxide of iron, the small amount of sulphur 

available for combining with any reduced iron, and the use of internal 

crucibles, the tendency to form, salamanders by the reduction of iron is 

very great. To avoid this we must weaken the deoxidizing action as 

far as possible, especially by diminishing the ratio of the volume of the 

furnace to its cross-section at the tuyeres (by making it low and by carrying its walls up straight, or even drawing them together towards the 

throat), and by smelting very rapidly with excess of blast, so as to 

diminish the sojourn of the ore in the furnace j by adding only acid 

fluxes (basic ones such as limestone would weaken the hold of the silica 

on the protoxide of iron and facilitate the reduction of the latter); charging in columns; using the minimum, of fuel, etc. 

Internal-crucible ftiraaees are generally employed, on accouut of the

(518)
HOWK.] SHAFT-FURNACE PROCESS FOR SULPHURETED ORES. 97

tendency of the black copper to set in the comparatively cold external 

crucibles. They should have a large aperture just above the bottom, 

closed while running, but easily opened to remove accretions.

The reactions are much the same as in ore smelting, except that, as 

the proportion of sulphur is so much smaller, the deoxidation of oxidized 

copper takes place more by the action of carbon and carbonic oxide 

with formation of metallic copper and less by that of sulphur and sulphides with formation of matte.

Here we may seek the explanation of the fact that while in the reverberatory method we do not obtain metallic copper until the matte 

has reached the condition of legule (say 80 per cent. Ou), in the shaft 

furnace we obtain black copper together with matte carrying sometimes* 

only 57 per cent, copper. Three causes suggest themselves:

(1) The deoxidizing conditions are so much stronger in pthe shaft fuiv 

nace than in the reverberatory that in the former a much larger proportion of iron is deoxidized. As iron has a stronger affinity for sulphurthan copper has it crowds the copper out of the matte, precipitating it ia 

the metallic state (Fe + Cu2S = 2 Cu + FeS), and we get with the metallic copper a matte impoverished in copper by the substitution of iron 

for copper. It is to be observed that the sulphur of the matte produced! 

along with metallic copper in the shaft furnace is really about as fully 

Maturated with metals as in the reverberatory process, only in the shaft, 

furnace this matte contains more iron and less copper than in the re«- 

verberatory.

(2) Owing to this same strong deoxidizing action in the cupola the/ 

copper oxides in the charge are brought directly to the metallic state bjr 

such reactions as CuaO + CO = 2 Ou + OO2 ; as we lack this deoxidizing 

action of carbon and carbonic oxide in the reverberatory, the oxides of 

copper are there chiefly deoxidized by sulphide of iron with the formation of sulphide of copper instead of metallic copper, Cu2O + FeS=a: 

Ou2S + FeO.

(3) In the reverberatory the matte has a stronger tendency to. absorbany already precipitated metallic copper than in the shaft furnace, be^ 

cause the two substances lie for a longer time in contact, because theicsurfaces of contact, as they lie spread out each in a thin sheet, are much, 

greater, and because the overlying slag rapidly carries oxygen from the,- 

comparatively strongly oxidizing atmosphere of the furnace to the iron, 

of the matte, whose sulphur readily parts with iron to take in its placer 

an equivalent of any previously precipitated metallic copper present,, 

with which it is in such extended contact and for which it has nearly aa 

strong an affinity as for iron.

This greater tendency to precipitate metallic copper in the shaft furnace impairs its efficiency in expelling arsenic and antimony, which are 

far more readily removed from matte than from metallic copper.

(519) 

Bull 26 7
COPPER SMELTING. [BULL. 26.

PRODUCTS.

1. Black copper, whose composition varies greatly. It is usually leaner 

than the blister copper of the reverberatory process, being contaminated with metallic iron so that its tenor in copper, rarely above 95 per 

cent., falls as low as 80 per cent, and occasionally even to 70 per cent. 1 

Indeed in some places the product consists of a mixture of cupriferous 

pig-iron and ferruginous black copper. On this account it is in general 

much harder to refine than the blister copper of the reverberatory process.

2. Matte, with slightly less sulphur, much less copper, and much moro 

iron than the regule of the reverberatory process from which metallic 

copper first precipitates. By limiting the thoroughness of the preceding 

roasting by adding pyritous ores, etc., mattes much richer in sulphur and 

leaner in copper may be produced and the precipitation of metallic copper or iron prevented.

TABLE XV. Composition of shaft furnace matte produced with black copper.

From 

Mansfeld.a

1.

15. 8-16. 3

20. 2l24. 4

57. 2-61. 2

From 

Mansfeld.a

2.

4.6

0.5

21.4

79 R

From 

Fabian. a

3.

17.2

0.7

24.5

57.8

From 

Riechelsdorf.a

4.

13.7

22.5

61.3

From Phonixhiitte.a

5.

16.3

22.3

60.0

From 

Ore Knob, 

Egleston. b

6.

20.66

23.44

54.03

From 

Swansea, c

7.

0

0

18.5

81.1

a, These from Kerl, Grundriss der HetaUhiittenkunde, 1881,1, p. 184. 

b Transactions of the American Institute of Mining Engineers, X, p. 44. 

c Regule of reverberatory process, Swansea (Le Play).

While, as already pointed out, mattes rich in copper like this second 

matte are most advantageously oxidized by the roasting-smelting of the 

Welsh process, yet it often happens that for the cupola process they 

are roasted in heaps, stalls, or reverberatory roasting furnaces. In 

these, owing to the small quantity of sulphur the matte contains, a large 

amount of fuel is needed to roast it, and the oxidation of the sulphur 

and iron is exceedingly difficult. After being roasted it is again smelted 

 exactly like the second matte, again yielding black copper, together 

with more or less rich matte.

3. Slags. These are generally ferruginous and about singulo-silicates. 

The following are from Kerl, Grundriss der Metallhiittenkunde, 1881, 

p. 184:

, Grundriss der Metallhiittenkunde, 1881, p. 183. 

(520)
HOWK] COMPARISON OF THE DIFFERENT METHODS. 99> 

TABLE XVI. Black copper shaft furnace slags.. (See, also, Table XII. )

Oxide of zinc ...............

Mansfeld .

31. 6-38. 1

6. 6- 7. 3

45. 1-52. 4

3. 4-11. 6

0. 1- 1. 5

0. C- 2. 9

1. 3- 5. 5

Stefanshiitte.

qt 7

62.3

0.4

0.1

0.9

...........

Eiechelsdorf.

31 7

2.8

4.7 ft

8 1

3 Q

1.1

Fahlun.

21. 0-32. 8

0. 0- 4. 2

0. 0- 1. 2

1 R_ o o

1. 0- 1. 6

0. 0- 0. 2

Eoraas.

30.9

4.0

66.3

0.5

6.0

Phonixhiitte.

25.36

70.13

0.15

0.20

............

These slags often contain injurious impurities to such an extent that, 

it is best to smelt them by themselves for an inferior grade of copper,, 

though they are frequently used to flux silieioirs ores in the ore-smelting 

cupola. .They are, indeed, often so free from copper that they may be 

thrown away.

SHAFT FURNACE PROCESS FOR OXIDIZED ORES AND NATIVE

COPPER.

These are smelted directly and very much like thoroughly-roasted 

matte; as they are less ferruginous, the tendency to form salamanders 

is weaker, and the deoxidizing action may therefore be stronger; indeed, 

in the case of oxidized ores it is frequently necessary to make the reducing action very strong to prevent scorification of copper.

On account of the tendency of the product, black copper, to set, it is 

generally separated from the slag in internal crucibles.

COMPARISON OF THE REVERBERATORY AND THE SHAFT FURNACE

METHODS.

1. Composition of charge. With very silicious, aluminous, calcareous, or magnesiau ores the reverberatory possesses a great advantage 

in being able to treat mixtures so refractory that they cannot be completely fused, but have to be dragged out of the furnace in skimming. 

These ores would require heavy fluxing in the shaft furnace where their 

complete fusion is imperative. With very ferruginous ores the shaft furnace, especially if water-jacketed, has the advantage, since these ferruginous slags strongly corrode the reverberatory, and its oxidizing atmosphere tends to form refractory high oxides of iron, which in the shaft 

furnace pass into the fusible silicates of the protoxide of iron. With 

mixtures suddenly varying between extreme limits the reverberatory 

has the advantage, since these variations do not derange it as they do 

the shaft furnace.

2. Labor and fuel. White for simple smelting, whether of ore or of 

matte, the number of days of labor required per ton of burden is about 

the same for shaft furnaces a:od reverberatories, the latter demand much 

more highly skilled men, so that the actual cost for labor for the rever-

(521)
100 COPPER SMELTING. [BULL 26.

beratory is considerably higher and in remote places often very much 

higher, than for the shaft furnace.

The fuel consumption is moreover enormously greater in the reverberatory than in the shaft furnace. Vivian1 estimates the average 

ratio of burden to fuel in the reverberatory at 2.2:1. In shaft furnaces, 

"'with, fair coke, it should not fall below 5.5:3, even with refractory ores, 

r-and it rises even to 9:1 with well-managed furnaces and fusible ores (STos. 

3 and 10, in Table 12), or more than four times the average reverbera-

 tory duty. For the shaft furnace we must, however, use coke, charxjoal, anthracite, or a decidedly dry bituminous coal, which coheres in

burning, but does not cake. For the reverberatory we may use any

form of fuel, from anthracite to spent tan and sawdust. The cupola or

 reverberatory will have the advantage as regards fuel consumption according to whether the price of coke, anthracite, or charcoal is less or 

snore than, say, three times that of wood, bituminous coal, etc., per 

tinit of calorific power. In the majority, and perhaps in the great majority of places the cupola has in this respect an advantage so enormous

 as to greatly outweigh all other considerations. This is especially true 

«f works situated at a distance from coal-fields, the freight on coke by 

land being but little, if at all, greater than that of coal, and, of course, 

very much less than that of wood, per unit of calorific power. By sea 

freights still greatly favor coke per unit of actual smelting power (on 

account of its high efficiency in the cupola), though they are heavier 

on coke than on coal per unit of calorific power.

The use of gas furnaces would greatly diminish the disadvantage of 

the reverberatory as regards fuel consumption, but hitherto their saving in fuel has been outweighed by their increased cost for repairs.

3. Arsenic and antimony, it is generally stated, are much more completely expelled in the reverberatory than in the shaft-furnace process. 

While reasons have been given for believing that in the fusion of the 

toasted ore the cupola may be quite as effective in expelling these ele 

inents as the reverberatory is, if not more so, in smelting the roasted 

matte the reverberatory fusion favors their expulsion more than the 

<cupola does. This is at least partly because in smelting the roasted 

anatte the tendency of the shaft furnace to precipitate metallic copper 

is much stronger than that of the reverberatory. Most of the arsenic 

and antimony present concentrate in this metallic copper, from which 

their removal is far more difficult than if, as in the reverberatory, they 

ihad remained in a rich matte.

Reverberatory roasting, generally associated with reverberatory smelting, expels arsenic and antimony more completely than pile and kiln 

roasting, which are generally associated with cupola smelting. But 

these associations are by no means necessary, and, while the factor 

% which generally causes the adoption of the reverberatory smelter, cheap

1 Copper Smelting, its History and Processes, p. 19. 

(522)
HOWB.] COMPARISON OF THE DIFFERENT METHODS. 101

bituminous coal, often at the same time favors reverberatory rather 

than pile roasting, yet reverberatory smelting is often preceded by pile 

roasting and cupola smelting by reverberatory roasting.

4. Technical skill. The successful conduct of the reverberatory 

method depends, in a large degree, on the skill of the workmen and relatively less on the skill of the metallurgist in charge than does that of 

the shaft-furnace method. In the former, much depends on the proper 

care of the fire, skillful skimming, careful fettling, etc. In the latter, 

as in the iron blast furnace, success depends almost wholly on the skill 

of the metallurgist, the proper composition of the charge, ratio of fuel 

to burden, pressure of blast, size and number of tuyeres, etc.

5. The first cost of construction is in general somewhat greater per 

unit of daily capacity for reverberatory than for shaft-furnace plants. 

This is especially true in remote places on account of the much greater 

weight of the reverberatory plant, and the difference in favor of the 

shaft furnace is greater in large establishments, since the cost of the 

blowing apparatus does not increase in proportion to the capacity of 

the plant.

6. Repairs also are considerably heavier in the reverberatory than 

in the shaffc-furnace method, at least in the case of water jacketed shaft 

furnaces. In remote places this tells strongly against the reverberatory.

7. The loss of copper in the slags is much less in the cupola than in 

the reverberatory, because in the former the powerful reducing action 

of the fuel hinders scorification of copper, and because the separation of 

matte and slag is more complete as the slag gently flows from above 

the matte in the cupola than when it is skimmed in the reverberatory. 

Even in smelting roasted matte for black copper in the cupola the slags 

are often clean enough to throw away, while in the case of the reverberatory such slags must almost always be resrnelted.

8. Fines. The objection to the cupola frequently urged, that great 

quantities of slags must be added to enable any considerable amount of 

fine ore to be smelted, is not sound. In the Easchette furnace as much 

as 80 per cent, of the total burden may be ungrouted fine ore without 

necessarily deranging the working of the furnace; by grouting and 

bricking them the proportion of fines can be raised still higher.

9. Salamanders. The objection frequently made to cupolas on account of the formation of salamanders deserves little weight.1 With 

proper furnaces, mixtures, and precautions to avoid excessive deoxidizing action they do not occur. There are cupola smelting works in this 

country which ha.ve been run on most ferruginous mixtures for years 

without the formation of a single serious salamander.

10. Rapidity. The cupola process, thanks to its smaller number of 

operations, recovers the copper from the ore somewhat quicker than the 

reverberatory process.

1 Vivian, op. oit., p. 19. 

(523)
102 COPPER SMELTING. fBULL.2&

11. Size of establishment. The reverberatory process is so complex, 

and consists of so many different and delicate operations, at least when 

low-grade ores are treated, that the large staff of skilled meii it requires 

can only be employed to the best advantage where the output is very 

large. It is especially hard to maintain in remote places. So, also, the 

large number of furnaces which it is desirable to have so as to reserve 

each furnace for a special class of work fits this method for large 

rather than small establishments. The simple cupola process, however, 

needing but few skilled men and few furnaces, is applicable to both 

large and small works.

12. Bringing forward. For "bringing forward" rich mattes (blue and 

white metals, etc.) the reverberatory has special advantages. The small 

portions of sulphur and iron in these rich mattes are with difficulty oxidized by ordinary roastings and hardly at all in smelting in shaft furnaces, but they are very readily oxidized in the slow oxidizing fusions 

of the reverberatory, which thus, in addition to the fusion which may be 

effected equally well in the cupola, at the same time accomplishes work 

which in the cupola method has to be done by separate roastings. Hence 

the reverberatory may be advantageously used for bringing forward in 

places where its great fuel consumption would preclude its use for ore 

smelting.

RESUME.

To sum up, for SMELTING ORE the cupola is especially advantageous >

I. With highly ferruginous ores.

II. Where the cost of anthracite coke or charcoal is not excessively 

greater than that of bituminous coal, wood, and other fuels fitted for 

the reverberatory only.

III. For oxidized ores.

IV. For low grade native copper.

V. Where, as in the case of lean ores, clean slags are a necessity. 

The reverberatory is especially advantageous 

VI. With highly refractory silicious, aluminous, calcareous, or magnesian ores.

VII. Where the composition of the ore changes suddenly and greatly.

VIII. Where bituminous coal, wood, or other reverberatory fuel is very 

much cheaper than anthracite, coke, or charcoal.

I.. For smelting and immediately refining rich native copper.

.. Its disadvantage in yielding richer slags than the cupola weigha 

less heavily in case of rich ores.

For SMELTING FURNACE PRODUCTS of the several grades the following are the chief considerations which should influence oar choice between the cupola and the reverberatory:

(524)
HOWK.J ' K£SUME. 103

XI. The reverberatory expels arsenic and antimony from furnace 

products to si greater extent than the cupola does.

XII. Eeverberatory smelting exerts an oxidizing action on the sulphur and iron of mattes which are rich in copper which the cupola does 

not exert at all, and which can be effected only with great difficulty in 

roasting operations strictly so called. This consideration and the preceding one apply with the greater force the richer the material to be 

treated is in copper.

XIII. Cheap coke, etc., favor the cupola; cheap bituminous coal, etc., 

the reverberatory.

XIV. The reverberatory bringing forward method, especially with 

low grade products, demands a large staff of skilled men, very difficult 

to maintain and relatively very costly in remote places, and advantageously occupied only in large establishments; while the simple cupola 

method, needing the minimum of skilled men, is applicable alike to large 

and small, remote and central establishments.

(525)
ADDENDUM.

MATTE BOASTING IN OPEN BEVEBBEBATOBY FUBNAOES AT THE 

WOBKS OF THE OBFOBD COPPEB AND SULPHUB COMPANY, BEEGEN POINT, N. J.

The matte treated in this operation is that produced in ore smelting 

(column 15 in table of smelting in cupola or shaft furnaces). The 

roasted matte is smelted, with the results given in column 16 of the 

same table. (See pages 78 and 79.)

The principal features of this roasting are as follows:

Dimensions of furnace: 

Length of hearth inside ........................................ 6(X

Width of hearth inside......................................... 12'

Length of grate................................................ 5'

Width of grate..... ........................................... 3'

Depth of grate below top of bridge............................. 2'

Height of roof above bridge.................................... 0' 9"

Height of roof above hearth at bridge .......................... 2' 6"

Ratio of hearth area to grate area.............................. 48:1

Square feet of hearth area per ton of matte roasted per 24 hours.. 60

Boasting operation: 

Thickness of charge on hearth...........................:...... 7"

Honrs roasted ........ ......................................... 24

Tons roasted per 24 hours ...................................... 12

Percentage of copper in matte treated .......................... 30 to 60

Percentage of sulphur in the roasted matte ..................... About 5

Outlay of labor and fuel: 

Kind of fuel employed ......................................... Bituminous coal.

Fuel burnt per shift, tons ...... ................................ 2

Tons fuel per ton matte roasted................................. 0.33

Men employed at furnace per 24 hours .......................... 8

Days of labor per ton of matte roasted ......................... 0.67

All tons given in the above table are of 2,000 pounds. Sixty-seven 

parts of this roasted matte, mixed with 17 parts of the same matte unroasted and 16 parts of rich slags, are smelted in cupola furnaces. (See 

column 16, table of smelting in cupolas or shaft furnaces, pp. 78, 79.) 

The product obtained in this smelting operation consists of about 67 

per cent, of black copper and 33 per cent, of rich matte, containing 

about 80 per cent, copper. The slag produced at the same time contains 

from 0.75 to 2.66 per cent, of copper, and is resmelted in cupola furnaces 

with a small quantity of raw cupreous pyrites, yielding a matte containing 35 per cent, copper and a new slag containing 0.6 per cent, copper, which is thrown away.

(626) 104
USTDEX.

Page.

Arsenic and antimony, expulsion of, in roasting.............................. 25

decomposition of........................................................ 54

expulsion of, in shaft-furnace process .................................... 82

expulsion of, in reverberatory and shaft-furnace process, compared ....... 100

Batter of chimney .......................................................... 38

Binding, erection of......................................................... 32

Binding of furnace .......................................................... 30

Black copper, in shaft-furnace process ....................................... 98

Blast, hot, in shaft-furnace process ...... .................................... 91

Blistered copper, roasting-smelting raw white metal and regule for........... 66

Blue metal, smelting roasted coarse metal for ................................ 62

Bottom of furnace, preparation of............................................ 33

Bottoms and regule, roasMng-smelting blue metal for......................... 63

Brick vs. iron chimneys...................................................... 38

Brick vs. water-jacketed walls................................................ 88

Bringing forward, comparison of, in shaft-furnace and reverberatory methods. 102

Carbon, reducing-smelting with ............................................. 73

smelting without...................... .................................. 74

Cast vs. wrought iron jackets ................................................ 90

Charge, composition of, in reverberatory and shaft-furnace methods .......... 99

Charging filter.............................................................. 95

Charging, mechanical.................................. ..................... 94

Chemical reactions........................................................53,61,64

Chilian practice for roasting-smelting process................................ 69

Chimneys.................................. i................................. 35

Crucible, disposition of, in shaft-furnace process ............................. 86

Cupola-smelting, examples of................................................. 78

Deoxidizing effect of shaft-furnace smelting ................................. 80

Draft of chimneys ........................................................... 35

Filter-charging ............................................................. 95

Fine ore, furnaces for, in reverberatory method .............................. 19

in shaft-furnace process ................................................. 95

Fire-box...........................................................!........ 28

Fire-bridge ................................................................. 29

First matte, roasting of..................................................... 54

smelting the roasted, in shaft-furnace process ............................ 96

Furnace, construction of ..............................;..................... 28

volume of, in shaft-furnace process ....................... ............... 83

Furnaces, for fine ore ....................................................... 19

' gas...................................................................... 39

for smel ting roasted coarse metal for blue metal........................... 62

Raschette, in shaft-furnace process ...................................... 85

Fusibility of silicates ....................................................... 50

(527) , 105
106 v » INDEX.

	Page. 

Gas furnaces................................................................ 39

Gersteuhofer furnace ........................................................ 19

Gibbs furnace... ............................................................ 24

Hasenclever and Helbig furnace.............................................. 19

Heap-roasting, examples of.................................................. 17

Heaps, roasting in, in reverberatory method ................................. 16

Hearth of furnace .................................... ..................... 33

Hot blast in shaft-furnace process ........................................... 92

Introduction................................................................ 11

Iron vs. brick chimneys...................................................... 38

Kilns, roasting in, in reverberatory method ................................... 18

Labor and fuel in reverberatory and shaftrfurnace methods................... 99

Linings of chimney ......................................................... 38

Maletra furnace............................................................. 19

Masonry of furnace .......... ............................................... 32

Matte, proportion of, in charge .............................................. 47

in shaft-furnace process ................................................. 92,98

Matte-roasting ............................................................ 22,54,57

Mechanical charging........................................................ 94

Muffles .................................................................... 24

Native copper, reverberatory method for..........................«.......... 73

shaft-furnace process for ................................................ 99

Ore-roasting in reverberatory method....... ................................. 16,22

in shaft-furnace process ................................................. 76

Ore-smelting in shaft-furnace process ........................................ 76

Ores, oxidized and native copper, reverberatory method for .................. 73

oxidized, shaft-furnace process for....................................... 99

Ores and slags, classification of.............................................. 70

Piles, roasting in, in reverberatory method.............................. ..... 16

Products in shaft-furnace process...... ...................................... 92

Pyrites kilns.................................................. i............. 18

roasting of, iu furnace for fine ore ....................................... 21

Raschette furnaces.......................................................... 85

Reactions, chemical.......................................................53,61,64

Reducing-smelting with carbon.............................................. 73

Regule and bottoms, roasting-smelting blue metal for ........................ 63

Re'sume'.. ................................................................... 102

Reverberatory and shaft-furnace methods, comparison of..................... 99

Reverberatory furnaces.............. ...................^.......--..-..---..- 21

ReA^erberatory smelting, examples of .............. .......................... 40

Revolving cylinders...... ...... .... .... ................ ..................... 21

Roasted first matte, smelting the, in shaft-furnace process.................... 96

Roasted ore, smelting of, in reverberatories .................................. 28

Roasting, objects of ............................... ........................ 25

Roasting-smeltiug process, Chilian and Swansea practice in .................. 69

Salamanders, formation of, in cupolas...... ............................:..... 101

Schaffner furnace ........................................................... 19

Scorificatiou ................................................................ 52

Shaft-furnace and reverberatory methods, comparison of..................... 99

Shaft-furnace process, for sulphureted ores...................... ........ - -. 74

for oxidized ores and native copper ...................................... 99

Siemens furnace .............................................-.- »* - - - 39

Silicates, fusibility of ....................................................... 50

(628)
INDEX. 107

Page. 

Slag, proportion of, in charge................................................ 47

Slags, classification of............................... . ................ 60,72

composition of.......................................................... 93,94

in shaft-furnace process ................................................. 98

Smelting .................................................................44,47,6fc

Spencefurnace.............................................................. 20

Stalls, roasting in, in reverberatory method .................................. 18

Stetefeldt furnace .......... ...... ............................................ 21

Sulphureted ores, reverberatory method for .................................. 15

shaft-furnace process for .........J...................................... 74

Swansea practice for roasting-smelting process............................... 69

Tuyeres in shaft-furnace process............................................. 91

Water-jacketed 0«. brick walls ................................ .... ... 88

White metal, smelting for................................................... 58

Wrought va. cast-iron jackets................................................ 90

(529)