REPORT TO THE INTERNATIONAL COMMITTEE ON

ELECTRICAL UNITS AND STANDARDS OF A SPECIAL TECHNICAL COMMITTEE APPOINTED TO

INVESTIGATE AND REPORT ON THE CONCRETE STANDARDS OF THE INTERNATIONAL ELECTRICAL UNITS AND TO

RECOMMEND A VALUE FOR THE

WESTON NORMAL CELL

JANUARY 1, 1912

WASHINGTON

GOVERNMENT PRINTING OFFICE

1912



REPORT TO THE INTERNATIONAL COMMITTEE ON

ELECTRICAL UNITS AND STANDARDS OF A SPECIAL TECHNICAL COMMITTEE APPOINTED TO

INVESTIGATE AND REPORT ON THE CONCRETE STANDARDS OF THE INTERNATIONAL ELECTRICAL UNITS AND TO

RECOMMEND A VALUE FOR THE

WESTON NORMAL CELL

JANUARY 1, 1912

WASHINGTON

GOVERNMENT PRINTING OFFICE

1912

REPORT ON THE CONCRETE STANDARDS OF THE INTERNATIONAL ELECTRICAL UNITS

CONTENTS

Page

I. INTRODUCTION 4

II. CONCLUSIONS and recommendations of the International Technical Committee 7

III. MINUTES of the meetings » 9 IV. APPENDIXES 43 A. Reports, List of papers and suggestions tendered to the committee

by the delegates at the beginning of the work 43

B. List of apparatus, standard cells, and materials brought by the

delegates 81

C. Description of the experiments 82

1 . Resistance measurements 82

2. Standard cell comparisons 96

3. Description of the experiments on the voltameter 126 D. Tables of results of the experiments with the silver voltameter 145 E- Reports of subcommittees 159

r. Subcommittee on weights 159

2. Comparisons of four different electrolytes in small porous cup voltameters 161

3. Subcommittee on the investigation of special questions

regarding the silver voltameter 163

4. Methods of testing for various impurities in silver nitrate . . 171

5. Neutrality tests of electrolytes 177

6. Permanganate tests 178

7. Special tests on three samples of silk 179 F. Various reports given to the committee . 180

r. Connection with previous work 180

2. Interpretation of results by W. Jaeger 182

3. Interpretation of results by E. B. Rosa 186

4. Interpretation of results by F. E. Smith 194

5. Interpretation of results by F. Laporte 195

6. Provisional specifications for the silver voltameter 199

7. Subcommittee on the maintenance of the units 200 V. rHsum£ ; 201

3
4 Report on Concrete Standards

I. INTRODUCTION

The International Conference at London in 1908 adopted specifications for the mercury ohm, the silver voltameter and the

Weston Normal Cell, and fixed a provisional value (1.0184 international volts at 20 C) for the latter. The specifications for the

mercury ohm and the Weston cell were more or less complete,

but for the silver voltameter the specifications were very inadequate, and since the value to be assigned to the Weston cell necessarily depends upon the specifications for the silver voltameter,

and the results of different investigators were not in close agreement, the conference selected an approximate value which it adopted as provisional only, until further experiments could be

made and more precise values determined.

In order that such experiments might be encouraged, and that

different countries might cooperate in fixing and maintaining

uniform throughout the world the values of the electrical units,

the London Conference established an International Committee

on Electrical Units and Standards, charged with the duty of promoting investigations in electrical standards and electrical measurements, and of securing the intercomparison of the standards of

different countries.1 The first and most important undertaking for this committee was to ascertain more definitely the value which should be assigned

to the Weston cell in accordance with the definitions of the London Conference. This involved completion of the specifications

and a series of careful experiments with the silver voltameter,

whereby the electromotive force of the cell would be determined

from the amount of silver deposited, the resistance and the time,

the electrochemical equivalent of the silver being taken as 1.1 1800

mg per coulomb. Many investigations of the silver voltameter were made between Rayleigh's work of 1884 and the London Conference of 1908, but at that conference principal weight was given

to several investigations, then only recently completed, at the

national laboratories of England, Germany, and France.

1 In specifying the duties of the Internationa] Committee, the London Conference uses these words: "* * * t formulate a plan for and to direct such work as may be necessary in connection with the maintenance of standards, fixing of values (this will include the reconsideration from time to time of the emf of the Weston Normal Cell) intercomparison of standards, and to complete the work of the confer- ence."
International Electrical Units 5 An extended investigation at the National Physical Laboratory had been carried out in 1906-7, in which the silver voltameter had been studied, and the electrochemical equivalent of

silver determined to be 1.11827 mg per coulomb in terms of the

absolute ampere, as measured by the current balance of that

institution. The electromotive force of the Weston Normal Cell was given as 1.01819 at 20 , using the international ohm as given

by their own mercury units. The Rayleigh form of voltameter was most used in these experiments, but the Richards form with

porous cups was also used, as well as the siphon and other forms.

All forms were found to give substantially the same results. In 1907-8 an extended series of experiments was carried out at the Physikalisch-Technische Reichsanstalt to determine the elec- tromotive force of the Weston Normal Cell, in terms of the electrochemical equivalent of silver taken as 1.11800 mg per coulomb,

the value adopted at the Chicago Congress of 1893 and later

adopted by Germany, and by the London Conference of 1908.

The results gave a mean of 1. 01 834 (for cells with new mercurous

sulphate) which was in fairly good agreement with the results of

the National Physical Laboratory. The provisional value adopted

at the London Conference of 1908 (1.0184 volts at 20 ), was a mean between the results of the NPL (1.01 843) and the PTR

(1.01 834), although the latter value was not yet published.

At the Laboratoire Central d'Blectricite experiments were made

in 1908 with the Rayleigh form of voltameter, in which taking the

value of the Weston cell as 1. 01 869 volts at 20 (value found by

current balance and resistance differing by 1/ 10000 from that

used at the NPL and PTR) they found for the electrochemical

equivalent of silver 1.11821. This gave for the Weston cell

1.01 8 79 when referred to silver as 1.11800 after correcting jfa

per cent for the difference in the resistance.

At the Bureau of Standards an extended series of experiments was made in 1907, 1908, and the early part of 1909, with the

Rayleigh form of voltameter, and some experiments with the

Richards. The results with the Richards form were 1. 01837

volts at 20 for the Weston Normal Cell, as the mean of six deposits

made December 22, 1908, and February 11 and 27, 1909, taking

i.i 1800 as the electrochemical equivalent of silver, and with the
6 Report on Concrete Standards

Rayleigh form about i. 01863, as the average of 28 deposits in

1908 and February, 1909. Fifty-four deposits in the Rayleigh

voltameter in 1907 had given a slightly higher value for the value

of the standard cell. With two sheets of filter paper still higher

values were obtained. The above results obtained at the Bureau

of Standards are, however, still unpublished.

Summing up the figures given above we have:

Taking 1.11800 Mg Per CoulombVolts at 20 . At Nat. Pliys. Lab., using filter paper 1.01843 At Phys.-Tech. Reichs., using silk and porous cups 1.01834 At Bureau of Standards, using porous cups 1.01837 At Bureau of Standards, using filter paper 1.01863 At Lab. Cen. dljlec, using filter paper 1.01879 This is the way the figures appeared on the first of March, 1909, at the Bureau of Standards. In view of the fact that so large

differences had been found at the Bureau between the Richards

and Rayleigh forms, whereas at the National Physical Laboratory

they were found to be alike, it seemed difficult to come to an agreement without further investigations, and in order to reach such

agreement as speedily as possible, it appeared desirable that the

men who had made the several investigations referred to above

might come together in the same laboratory and work out together

the solution of their differences.

It had been suggested at the London Conference of 1908 that

delegates from the several national standardizing laboratories

might come together under the auspices of the International Committee for cooperative work on standards whenever that seemed

necessary, and this was a case where it did seem necessary.

Accordingly, it was suggested to the president and vice president of the International Committee by Drs. S. W. Stratton and

K. B. Rosa jointly in letters dated March 15, 1909, that such an

investigation be carried out at Washington, in the laboratories of

the Bureau of Standards. It was suggested in this letter that if the representatives of the several laboratories spent " a month or two setting up cells and working with the silver voltameter, that

we might perhaps come to complete agreement, not simply as to

numerical values, but as to specifications and procedure." This

proposal met with a very cordial approval, and accordingly the
International Electrical Units 7

following circular letter was sent out to the International Committee in June:

Dr. Stratton and Dr. Rosa have made the proposal that a member of the scientific

staff of each of the two institutions, the National Physical Laboratory and the Physikalisch-Technische Reichsanstalt, shall be sent to Washington in October, 1909, for a period of one or two months, for the purpose of carrying on joint experiments with

the Bureau of Standards upon the standard cell and the silver voltameter. An

attempt would be made in these investigations to come to an agreement upon numerical

values and specifications. The treasurer of the committee, Dr. Stratton, stands ready

to procure the necessary funds for covering the traveling expenses. The work would

be regarded as undertaken by the International Committee, to which a report of the

results would be submitted. The undersigned hereby move the acceptance of this plan, and respectfully request

that you send an expression of your opinion to the president.

The proposal to have only two representatives was due to the

desire to limit the expenses, as no funds are provided for the work

of the committee, and it was necessary for the treasurer to solicit money to defray the expenses. Later it was arranged that a third

delegate from Europe be sent, to represent the Laboratoire Central d'Blectricite.

The traveling expenses of the delegates were defrayed from a

fund provided by the following American societies, each of which

contributed $500: The American Institute of Electrical Engineers,

National Electric Light Association, Association of Edison Illuminating Companies, and Illuminating Engineering Society.

The generosity of these societies in this matter is greatly appreciated by the treasurer and the International Technical Committee.

Ample laboratory facilities for the work and a considerable

number of scientific assistants were provided by Dr. S. W. Stratton,

the Director of the Bureau of Standards, who took a deep personal

interest in the work of the delegates from the several institutions,

and did everything possible to make the work successful.

II. CONCLUSIONS AND RECOMMENDATIONS OF THE

INTERNATIONAL TECHNICAL COMMITTEE

The International Technical Committee assembled at Washington April 4, 1910, under the presidency of Dr. S. W. Stratton,

Director of the Bureau of Standards, and treasurer of the Inter- national Committee on Electrical Units and Standards.
8 Report on Concrete Standards

The committee unanimously elected as chairman Dr. K. B.

Rosa, Physicist of the Bureau of Standards, and secretary of the

International Committee.

The International Technical Committee consisted of the following persons:

Dr. E. B. Rosa, Chairman.

Dr. W. Jaeger, Geheimer Regierungsrat, Mitglied der

Physikalisch-Technischen Reichsanstalt.

Prof. F. Laporte, Sous-Directeur du Laboratoire Central

d'Blectricite.

Mr. F. E. Smith, Principal Assistant, National Physical

Laboratory.

Dr. F. A. Wolff, Associate Physicist, Bureau of Standards.

The committee unanimously appointed Dr. F. W. Grover

secretary for the preparation of the minutes and records.

From April 4 to May 25, 1910, the committee has held 19

meetings, has made or has had made 17 series of experiments on

the silver voltameter, besides numerous comparisons of resistances,

of standard cells and of weights.

The apparatus and installations which were used in carrying out

these experiments and these comparisons were those which are in use at the Bureau of Standardsy except such of the voltameters,

resistances, standard cells, weights and chemical materials as were

brought by the delegates.

The committee appointed several subcommittees charged with

conducting experiments and preparing reports.

After examination of the results obtained and discussion of the

reports, the International Technical Committee decides to present

to the permanent International Committee the following reso- utions adopted unanimously:

(1) The committee decides to choose as the value of the Weston Normal Cell the mean value of the cells presented by the delegates of the four laboratories. This mean was determined in the following way: There was first determined the mean

value of the normal cells presented by each delegate, then the mean was taken of the

four numbers thus found.

(2) The committee decides to choose, for the present and until there are other mercury ohms prepared, as the value of the international ohm, to be recommended to

all countries for general use, the mean of the values of the units realized at the Physikalisch-Technische Reichsanstalt and at the National Physical Laboratory.

Although the international ohm as defined by the London Conference has not yet been
International Electrical Units 9

strictly realized, the committee believes that its value has been attained in two lab- oratories independently with a good degree of precision, and that future work is not

likely to change it by more than 2 or 3 parts in 100 000.

(3) In view of the fact that the mean of the results with the silver voltameter obtained by this committee will probably not be changed by more than a few parts in 100 000 when the specifications are finally completed, the committee decides to rec- ommend to the International Committee on Electrical Units and Standards the fol- lowing value for the electromotive force of the Weston Normal Cell: E=1.0183 INTERNATIONAL VOLTS AT 20°C

On the subject of the standard cells, the committee is of the opinion that new experi- ments are necessary before completing or changing the specifications of the London

Conference. On the subject of the ohm, the committee expresses the hope that new international ohms, fulfilling all the specifications of the London Conference, may be realized soon

in different laboratories. On the subject of the silver voltameter, the committee is of the opinion that the

specifications for the silver voltameter should not be completed until further experi- ments shall be made by the members of the committee in their respective laboratories on subjects which are not considered settled at the present time, and that after these experiments, the committee shall complete the general specifications.

The committee decides that no publication shall be made of the results obtained or

of any details of the work without the permission of the International Committee on

Electrical Units and Standards. The committee decides that a complete copy of the report shall be sent to the presi- dent of the International Committee on Electrical Units and Standards, and to each

of the national laboratories represented on the Technical Committee, and that it make

no recommendation with respect to its publication.

Washington, May 25, 1910.

III. MINUTES OF THE MEETINGS

FIRST MEETING, APRIL 4, 1910 The first meeting of the delegates from the PhysikalischTechnische Reichsanstalt, the National Physical Laboratory,

the Laboratoire Central d'E^lectricite and the Bureau of Standards, constituting a special Technical Committee, acting under the

auspices of the International Committee on Electrical Units and

Standards, to carry on a joint investigation on electrical standards, was called to order by Dr. S. W. Stratton, Director of the Bureau

of Standards, at 3.30 p. m., Monday, April 4, 1910.

The delegates present were the following

:

From the Physikalisch-Technische Reichsanstalt Dr. W. Jaeger

From the National Physical Laboratory Mr. F. E. Smith

From the Laboratoire Central d 'Electricite Prof. F. Laporte

From the Bureau of Standards Dr. E. B. Rosa

Dr. F. A. Wolff
IO Report on Concrete Standards

The Director welcomed the delegates to the Bureau, and made

some appropriate remarks respecting the work to be undertaken.

In reply, the several European delegates expressed their appreciation of the manner in which they had been received, and particularly of their entertainment in New York, where Dr. C. H.

Sharp had acted as representative of the Bureau, as well as representative -of the electrical interests of New York City.

Director Stratton then stated that while he intended to keep in

touch with the work of the committee, he could not be present at

its meetings regularly, and therefore invited the delegates to elect one of their own number as chairman. Mr. Smith nominated Dr.

Rosa as chairman. This nomination was seconded by Dr. Jaeger

and M. Laporte, and the Director declared Dr. Rosa elected

chairman.

Dr. Rosa then took the chair, and after expressing his appreciation of the honor accorded him, asked whether the committee

would prefer to elect one of their own number as secretary, or would have some one not a delegate. A general preference was

expressed for the latter, and Dr. E. W. Grover was suggested by

the chairman for the position of secretary to the committee. By

unanimous consent Dr. Grover was appointed secretary.

Some discussion followed as to the form of the report which

should be presented by this committee to the International Committee on Electrical Units and Standards, and the chairman asked

Mr. Smith to draw up a resolution embodying some suggestions

he had made for consideration at the next meeting.

After some further informal discussion concerning the work to

be done, the committee adjourned to meet at 10 a. m., April 5. SECOND MEETING, APRIL 5, 1910 The meeting was called to order at 10.25 a- m-> Tuesday, April

5, 1 9 10, all members present. The minutes of the preceding

meeting were read and approved.

The chairman then called upon Mr. Smith to present his reso- lution (postponed from the preceding day) , on the form in which

the report of the committee shall be published

:

That since it is highly desirable to have a unanimous report, the experiments be

made, so far as is practicable, in an impersonal manner, and in compiling the report

references be made to laboratories and samples and methods, and not to individuals.
International Electrical Units 1

1

Mr. Smith explained that the motion was not fully descriptive

of his desires, but he thought that the committee would see his reasons for such a proposal, and he hoped that some agreement

might be reached. After some discussion the motion was withdrawn, although it was understood that the committee were unanimously of the opinion that the idea embodied in the motion

should be carried out. The suggestion of the chairman that a list of all the standard

cells, resistances, weights and other apparatus intended to be

used by the committee be handed to the secretary, was agreed to. It was also agreed that the delegates hand to the secretary a

list of such apparatus and chemicals as they might wish to place

at the disposal of the committee.

The following subcommittees, proposed by the chairman to

take especial charge of these intercomparisons, were approved:

Dr. Wolff and Mr. Smith, subcommittee on resistances.

Dr. Wolff and Dr. Jaeger, subcommittee on standard cells. Dr. Rosa and M. Laporte, subcommittee on weights.

It was decided that the subcommittee on standard cells should

report to the committee as soon as possible a list of standard cells,

the mean value of the electromotive force of which shall be taken

as representing provisionally the value of the Weston Normal

Cell, to be used by the committee in its work; this report to be a recommendation subject to action by the committee. Similarly,

it was agreed that the subcommittee on comparisons of the standards of resistance should recommend to this committee a provisional value for the international ohm, to be used by the committee

in its work.

A list of suggestions and papers already received from the

different members was read and declared to be correct. The meeting was adjourned at 11.15 a. m. THIRD MEETING, APRIL 7, 1910 The committee was called to order at 10.25 a. m., all members

being present. The minutes of the last meeting were read and

approved.

Dr. Rosa for the subcommittee on weights, and Dr. Wolff for

the subcommittees on resistance and standard cells, reported prog-
12 Report on Concrete Standards

ress, and stated it would probably be possible to make a formal

report by Saturday, April 9. Some discussion followed, relating to points which should be

treated in these reports.

The chairman theTi made a formal announcement to the effect that the first experiments on the silver voltameter would take

place on April 8, in which the current should be passed through

10 voltameters in series, two cups belonging to each of the delegates (except in the case of the Bureau of Standards, which would

include two large voltameters and two of smaller size) , each voltameter being set up and manipulated according to the practice

of the country to which it belongs.

It was moved by Mr. Smith, and approved by the committee,

that a meeting be held every day, if only for a few minutes, whereupon the meeting adjourned at 11. 15 a. m. FOURTH MEETING, APRIL 8, 1910 The meeting was called to order at 10 a. m., and immediately

adjourned in order that the members could attend to experimental work in progress.

FIFTH MEETING, APRIL 9, 1910 The meeting was called to order at 10 a. m., and immediately

adjourned in order that the members could attend to experimental work in progress.

SIXTH MEETING, APRIL 12, 1910 The meeting was called to order at 10.50 a. m., all members

being present.

The chairman made a statement to the effect that, owing probably to some contamination of the electrolyte used in the Bureau

of Standards voltameters, the deposits obtained therein in the

experiments on the preceding Saturday were abnormal, being not

only discordant in weight but showing a dark band along the upper

edge of the deposit. Examination under the microscope showed

that a dark substance had deposited along with the normal silver

crystals and this foreign substance was supposed to be colloidal

silver. The same substance was also seen in the deposit in the

voltameters of the National Physical Laboratory.
International Electrical Units 13

Accidents were also met in one of the voltameters of the Physikalisch-Technische Reichsanstalt and of the Laboratoire Central

d'Fylectricite. The first experiment was therefore regarded as preparatory merely.

The following program for the week was agreed upon: First, a

second comparison run of 10 voltameters in series, a repetition of

the experiment of April 9, with the single difference that in two of

the voltameters of the Bureau of Standards silk shall be used for a septum; second, the Bureau of Standards was authorized to

make some side experiments with the different samples of silver

nitrate brought by the delegates. For this purpose, it was agreed

to make up the electrolytes for Friday's experiment on Thursday,

and that portions of these be taken, diluted when necessary to

10 per cent concentration, and used in four of the Bureau of

Standards porous cup voltameters.

It was planned to devote the rest of the day in finishing the

weighings of the first experiment, and in a microscopic examination of the various deposits.

On motion of Dr. Wolff it was lesolved that the meetings take

place on call of the chairman or whenever requested by any

member.

Adjourned at 12.20 p. m. SEVENTH MEETING, APRIL 22, 1910 The meeting was called to order at 10.10 a. m., all members

being present. The minutes of the third, fourth, fifth, and sixth

meetings were read and approved.

A preliminary report of the subcommittee on standard cells was presented by Dr. Wolff. This report showed that the mean

values of the cells of the four laboratories are in close agreement,

and the average deviations of the individual cells are quite small.

The somewhat higher values of the French cells are in agreement

with those of cells made at the National Physical Laboratory and

the Bureau of Standards, from a sample of mercurous sulphate

from the Laboratoire Central d'LTectricite, made by the alternating

current electrolysis method. The report recommended that in

view of the constancy of the mean differences of each lot from the

Bureau of Standards reference cells, the voltameter measure-
14 Report on Concrete Standards

ments should be referred to the latter as heretofore, and that

appropriate corrections be applied to the results at the completion

of the work on the silver voltameter, and after agreement has been

reached as to the cells to be taken as defining the Weston Normal

Cell.A preliminary report of the subcommittee on resistances was

also submitted by Dr. Wolff, in which it was shown that although

the open resistance coils have shown changes with respect to the

sealed coils since their arrival, the standards of the PhysikalischTechnische Reichsanstalt, the National Physical Laboratory, and

the Bureau of Standards, do not differ among themselves probably

by more than 2 in 100 000.

The chairman next suggested that the committee agree to some

program for the experiments on the standard cell. It was moved

by Mr. Smith, and seconded by M. Laporte, that each delegate

receive samples of Hg2 S04 from each of the other delegates, and

that with this material and his own he make up 1 2 cells, 3 from each

of the samples, using the method of preparation which he chooses.

After some discussion, the motion was unanimously carried.

It was also moved by Mr. Smith, and seconded by M. Laporte,

that 3 cells be made by each delegate, using a single sample of

Hg2 S04 , but washing it in four different ways. This motion was

also carried unanimously.2 The question of a program for the special experiments on the

silver voltameter was next brought up by the chairman, who

discussed the results of experiments already done on the different

electrolytes. The experiments showed that the four electrolytes

of the delegates give substantially the same value as used in the

small porous cup voltameters. The chairman then outlined a number of experiments to settle differences in the behavior of the

different types, and to throw light on the question as to what

agreement can be reached when different observers use the same

type of voltameter. After a good deal of discussion, it was decided

to defer agreement on a program until another international

experiment like the two previous had been completed.

Adjourned at 12.15 P- m2 These last cells were not set up as proposed.
International Electrical Units 15

EIGHTH MEETING, APRIL 29, 1910 The meeting was called to order at 10.10 a. m., Friday, April 29,

all members being present. The minutes of the last meeting were

read and approved as corrected. The tabulated results of the

experiments to date were presented and examined.

Mr. Smith suggested that an estimate of the possible error in

the current be made after each experiment, before making the

weighings. This was agreed to. Dr. Jaeger called attention to the fact that since trouble had been

met in some of the previous experiments from uncertain contacts, a blank experiment should be carried out before the next regular

experiment to locate possible troubles of this kind. This was also

agreed to. A discussion followed as to whether further experiments should

be made using filter paper. Mr. Smith and M. Laporte expressed

themselves as satisfied that filter paper increased the deposit and

should be avoided in precision work with the voltameter. Dr.

Jaeger expressed himself as not satisfied that the filter paper

effect had been demonstrated, as the experiments at the Reichsanstalt on this subject were not yet finished, and he wished that

further experiments might be made. The chairman expressed

the hope that as little time as possible be expended on the investigation of filter paper if it was agreed that it should not be allowed

in the official specifications which are to be agreed to and recom- mended to the International Committee. Dr. Jaeger stated that,

according to his views, it was not the task of the committee to

propose a single type for the voltameter, but that different types

be permitted, and that the principal task of the committee was to compare the different types as used in the countries represented,

and to deduce from the results a value for the Weston Normal

Cell. This value should be given to 1 part in 10 000.

The chairman expressed the view that this committee should

undertake to agree upon uniform specifications for the silver voltameter, as had in large measure been done for the standard cell and the mercury ohm, and that in so doing as great liberty be

allowed as to details, as the committee can justify by its own

experiments taken in connection with previous work. It will,

22451°—12 2
i6 Report on Concrete Standards

therefore, in his opinion, be necessary to investigate further several important features of the voltameter. For example, (i) the

volume effect, or the reason why large voltameters give heavier

deposits than small ones. This seems probably due to impure

electrolyte, and if found to be due to this alone, it will prove to

be a valuable criterion by which to test the purity of an electrolyte; that is, if large and small voltameters agree in the weight of

the deposit, the electrolyte will probably be pure. If they disagree, the smaller voltameter giving the lighter deposit, the latter

will be more nearly the proper weight. (2) The effect of silk should be carefully studied to see if it can be used without increasing the weight of the deposit. It appears that even pure raw silk increases the weight of the deposit unless thoroughly washed, and

even then it may do so. This should be very thoroughly tested

before silk is permitted. (3) The larger weight of silver, using

large siphons, may be due to impure electrolyte, but this also

should be tested. (4) The size of anode and effect of anode slime on the weight of the deposit when no septum is employed between

anode and cathode should be tried. Other experiments of this

kind will probably be suggested as the work proceeds.

As no motion was made respecting the carrying on of such

experiments, the chairman, after considerable discussion had

taken place, asked whether the committee would permit Mr.

Smith and himself, as a subcommittee of two, to carry on a series

of side experiments to test the various questions suggested. This was unanimously agreed to by the committee. Dr. Jaeger emphasized that such experiments should not interfere with one or two further comparisons made with the voltameters as used in

the four separate countries.

On motion of Mr. Smith, seconded by M. Laporte, it was voted

±0 have two more 10-cup experiments, in the first of which filter paper should be used in some of the voltameters, and in the sec- ond such changes should be made in the electrolyte, size, etc., as were suggested after the results of the first experiment were

obtained.

The meeting adjourned at 3.20 p. m., a recess for lunch having

been taken between 12.30 and 2.00 p. m.
International Electrical Units 17

NINTH MEETING, MAY 16, 1910 The meeting was called to order at 2.15 p. m., all members

except Dr. Wolff being present. The minutes of the preceding

meeting were read and approved.

The chairman announced that the report of the subcommittee

of two, under whose auspices the special experiments on the silver

voltameter had been conducted, was not quite ready, but would

be presented in the near future. He asked for suggestions for

experiments to be done in the current week, and none being

advanced proposed that another experiment be made to confirm

the important effects observed in the preceding two experiments,

when acid or alkali were added to the electrolyte. Such an

experiment could be carried out on the following day during the

absence of the delegates in New York.

It was decided that although further experiments could not be

regarded as the work of the committee, the results of such experiments might be taken into account in the same way as other

work of the Bureau of Standards, before the meeting of the committee, has been presented for the information of the delegates.

The proposal of Dr. Jaeger that each delegate should tabulate

and discuss the results of the experiments to aid in their interpretation was accepted.

It was then proposed by the chairman that certain points relative to the framing of general specifications for the silver voltameter be selected, to be considered by each delegate for himself

and discussed at the following meeting. After a good deal of discussion the following general subjects were agreed upon to be

considered in outlining the specifications

:

r. Methods for purifying the electrolyte, and the criterion for determining when a

sufficient degree of purity has been reached.

2 . The extent to which the solution may depart from neutrality at the beginning

of the experiment, and the allowable change during the deposit.

3. The limits of concentration of the electrolyte.

4. Whether silk can be recommended as a septum, and if so, how it shall be pre- pared and used.

5. Whether a porous pot can be recommended as a septum, and if so, how shall it be prepared and used.

6. Whether use of filter paper can be recommended as a septum or in the preparation of the silver nitrate.
18 Report on Concrete Standards

7. Under what conditions the voltameter may be used for purposes of highest precision, without any septum.

8. The size and method of preparation of the anode.

9. The allowable limits of the current density.

10. The best values of current to be employed.

The meeting adjourned at .4.20 p. m. TENTH MEETING, MAY 18, 1910 The meeting was called to order at 11 a. m., all members being

present.

Dr. Jaeger proposed that the report to be submitted to the

International Committee should give full details of the manner of

making the experiments, the apparatus used, methods of calculation of results, and the like. It was agreed that the value of

the Weston cell at 20°, in terms of the group mean of the cells of

the four countries, be the only value tabulated in the report, the

difference from the observed value at 25 to the value at 20

being stated. The chairman asked that the subcommittee on

standard cells should submit a report on the following day, showing the relation between the standard cell used in the voltameter

experiments and the mean of those cells which are to be used in

defining the Weston cell. This led to the discussion of the method

to be adopted in combining the results on the cells of the four

countries. In this connection Dr. Jaeger moved that the method

of calculating the mean value of the standard cells submitted by

the four different laboratories which shall be employed at this

time, should not be considered a precedent for the future. After some discussion this was agreed to. With this understanding,

M. Laporte moved that the arithmetical mean of all the cells,

excepting those which in the judgment of the maker are to be

regarded as abnormal, be taken. This was seconded by Mr.

Smith. Dr. Jaeger moved as an amendment that the arithmetical

mean be taken of the mean values of the four groups of cells of the

four countries. The motion, as amended, was seconded by Dr.

Wolff, and was carried unanimously.

M. Laporte called attention to the fact that the Daboratoire

Central d'Slectricite had found itself in a different position from

the other laboratories with regard to the preparation and selec-
International Electrical Units 19

tion of cells for the experiments, since it had had only three weeks

at its disposal for this purpose.

The next question, as to what unit of resistance the results of

the voltameter experiments should be referred, was after some

discussion reserved for further consideration until after the noon

recess. The meeting was again called to order at 1.45 p. m., after a

recess of an hour and a half, all members being present except

Dr. Wolff.

It was suggested by the chairman that some of the Bureau of

Standards coils be carried back to Europe and compared with the

standards of the Physikahsch-Technische Reichsanstalt, National

Physical Laboratory, and the Laboratoire Central d'E^lectricite,

the results to be incorporated in an appendix to the report to the

committee. Mr. Smith preferred that the comparisons should be

made as near as possible at the same time as comparisons of the

wire standards with the mercury ohm were made. The chairman

and Mr. Smith emphasized the distinction between the comparison

of the mercury ohms of the different laboratories, and intercomparisons of their wire standards alone. According to the London

Conference, the relation between the units of the various laboratories ought to be determined by comparison of their mercury

ohms, the wire standards simply serving as intermediaries. The

chairman proposed as a recommendation to the committee that

at some stated time, say April of next year, intercomparisons of

the mercury and wire standards of each laboratory be made, the

traveling comparison coils being carefully selected for constancy,

inasmuch as they must be assumed to remain constant during the

comparison.

ELEVENTH MEETING, MAY 19, 1910 The committee was called to order at 2.25 p. m. In the temporary absence of the chairman, Dr. Wolff took the chair. The

minutes of the ninth and tenth meetings were read and approved

after correction.

M. Laporte brought up the question of what data should be

included in the report of the experiments, and the following pro-
20 Report on Concrete Standards

visional form for the presentation of the results of the voltameter

experiments was drawn up

:

No. of experiment Date Room temperature (or temperature of oil bath)

Time

Standard resistance used, value in terms of unit agreed upon

Standard cell used, value in terms of international group mean agreed upon

Limit within which the current is supposed to be known

Laboratory Cup Type Anode

Electrolyte Weight

(to o.oi mg)

Weston cell at 20 (reduced to group mean) Remarks

Kind Volume

I

General remarks.

It was agreed that one of the experiments should be tabulated

in this manner and submitted to the committee for approval or

revision.

(Dr. Rosa then took the chair.)

Dr. Wolff reported for the subcommittee on standard cells, that

the group mean of the cells submitted by the delegates as normal,

and combined as was voted in the preceding meeting, was 26

microvolts higher than the reference cells of the Bureau of

Standards.

The consideration of those headings, which it was proposed

at the ninth meeting to treat in forming the general specifications

of the voltameter, was next taken up. Mr. Smith asked that

those points which after discussion remained in doubt should be

dismissed until the end.

The chairman asked that in order to promote discussion he be

permitted to read what seemed to him were the general points

which might be specified regarding the electrolyte:

The electrolyte shall consist of a solution of silver nitrate in distilled water, having from 10 to 20 g of silver nitrate in 100 cc of the solution. The electrolyte must be

free from organic or other reducing substances, as shown (i) by a suitable chemical

test, (2) by giving a crystalline deposit free from striatums, (3) by giving the same

weight of deposit in a large and in a small voltameter. The silver nitrate is purified

by crystallization, and if the chemical test for purity be omitted it should be recrys- tallized until further crystallization does not change the weight of the deposit.
International Electrical Units 21

The voltameter should contain not less than 75 cc in the cathode chamber, and the

deposit should not continue long enough to reduce the mean concentration of the

electrolyte in the cathode chamber below 5 per cent. If no septum is used, no greater weight of silver should be deposited in a single experiment than is contained in the

electrolyte at the start. The electrolyte when ready for use must be neutral or very slightly acid, as tested by iodeosine. As one part in a million of alkali may increase the deposit appreciably,

it is better to have a slight acidity (say one part in a million) than to take the risk of

slight alkalinity in attempting to make it strictly neutral. The electrolyte must be

neutral or slightly acid at the end of the experiment, no alkalinity and not more than a trace of acid being permissible. Any septum or other substance which produces

appreciable alkalinity or acidity must be avoided.

It was decided to discuss these points one at a time, distinguishing between what has been found in experiments of the committee

and the results of previous work. With regard to the limits of

concentration, the following were agreed upon:

No special experiments have been made by the committee to investigate the effect of varying concentration, although concentrations between 10 and 20 per cent have

been used in the experiments without evidences of differences due to this cause being

detected. Previous experiments in two of the laboratories have shown no certain differences when the concentration was varied between the limits 1 per cent and 50 per cent, and

5 per cent and 25 per cent, respectively, so that 10 per cent to 20 per cent would appear

to be safe limits. The limit below which the concentration of the electrolyte in

the cathode chamber, if this be distinct from the anode chamber,

should not be allowed to fall during an experiment, was next

considered. The chairman expressed the opinion that although

his suggestion of a limit of 5 per cent was to some extent arbitrary,

it had the advantage of being a round number and was sufficiently

large to be safe. After some discussion it was agreed "that the

average concentration of the electrolyte in the cathode chamber

(if it is distinct from the anode chamber) during an experiment

should not be allowed to fall below 5 per cent."

The detection of impurities in the electrolyte. —The chairman in

his draft proposed "that the electrolyte should be free from

organic matter and reducing agents as shown by chemical tests, or, in lieu of these, as shown by its giving a crystalline deposit free

from striation, of the same weight in large as in small voltameters,

and which is not changed after recrystallization." It was agreed

to discuss the separate points of these proposals one at a time.
22 Report on Concrete Standards

Mr. Smith expressed the opinion that there is no suitable chemical test known for some of the impurities which may be present.

A discussion of the permanganate test for reducing substances

followed, and it was pointed out that this test is not a sure indication of the presence of all kinds of organic material. The

chairman stated that there is evidence that on fusion of the silver

nitrate, organic substances present in the salt are often put into

condition to be acted on more readily by permanganate, and may

thus be detected although not found in the test of the crystallized

salt before fusion. With respect to the absence of striation as a

criterion for the purity of the electrolyte, the chairman stated

that although an impure solution might give a deposit free from

striae, he had never seen a striated deposit from an electrolyte

which was shown by chemical tests to be pure. Dr. Jaeger

remarked that the silver deposits in his cups, in the opinion of

the chairman, often showed striations, although the weight of

silver was normal, and that, therefore, the striations can not be a

sufficient criterion for abnormal deposits. The chairman replied

that it was on account of the difficulty of reaching a certain result

from any one test alone that he had proposed three criteria to be

taken in conjunction "with one another.

With respect to the volume effect, Dr. Jaeger said that there

might be such an effect, but that he did not think the experiments were conclusive.

Mr. Smith expressed the opinion that the experiments had

shown a volume effect to be present in some of the electrolytes,

and that he could not conceive of such an effect being present

with a pure electrolyte.

It was decided to postpone action on these points until the

report of the subcommittee on the special experiments should

have been presented.

Adjourned at 5.30 p. m. TWELFTH MEETING, MAY 20, 1910 The meeting was called to order at 10.30 a. m., all members

being present.

Dr. Jaeger asked if the report of the subcommittee on side

experiments was ready. The subcommittee reported that it had
International Electrical Units 23

not been possible to finish it as yet. Dr. Jaeger suggested that

the meeting adjourn until this report was at hand, as nothing else for the moment required action.

Adjourned at 10.40 a. m. THIRTEENTH MEETING, MAY 21, 1910 The meeting was called to order at 10.15 a - m- by the chairman

(Dr. Burgess being elected secretary pro tern in the absence of

Dr. Grover) . All members present.

The chairman called for reports of the subcommittees on standard cells and resistances.

Dr. Wolff gave a summary of the report on standard cells,

which showed that in terms of the unit agreed upon by the committee, namely, the mean of the group means on a basis of eight

comparisons, the NBS reference cell No. 109 was 23 microvolts

low.

Messrs. Wolff and Jaeger submitted a form of report that they

had agreed on as a subcommittee on the comparison of standard

cells, as follows:

Comparison of Standard Cells

Object.—Direct comparison of standards of emf of different laboratories; accuracy

of reproduction; and basis of expressing results of voltameter experiments. The cells. —PTR, NPL, LCE, and NBS cells. Give table for each and supplementary table of additional cells for NPL, LCE,

and NBS.

Table or footnote should give information concerning materials, Hg, Cd, CdS04 , Hg2 S04

. Method of washing and such other details as may have a bearing on the subject.

The comparison baths.

Electrical measurements. The results. Reference cells of NBS.

Cells of each country in separate tables. Additional cells of each country in separate tables. Values of exchange cells at NBS (English and miscellaneous). Table of present values of cells previously tested abroad or belonging to same set. The above was accepted.

It was also decided to put the results on abnormal cells in a

separate table if they were found by the committee to be useful,
2 4 Report on Concrete Standards

and that the relative values of all cells as found at the Bureau of

Standards and in the home laboratories could be added as an

appendix.

Messrs. Smith, Jaeger, and Laporte presented a draft of a form

that the final report to the International Committee on Electrical

Units and Standards should take. This form was agreed upon in

principle, as follows:

The report of the International Technical Committee consists of the following

portions:

1. The conclusions and recommendations of the International Technical Committee.

2. Minutes of meetings.

3. Appendixes:

(a) Reports, papers and suggestions of the delegates already in the hands of the secretary of the committee (10 papers).

(b) List of apparatus, standard cells and materials brought by the delegates

for the work of that committee.

(c) Description of experiments.

(d) Data of experiments.

(e) Reports of subcommittees on weights, resistances, standard cells, volta- meters. After considerable discussion as to the publishing, printing and

distribution of the report, it was voted, on motion of Mr. Smith,

and seconded by M. Laporte, that one copy of the complete report

be sent to the president of the International Committee on Electrical Units and Standards, and to each of the national laboratories represented at Washington, and that this Technical Committee could make further recommendations later regarding the

other matters.

Dr. Wolff presented a further report from the subcommittee on

resistances which, after reading and discussion, was referred to

the subcommittee for completion and incorporation in a complete report from that committee.

On motion of Mr. Smith, seconded by Dr. Wolff, Messrs. Jaeger

and Daporte were made a subcommittee to draw up in more detail

the form of the final report to the International Committee on

Electrical Units and Standards. After some discussion regarding

future meetings and program, it was agreed to adjourn at 11.35

a. m. until 1.30 p. m. in order to give time for the subcommittees

to complete their reports.
International Electrical Units 25

FOURTEENTH MEETING, MAY 21, 1910 The fourteenth meeting was called to order at 2.15 p. m., all members being present. After inspection of the tabulated results

of an experiment arranged according to the form agreed upon in

the eleventh meeting, this form was approved.

The minutes of the preceding meeting were examined and

approved after correction. The chairman asked for the report of

the subcommittee on resistance comparisons. This was presented

by Dr. Wolff, who indicated briefly the following relations. The

intercomparisons of the resistance standards indicate the following values for the difference in the values of a given coil when

measured in terms of the Physikalisch-Technischen Reichsanstalt

unit and the Bureau of Standards provisional unit:

PTR-NBS using— Millionths. First measurement —6

Last three measurements +8

Last measurement +9

All the measurements +2

The difference between the value of a given coil when measured

in terms of the mean of the units of the Physikalisch-Technische

Reichsanstalt and National Physical Laboratory, and when measured in terms of the provisional unit of the Bureau of Standards

is (omitting L87, which is only a current standard)

:

Mean of PTR and NPL-NBS using— Millionths. First measurement +2

Last measurement +9

All measurements +7

The measurements on the PTR 1000-ohm coil, using the values

found at the Physikalisch-Technische Reichsanstalt by Dr.

Lindeck, give the value

PTR-NBS=+8 millionths. The subcommittee suggested in conclusion that the results of

the voltameter experiments should be referred to the mean of the

units of resistance maintained at the Physikalisch-Technische

Reichsanstalt and the National Physical Laboratory, and that

in accordance with the above data the value of the resistance of a

coil measured in terms of this unit is to be regarded as 7 millionths

higher than the value found in terms of the basis of reference o the
26 Report on Concrete Standards

Bureau of Standards. This is equivalent to the statement that the

mean of the values of the mercury ohms of the PhysikalischTechnischen Reichsanstalt and the National Physical Laboratory

is 7 millionths smaller than the value of the ohm maintained by

the Bureau of Standards wire coils. Taking this value in conjunction with the difference between the

group mean of the cells of the four laboratories and the mean of

the reference cells of the Bureau of Standards, the values of the

Weston Normal Cell found by voltameter measurements on cell No. 109 (whose value is 3 millionths higher than the mean of the

Bureau of Standards reference cells) should be corrected by

26 —3 +7=30 millionths.

These suggestions were adopted.

The consideration of the report of the subcommittee on the

special voltameter experiments was next taken up. In order to

be better able to take part in the discussion Dr. Rosa asked Dr.

Wolff to take the chair.

1 . Mr. Smith wished to especially emphasize the clause which

states that this report has been presented in a form convenient for

discussion, and recommended that the points be considered in the

order in which they appear in the report. Since, however, the

report had been in the possession of the members for only half an

hour before the meeting, he would suggest deferring action on the

report until the members had had more opportunity to examine

it. He would amend the first line on page 164 to read "by

recrystallizing three times and fusing. It is then neutral, etc." This was agreed to. The first line of the second paragraph on page 1 64 was amended

as suggested by M. Laporte to read "Table XLVIII gives the

difference on three electrolytes, etc.," and on suggestion of Dr.

Jaeger the next to the last line of the second paragraph on page

164 to read "required before fusion., as used by the Laboratoire

Central d'Fylectricite, 0.5, and after fusion 5 or 6 cc," etc. A discussion followed, introduced by Dr. Jaeger, on the behavior

of the French salt which gave no test with the permanganate

before fusion but showed the test for reducing agents after fusion.

M. Laporte asked the subcommittee if the permanganate test made
International Electrical Units 27 on a salt after fusion gave any indication of the purity of the salt before fusion. Has it been shown that the same deposit will be

obtained from a given salt unfused and showing no permanganate

reaction as is obtained with the same salt fused and giving a reac- tion with permanganate ? The subcommittee stated in reply that

this experiment had not yet been tried either by the subcommittee

or by either individually. In the case of the French salt only one

fusion had been made, and it could not be definitely stated that it was impure. In general, it was their opinion that a salt which

showed the volume effect and was always observed to give a reac- tion with permanganate, should be regarded as impure. There

are samples of AgN03 which show no permanganate reaction

either before or after fusion. The subcommittee wished again to emphasize their belief that the permanganate test alone is a useful

but has not yet been shown to be an absolute test, for certain

impurities of the salt. Dr. Jaeger, referring to the fact that a permanganate test of

5 cc corresponds to only two in a million of furfural, asked if tests had been made to show that this quantity of impurity should be

avoided. In reply Dr. Rosa stated that it can be regarded as established from the heavy deposits obtained with such salts, that such an amount of impurity is appreciable.

Dr. Jaeger called attention to three deposits obtained in the

French cups which, with the other experiments, seemed to indicate a negative volume effect. Prof. Rosa explained that since

the individual three deposits referred to were made in mediumsized cups only, and not some in large and some in small voltameters, they could not, in his opinion, be regarded as conclusive

evidence against the volume effect. M. Laporte inquired if Mr. Smith had in previous work found

the volume effect with his new form of voltameter. Mr. Smith

stated that he had always used salt in this form which other tests had shown to be pure. With an electrolyte proven by other tests to be impure he had observed three years ago an effect as great as 8 in 10 000. It was not, however, tested by means of potassium

permanganate.

2. The committee next considered the section on the siphon

voltameter. The suggestion of Dr. Jaeger that the relative values
28 Report on Concrete Standards

of the deposits in the experiment, using siphon voltameters (14th),

should be referred to the mean of all the deposits, was adopted,

as was also the proposal that the differences between the siphons

in large and small voltameters should be given.

Dr. Rosa gave it as the experience at the Bureau of Standards

that the siphon form of voltameter, although theoretically reliable,

had in practice always given higher results than with the porous

pot or with no septum. If a porous pot is placed over the cathode

end of the siphon, the deposit is the same as that found in the

same cup with a porous pot. If a porous pot is placed over the

anode end of the siphon, the deposit is larger. He attributed

this to the volume effect, the effect being increased, due to the

added volume of the electrolyte in the siphon.

Mr. Smith stated that he had always taken the siphon form as the standard by which to judge other forms, and to test whether

the anode was producing any disturbance,, and had always obtained

identical values with electrolytes believed to be pure.

Dr. Rosa replied that the siphon form had never been used at the Bureau of Standards with electrolyte in which the deposit was

the same in both large and small cups. With a solution in which

the deposit was larger in the large cups by only 3 or 4 in 100 000,

the volume effect was larger using the siphon and still larger with

two siphons in parallel. He supposed that Mr. Smith's salt had

been pure, and regarded the siphon as a very severe test on the

purity of the electrolyte. In practice it is a very awkward form

to use, and has little to recommend it. Dr. Jaeger called attention to the slightly larger values with

siphons in the NPL electrolyte over those with the new form.

M. Laporte pointed out that the values with the siphons in this case were the same with two sizes of cups, a result not to be

expected if the solution were impure.

3. Effect of silk. Mr. Smith suggested that the first sentence

be amended to read "silk unless thoroughly washed can greatly

increase the deposit." Dr. Jaeger expressed the opinion that

those values indicating a light deposit with well-washed silk might be explained as due to accidental errors. The discussion of the chemical report submitted as a part of

the report of the subcommittee was postponed until the next day.
International Electrical Units 29

Dr. Jaeger brought up the question of the method in which the

experiments on the voltameter should be combined in obtaining

the value of the standard cell. Leaving out of account all deposits

where the impurities were purposely introduced into the electrolyte he found

including results with filter paper 1. 01 833

not including results with filter paper 1 .01 832

with a maximum deviation of 8 in 100 000.

Taking only the deposits in his own cup, he found

including results with filter paper 1. 01 833

not including results with filter paper 1 .01829

Dr. Rosa suggested that in finding the mean only those deposits

should be included in which the voltameters conformed to our own specifications. If it was agreed that those deposits where

acid was purposely added to the electrolyte should not be included

in taking the mean, then why should not those deposits be ex- cluded also where the electrolyte was shown to have become acid

during the experiment ? M. Laporte expressed the opinion that the importance of the

work of the committee would be very much lessened if the members should go home without being able to connect their former

practice with voltameters conforming to the new specifications.

His results with filter paper here had agreed with those in Paris,

but he was not sure that in using a new kind of voltameter his

results would agree with those of other observers. Dr. Rosa

called attention to the fact that the use of the voltameter rests on the assumption that different observers will obtain the same

results with voltameters conforming to the same specifications.

Dr. Jaeger expressed himself as not in favor of specifying the

voltameter. Mr. Smith read the following extracts of letters from

Dr. Warburg (to Dr. Stratton, Feb. 4, 19 10) upon the specifications of the voltameter: " It is, however, of importance to indicate

the factors which must be avoided or observed in making up the

chemicals, etc.," and he then refers to the Report of the London

Conference, page 21, and appendix, page 3. The last-named ref- erence reads as follows: "In this appendix certain institutions
3° Report on Concrete Standards

have described in more detail methods which are believed to fall within the general international specifications. When international cooperation in standardizing work has been further developed, mutual agreements on methods of procedure will no doubt

be secured with a corresponding degree of accuracy. At the present time the international comparisons which have been made

indicate that the various methods of procedure give very nearly

identical results." Mr. Smith believed from this that one of the

main objects was to agree upon methods of procedure.

Dr. Rosa emphasized that he did not wish to specify one form

of voltameter but merely that the committee should rule out

what, in their opinion, must be regarded as sources of error. He

would suggest that each member of the committee write out a

draft of those points which he believed it well to specify, and that

these drafts be compared and discussed on Monday. This was

not agreed to, and the discussion of the report of the subcommittee was continued.

Dr. Jaeger moved "the committee is of the opinion that from

the information at hand the existence of a volume effect can not

with certainty be deduced." Under this motion he stated that

he would include only those electrolytes in the report of the subcommittee. Prof. Rosa wished to substitute "with a high degree

of probability " in place of " with certainty." Mr. Smith suggested

that the motion be amended to read: "The committee is of the

opinion that the information at hand does not indicate with probability the existence of a volume effect in any electrolyte in the

experiments of the subcommittee." He could then vote against

the motion. Neither the motion nor the amendment was

seconded.

Dr. Jaeger moved also "that the relation between the volume

effect and the test with permanganate has not been established,

and it appears doubtful that the impurity indicated by the permanganate (two or three in a million) is of importance." This

•motion was not seconded. Mr. Smith emphasized that the subcommittee had nowhere claimed the certainty of the relation between the permanganate test and the volume effect. M. Laporte believed that it would be well to remember after

this long discussion that a very satisfactory series of experiments
International Electrical Units 3i

have showed the concordance of results given by the four electrolytes in voltameters of small dimensions. He regretted that these

experiments, favorable for an agreement, had not appeared in the

report of the subcommittee.

Adjourned at 6.05 p. m. to meet at 10 a. m. May 22. FIFTEENTH MEETING, MAY 22, 1910 The committee met at 10 a. m., all members being present, Dr.

Wolff in the chair and Dr. Burgess acting as secretary.

After informal discussion of the form of final specifications, the

committee proceeded to consider further the report of the subcommittee on the special voltameter experiments.

Dr. Jaeger called attention to paragraph 5, page 166, of this

report, and asked if the accompanying report of the chemist,

Dr. McDaniel, expressed the views of the subcommittee. Messrs.

Smith and Rosa stated that the chemist's report was transmitted

to the Technical Committee for its information, but that the subcommittee was not responsible for its contents. A long discussion ensued concerning the experiments carried

out by the subcommittee, particularly with reference to the tests for acid and organic impurity in the electrolyte, and the effect of

acid and silk upon the weight of the silver deposited. It was

held by Messrs. Jaeger and Laporte that the information con- tained in the report of the subcommittee, together with the report

of the assisting chemist, Dr. McDaniel, was not sufficient to justify

the committee in excluding silk from use in the silver voltameter,

or in requiring that the electrolyte be strictly neutral, or contain

only a trace of acid.

Dr. Rosa, remarking that agreement on uniform specifications was apparently impossible at present in all subjects, such as silk,

acidity, purity, etc., he would defer such matters for future settle- ment by correspondence, and he therefore moved

:

It is the sense of the committee that the specifications for the silver voltameter

should not be completed until further experiments shall be made by the members of the committee in their respective laboratories on subjects which are not considered

settled at the present time, and that after these experiments, the committee shall complete the general specifications.

The motion as amended was carried unanimously.

22451°—12 3
32 Report on Concrete Standards

Dr. Wolff retired, and Dr. Rosa took the chair. After informal

discussion of the significant figures to represent the value of the

Weston cell from the work here, the committee adjourned at

12.55 p. m. to meet at 10 a. m. the day following.

SIXTEENTH MEETING, MAY 23, 1910 The meeting was called to order at 10.30 a. m., Monday, all members being present.

The typewritten minutes of the fifteenth, fourteenth, and the

tenth meetings of the committee were examined in turn and

corrected.

It was agreed that it would be instructive and interesting for

each delegate to group and average the results of the experiments,

and an informal discussion followed on the different ways of

grouping.

M. Laporte suggested that it would be well for each delegate to

present in the report all the results found, using his own type to

show the agreement with previous work which had been obtained.

A recess was taken from 12.40 to 3.15 p. m. The chairman asked that the first and third reports of the

Bureau of Standards on the voltameter be included in the list of

papers of the committee. This was agreed to. Mr. Smith and Dr. Jaeger submitted tables of the results of the

experiments with the different forms of voltameter, subject to

possible later correction and modification.

The chairman proposed that each member should add signed

comments to either or both of the tables.

Mr. Smith moved "that we recommend to the International

Committee the value 1.0183 international volts for the value of

the Weston cell at 20 ." This was seconded by Dr. Jaeger.

M. Laporte wished to amend this to read "for the value, at the

present, of the Weston cell at 20 ." He called attention to the

fact that no work on the mercury ohm has been carried out in

accordance with the specifications of the London Conference, and

that, therefore, any value assigned at present to the Weston cell

is subject to revision.

Mr. Smith stated in reply that provision had been made by the

London Conference for the revision from time to time of the value
International Electrical Units 33

of the Weston Normal Cell in international volts, and referred to

Schedule D of the London Conference.

It was suggested by the chairman that the recommendation for

the value of the Weston cell be introduced by preamble, explaining that the international ohm is at present not as specified by

the London Conference. This was agreed to. The motion, modified to embody the suggestions of the various members, was as

follows

:

Although the international ohm, as defined by the London Conference, has not

yet been strictly realized, we believe that its value has been attained in two laboratories independently with a good degree of precision, and thatfuture workisnot likely

to change it by more than 2 or 3 parts in 100 000, and, further, In view of the fact that the mean of the results with the silver voltameter obtained

by this committee will probably not be changed by more than a few parts in 100 000 when the specifications are finally completed,

Resolved, That we recommend to the International Committee the value 1.0183 international volts (instead of the provisional value 1.0184) as the electromotive

force of the Weston Normal Cell at 20 . This was seconded by Dr. Jaeger and carried unanimously.

The chairman then asked the committee if it would allow the

incorporation of one more experiment in the report of the committee. Within a few days Dr. McDaniel had prepared a salt which

answered all the tests for purity which had been suggested, and

four deposits had been made in large and small cups, using an

electrolyte prepared from this salt. On account of the interest

pertaining to the salt, he would like to see these four deposits

which could not appreciably change the mean found from the previous experiments, included with the other deposits. This was

agreed to. The chairman then stated that he would be glad if the committee would make out a list of the experiments in continuance of the

work of this committee which should be done by the members

after their departure from Washington.

The foliowing list was compiled from suggestions of the various

members

:

1. The effect of acid and alkali, and the limits of acidity and alkalinity which

can be allowed. Tests for acidity and alkalinity should be made at the beginning

and end of the experiment.

2. Methods for purifying silver nitrate and testing for organic impurity.

3. Effects of added impurities, organic and inorganic.
34 Report on Concrete Standards

4. Limits of current density that can be allowed at anode and cathode.

5. Is the deposit independent of the volume of the electrolyte ; if not, what are the causes of any observed variation? Find the quantitative relation between impurity and excess of deposit.

6. Study the relation between the degree of electrolysis and the excess of the

deposit with an impure electrolyte.

7. Influence of organic septa, especially silk. 8. The best treatment of porous cups as septa.

9. Under what circumstances may one use the voltameter without any septum ? 10. Can an electrolyte be safely used more than once ? The chairman instructed the secretary to make a list of all formal resolutions of the committee.

With respect to the transmission of the report after it shall be

finished, the chairman suggested that a copy be sent first to each

of the delegates, and that any necessary changes be made by cor- respondence, after which the reports will be turned over to the

directors of the various laboratories.

Mr. Smith moved "in the opinion of this committee, that there

is no complex anode ion." The chairman suggested that this be

qualified to read "that in a pure neutral electrolyte within proper

limits of current density, we believe that Faraday's law is undisturbed by side reactions or the formation of complex ions." No

action was taken.

Adjourned at 5 p. m. SEVENTEENTH MEETING, MAY 24, 1910 The meeting was called to order at 10.15 a- m-> au members

being present.

Dr. Jaeger recommended making a list of what should be at- tempted in the time remaining, and the following list was suggested

by the different members

:

1. Formal consideration of the tables presented by Dr. Jaeger and Mr. Smith.

2. To connect results obtained by the committee with the work of the delegates

before coming to Washington.

The chairman proposed that Mr. Smith, whose suggestion this

was, should, with the collaboration of the other delegates, undertake the preparation of such a report. This was agreed to.

3. The maintenance of the international ohm.

4. The maintenance of a concrete international average Weston Normal Cell.

5. Exchange of Hg,S04 samples.

6. Revision of the minutes and examination of reports.

7. Exchange of samples of silk.
International Electrical Units 35

Mr. Smith next brought up the question of preparing provisional specifications for the voltameter, in order to indicate

where there is a difference of opinion on this subject. The chairman pointed out that this should be done to make it easily possible for the International Committee to check up the value of

the cell found by this committee, as it is likely to wish to do.

Prof. Egoroff has suggested that the results obtained by this committee should be confirmed by experiments made by other members of the International Committee. The chairman suggested

that the points where there was disagreement could be printed in

italics and alternative specifications could be prepared to cover

these points.

M. Laporte believed that in those cases where experimental

data is not at hand, the specifications should comprise the limits of

actual practice in these experiments.

Dr. Rosa asked Dr. Wolff to take the chair that he might be free

to make the following motion:

That some member of the committee shall prepare provisional specifications for the voltameter and submit them to each member, and that before or after leaving Washington each member shall underline that which he thinks should be omitted or shall replace such passages by something else, or substitute an entirely new set of specifications, or shall make any comments he shall see fit over his signature, and that such

provisional specifications be added to the report. Vote: Yes; except Dr. Jaeger, who did not vote. Dr. Rosa recommended that the members should do this either

before leaving Washington or after their return home, and in the

former case they should be free to make revisions later. Mr. Smith moved that Dr. Rosa should be requested to draw up

such provisional specifications. This motion was seconded and

agreed to by the committee.

Mr. Smith moved two alternatives "that in the specification of

cadmium amalgam either the percentage composition be changed

or else the temperature limits be changed."

Dr. Jaeger believed this to be of less importance than other

matters, and wished to consider something else. It was moved by Prof. Rosa, and seconded by Mr. Smith, that

the amalgam be considered. Vote: All yes; except Dr. Jaeger,

who did not vote.
36 Report on Concrete Standards

Dr. Jaeger rose to a point of order, but the motion was ruled to

be in order by the chairman.

Mr. Smith moved "that in all cases for which the Weston cell

is used for purposes of precision between o° and 12 C, the percentage of the cadmium amalgam be reduced to 10 per cent, and

that between 12 and 40 a 12^ per cent amalgam may be

used." This was not seconded, and was withdrawn.

Dr. Rosa moved that, in order to use the time advantageously,

the points already suggested for consideration might be considered

in the following order:

1. Cooperative work:

(a) Plan for maintenance of a concrete ohm.

(b) Comparison of cells.

(c) Outline for future work on the silver voltameter.

2. Report of Mr. Smith connecting results of previous work with that of this committee.

3. Final review of resolutions and minutes.

4. Receiving report of committee on standard cells, and consideration of specifications.

5. Report of subcommittee on weights.

6. Final report of subcommittee on resistances.

7. Report of subcommittee on the form of the report to the International Committee.

8. Consideration of the results on the silver voltameter.

9. Provisional specifications for the voltameter. This was seconded by Mr. Smith.

Dr. Jaeger wished to put No. 8 first. This was agreed to, and

the motion thus amended was carried unanimously.

Dr. Rosa asked that a subcommittee be appointed to bring

in resolutions on heading No. 1 on the next day. This was sec- onded by M. Laporte, and agreed to unanimously. By general

agreement, Dr. Wolff and M. Taporte were selected to serve. Adjourned at 12 o'clock m. EIGHTEENTH MEETING, MAY 24, 1910 The meeting was called to order at 3.25 p. m., with all members

present, and Dr. Wolff in the chair.

The first matter under consideration was the voltameter experiments. Mr. Smith suggested that each member write out a state- ment of what conclusions he would draw from the voltameter

experiments, and read those comments which he had written concerning the table he had already presented.
International Electrical Units 37

Dr. Rosa moved that those comments on the tables may be

revised or added to by the delegates after their return to their

laboratories, so that each member may have opportunity to

make changes after having seen the comments and tables of the

other delegates. This was seconded by Mr. Smith.

M. Laporte thought it very important that a draft of all these

comments and conclusions be prepared before leaving Washington

in order that possible agreement on some of the points may be

reached at the present time.

The motion of Dr. Rosa was unanimously carried.

The report of the subcommittee on the subject of cooperative

experiments was deferred until the next day.

Mr. Smith stated that the statements of the concordance

between the present experiments and earlier work of the delegates

had already been prepared, and moved that they be accepted

without discussion as being mere statements of the facts. This was agreed to. In this connection, M. Daporte suggested that

Mr. Smith prepare a short note on the conclusions which may

be drawn from an inspection of these statements. This was

agreed to. Mr. Smith submitted the following note after the adjournment

of the committee:

I have made an examination of the four reports which connect the past and present

work on the silver voltameter of members of this committee. The main results are conveniently tabulated thus:

Laboratory Form of voltameter used

Value found

in own country

for emf of cell at 20°

Value found

inWashington

for emf of

cell at 20°

Difference

LCE Rayleigh 1.01845 1.01827

1.01834 1.01827 ±2

1.01844

3 1.01828

« 1.01829

1.01829

1X10—

«

1X10— 5X10—

2X10—

NBS

PTR

NPL

With silk and with porous pots. . .(mean).

.

New form, no septum

3 With larger voltameters higher values were obtained, but since Dr. Rosa has found, that with impure

electrolytes the larger the voltameter, the larger is the mass of the deposit, he considers the results with the small voltameters to be the most reliable.

4 In this case the value obtained at Washington is that with the cups of the Reichsanstalt excluding

filter paper. Silk was used as a septum, except in one case where no septum was used. The results are certainly most gratifying, and should help pave the way for an agree- ment on a type of voltameter which all may use with satisfaction.
38 Report on Concrete Standards

M. Laporte thought it would be well to prepare in concise form

a draft of all the conclusions adopted and recommendations made

to the International Committee, and agreed to draw up such a

draft for action by the committee on the following day.

Dr. Wolff gave an informal statement concerning the new cells set up by the delegates > and promised to report more at length on this subject at the next meeting.

The question of the further specification of the Weston Normal

Cell was next brought up and discussed. Dr. Rosa wished that

the opinion of the committee might be expressed as to whether an

attempt should be made to agree on more uniform procedure or

not. Mr. Smith believed that on account of the relatively good

agreement of the cells with great differences in the mode of construction, it was a very difficult matter to draw up specifications.

M. Laporte believed after a trial of other methods that it was

difficult to choose between them, although he preferred his method

of alternating current electrolysis.

Dr. Rosa wished that a series of questions might be formulated

to aid in deciding what points in the present methods of procedure

required further study. It was agreed that a study of the methods

of washing the Hg2 S04 was, perhaps, the most important single

subject. The chairman called attention to those subjects which

he had recommended for further study in his report submitted to the members at the beginning of this work.

Dr. Jaeger thought that there was not time to discuss these

subjects, and that the committee ought to proceed to decide

which cells are to be interchanged.

Dr. Rosa wished to learn the opinion of the committee as to

whether the members could not agree to cooperate in the future

to the bringing about of uniformity in procedure with the standard cell, and moved "that although the Weston cells brought here

by the several delegates are in good agreement, there is still room

for improvement with respect (a) to the cells taking up their

values quickly, (b) to holding their values constant, and (c) showing small hysteresis, and, therefore, that it is the sense of this

meeting that the four laboratories should cooperate in the future

to improve the specifications of the Weston Normal Cell, if possible, and to adopt a uniform practice." This was seconded by

Dr. Jaeger, and carried unanimously.
International Electrical Units 39

The report of the committee on weights was deferred until the

following meeting. The report of the committee on resistances was unanimously adopted.

Dr. Rosa stated that the provisional specifications for the

voltameter, which he had drawn up as requested by the committee,

and which had been submitted before the meeting, were to be

accompanied by explanatory notes, as indicated, and asked that

he be allowed to submit these later but before the final report be

prepared, and that the specifications be inserted with the state- ment that they are for the guidance and information of the

International Committee.

Mr. Smith suggested that as these questions have been so thoroughly discussed already, that these specifications be voted upon

section by section in order that the opinion of the different members on the various points might go on record. A decision on this

point was deferred until the meeting of the following day.

Dr. Rosa submitted the report on the results with four electrolytes in the small cups, and read the report of the experiments of

Dr. McDaniel on silk. It was moved by Dr. Jaeger and agreed

to, that these reports be included in the papers of the committee.

The order of business for the next meeting was next discussed.

The secretary was instructed to prepare a list of all tables,

papers, etc., and to number them consecutively.

Adjourned at 5 p. m. NINETEENTH MEETING, MAY 25, 1910

The meeting was called to order at 10.40 a. m., all members

being present, and with Dr. Wolff in the chair.

The report of the subcommittee on weights was submitted and

adopted. The chairman suggested that all reports adopted should

be subject to correction of clerical errors. As requested in the previous meeting, M. Daporte submitted

the draft of the conclusions and recommendations of the Inter- national Technical Committee, which summarized the work and

proceedings of the committee. This report contained several

proposals not already acted on by the committee, namely

:

(a) The committee decides to accept as the international ohm the mean of the units

of the Physikalisch-Technische Reichsanstalt and the National Physical Laboratory.
4-0 Report on Concrete Standards

It was agreed to amend this, as suggested by Dr. Rosa, to read

"decides to accept for the present and until mercury ohms are prepared in other laboratories the mean of the units, etc."

(6) The committee is of the opinion that new experiments are necessary before changing the specifications of the standard cell given in the appendix to the London

Conference.

(c) The committee expresses the desire that the new mercury ohm as specified by

the London Conference shall be realized as soon as possible in the various laboratories.

(d) The committee decides that no publication shall be made of the results obtained

or the details of the experiments without the permission of the International Committee.

Mr. Smith seconded this motion, and it was carried unanimously.

Dr. Jaeger suggested that the wording of the decision of the

International Committee, appointing this committee, should stand

at the head of this report, and any possible inconsistencies with

this could be modified.

Mr. Smith moved the adoption of this report, which was done

unanimously.

The report of the subcommittee to draw up the form for the

final report was submitted by Dr. Jaeger, and adopted.

The report of Mr. Smith on the connection of the present work

with former experiments was adopted.

(Dr. Rosa in the chair.)

The minutes of the seventeenth and eighteenth meetings of the

committee were next examined and accepted.

It was agreed to have the report of M. Daporte on the " conclusions and recommendations of the committee" translated and

presented in final form to the members before their departure.

The provisional specifications of the silver voltameter were next

considered. Dr. Jaeger objected to the clause which specified

that the surface of the cathode should be bright, that it had nothing to do with the precision of the measurements. The chairman

stated that if Dr. Jaeger would agree to the rest of the specifications he was willing to have this clause canceled. * Mr. Smith suggested that the specification of the current should

be amended to read "the current during a deposit is preferably

not more than i ampere."

Mr. Smith then asked that the committee vote on the different

sections of the provisional specifications section by section in
International Electrical Units 41

order to show for the guidance of the International Committee

just what are the points on which the members of this committee

are in agreement, and where they have a difference of opinion.

Dr. Jaeger believed there was not time for this. Mr. Smith

thought that it need not consume more than ten minutes. In

case any member had not made up his mind on any point he could

go on record as not voting on this point. Dr. Jaeger expressed

his opinion that these specifications touched on points that it was

not necessary to specify. Mr. Smith thought they were, on the

contrary, very general. M. Laporte had not had time to study

the specifications sufficiently, and had not arrived at an opinion on all the points. He preferred, therefore, not to express an

opinion, even provisionally, before having made up his mind with

regard to the whole.

It was finally agreed that Dr. Rosa and Mr. Smith should go on

record as adopting provisionally these provisional specifications,

that Dr. Jaeger did not agree with some of the conclusions, it being his opinion that a number of points in the proposal would

indicate that the past experiments on the voltameter at the

Physikalisch-Technische Reichsanstalt, as well as the work here,

would have to be considered of minor value, and that M. Laporte

preferred to defer expressing his opinion until he had reached a more definite opinion on some of the points.

Dr. Wolff next submitted two reports, one on the resistance

intercomparisons, and the other on the standard cells. These

were accepted after revising on page 92 of the report on resist- ances, the statement regarding the National Physical Laboratory

standard of resistance.

Dr. S. W. Stratton, Director of the Bureau of Standards, who

had opened the meetings of the committee on April 4, was now

informed that the committee had completed its deliberations and

was prepared to report to him upon its work. Upon his appear- ance with the committee, the chairman, speaking for the committee, said that the members of the committee had all taken a

deep interest in the work, and had endeavored to come to an agreement on as many of the questions at issue as possible. Some of

the questions were, however, difficult to settle in a short time,
42 Report on Concrete Standards

and many points of importance had been deferred for further

consideration. It was the sense of all the members of the committee that further experimental work was necessary, and that it should be carried out during the next ten months, if possible, so that by April i, 191 1, agreement could be reached concerning the

completion of the specifications of the silver voltameter and the

standard cell. The chairman added that if it appeared that the

committee had not made as much progress as was expected, it should be remembered that much time is often required to clear

up seemingly minor difficulties. Dr. Stratton then expressed the hope that the work of the

committee would not be regarded as complete until the members

could come to a definite agreement on the principal points. He

stated that he would be satisfied with the final decision when it shall have been reached, and, although he had hoped that the

report could be finished before the departure of the delegates, he

thought that, considering the largeness of the subject, it was

hardly to 'have been expected that this should be accomplished.

In expressing his appreciation of the work of the committee he

dwelt upon the urgent need of uniformity in all units, and hoped

that this meeting would serve as a precedent for others in the

future for bringing about this desired end. In conclusion, he

thanked the delegates for their patience in putting up with all inconveniences or insufficiencies of the equipment, which in the

nature of things he supposed had not been absent.

Dr. Jaeger expressed his appreciation of the kindly reception

tendered the delegates on their arrival in New York and elsewhere.

He thought that on the whole the committee should be satisfied

with the results and believed that after calmly looking over the

results rather than the differences, the reasons for satisfaction

would be better appreciated. He had found it a great advantage

to become acquainted personally with other workers in the same

line as his own, and to exchange views on these subjects.

Mr. Smith wished to thank Prof. Stratton and all members of

the Bureau for the kindnesses accorded to the committee, and was

very glad to have had the opportunity of being here.

M. Laporte, in concurring with what had already been said,

wished particularly to congratulate Prof. Stratton on having inaugurated this, the first meeting of its kind.
International Electrical Units 43

Mr. Smith wished also to move a vote of thanks to Dr. Rosa for

having acted as chairman, and M. Laporte asked that this vote

be extended to include Dr. Burgess and Dr. Grover for their con- nection with the work.

Dr. Rosa, in acknowledgment, expressed the hope that the work

begun may go on as successfully in the future.

The meeting was declared adjourned by Prof. Stratton at 12.50 p. m.

rV. APPENDIXES

APPENDIX A. REPORTS, PAPERS, AND SUGGESTIONS TENDERED TO THE

COMMITTEE BY THE DELEGATES AT THE BEGINNING OF THE WORK

1 . First report of the Bureau of Standards on prelimin ary investigations of the silver voltameter. (See p. 44.)

2. Second report of the Bureau of Standards on the silver

voltameter.

3. Third report on the work of the Bureau of Standards on the

silver voltameter.

4. Suggestions of the Bureau of Standards respecting cooperative work in Washington. (See p. 55.)

5. Notes on the Weston Normal Cell (from Bureau of Standards)

.

(See p. 59.)

6. Instructions for the German delegate taking part in the joint

experiments at Washington, April, 19 10. (See p. 61.)

7. Report of experiments on the silver voltameter (from Physikalisch-Technische Reichsanstalt) . (See p. 63.)

8. The last intercomparison of the new cadmium standard cells of the Physikalisch-Technische Reichsanstalt, etc. (See p. 65.)

9. Report of work on standard cells and the silver voltameter

at the National Physical Laboratory. (See p. 67.)

10. Suggestions of Mr. F. E. Smith for the experimental work to

be done at Washington. (See p. 78.)

11. Recherches effectues au Laboratoire Central d'jfilectricite sur 1' equivalent electrochimique de l'argent par MM. Laporte et P. de la Gorce (Bull. Soc. Int. Elect., vol. x, p. 157, 1910).

12. Recherches faits au Laboratoire Central d'Fylectricite sur

l'etalon de resistance et l'etalon de force electromotrice par M. R.

Jouaust (Bull. Soc. Int. Elect., vol. x, p. 187, 1910).

13. Suggestions of M. F. Laporte for the experimental work to be done at Washington. (See p. 79.)
44 Report on Concrete Standards

Nine of the thirteen papers are reproduced here in full. Of the

other four, Nos. 2 and 3 (second and third reports of the Bureau

of Standards) are to be included substantially as presented in a

paper shortly to be published in the Bulletin of the Bureau of

Standards as part of the researches of the Bureau on the silver

voltameter. The other two, Nos. 11 and 12, are researches by the

Laboratoire Central d'Electricite which have been published in

full in the Bulletin de la Societe Internationale des Jjlectriciens. It is therefore unnecessary to reprint them here.

The numbering of the tables and footnotes in these papers has

been left as when the papers were originally presented and are

therefore not consecutive with those in the main body of the report.

1. FIRST REPORT OF THE BUREAU OF STANDARDS ON PRELIMINARY INVESTIGATIONS

OF THE SILVER VOLTAMETER.

Introduction.—The International Electrical Conference, which

met in London in October, 1908, adopted the following definition

of the International Ampere

:

The International Ampere is the unvarying electric current which, when passed

through a solution of nitrate of silver in water, in accordance with the Specification B,

attached to these resolutions, deposits silver at the rate of 0.00111800 of a gram per

second. Specification B as adopted by the conference is as follows

:

Specification relating to the Deposition of Silver. —The electrolyte should consist of a

solution of from 15 to 20 parts by weight of silver nitrate in 100 parts of distilled water. The solution may only be used once, and only for so long that not more than 30 per

cent of the silver in the solution is deposited.

The anode shall be of silver, and the cathode of platinum. The current density at the anode shall not exceed one-fifth ampere per square centimeter, and at the cathode

one-fiftieth ampere per square centimeter. Not less than 100 cubic centimeters of electrolyte shall be used in a voltameter. Care must be taken that no particles which may become mechanically detached

from the anode shall reach the cathode. Before weighing, any traces of solution adhering to the cathode must be removed

and the cathode dried. The means which are to be employed to insure "that no particles which may become mechanically detached from the anode

shall reach the cathode" were not specified. These and other

particulars of the preparation of the materials used in the silver

voltameter, as well as particulars of the manipulation of the voltameter, were left to be agreed upon and formulated by the
International Electrical Units 45

International Scientific Committee which was appointed by the

conference.

To aid in coming to such an agreement, it has been arranged to

have a joint investigation by representatives of some of the

National Standardizing Laboratories, to take place in the laboratories of the Bureau of Standards, Washington, beginning April i,

1 910. As a preparation for such investigation we have been

carrying out in the Bureau of Standards a careful study of different

forms of voltameters, and we present herewith a brief report on

one phase of this research. We invite a critical examination of our observations and conclusions, and after such time as is required

for any necessary verification, an expression of opinion respecting our proposal (p. 53).

Apparatus Employed and Procedure Followed.—1. In our work

on the silver voltameter, we have used ten platinum cups and

two gold cups. Four platinum cups were 10 cm diameter by

7 cm deep ; four were 8 cm diameter by 5 cm deep ; two platinum

cups and two gold cups were 6 cm diameter and 7 cm deep. Their

capacities were 350 cc, 175 cc, and 125 cc, respectively. The four

large cups were adjusted to the same weight, 80.277 S> three were

used as cathodes, and one was reserved as a tare. Similarly, one of

the four medium-sized cups (each weighing 55.098 g) was used

as a tare. The small cups weighed 39.113 g and were counterpoised by platinum. Generally the deposit was timed to weigh

about 4.100 g, and gold-plated silver weights of 4.100 g were used

as counterpoises in the weighing, the small difference being made

up with platinum weights or riders. In most cases the cups

after being weighed against the tare were also balanced against each

other as a check.

2. Three balances were employed. One by Rueprecht, capacity 200 g; one by Oertling, capacity 100 g, similar to the one used

by Smith at the National Physical Laboratory; one by Stuckrath,

capacity 200 g, similar to the one used by Jaeger and von Steinwehr

at the Physikahsch-Technische Reichsanstalt.

The large cups were weighed on the Oertling balance, the medium

cups on the Rueprecht, the small ones on the Stuckrath. On the

latter, the cups are interchanged and the riders manipulated at a

distance by means of rods and levers.
46 Report on Concrete Standards

3. The weighings were made in a balance room built in the

basement especially for the purpose. One-half of this basement

room, which has massive concrete walls, was lined on sides and

ceiling with hollow tile, an additional air space being left between

the tile and the concrete wall and the tile plastered inside. A

tile partition separated the balance room from the other end of

the basement room, in the partition being double doors (with

vestibule between) and two double windows.

Weighings were made from outside the balance room by means

of telescopes extending through the windows. The cups were

placed on the balance pans (often using all three balances at once)

and allowed to swing for half an hour before taking readings.

The temperature and humidity of the atmosphere in the bal- ance room were very constant, changing but little in 24 hours;

they were recorded on a thermograph and hydrograph. Means

were provided for reducing the humidity when necessary, but

this was seldom required. The precision of the weighings is very

satisfactory.

4. The voltameters were mounted upon substantial supports,

each under a bell jar, and ample electrical insulation insured.

The electrolyte was always carefully prepared (15 g of AgN03 to 85

g of water) , and handled in Jena glass vessels. A set of numbered

beakers was reserved for each voltameter with which to handle

the solution and perform the washings of the cups at the end of

the runs. Everything was arranged systematically to avoid confusion or accident.

5. The current was derived from a storage battery of 120 volts

and 25 amperes (normal charging current) capacity. The current was measured by means of Weston normal cells, standard resist- ances, and potentiometers. In some cases two observers, each

with a complete equipment, observed at once, one keeping the

current as constant as possible and the other observing the slight

fluctuations of the current. The Weston cells were in an oil bath, the temperature being

regulated by a thermostat.

The time was measured by means of a chronograph and a

Riefler standard clock. The current has usually been either one ampere for one hour, or one-half an ampere for two hours.
International Electrical Units 47

6. The deposits have been examined by means of a microscope,

and in some cases qualitative runs have been made in a small

voltameter in the field of a microscope. Many qualitative runs have also been made in smaller platinum cups, using the same

current density as in large platinum cups. Microphotographs

have been made of many deposits, and samples of the deposits

prepared as slides suitable for microscopic examination.

7. The silver nitrate employed has been purchased as pure from

the J. T. Baker Chemical Company, Phillipsburg, N. J., and the

Gold- und Silber-Scheide-Anstalt, Frankfurt; some of it has been

recrystallized, but more has been used as purchased. The anodes

have been of pure silver, generally electrolytically deposited, as described by Smith.

8. The washing, drying, and weighing have been done with the

utmost care, the drying being in an electric oven at 150 C. Ample chemical facilities have been available for the work.

The Observations.—9. We have made many quantitative determinations, as well as numerous qualitative runs, under very many

conditions. In our present report we do not wish to discuss the

actual values found, more than to say that with the Richards and

Kohlrausch forms we nearly agree with the values found by

Jaeger and Von Steinwehr when using the porous cup (being a few

parts in 100000 less), and hence still more under Smith's value,

which is about 1 2 parts in 100 000 larger than the latter. With the

Rayleigh form we get widely different results, according to the procedure followed, always getting a heavier deposit than with the

others, the larger differences and the greater striations being

associated together. If we always follow exactly the same procedure, we get substantially the same results. But, having become

convinced that any use of filter paper in a voltameter is very undesirable, we deem it necessary, in view of the considerable use of

the Rayleigh voltameter and the strong preference for it at the

National Physical Laboratory, to give very fully the grounds for our objections.

10. Remembering that the heavier deposit found by various

investigators in the Rayleigh voltameter, as compared with the

Richards, had been attributed to the imperfect separation by the

filter paper of the heavy anode liquid from the cathode solution,

22451 —12 4
48 Report on Concrete Standards

we tried the effect of using two, or even three, thicknesses of filter paper instead of one. Instead of agreeing better with the result

obtained with the porous cup, the deposits were still heavier, two

sheets of filter paper giving an excess about double, and three an

excess about treble that due to one sheet. That is, the excess in

weight was proportional to the quantity of filter paper, and was

therefore not due to the filter paper being an imperfect filtering

medium. This result also followed when the finest grades of

filter paper were used, the excess weight above the normal weight

in a Richards voltameter being practically the same for all filter paper tried if the weight of filter paper submerged in the electrolyte was the same. The excess weight J of silver, with a rela- tively large amount of filter paper, may be as much as o.i per

cent.

1 1 . Striations are more marked as the quantity of filter paper is greater, so that one can predict a heavy deposit (large value of 4)

by its appearance. It is not necessary to use filter paper during

the run to obtain striations and an excess of weight. If a sheet of

filter paper is allowed to stand for some time in the solution of

silver nitrate before putting the latter into the voltameter, the

deposit will be striated and too heavy, even though no filter paper was present during the run. If several sheets are used, and it stands several hours, the deposit is very strongly striated, and is large. If the filter paper is allowed to stand in distilled water for some time, and the latter is then poured off and used in preparing

the electrolyte, the deposit is striated and the weight excessive,

the filter paper itself not coming into contact with the silver

nitrate. The conductivity of pure distilled water is immediately

increased when filter paper is added to it. Filtering silver nitrate solution through filter paper will con- taminate it, and enough to be very evident both in the appearance

and the weight of the deposit if the solution is hot, even though

the quantity of filter paper is small.

These remarks apply to all grades of filter paper, including the

finest of quantitative papers. Heavy papers produce a greater

effect because of their greater mass.

12. If both porous cup and filter paper are used in the same

voltameter, the deposit is striated and heavy if the filter paper sur-
International Electrical Units 49

rounds the porous cup. If the filter paper is inside the porous cup,

the deposit is normal in appearance and weight, provided the

external electrolyte be pure and not have been brought into contact with filter paper.

13. Cotton, linen, and silk textiles used as separators instead

of filter paper, produce similar effects, but cotton less than linen.

Rag paper, blotting paper, wood-fiber paper and pine wood all produce the same effects, the last named giving greatly exaggerated

effects. Glucose, gelatine, and some other organic substances

produce striations. Cane sugar and starch do not, except after

long contact with the electrolyte.

14. Striations are closely spaced with large current density, and

widely spaced with small current density. When fine and not

very pronounced, they disappear, if the current runs long enough;

that is, where the silver deposit is relatively thick. For this reason an impure electrolyte may give a nonstriated deposit. In a 7 g

deposit the striations will be less marked than in a 4 g deposit for

the same reason.

15. But although the appearance to the eye of the deposit may

change with the depth of deposit, the appearance of the deposit

under the microscope indicates whether it has come down from an

electrolyte containing filter paper, or the products of filter paper

or other organic impurity, or whether it has come down from a pure

electrolyte of AgN03 and water, uncontaminated by such foreign

substances. In the first case the deposit is noncrystalline or imperfectly crystalline, according to the quantity of the impurity.

It may resemble molten metal that has been dropped on a cold

plate and spattered, or lava having a rough, irregular surface, and

the deposit more or less massed together; or it may be in needleshaped crystals, or imperfectly crystalline when the impurity is slight. The color may be grayish or tarnished when considerable

quantities of impurities are present. The pure electrolyte in a Richards or Kohlrausch voltameter gives a beautiful crystalline

deposit, the crystals having well-defined planes and angles, and

looking much like glass or diamonds under the microscope, and, by

reflected light, are generally without a metallic luster. Sometimes,

however, there is a metallic luster, with some planes and angles,
5o Report on Concrete Standards

and the appearance is more like nuggets of metal. In the larger

cups (with one-half ampere for two hours) the crystals are well

separated, the clean platinum surface showing between them, and

they are approximately equiaxial. In the smallest cups, where

the quantity of silver is twice as much per unit of area, the crystals are elongated, but otherwise similar.

1 6. We discover no difference in size or appearance between the

crystals given in the Richards and Kohlrausch voltameters, nor

in those deposited on gold from those on platinum for the same

current density and quantity of silver per unit of area. The

presence of a small quantity of acid reduces the size of the crystals

;

that is, the deposit starts at a larger number of points, and therefore there is a larger number of crystals of a smaller size. The

presence of a small quantity of organic matter affects the appear- ance of the crystals, and in larger quantity destroys the crystalline

character entirely.

17. The porous cups may be so thoroughly cleansed that they can stand for hours in distilled water without greatly increasing

its conductivity. Filter paper increases it instantly, and the

increase goes on gradually with time.

18. When a large quantity of filter paper is allowed to stand some hours in a solution of silver nitrate before it is placed in the

voltameter, the deposit on the bottom of the cup grows up in stiff rods like trees. If a hot solution is filtered through filter paper,

the deposit is wooly. In some cases of striated deposit, the striae are tenacious and the deposit comes off in strips. Under the

microscope the silver looks something like slag.

19. Richards, Smith, and others have attributed the striae to

the heavy anode liquid, in connection with the upward currents

of weak electrolyte along the surface of the cathode. That the

direction of the striae is determined by these convection currents

of the electrolyte seems demonstrated by the inclination of their

direction produced by rotation, and by the further fact that they

disappear when the silver is deposited on the under surface of a

horizontal cathode plate. But, we do not find reasons for thinking that the striae are produced by the heavy anode liquid. Indeed,

if the filter paper around the anode be removed (all other cir- cumstances remaining the same) the strice disappear. The heavy
International Electrical Units 5i

anode liquid would then flow down as before, or even more freely.

Moreover, we always obtain striae when filter paper is used provided the quantity of silver deposited is not great enough to cover them up, even though percautions are taken to keep the heavy

anode liquid from the cathode. With the small current density

the striae are farther apart and easily seen; with larger current

density they are nearer together and not so conspicuous. Also,

when very little filter paper is used, they are less conspicuous

and the deposit might be considered nonstriated even if the quantity of silver is not large. In short, we believe striae are always

produced by filter paper; and, according to quantity of filter paper, current density, and quantity of silver deposited per square

centimeter, they are more or less distinct, between the extreme

limits of heavy ridges and barely perceptible striae. 20. The reason why striations are never seen in the Richards

and Kohlrausch voltameters (when pure electrolyte is employed)

is not because the heavy anode liquid is kept from the cathode,

but merely because the organic impurity due to the filter paper is absent. If filter paper has been employed in the preparation of

the silver nitrate, however, striations may appear in these voltameters, unless the salt has subsequently been sufficiently purified

by recrystallization. Silk, cotton, linen, and all organic matter,

as well as filter paper, should therefore be scrupulously avoided.

Glucose, furfuraldehyde, formaldehyde, and many similar strong

reducing agents when added in minute quantities to a pure solution

of silver nitrate produce striations and render the deposit less crystalline. Milder reducing agents do not produce these results. Since furfuraldehyde is always produced in greater or less amounts

by the hydrolysis (often by water alone) of all kinds of vegetable

and animal textile fibers, it seems probable that this substance,

partially at least, accounts for the observed effects produced by

filter paper, silk, etc. This possibility is being investigated and

will be reported upon later. That the action of filter paper is due to the products formed

by the action of water or electrolyte alone upon the cellulose

fibers, and not to the presence of soluble impurities in the filter paper, is shown by the fact that filter paper which has been repeatedly extracted with hot water is still capable of producing strong
52 Report on Concrete Standards

striations. In a particular case, filter paper which had been

extracted with water for six hours in a Soxhlet apparatus was

immersed in the silver nitrate electrolyte for ten minutes, and

the liquid filtered off through purified asbestos and electrolyzed

under usual conditions. Very pronounced striations were formed.

21. With relatively large anodes of pure silver, the "heavy

anode liquid" is not appreciably abnormal. We have used the

solution saved from the inside of the porous cups on previous

runs, and obtained a deposit normal both in appearance and

weight. The used solution from the cathode space of a Richards

voltameter also, as might be expected, gives normal deposits.

With the Rayleigh voltameter, used solutions generally give

heavy deposits. We do not mean to say that used solutions

from the Richards voltameter give absolutely normal deposits, as we have not made runs enough to establish that fact. But

as far as we have tried them, they give substantially normal

deposits; that is, within a very few parts in iooooo. We think

the role of the "heavy anode liquid " has been greatly exaggerated.

On the other hand, the evil effects of organic matter have not

been fully appreciated.

22. It was pointed out by the Reichsanstalt in 1902 that filter paper reacted on silver nitrate, and might be a source of error in

the voltameter. Others have warned against it without having

investigated it. F. E. Smith, in his elaborate investigation of the

subject recently published, repeatedly cautions us against the evil effect of filter paper. He found it increased the weight of the

deposit when the silver nitrate was filtered hot, and when there was a large quantity of filter paper. He does not say that a

single sheet used in a large voltameter produces no effect, but only

claims that in the voltameter as he used it, the effect was negligible,

and the voltameter was accurately reproducible. Although

Smith's work was extremely well done, we doubt whether the

effect of filter paper in his work was really entirely negligible.

23. We think that we have shown that the effect of filter paper

is more serious than has been supposed, and that to permit its use

in any degree is unwise. Because a voltameter is accurately

reproducible when used with a large cup and a large quantity of

electrolyte, and a heavy deposit with a single sheet of a particular
International Electrical Units 53

kind of filter paper, is not sufficient. A source of contamination

so serious should be utterly avoided, and if possible a voltameter

should be specified which is consistent with itself throughout a

considerable range of dimensions and deposits.

24. We have recently employed a new form of voltameter in

which an asbestos mat in a perforated glazed cup is used instead

of the filter paper or porous cup. The purified asbestos is renewed

each time, and of course the glazed porcelain is easily cleaned.

This avoids the troublesome cleaning of the porous cups and perfectly separates the anode chamber from the cathode, without any

reaction whatever on the electrolyte. In practice this form of

voltameter is very satisfactory, provided there are very many fine

holes in the glazed porcelain cups, so that the resistance is not

excessive. The deposit has exactly the same appearance as in the

Richards and Kohlrausch forms. We shall give more details of

this form after we have had a larger experience with it. Proposals and Suggestions of the Bureau of Standards.—1 . That

neither filter paper nor any other organic substance or impurity

be used in the silver voltameter, and that the use of filter paper

be entirely avoided in the preparation of the silver nitrate salt and

the solution of the salt.

2. That when a porous cup is used it should be a thin finegrained cup such as made by the Konigliche Porzellan Manufaktur, Berlin, and the method employed of freeing it from acid

or alkali should be controlled by noting whether the washed cup

increases the conductivity of very pure distilled water on standing

in it for some time.

3. That when a porous cup is not used to separate the anode and

cathode, but a glass cup is used after the manner of Kohlrausch,

that the anode should have as large an area as practicable, and be

placed down in the bottom of the cup, so that the current flows

up and over the edge of the cup. It is also well to have a glass

guard ring in the surface of the solution to prevent particles

brought up from the. anode by bubbles of gas floating away and

dropping down into the cathode deposit. The cup and guard

ring should be so mounted that at the end of the run they and

the anode can all be lifted out together.
54 Report on Concrete Standards

4. That whatever form of voltameter be used, the deposit

should never be considered normal unless free from striations, and

appearing under the microscope as a mass of separate crystals, some of which have well-marked planes and angles. These crystals appear in the microscope more like glass or diamonds than a

metal, except that in some illuminations they may have a metallic

luster. Their appearance is a valuable check on the purity of

the electrolyte.

5. That our observations respecting the effects of filter paper

and other organic substances (cotton, linen, silk, wood, etc.) be

verified by the other laboratories.

6. That our observations concerning the appearance of the

deposit when examined under a low-power microscope and the

criterion which it offers respecting the presence of impurities be

verified.

7. That our experience with porous cups be checked, and any

laboratory having a different experience should report to us, and

if possible exchange cups with us, that we may aid in locating

the cause of the difference.

8. That very careful comparisons be made between large cups

and small cups, the electrolyte and the separator being the same,

to see if a difference in the weight of deposit is found, and if so, to try to determine the reason.

9. That careful comparison be made between the Richards and

Kohlrausch forms of voltameters (the electrolyte and size of cups

being the same) to see whether any difference in weight occurs.

10. That the electrolyte employed in these investigations be

prepared from the purest of silver nitrate and very pure distilled

water, and that if any solution be used more than once, the

record shall indicate its past history very carefully.

1 1 . That in the use of the Richards form of voltameter special

attention be given to determining whether there is any difference

between a new porous cup and one that has been used before,

and in the use of the Kohlrausch form attention be directed to

devising a form of glass cup and mounting for the same that is convenient and satisfactory in practice.

12. Since the side reactions at the anode, and the size of crystals and adherence of deposit on the cathode, depend on the
International Electrical Units 55

current density and total mass of silver dissolved, or deposited

per square centimeter, respectively, that attention be given in the

investigation to ascertain what are the best values of these quantities for work of highest precision. The specifications adopted

in London only set upper limits.

4. SUGGESTIONS OF THE BUREAU OF STANDARDS RESPECTING COOPERATIVE WORK

IN WASHINGTON ON STANDARD CELLS A new room has been especially fitted up for the cell comparisons, and ample space will be provided in the automatically

regulated petroleum tanks for any number of cells which the representative of your institution may desire to bring here. In view

of our experience with sealing wax and other sealing compounds,

it is, however, urgently recommended that all cells be hermetically

sealed. We have besides found this far simpler than the use of

wax seals. To make our arrangements complete, and to avoid delay in

beginning the comparisons, we would be pleased to have you indicate in advance the approximate number of cells you propose to

bring, and also their dimensions, diameter of limbs, distance

between limbs, etc., so that we can have prepared any special

mountings which might be necessary.

The necessary facilities will also be provided for setting up cells at the Bureau, and for such chemical work as may be found

desirable.

With reference to the materials, we understand that you will

bring with you sufficient quantities of all the chemicals employed

in setting up your cells, so that if necessary check cells may be set. up at the Bureau to determine the cause of any differences which

might be found on comparison of the cells set up at the different

laboratories. On our part, we shall have on hand an ample supply

of all the materials, so that it will be possible to undertake any further investigations which might suggest themselves after conferring with each other.

With reference to the details in the specifications for the Weston

cell, it may be advisable for each laboratory to indicate, after

looking over the preliminary specifications submitted to the London Conference, any special points which might seem to call for

further investigation.
56 Report on Concrete Standards

Our own views may be put as follows

:

A. Mercury.—In regard to the mercury, it will be readily

agreed that it would be well to specify a preliminary treatment for

the removal of accidental impurities, which might have a large

influence on the electromotive force, with a subsequent distilla- tion in a vacuum still, or under reduced pressure in a Hulett still. In the opinion of the Bureau, the most effective method for the

preliminary treatment is method b, page 4, Appendix to Report

of London Conference. If facilities are available for the electrolytic

preparation of mercurous sulphate, the same apparatus, with

slight modification, can be used, making the method the simplest

as well. This method has been subjected to a rigorous investigation at the Bureau, where it has been found that mercury, even

contaminated with large quantities of zinc and cadmium, when

subjected to the anode purification gave the same electromotive

force to within several microvolts as mercury purified by Hulett's

method. The differences were so small that they may have been

due to slight differences in manipulation in setting up the cells employed to test the electromotive properties.

This result is readily accounted for since the impurities having a higher electrolytic solution tension than mercury will leave the

mercury until their solution pressure is diminished by dilution to

the solution tension of mercury. In addition, it appears from some recent work of Hulett's on the electromotive force of dilute

amalgams that pure mercury in contact with cadmium sulphate

solution reacts with the latter to form an extremely dilute cadmium amalgam, an equivalent amount of mercury going into solution in accordance with the principle of chemical equilibrium.

As a special precaution it is recommended that mercury thus

purified be subjected to distillation in an ordinary vacuum still, or by Hulett's method, at greatly diminished pressure with a cur- rent of air passing through the mercury, by which bumping is practically eliminated. The additional function of the air in

Hulett's method, of oxidizing impurities vaporized with the mercury, is no longer of importance since all the oxidizable impurities

have practically been removed.

b. Mercurous Sulphate.—It is evident that the method of preparation should be selected which gives the best results as judged
International Electrical Units 57

from the rapidity with which the cells attain"their normal values,

their constancy under the most favorable conditions (when maintained at constant temperature) as well as the rapidity with which

they adjust themselves to temperature changes.

In the opinion of the Bureau, it is desirable to have mercury

distributed throughout the paste, and this can not be satisfactorily accomplished with white samples, without grinding them,

by which a "size of grain" effect would be introduced. The best

way, therefore, of introducing it is in its manufacture. Samples

prepared by methods a, c, and d of the preliminary specifications,

all contain finely divided mercury, so that by specifying one of

these methods for the preparation of the mercurous sulphate, one

step, the mixing of the mercury in the paste, can be omitted.

c. Cadmium Sulphate.—Apparently the preliminary treatment

of the commercial CdS04 for the removal of iron by heating the

solution to which an excess of basic cadmium sulphatea and a

small quantity of H,02 have been added, filtering, precipitating

by evaporating the water and finally slowly recrystallizing at room

temperature from a solution either neutral or very slightly acid,

will give a product answering all purposes.

d. Cadmium Amalgam.—It will be necessary to specify either a method for the preparation of pure metallic cadmium, or a method

for the preparation of cadmium amalgam by electrolysis of a cadmium sulphate solution made from previously recrystallized CdS04

. In the opinion of the Bureau, it would be simplest to specify the

second method, as the preparation of pure cadmium is a much

more difficult operation.

With regard to the composition of the amalgam, no difficulty

should be found in coming to an agreement, since the two phases

persist over a relatively wide range of composition and temperature. In this connection, the question is raised as to whether it might

not be regarded as a proper function for the national laboratories

a The basic cadmium sulphate is prepared as follows: To a concentrated solution of cadmium sulphate add enough strong ammonia to dissolve the precipitate which is first formed. Filter into a large volume of distilled water, filter off the precipitated basic sulphate and wash thoroughly with distilled water. Dry in an air bath and finally ignite, with frequent stirring, in a porcelain dish over a Bunsen burner to remove ammonium salts. The product is probably a mixture of oxide and sulphate, or basic sulphate. It is better to use this product than to attempt to prepare cadmium oxide by precipitation with fixed alkali, on account

of the difficulty of completely removing the latter.
58 Report on Concrete Standards

to furnish, to investigators and others, specially prepared or

purified materials for use in standard cells. It appears to us

that in this way the highest accuracy of reproduction would be

obtained. Such materials, prepared at the different institutions,

could be interchanged, and cells set up at each institution would

bring to light any electromotive differences which might exist

before their distribution is undertaken.

e. The Paste.—Especial attention is directed to the desirability of further investigating the cause of abnormal values sometimes found. In the work done at the Bureau on the temperature

coefficient of the Weston cell, it was found that in most cases cells exhibiting abnormal initial values, as well as those falling to abnormally low values, showed considerable hysteresis when subjected to temperature changes. In some cases this was undoubtedly due to an improper mixture of the ingredients of the paste.

This subject is regarded as of the greatest importance in the

specifications, and will receive further attention at this laboratory.

In view of this, the Bureau desires to propose that all cells used

for reference work be tested for hysteresis by transferring them

from a bath maintained at 20 or 25 to another 5 or io° lower,

in which they should be kept at least 48 hours and then raised to the original temperature. Measurements should be made soon

after the temperature changes, and at intervals, to determine the

magnitude of the hysteresis, and any cells which do not come to

normal values, within certain limits to be agreed upon and stated

in the final specifications, should be rejected as untrustworthy.

Some success has been found with mercurous sulphate, prepared

in acid solution by several different methods, and washed with

absolute alcohol and anhydrous ether. It is hoped that in this

way it may be possible to obtain dried mercurous sulphate which

can be kept without suffering change, and which can be used

without further treatment in making up the paste.

It is suggested that cells set up in connection with the international cooperative work be tested to determine whether they

exhibit any appreciable hysteresis. In the temperature coefficient

work it was found that much more marked hysteresis was exhibited on lowering the temperature than on raising it.
International Electrical Units 59

With regard to the setting up of cells, we wish to inquire whether

any new cells have been set up and, if so, whether we could obtain a preliminary report of their behavior and their values in terms of

the Bureau cells which may be in your possession. On our part

we will shortly be prepared to set up a considerable number of cells in strict accordance with any special directions you may desire to submit. We would be greatly obliged for a sample of mercurous

sulphate made by you, and in return we are sending you a sample

of electrolytic mercurous sulphate recently made here. In this

connection we would point out that in setting up cells, a better

estimation of the accuracy of reproduction will be obtained if a

separate lot of paste be made up for each cell or for, at most, two

cells at a time.

5. NOTES ON THE WESTON NORMAL CELL

From the Bureau of Standards OUTLINE OF MATTERS TO BE SUBMITTED FOR DISCUSSION

A. Revision of definition of Weston Normal Cell. B. Purification and preparation of materials.

(a) Mercury.

(b) Mercurous sulphate.

(c) Cadmium sulphate.

(d) Cadmium sulphate solution.

(e) Cadmium amalgam; cadmium; composition of amalgam.

C. Setting up the cell. (a) Washing mercurous sulphate; use of material already washed and dried.

(6) Composition of paste ; Hg2 S04 ; CdS04

; solution: mercury in paste.

(c) Amalgamation of platinum terminals.

(d) Purity of platinum.

(e) Sealing. D. Hysteresis test. E. Proposal for distribution of purified materials for standard cells by National Laboratories under the auspices of the International Scientific Committee.

F. Value to be adopted for Weston Normal Cell. G. Should value be changed to correspond to voltameter measurements made from

time to time if apparent changes are within limits of accuracy with which the Weston Normal Cell can be produced. H. Best method of maintaining international agreement of values of Weston cell. DETAILED

A. Schedule C should be replaced by a definition of the Weston Normal Cell and

separate specifications and notes to the specifications. B. It is preferable to specify a single method unless a number of different methods

have been shown to lead to identical results.
6o Report on Concrete Standards

Methods should be selected which give minimum hysteresis and prompt attain- ment of normal values.

(a) Mercury

Preliminary purification. Alternative methods may be indicated. Bureau of Standards recom- mends anode purification. Final purification. Either in vacuum still or Hulett still. (b) Mercurous sulphate.

Electrolytic method advocated on account of uniformity of product,

ease of specification, absence of other materials than sulphuric acid, water, and mercury (with exception of platinum terminals and

glass).

(c) Cadmium sulphate.

Purification by method in use here recommended.

(d) Preferable to have cadmium sulphate solution saturated to avoid possibility of leaching the CdS04 +8/3H2 crystals out of the paste.

(e) Preparation of metallic cadmium advocated if distribution by National

Laboratories is decided upon. Amalgam to be prepared by heating

together appropriate quantities of the ingredients.

Otherwise, electrolytic method of preparing the amalgam is recommended.

Compositions may be changed to 10 per cent. Temperature limits of two- phase amalgam to be specified. C. (a) Washing mercurous sulphate.

Washing with acid, alcohol, and ether, and drying in vacuo, and pres- ervation in vacuo, recommended if distribution is to be undertaken by

National Laboratories. Otherwise, washing with saturated CdS04 solution is simplest to specify.

First method would involve specifications for purification of the alcohol and ether.

(6) Composition of paste. Hg2SO : CdS04 +8/3H2 0=4 : i by volume. CdS04 +8/3H,0 to be very finely ground.

Sufficient CdS04 solution to make paste flow easily through filling tube.

(c) Amalgamation of platinum terminals recommended as a special precaution.

(d) Purest Heraeus platinum might be specified.

(e) Hermetical sealing recommended.

D. Hysteresis. Test should be made to determine amount of hysteresis of each cell. All

cells having abnormal hysteresis should be rejected. E. Strongly advocated by Bureau of Standards.

F. Must be decided after voltameter measurements.

G. Bureau would advocate retaining same value under the conditions stated in same way as has been done at the Reichsanstalt. H. By periodic interchange of materials and cells and setting up new cells. Each

laboratory to base its results on the mean value of a considerable number of

cells. Values to be assigned to mean from results of international intercomparisons.
International Electrical Units 61

6. INSTRUCTIONS FOR THE GERMAN DELEGATE TAKING PART IN THE JOINT EXPER- IMENTS IN WASHINGTON, APRIL, 1910

[Translation.] Principal Aim of the Work.—At the London Conference in

1908 the value 1.0184 volts at 2o°- was provisionally adopted for

the electromotive force of the Weston Standard Cell, but up to

this time has been adopted in England only. Furthermore, a

decision of the International Committee (circular of June 1, 1909)

states

:

It appears advantageous that a definite value for the Weston Standard Cell be

adopted in the different countries simultaneously. For this purpose the values for the cell obtained by different observers from measurements with the silver voltameter should be in such agreement that the deviations of the different values from their mean

value are less than o.oooi volt. It was decided to postpone the adoption of a definite value for the standard cell until in the opinion of the committee such an accuracy

has been obtained.

It is therefore to be regarded as the primary purpose of the

projected joint work at Washington to lay the foundation for

such a decision of the committee, in order that, by international

acceptance of the value found, the long-striven-for uniformity

in electrical units may be attained as soon as possible.

Plan of the Work.—(a) In order to fix with all the certainty

possible the standard to which the measurements are referred, a more frequent comparison of the standards belonging to the dif- ferent countries—resistances, standard cells, weights, etc.-—will

have to be made. It will be advantageous that a comparison of

standard cells shall take place on every convenient occasion; the

comparison of the other standards is necessary less frequently.

The measurements will themselves show best upon what, in this

connection, the greatest attention is to be laid.

(b) With the principal measurements it will be best so to carry

out the work that, first of all, a sufficient number of measurements

shall be undertaken in which all the cups shall be connected in

series and in which the cup of each delegate shall be set up and

manipulated according to the manner customary in his country.

The value of the current, which flows through all the cups in com- mon, and likewise the quantity of silver to be deposited must be

agreed upon by the delegates. It appears to be unnecessary to

hold the current by regulation at a constant value in the experi-
62 Report on Concrete Standards

ments. It is sufficient if it is measured at suitable intervals.

The measurements on the silver voltameter give simultaneously

with the absolute values of the standard cell a relative comparison

of the different silver voltameter methods.

(c) Special questions respecting the silver voltameter, such as, for

example, the influence of the filter paper, weight of cup, etc., will best

not be included in these measurements, but be reserved for further

purely relative measurements. How far these shall be extended can not previously be estimated and must be left open to the later

decision of the assembled delegates. The same is true with

respect to questions having to do with the standard cell, preparation of the mercurous sulphate, etc. The extent of these special

investigations will depend on how much time remains for them.

Order of Business.—In order to organize the joint work efficiently

and to submit the results of the experiments in a form free from

objection, it is to be recommended that an agreement may be

reached on the following points. These individual points are to be

regarded as proposals, which may be laid before a conference of

the delegates in Washington.

(a) First of all a council of the delegates with Director Stratton

as chairman (or a substitute appointed by him) shall be held to

discuss a plan for the work to be undertaken, the distribution of

the various parts of the work among the participants, the allot- ment of the apparatus, etc., the minutes of which meeting, signed

by the delegates, shall be prepared for the proceedings of the

International Committee. This shall be done in the case of all other general discussions on the work. Copies of the minutes

shall be given to each delegate.

(&) The original notes of the observations (numerical data) of

each observer shall be delivered to the secretary of the International Committee and kept sealed for the proceedings of the committee. Each delegate shall receive copies of these minutes, upon

which the calculation of the results shall be made to rest. A common record of the arrangement of each experiment is to

be prepared and signed, of which the individual delegates shall

each, in like manner, receive a copy.
International Electrical Units 63

(c) At the close of the work a report to the International Committee shall be prepared by the delegates in common, which shall

contain the essential results of their investigations. In this it will

be well to submit those points upon which all the participants are agreed as being the common opinion of the delegates, but to expressly state the dissenting opinions of the single delegates on

those points on which there remains a difference of opinion.-

The report shall then be sent, printed in three languages (German, English, French) and with such numerical data as shall seem

requisite to the delegates, to all the members of the committee,

for their information and consideration.

(Signed) E. Warburg.

7. REPORT OF EXPERIMENTS ON THE SILVER VOLTAMETER

From the Reichsanstalt

[Translation.] In the following are communicated the results of experiments

carried out by Dr. Feustel at the Physikalisch-Technische Reichsanstalt as a result of the stimulation of the Bureau of Standards

to the investigation of the effect of organic substances on the silver

equivalent.

First of all were considered relative measurements in which

part of the silver anodes were wrapped in silk and part were without covering. In all of the experiments little glass cups were

placed under the anodes.

The silver nitrate which was obtained from the gold and silver

refining institution at Frankfurt was washed before being dissolved to remove any organic substance possibly adhering to it and was used unfiltered.

The treatment of the cups was the same as described in the

work of Jaeger and von Steinwehr.

The silk was kept for a week in distilled water, daily renewed,

and was carefully freed from the adhering anode slime after every

experiment. The silk wrapping was attached with threads of the same piece of silk. The current was 0.3 ampere in all the experiments; the length

of the electrolysis varied between 1 hour and 3^ hours. The

22451°—12

s
64 Report on Concrete Standards

quantity of silver deposited amounted, accordingly, to from 1.2 grams to 4 grams. No effect of the length of the electrolysis, and

therefore of the weight deposited, on the relative weights was

detected.

In Table I are contained the results of the relative comparisons

with and without silk. From Table II it can be seen that a differ- ence between the experiments with and without silk could not be

established.

Further, other experiments on the influence of filter paper were

carried out, which, however, are not yet finished. They indicate no effect on the amount of the deposit when small quantities of

filter paper are present. Using larger quantities of filter paper,

especially when finely divided, larger deposits were obtained. In

particular, there seems to be present an influence working in the same direction, due to the illumination of the silver nitrate solution containing the filter paper.

The maximum increase of the silver deposits in the experiments,

due to the use of filter paper, amounted to 20 parts in 100 000 of

the whole value. TABLE 1

Results of Experiments

Number of experiment Number of cup

Quantity of silver Difference A Mean A in parts in 100 000

inIV* HI*

IV

I III IV*

I

III IV*

I

II *

III IV*

g

1.2

2.8

4.0

mg

+0.127

—0.127

+0.165 -0.166

+0.162

-0.181 +0.020

-0.031

-0.088 +0.118

+0.261 -0.184 +0.163 -0.241

mg

1199.912

1193.977

2413.482

3994.800

+ 10.6 -10.6 + 13.8 -13.8 + 6.7 - 7.5 + 0.8 - 1.1 - 3.2 + 4.2 + 6.5 - 4.6 + 4.1 - 6.0

The cups marked with an * had anodes with silk wrapping.
International Electrical Units 65

TABLE 11

With silk Without silk

Number of experiment Deviation in parts in

100 000 Number of experiment Deviation in parts in

100 000

1 -10.6 1 +10.6

2 +13.8 2 —13.8 3 + 0.8 3

| + 6.7

1 - 7.5

4

1 + 4.2

4 - 3.2

f - 4.6

5 J + 6.5 5

{ - 6.0 1 + 4.1 Mean - 3.5 Mean + 3.4

Chari,ottenburg, Germany, March 21, 19 10.

8. THE LAST INTERCOMPARISON OF THE NEW CADMIUM STANDARD CELLS OF SEC- TION I OF THE PHYSIKALISCH-TECHNISCHE REICHSANSTALT AND A FEW CELLS

OF THE BUREAU OF STANDARDS AND NATIONAL PHYSICAL LABORATORY

German Cells

Cell Emf Cell Emf Cell Emf Cell Emf Cell Emf

xmi 1.01866 ymi 1.01867 zmi 1.01867 ami 1.01871 0mi 1.01867 D, 867s Ei 869 zm2 867 Gi 873 Hi 869 D2 8675 E2 867 Fi 870 G2 872 H2 8695 D3 867 E3 868 F2 869 G3 873 H3 869 D< 8685 E< 868 F3 869 Gt 873 H4 869 D5 8675 E5 867 F, 869 G5 872 H5 869 D6 871 E6 868 F5 869s G6 873 H6 869s D7 867 E7 866 F6 872 G, 871 H7 8685 De 867 E8 866s F7 869 G8 872 H8 867 D9 868 E9 867 F, 870 G9 873 H9 869 D10 8676 E18 . 8676 F9 870 G10 8735 H, 871 Du 867 E11 866 F10 869 Gn 874 Hn 870s D12 86S E12 867 Fn 8675 Gij 874 Hi2 869s E13 867 F12 867

1.018672 1.018672 1.01869o 1.01872, 1.01869o

The sample of mercurous sulphate for each series of cells is designated by the same letters as for the first cell of the series;

that is, xm„ ym^ etc. The cells taken to America were D1; D2 , D3 , D4 , Ei , En , ~E12 , Bi3 , F7 , F8 , F9 , F10 , H,, H2 , H3

.
66 Report on Concrete Standards

Other Cells

German American English

Emf Cell Emf ^ ell Ami Cell Emf Cell Emf

Imi 1.01868 rami 1.01871 nmi 1.01874 W183 1.01866 NCi 1.01867 lma 869 mm"i 870s qmi 872 W184 865s CBi 866

lm,j 868 mm'i 871 rmi 872 PW8 865 AH6 815

8685 rm'i 873 img 868 Rm'i 871 sm] 875

875 wmi 8765 ami 853 bmi 861 bm'i 869 bmj 871

ap3 872

api 868

I.OI8683 1.01870s 1.01865s

As an arbitrary unit the electromotive force of a cell of the

Weston Company was taken as 1. 01 896 volts. The measure- ments were made on March 14, 19 10, between noon and 1 o'clock at 1 8? 8 C. The values are not reduced.

Measurements in Section II on March 9 and 11, 1910

American cells English cells

Cell Mar. 9 Mar. 11 Cell Mar. 9 Mar. 11 W 213 1.01860 1.01860 NPL08 1.01862 1.01863 215 860 860 HA6 811 811 216 858 859 CBi 863 864

217 858 859 NCi 864 864

105 859 860 H 29 828 828

188 860 861 P55 766 767

193 860 860 C 117 837 836 PW8 860 859 C 12 858 858 W 184 862 863 NPL05 857 857 W 183 863 863 U 864 864 La 864 864 U 865 864 Zi 864 864 z2 865 864 z3 865 864
International Electrical Units 67

Values are in terms of W 2 1 3 , which was arbitrarily taken as

1.01860. Observations on March 9, 1910, were at 17^8 C, and

on March 11, 1910, at i8?5 C. PW 8 had a high resistance.

9. REPORT ON RECENT WORK ON THE WESTON NORMAL CELL AND THE SILVER VOLTAMETER BY THE NATIONAL PHYSICAL LABORATORY

In 1907 three papers dealing with electrical standards were

published by the National Physical Laboratory. These are:

(1) "A New Current Weigher and a Determination of the emf of the Normal Weston Cadmium Cell." (Ayrton, Mather, and Smith.)

(2) "The Normal Weston Cadmium Cell." (Smith.)

(3) "The Silver Voltameter." (Smith, Mather, and Lowry.)

Since 1907 we have made many experiments with standard cells and with the silver voltameter; from time to time we have also

determined the emf of the Weston Normal Cell by the aid of the

Ayrton-Jones current balance and a standard resistance. The

last of such emf determinations was made during the present

month (March, 19 10), and it is now of interest to compare the

emf's of cells measured in 1 905-1 907 and 19 10. The results of ex- periments with the silver voltameter are also given in this report,

and these serve to show what defects in the voltameter remained

undiscovered in 1906-7. In conjunction with the international

ohm, the determinations also helped to*fix the emf of the Weston

Normal Cell in international volts. In order to make the results of general interest and to enable

them to be confirmed or otherwise, we have chosen May, 1907, as the date from which changes are most conveniently reckoned.

The reason for this choice is that in that month 24 English and

American (United States) cells were compared at the NPI, and

afterwards distributed among the following laboratories: Taboratoire Central of Paris, the Reichsanstalt, the Bureau of Standards,

and the National Physical Laboratory. It is possible to state the emf in 1907 of all these cells and the present emf of two of

the cells which were left at Teddington. At first we will limit our attention to the latter two cells, which are numbered W 181

and W 182.

These two cells were made at Washington in April, 1907, and

the emf of either of these did not differ by so much as 1 part in

100 000 from the emf of any one of 21 of the other cells. The
68 Report on Concrete Standards

remaining cell (W 105) was 1 part in 100 000 lower in emf than

W 181 and W 182. We may safely assume therefore that in 1907

the four previously mentioned laboratories were in possession of

cells of identical emf.

The emf of W 181 and W 182 can be obtained from papers (1)

and (2). Referring to page 403 of the paper on the Weston Cell,

we find the statement:

The mean emf of the 12 National Bureau of Standards' cells is less than the mean

emf of the 12 NPL cells by 3 microvolts. Also the mean emf of the 12 NPL cells is not quite the mean of all the NPL cadium cells which are believed to be normal; the

latter cells have the higher mean by about 2 parts in 100 000. Table I of the same paper gives the emf of 60 cells. The first 50 of these are regarded as normal and their mean emf is 1. 01 8293

at 1

7

C, agreeing almost exactly (as it should do) with the value

1 .018297 (or in round figures 1. 01 830) obtained with the aid of

the current balance and the international ohm. (See p. 536).

We conclude, therefore, that the mean emf at 17 C of the 24

cells was

1.018293 — 0.000023=1.01827 very nearly,

this value being in terms of the ampere as realized by the current

balance and the international ohm as realized at the NPL.

Further determinations- of emf by means of the balance and a

standard resistance were made in January, 1908; March and

April, 1909; and in March, 19 10. From intercomparisons of the

cells W 181 and W 182 with others, the emf 's of which were directly

determined, we obtain the following results: TABLE I

Date

May, 1907 January, 1908 March-April, 1909 March, 1910

Apparent change in 3 years

Cells W 181 and W 182 were set up 10 days before being sent

to the NPL, during which time there was a fall in the emf of 1.3 parts in 100 000.

Emf of W 181

at 17° C

Emf of W 182

at 17° C

1.01827 1.01827 26 27

24 25

24 25

0.00003 V 0.00002 V
International Electrical Units 69

Having indicated the manner in which we have endeavored to determine the change in emf of standard cells, it will be sufficient to give the emf 's of certain cells of general interest.

In 1904 Prof. Carhart gave to Dr. Glazebrook the two cells referred to in the paper by Carhart and Hulett as D 1 and D 2 . The

probable emf 's of these cells on various dates are as follows:

TABLE II

Date

October, 1904... May, 1905 October, 1905... February, 1906.

.

October, 1906... May, 1907 May, 1908 September, 1908 May, 1909 September, 1909 March, 1910

D 1 at 17° D 2 at 17°

1.01827 1.01826 26 24

26 23

24 22 20 17

10 05 04 00

03 1.01798 1.01796 93

91 89

82 82

Both cells contain electrolytic HgoSOi.

In October, 1908, Dr. Rosa brought a number of cells to Teddington, which were set up by Dr. Wolff and Dr. Waters at the

Bureau of Standards. Four of these cells were left in our possession, and we conclude that the emf 's have changed as shown in

Table III. The values given are at 17 C. TABLE III

Date W 206 W 208 W 211 W 212

October, 1908 1.01825 1.01825 1.01825 1.01825 March-April, 1909 25 24 23 25 March, 1910 25 24 23 24

All of the cells in Table III contain electrolytic mercurous sul- phate.

From Prof. Janet we have received six cells. In June, 1909, we

received also a sample of electrolytic mercurous sulphate and

some of it was used in setting up six cells. Three of these we sent
7o Report on Concrete Standards

to Paris, but they were hopelessly damaged in transit; the remaining three are at Teddington and we have numbered them JAN

1,2, and 3, respectively.

The electromotive force of all the French cells are given in

Table IV. Values at 17 C.TABLE IV

Cell

E 10... E8.... V

J 6 J7.... S6.... JAN1. JAN 2. JAN 3.

Hg.SOj

El. A. C

do Chemical (acid). El. D. C

.....dodo

do

dodo

June, 1908

1.0183938

14

September,

1908

1.0184138

15

February,

1909

1.01826

24

33

June, 1909

1.0183030

30

August,

1909

1.01833

32

15

15 1.01792

1.0181931

31

31

March,

1910

1.01833

32

1505

1.01793 1.018203131

31

We have not received any cells from Berlin, but in July, 1908,

Dr. Warburg very kindly forwarded a dry sample of mercurous

sulphate which had been washed with water. The salt was quite

white. In September, 1908, we used this salt in the preparation

of 17 cells. At the same time we prepared some mercurous sul- phate and washed part of it with water and part with saturated

cadmium sulphate solution. The results of our observations are given in Table V.
International Electrical Units

TABLE V

Values at 17° C

7i

Cell September, December,

1908 1908 September, December,1909 | 1909 March,1910

T 1 T 2 T 3

PTR, mixed with cadmium sul- phate crystals and made into paste

f 1.01828

1 28

28

1.0183029

29

1.0182929

29

1.0182929

28

1.0182829

29 T 4 [ 28 28 29 28 28 T 5 30 26 18 14 09 T 6 T 7 T 8 T 9

PTR, washed with 2 lots of water

for 30 minutes before making

into paste

30

3130

30

2828

28

28

21

27

2626

1728

2727

13272627 T 10 30 28 22 22 21 T 11 T 12 |.NPL, washed as T 1 to 4

I 28

1 28

292928

28

28

28

2828 V 1 28 28 26 25 24 V 2 PTR, in contact with 150 cc ol 28 24 24 22 22 V 3 water for 3 days; water changed 28 28 27 24 23 V 4 6 times 28 28 23 21 21 V 5 28 27 25 25 25 V 9 INPL, washed with cadmium f 26 24 25 24 24 V10 [ sulphate solution only 1 25 25 25 24 24 We have now to report on the cells made at the NPL, and

we think it desirable, in the first place, to indicate the changes

which have resulted in the cells reported- on in the paper on the

Weston Normal Cell. The values are given for December of

each year. Temperature, 17 C.
72 Report on Concrete Standards

TABLE VI

HggSOi

Chem. pptd do

do

do.4 ....do Chem

do

do :. do ...do

do

do

Electrolytic do

dO........;. do

do

....dodo

do

dodo

.. .dodo Fuming H.tS04 do

....do ...dodo Chem. pptd do

do

do

do.... do

Recryst ...do

....do

Electrolytic ....dodo

do Chem

do

do.... do Chem

do

do

do

December, 1904

1.01830

2931

3230

3230

31

30

3331

29

December,

1905

1.018302830

31

32322932

30

31

29

2634

3333

30

28

2828

29

3032

3132

December, 1906

.01829

29

29

2828

2928

2830

31

31

29

28

3230

2826

33

31

3134

272426

3132

3132

303030

32

313030

3232

32

2929

31

27

3130

30

28

December,

1907

Broken open Broken open Broken open Broken open

1.0183030

30

2829

293030

December, 1908

1.01829 1.01827 1.01826 28 27 27 29 28 28 27 24 25 27 27 27

27 26 27

28 28 27

28 28 27 31 31 32

31 29 29 30 27 27

27 27 27

26 25 24 30 26 25 28 26 25

20 19 16 Broken

Broken

1.01831 30 30

30 29 29 30 29 30

28 28 28 23 22 20

26 26 26 30 30 30

31 30 31

31 30 31

31 30 31

30 31 30

26 1.01794 1.01723 28 1.01817 1.01807

24 00 1.01796 30 24 1.01816 27 24 22

27 25 20

31 31 31

31 30 30

31 31 30
International Electrical Units 73

TABLE VI—Continued

Cell Hg2S04 December, 1904 December,

1905 December, 1906 December,1907 December, 1908 December, 1909

AB 1...

2 D 1...

2

Nord

do

Electrolytic do

2220

22

17

15

2626

Broken open

21190710

07

23

20

21

18 1.01792 Broken open Broken open

1.0181916

21

17 1.01741

20

17 1.01705

3 do

4... 5 M 6...

7..

Nord

do

1.01810001.01806

1.01789

8...

Note.—The last ten are given as examples of abnormal cells.

It is of interest to note that of the cells which in 1907 appeared

to be quite normal, the cells HA 1 to 6 have since changed considerably. These cells were used to obtain the recovery curves

after short circuiting, shown on pages 412-413 of the paper on

the Weston Normal Cell. Since 1907 very many cells have been made. These contain

many different samples of mercurous sulphate. On December 10,

1909, 210 cells were intercompared. The emf 's at 17 C were as follows

:

TABLE VII

No. Remarks Emf Mean

5 Emf's greater than 1.0183030

28

27

26

25

2423

22

21 1.01820

1.01825

6 Emf's equal to

8 do

25 do

26 do

63 do

56 do

9 do

8 do

1 do

3 Emf's less than

Observations on cadmium amalgams have been published in

full and are not referred to in this report.

The silver voltameter,—In determining the electrochemical

equivalent of silver we have measured the current by a combina-
74 Report on Concrete Standards

tion of a number of cells in parallel and a standard resistance, the

combination being frequently standardized by means of the cur- rent balance.

Our solutions contained either 10 or 15 per cent of silver nitrate,

the latter being obtained from a number of sources. At times the

salt was fused in a platinum crucible in an electric oven, the crucible being covered over with glass so as to exclude all dust, etc. The form of voltameter termed "New Form" is not described

here, but four such voltameters will be brought to Washington.

With regard to the deposits, close inspection showed that those

in the Rayleigh form of voltameter were always slightly striated

and those in other forms were either free from striae or only slightly

striated.

In no instance (except on January 30, 19 10, and observations

previous to November 8, 1909) were the solutions filtered through

filter paper before using; purified asbestos was, however, used.

The results are given in Table VIII.

TABLE VIII

Date Silver nitrate Voltameter Deposit E. C. E.

Rayleigh greater than

Syphon New

Form

Richards

1909 Feb. 11

Mar. 11

30

Apr. 519 Nov. 8

16

Recryst. F. E. S.

.

Do

Harrington (1) Harrington ( 2) Recryst. F. E. S-.

Harrington (2) Do

Recryst. F. E. S.

.

Recryst. Barr Ham. (2) Recryst.

Recryst. F. E. S.. Harn.(3) Harn. (3) Recryst.

Recryst. Barr

Recryst. Barr Merck's Do

Harrington (1)

Rayleigh

.

do...

do...

....do...

....do...

....do...

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

....do...

....do...

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

....do...

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

Syphon... Rayleigh

.

Syphon...

6.99962

6.99942 6.99874

6.99842

7.00122 7.00060

7.00051 7.00115

7.19855

7.19860

7.19876

6.99959 6.99868

6.99900

7.00083

7.00554

7.00518

7.00138 7.00166

1.118262

823i 825o

820o 8283 818a

817i

827i 8227 823s

826o 8446 830j

827i 830a

-4
International Electrical Units

TABLE VIII—Continued

75

Date

1910 Jan. 13

17

20

27

30

16

28

Silver nitrate

14

Recryst. F. E. S..

.

Recryst. F. E. S.

Recryst. B. & T. (fused). .

.

Recryst. F. E. S

Do

Recryst. B. & T. (fused). . -

(Filter paper)

Recryst. F. E. S

(Filtered through paper)

.

Recryst. F. E. Do

DoDo

S....

Recryst. F. E. S. . .

.

Recryst. F. E. S

Harn.(l).

L. C. E

Recryst. F.E.S... Do

Recryst. F.E.S...

Recryst. B.&T....

Merck's Do

Recryst. F. E. S... Do

Do

Voltameter

Rayleigh Do

Syphon

Rayleigh Do

Syphon

Richards

Rayleigh Syphon

Rayleigh Syphon

Rayleigh Syphon

Rayleigh fc ....do Syphon

Richards Do

Rayleigh Richards

Rayleigh Syphon

Rayleigh New Form . .

.

Rayleigh New Form . .

.

Richards

Rayleigh New Form . .

.

Rayleigh do New Form . .

.

Rayleigh dodo New Form . .

.

Rayleigh New Form . .

.

do

Deposit

7.00711 7.00716

7.00642 7.00349

7.00355

7.00315 7.00263

7.01432 7.01438

7.01441 7.01354

7.02488

7.02408

7.02617 7.00625

7.00618

7.00606

7.00596

7.00090 7.00000

7.00092

7.00071 6.99832

6.99749

6.99879

6.99815

6.99808 7.00040

6.99979

6.99980

6.99952 6.99876

7.00032

7.00050 7.00026

6.99966

7.00078

7.00027

7.00001

E. C. E.

1.11827, 8144 8252 815o

814o 828o 8184 8304 826

814

824

826s

823i 8135 8259 817i 8135

Rayleigh greater than

<,,,„.„„ New STMhon Form

Richards

12

3

4

13

13

& In this case 4 large filter papers were inserted in 500 cc of the solution and the latter put on one side

for 7 days. The solution was then used in the Rayleigh form.
7 6 Report on Concrete Standards

The values for the electrochemical equivalent as obtained from

the Rayleigh form with electrolyte believed to be pure are: i.ii826j i.ii822 7 1.11830, I.Il826

231 235 27, 24

25o 26 252 268 282 302 280 231

27i 27x 304 259

Mean = 1. 1 1 8263, a value agreeing within less than 1 part in

100 000 with that of 1905-7.

The values for the electrochemical equivalent as obtained with

the New Form are

:

1. 11814, 1. 118135

i5o i7i 184 i3s

Ho

Mean = 1.11815!, which is 10 parts in 100 000 less than with the

Rayleigh form as we have used it. We have found this New

Form to be very convenient in practice.

We think it best to now state the emf of the standard cells which we propose to bring to Washington. Of the cells already

reported on we have chosen a number of abnormal ones, as an

examination of them may be profitable. In addition we are bringing 34 cells, of which 33 have been set up since October, 1909.

These 33 cells are in nine groups, and no two groups contain mercurous sulphate from the same sample. The amalgams in the

33 cells contain 10 per cent of cadmium. Without exception all of the cells have fallen in emf by 1 to 2 parts in 100 000 since the

day on which they were set up.

S 35 was made in March, 1909, and during the whole of last summer it was exposed to the action of direct sunlight. The

exposed surface of the paste is now coal black.

The emf's are given in international volts at 20 C, the international ohm being taken as equal to the ohm realized from the

NPL mercury standards of resistance, and the international ampere

that realized when the New Form of voltameter is used with a pure electrolyte.
International Electrical Units 75 TABLE IX

Values in International Volts at 20° C

Cell Value Cell Value

[E 8 1.01833 T 1 1.01829 jv 1.01816 T 2 1.01830 |S 6 1.01821 T 5 1.01810 (jAN 1 1.01832 T6 • 1.01814 jDl 1.01783 V3 1.01824 Id 2 1.01783 181 1.01825

New Cells

Cells Paste Set up— Mean emf February, 1910

A. 1. 2. 3. 4. 5. A October, 1909 1.01825-6 B. 1. 2. 3. B Do. 26-7 C. 1. 2. C Do. 26-7 D. 1. 2. 3. D November, 1909 27-8 E. 1. 2. 3. 4. E Do. 27-8

F. 1. 2. 3. 4. F Do. 27-8 G. 1. 2. 3. 4. 5. G January, 1910 28-9 H. 1. 2. 3. 4. 5. H Do. 28-9 K. 1. 2. 3. K February, 1910 27-8 S. 35 S March, 1909 27 Mean c 1.01826-7

c If made with per cent amalgam probable value=i.01828—9.

It is now desirable to state the results of our observations on

normal and abnormal cells. It has been previously shown that the

presence of free acid in a cell results in a lowering of the emf and

Hulett has suggested that the fall of emf of his cells (such as D 1 and D 2) is due to hydrolysis of the mercurous sulphate by

cadmium sulphate solution in the absence of acid. Cells containing free acid, although lower in emf, are quite stable—in

fact they appear to be more stable than cells believed to be acid

free.Examination of Table V suggests that if part of some freshly

precipitated mercurous sulphate is washed in the usual way with
78 Report on Concrete Standards

cadmium sulphate solution until apparently free from acid, and a

second part is washed with water, cells containing the two samples will differ in emf by about 4 to 5 parts in 100 000, the cells with water-washed mercurous sulphate having the higher voltage.

If the washing with water is not prolonged the cells containing the

water-washed salt appear to remain stable—at least for several

years. On the other hand prolonged washing appears to result

in the cells remaining stable for a considerable time, such as 12

months, but afterwards irregularities become very marked.

Most of our cells which we regard as stable vary in emf from

1 .01825 to 1. 01 830 international volts at 20 C. Very few are lower than 1. 01825. It appears to us to be probable that in many

cases the mercurous sulphate has retained a small quantity of acid

which has been slowly liberated after the cell has been set up and

as a result there has been a gradual fall in emf to a steady value

approximating to 1. 01 826. The presence of this small quantity

of acid appears also to be favorable to the stability of the cell. In a few cases the washing has been very thorough—in some cases the process being conducted a second time after an interval of

some months. These cells have been slightly higher in emf and

in some cases have become unstable after a number of years. At

present we have a number of cells under observation which contain paste washed in different ways, but two or three years must

elapse before decisive evidence is obtained.

From all the observations recorded in this report we conclude

that the emf of the Western Normal Cell is

1.01827±0.00002 International Volts at 20° C. The best value stated to 1 part in 10 000 appears to be 1.0183, the

international ohm being obtained from the NPL mercury standards

of resistance and the international ampere from a form of silver

voltameter in which the electrolyte is uncontaminated with filter paper either before or during electrolysis.

10. SUGGESTIONS FOR EXPERIMENTAL WORK AT WASHINGTON, D. C. By F. E. Smith

i. Consideration of reports and suggestions handed in by the

four delegates.
International Electrical Units 79

2. Consideration of the form of the report to be prepared by the

delegates.

3. Comparison of resistance coils, standard cells, weights.

4. Decision as to the limits within which the emf of the cell shall be stated.

5. Examination of the voltameter circuit, especially as regards

insulation of parts, etc.

6. Choice of some cells to temporarily represent the Weston

Normal Cell.

7. Choice of one or more forms of voltameter to be experimented

with.

8. Comparison of the different samples of silver nitrate.

Decision to be arrived at as to the best mode of preparation.

9. Decision as to effects of temperature, pressure, anodic

impurities, organic matter.

10. Comparison of the different forms of voltameters.

11. Determination of the emf of some cells. 12. Decision as to: (a) Depolariser, i. e., its preparation and

washing; (b) the amalgam, its preparation and composition;

(c) the range of temperature.

13. Comparison of results at Washington with previous results at Washington, Berlin, Paris, and Teddington, and decision as to value of the emf of the cell.

13. SUGGESTIONS FOR EXPERIMENTAL WORK

By M. F. Laporte

[Translation] Before the value of the electromotive force of the Weston

Normal Cell in international volts can be fixed, it is necessary to

carry out first the following preparatory work:

1 . To determine the best procedure in assembling the voltameter

and for purifying the electrolyte to assure the constancy of the

deposit.

2. To determine the method of making and purifying the

chemicals and the construction best suited to yield cells of the same electromotive force.

22451 —12 6
8o Report on Concrete Standards

3. A comparison of values obtained for the ohm by the indirect means of comparing the metallic copies.

The work might be carried out as follows:

1 . The Silver Voltameter.

(1) A comparison of weights of deposit in several voltameters in series.

(2) A determination of satisfactory forms.

(3) A determination of a satisfactory process of purifying the silver nitrate.

(4) The limits observed in previous experiments for the current density, the

concentration, the temperature, and the pressure should be indicated as provisional limits of precision to be verified later on. In the course of the work the verification of the method of microscopic examination (of the deposits) should find its place.

2. Standard Cell.

(1) A comparison of cells made in different laboratories.

(2) A comparison of cells made at the Bureau of Standards from materials pre- pared by different methods in different laboratories. (A further study in case of differences arising.)

(3) A determination of how the mercurous sulphate should be washed to yield a cell that will at once assume its normal electromotive force.

3. The Ohm.

(1) A comparison of metallic copies and a determination of the relative values

of the ohm.

This work can be only partially done (the ohms of M. Benoit not

being finished, but their comparison in the future with the metallic

resistances expressed in terms of the present LCE ohm will permit

them to be connected with the other values). The differences

between the ohms will moreover be certainly less than 1 part in

10 000. Thus it seems that agreement can be reached for the

electromotive force of the Weston element if one is content with

four decimal places.

If this program can be carried out then the value resulting

from new experiments will show directly the value of the electromotive force of the Weston Cell under the most favorable circumstances, and, if possible, without a correction factor.

This determination will be made in terms of a provisional value

of the ohm pending the final value, which can not be obtained

until the termination of the researches now in progress.
International Electrical Units 8

1

APPENDIX B. LIST OF APPARATUS, STANDARD CELLS, AND MATERIALS

BROUGHT BY THE DELEGATES FOR THE WORK OF THIS COMMITTEE

1. FROM THE PHYSIKALISCH-TECHNISCHE REICHSANSTALT

(a) Resistances , Standard Cells, Weights, etc. —Two i-ohm coils of manganin, O. Wolff, No. 2836, 2838; 1000-ohm coil in paraffin oil, O. Wolff, No. 4089; brass weights (3, 2,

1, 1 g); platinum and aluminum weights (400, 300, 200, 100, 40, 30, 20, 10, 4, 3, 2,

1 mg, and fractions of 1 mg); two platinum ballast weights of about 10 g and 50 g; 15 standard cells, viz (D(, D2 , D3 , D., of the xm," series; E10 , Eu , Ei2 , E13 of the ym,"

series; F7 , F8 , F9 , F10 of the zm/' series; H[, H2 , H3 of the ftm" series).

(b) Other Apparatus and Chemicals.—Two platinum cups marked I and III, with

accessory apparatus; 10 silver anodes, platinum tongs, etc. ; 1 kg silver nitrate (fused) from the Gold-und Silber-Scheide-Anstalt, Frankfurt a. M.; two samples of mercurous

sulphate in cadmium sulphate solution; one bottle saturated solution of cadmium

sulphate, 12^ per cent cadmium amalgam; 10 empty tubes for making standard cells; mercury.

2. FROM THE NATIONAL PHYSICAL LABORATORY

(a) Resistances, Standard Cells, Weights, etc.—One sealed manganin coil L 17; one

open strip manganin coil L 87; two weights (5 g and 2 g); 34 standard cells (NPL

cells, 1909-10), viz: A„ A2 , A3 , A4 , A5 ; B„ B2 , B3 ; C,, C2 ; T> v D2 , D3 ; Ei, E2 , E3 , E4 ; F2 , F3 , F4 ; Gu G2 , G3 , G4 , G5 ; H„ H2 , H3) H4 , H5 ; Ku K2 , K3 ). (b) Other Apparatus and Chemicals.—Four platinum bowls, spatula and tongs; 4 voltameter stands, with parts for the Rayleigh form and the new form; 6 silver anodes; 200 filter papers (as purchased); 2 porous cups; 36 H-vessels for standard

cells; two 4-limb vessels; 8-oz cadmium; 1 bottle of mercury (about 2 kg); 2 bottles

of cadmium sulphate solution sufficient for 200 cells; 2 bottles of cadmium sulphate

crystals sufficient for 200 cells; 5 samples of mercurous sulphate sufficient for 200

cells; 7 lbs silver nitrate (3 lbs recrystallized by F. E. S. , 2 lbs from Baird and Tatlock and 2 lbs from Merck); 2 glass siphons.

3. FROM THE LABORATOIRE CENTRAL D'ELECTRICITE

(a) Resistances , Standard Cells. —One box of five i-ohm coils, J. Carpentier, 1417-K;

one i-ohm coil, Otto Wolff, No. 3961; 15 standard cells, viz (Es , E12 , E13 , Ei4 ; D2 , D3 ; Pji F21 P3! S2 , S4 , S5, S7 , Sg ; Z2 ). (6) Other Apparatus, Chemicals, etc. —Two voltameter stands; 2 platinum cups for cathodes; 2 silver cups for anodes; 4 silver anodes (two hemispherical, two disks);

2 siphons; 1 glass spoon; 2 kg of pure silver nitrate (commercial) from the Maison

Poulenc freres; 400 to 500 g silver nitrate crystallized twice in a vacuum at less than

50°; 12 H -shaped tubes for standard cells; 1 bottle of purified cadmium sulphate;

1 bottle of mercurous sulphate, obtained by electrolysis with alternating current;

1 bottle of cadmium amalgam; filter paper 'free from chlorine," No. 595, from

Schleicher and Schull; congo paper.

4. FROM THE BUREAU OF STANDARDS

(a) Resistances, Standard Cells, Weights, etc. —Resistances used in the comparisons,

Nos. 3, 7, 8, 3939, 394°. (For list of standard cells selected for the intercomparisons,

see Appendix C, 2, Table VI.) Special weights, S, S, 2 and a box, NBS 6550.
82 Report on Concrete Standards

(b) Other Apparatus, Chemicals, etc.—Eight platinum cups; 2 gold cups; 10 mountings for voltameters; 2 kg silver nitrate from the Gold-und Silber-Scheide-Anstalt in Frankfurt (unfused); a collection of anodes for different forms of voltameters; a collec- tion of porous cups of different sizes for the Richards voltameter; 3 siphons for the siphon voltameter; 4 special glass vessels for the Kohlrausch form; pure silk thor- oughly washed for use in the Kohlrausch form ; filter paper and filter tubes for the Rayleigh form, besides apparatus and chemicals for investigations with the voltameters; materials for standard cells. APPENDIX C. DESCRIPTION OF THE EXPERIMENTS

1. RESISTANCE MEASUREMENTS

Each delegate brought with him one or more resistance standards with the object of furnishing additional data on the relative

values of the unit of resistance employed in the four laboratories,

and of deriving a basis for the voltameter measurements made in

Washington. The results obtained also served the further purpose of establishing the magnitude of one of the corrections to be

applied to the voltameter measurements previously made by the

delegates, to reduce them to a strictly comparative basis. The

unit, of resistance which it was agreed to adopt will also be employed in the voltameter work to be undertaken in the immediate

future. The opinion is further expressed that as soon as primary

mercurial standards, in strict conformity with the specifications

adopted by the London Conference, have been realized in the four

institutions, a common unit of resistance, based upon all such mercurial standards, will be adopted for international use.

Description of the Standards

(a) The Standards of the National Physical Laboratory.—Two

coils, L 17 and L 87, were submitted for comparison. L 17 is a

sealed standard, otherwise embodying the main features of the

Reichsanstalt type. The coil is wound with manganin wire, but

is not provided with potential terminals. It bears the date 1902,

the case having been reconstructed in 1909.

The temperature formula, as calculated from the chart submitted, was found to be

Rt = R20 { 1 +0.000 020 o (t — 20)— 0.000 000 4^ (t — 20) 2 } in the

range io° to 22
International Electrical Units 83

As this range did not include 25 , the temperature at which

practically all the measurements were made, the 20 — 25 differ- ence in value was directly determined in Washington, and was

used in reducing the results, as was also the case with all the other

coils except the Carpentier box of the Laboratoire Central, described below.

L 87 is an open coil, provided with potential terminals and constructed for high-current carrying capacity, being wound with

manganin strip about 8 mm wide on a frame composed of six

insulating posts, 12 cm long, equally spaced in a circle 8 cm in

diameter. It was brought to Washington for inclusion in the

voltameter circuit, and was not submitted as a resistance standard.

The temperature formula, calculated from the chart submitted

and covering the range io° — 22 , is as follows:

Rt = R20 {i +0.000 014 o (t — 20) —0.000 000 48 (t — 20) 2 }

The differences in millionths between the values at 20 and 25

by the above formulae, and by direct observation, are given below.

The agreement may be regarded as entirely satisfactory, particularly as the original observations did not extend to 25 .

Coil Differences by formula 25°— 20° Observed difference 25°— 20°

L 17 89 89 L87 58 57

(b) The Standards of the Physikalisch-Technische Reichsanstalt.—Two open i-ohm standards of the Reichsanstalt type, with

potential terminals, and one sealed small type iooo-ohm coil, all constructed by Otto Wolff, were submitted.

The i -ohm coils are provided with an extra pair of binding

posts so that they may be connected in a circuit without the aid

of mercury cups.

Wolff No. 2836 bears the mark K 108, and Wolff 2838 bears the

mark K 109. The following values were certified by the Reichsanstalt:
84 Report on Concrete Standards

Coil Rie" oia° As"

2836 1. 000 0705 + 000 013 5 -.000 000 42 2838 1.000 0695 + 000 013 4 , -.000 000 3 3

the temperature formula being of the form

Rt = Riao {

I + a(t - 1 8) + /3(t - 1 8)

2 } The iooo-ohm coil, No. 4089, contains paraffin oil which had

stood for a long time exposed to air of 55 per cent humidity.

The value certified from measurements made in the laboratory of

Prof. Lindeck, over the period December 30, 1909, to March 9,

1910, is 1000.055 ohms, at 18 C. The values given for a and /3 of the above formula are <*= + .000 014 o, /3= —.000 000 43 cor- responding to an increase in resistance of 77 parts per million

between 18 and 25 C.

(c) The Standards of the Laboratoire Central d'Electricite.—These

consisted of an open i-ohm Wolff standard, No. 3961, of the

Reichsanstalt type, marked PTR 97 1908, and a Carpentier box

of five i-ohm sections. The values found for No. 3961 and given

by M. Jouaust 5 are as follows:

TABLE I

Date Resistance at 18° Measurements at

Sept., 1908 0.999 981 July, 1909 0. 999 994 jpTR

Apr., 1909 0.999 977 NPL

Oct., 1908 1.000 10 Jan., 1909 1. 000 13 May, 1909 1. 000 115 Jlce

Aug., 1909 1. 000 116

5 Bull. Soc. Int. Elect., 10, p. 187; 1910. The Carpentier box is marked "141 7 K." The coils are wound

on threaded porcelain tubes, three coils in parallel forming each

i-ohm section. The terminals of the sections are permanently

connected, each by an independent rod, to six rectangular brass

blocks, situated between two parallel brass bars to which the

coils may be connected by the aid of plugs connecting the blocks
International Electrical Units 85

to the bars. The plugs are of special construction, the milled

head being hollow and threaded to receive the stem, which carries near its lower end a rectangular projection of such size as to pass

through the rectangular spaces between the bars and blocks. On

turning the head, the rectangular contact piece is rotated against

stops; and further rotation of the head clamps it against the under

side of the block and bar. The bars terminate in heavy copper

rods (bent downward at 8 cm from the bars) which serve to make

external electrical connections. As used at the Laboratoire Central, the box is placed in series with a standard, with which it is to

be compared, the standard or box being alternately short cir- cuited, which is accomplished in the case of the box by inserting

the two plugs in the holes at the ends of the same block. The

measurements are thus made by the substitution method, the

connecting resistance remaining practically the same. The variable length of the bar included is eliminated by making measure- ments with the plugs in the two possible positions, measurements

of the comparison coil being made with the plugs at the opposite

ends of both contact blocks in turn. For purposes of the very

highest precision, all forms of plug contacts are to be considered

objectionable, as the plug contact resistance is subject to some

variation which may amount to several hundred-thousandths of an ohm. The measurements given below were made at 20 , and

for the above reason the values of the coils were determined

between potential terminals.

These may be chosen in two ways, as each section can be con- nected through the contact blocks to the bars by inserting the

plugs at the two pairs of diagonally opposite ends of the terminal

blocks, thus including slightly different connecting resistances, the

coils being connected to the blocks by independent rods to either

side of the center. For this reason the connections were always

made in the following way: With the box turned so that its ter- minals are to the left of the observer, the plug making connections

to the upper bar was to the right of the corresponding plug making

connections to the lower bar. The small binding posts on the

blocks were used as current terminals, and the large binding posts on the bars were used as potential terminals.
86 Report on Concrete Standards

The values certified by the LCE from measurements by the

method of substitution were:

Coil Value at 20°

1 1. 000572

2 1. 000544

3 1. 000104

4 1. 000405

5 1. 000180

(d) The Standards of the Bureau of Standards.—The coils of the

Bureau of Standards here employed were 5 in number, all of the

sealed type.6 Three of them, numbered 3, 7, and 8, were constructed and sealed at the Bureau in 1907. Nos. 3939 and 3940

are coils especially constructed in 1909 by Otto Wolff, and sealed

at the Bureau in June 1909. In Nos. 3, 3939, and 3940, manganin wire, and in Nos. 7 and 8, manganin strip, is used. The

values assumed for them were derived from comparisons made at the Physikalisch-Technische Reichsanstalt in 1907 of two i-ohm

and 2 tenth-ohm well-seasoned Wolff standards of the PTR type.

On their return to the Bureau in September, 1907, they were compared with 8 other 1 -ohm and 5 other tenth-ohm standards of the same type, and the 2 sets were interconnected by directly determining their ratio, thus giving the relative values of all the coils on

the same basis. The values assigned to them were obtained by

giving equal weight to the comparisons made at the Reichsanstalt

for each of the 4 coils. The ten units and seven tenths were used

as a reference set until May, 1909, when they were replaced by 10

sealed units, equal weight being given to the values obtained

through the 10 units and through the seven tenths previously

used as the basis of reference. The values assigned in this report

to the 5 sealed units above described were expressed on this basis

by measurements on March 8 and 9, 19 10. A recomparison made

May 23 showed that none had changed relatively to reference set by more than 1 part in 1 000 000.

6 Bulletin, Bureau of Standards, 5, p. 413; 1908.


International Electrical Units 87

The Resistance Comparisons

The necessary comparisons were all made in a thermostaticallycontrolled and well stirred oil bath, by Dr. F. Wenner, the standards

being substituted in turn in the same arm of a Kelvin double

bridge. The connecting resistance, between the standard and an

auxiliary i-ohm coil, was eliminated without further adjustment

of the 10-ohm ratio coil employed on account of the relatively

small magnitude of the resistance in question, the coils under comparison all having approximately the same values, and the resist- ance of the connections to the auxiliary ratio coils being also very

low.

The main ratio arms consisted of a 10-ohm coil on the same side

of the bridge as the auxiliary i-ohm standard, the other arm being

in a number of sections, four of which were provided with shunt

dials producing changes in resistance of respectively, 0.000001,

0.00001, 0.0001 and 0.001 ohms per step, the minimum resistance

of the shunts corresponding to the zero setting of the shunt dials. The bridge was quickly balanced by finding the setting of the

shunt dials corresponding to zero deflection of the galvanometers.

Neglecting, for the moment, the connecting resistance to the main

ratio arm, the differences in the dial readings represent directly

differences, in parts of the whole, between the coils under comparison, the next lowest dial giving parts per million.

The small correction above referred to was determined by transferring the battery connection from the current terminal of the

standard to a terminal cup on the ratio arm, and rebalancing.

One-eleventh of the difference found corresponds to the correction, to be added to the dial reading for the corrected balance, since the

adjacent arms had resistances in the ratio of 1:10, and the

resistance in question was included in the ratio arm in finding the

principal balance.

Since with a test current of o. 1 ampere, a change in balance of

one-millionth corresponded to a deflection of 1 mm on current

reversal, the settings could be readily made to an accuracy of con

siderably better than one part per million. In the tabulated

results below, these are rounded off to the nearest 0.5 millionth.
88 Report on Concrete Standards

Since the galvanometer was permanently connected to the

bridge and the resistance under oil, the only source of error from

thermoelectromotive forces was in the galvanometer circuit

external to the bridge. These were small and sufficiently constant between reversals of the battery current to be entirely

negligible.

The Results

The measurements are expressed in terms of the mean value of

five sealed i-ohm coils as derived through comparisons of a number of i -ohm coils at the Reichsanstalt. In each case the differ- ence in parts per million between the given coil and the unit thus

defined has been given.

The resistances were all measured between the potential terminals except in the case of L 17, which has current terminals only.

According to M. Taporte, the IXE coil, Wolff No. 3961, is generally

measured between the current terminals at the Laboratoire

Central d'lSlectricite. The resistance in this case has been tabulated, using the observed difference of 18 millionths between the

potential terminals and the current terminals.
International Electrical Units 89

TABLE II

Physikalisch-Technische Reichsanstalt Coils

PTR value -

Date (1910) Temp. Measured value PTR value NBS value in Mean

milliontbs

No. 2836

Apr. 6 25° + 156.5 + 144. 5 —12.0

7 20 + 107.0 + 96.0 -11.0

11 25 + 150. 5 + 144.5 - 6.0 19-20 25 + 143. +144. 5 + 1.5 -2

30 25 + 139.0 + 144. 5 + 5.5 May 7 25 + 140.0 + 144. 5 + 4.5

14 25 + 139. 5 + 144.5 + 5.0

No. 2838

Apr. 6 25° + 146.0 +147 + 1.0

7 20 + 101. 5 + 95 -6.5

11 25 + 144.0 + 147 + 3.0 19-20 7.5 + 137.5 + 147 + 9.5 +6

30 25 + 134.5 +147 +12.5 May 7 25 + 135.5 + 147 + 11.5

14 25 + 133.5 + 147 +13.5

Relative values 2836-2838

Apr. 6 25° + 10.5 -2. 5

7 20 + 5.5 +1.0

11 25 + 6.5 -2.5

19-20 25 + 5.5 -2.5

30 25 + 4.5 -2.5 May 7 25 + 4.5 -2.5

14 25 + 6.0 -2.5

The values in the fourth column are taken from the PhysikalischTechnische Reichsanstalt data, using the Reichsanstalt formula.

In the last part of the table is given the difference between the

two coils as measured on the different days together with relative

values as given by the Reichsanstalt.

The two coils showed a decrease with respect to those of the

Bureau of Standards for the first four comparisons, and, further,

the difference between the two coils is about eight millionths
90 Report on Concrete Standards

greater than that given by the Reichsanstalt. The fifth column

contains the difference between the values of each coil as measured

at the Physikalisch-Technische Reichsanstalt and as measured

at the Bureau.

Sealed 1000-ohm No. 4089 of the Reichsanstalt at 25°

Date

Diff. in millionth s Reference coils

Apr. 22 + 124 Referred to 2 NBS coils May 17 + 124 Referred to same 2 coils 17 : +122 Referred to 6 NBS coils 23 + 118 Referred to 5 NBS 1-ohm coils

In the first comparison two iooo-ohm coils of the Bureau of

Standards were used; in the measurement of May 17 six 1000-ohm

coils, including the first two, were employed. The values of the

Bureau of Standards coils were assumed to have remained constant

since the step-up made from the five sealed units in February,

1910. The value for May 23 was obtained by stepping up from

two units to two thousands. The units were two of the five

referred to below, and were compared with the other three on

this date. The standard 4089 was compared directly with the

1000-ohm standards used in the step-up. All measurements are expressed in millionths of the nominal value.

The Physikalisch-Technische Reichsanstalt value given by

measurements from December 30, 1909, to March 9, 1910, is 1000.055 ohms at 18 . a= + 14.0 X io-6 /3= — 0.43 X io-6

The value at 25 calculated from these temperature coefficients

is +132111 in terms of the Physikalisch-Technische Reichsanstalt

standard of reference. Hence, values given by PhysikalischTechnische Reichsanstalt minus values given by Bureau of

Standards equals + 8 millionths.

The value found in the intercomparisons of November, 1908,

to January, 1909, for this same quantity was PhysikalischTechnische Reichsanstalt minus Bureau of Standards equals +8

millionths.
International Electrical Units 91

The Physikalisch-Technische Reichsanstalt standard is periodically checked against the primary mercurial standards, but the

unit as represented by four i-ohm manganin standards has not

been altered recently.

TABLE III

National Physical Laboratory Coils

NPL value

Date (1910) Temp. Measured values NPL values NBS value in Mean

millionths

L 17

Apr. 6 25° +113.0 ( + 123) ( + 10.0)

7 20 + 22.5 + 34 +11.5

11 25 + 111.0 ( + 123) ( + 12. 0) 19-20 25 +111.0 ( + 123) ( + 12. 0) +12

30 25 + 110.5 ( + 123) (+12.5) May 7 25 + 112.0 ( + 123) ( + 11.0)

14 25 + 110.5 ( + 123) (+12. 5)

L 87

Apr. 6 25° +327. 5 +325 - 2.5

7 20 + 278.0 +263 -10.0

11 25 +342. +325 -17.0

19-20 25 +334. 5 +325 - 9.5 -12

30 25 +334. +325 - 9.0 May 7 25 +341.0 +325 -16.0

14 25 +347. +325 -22.0

Relative values L 87—L 17

Apr. 6 25° +214. 5 (+202)

7 20 +255. 5 (+234)

1 : 25 + 231.0 ( +202) 19-20 25 +223. 5 ( + 202) 30 25 +223. 5 ( + 202) May 7 25 +229. ( +202)

14 25 +237. 5 (+202)

The values in the parentheses are calculated using the mean

difference between 20 and 25 measured at the Bureau of Standards, since the National Physical Laboratory observations did not

extend beyond 2i?5.
9 2 Report on Concrete Standards

The open coil L 87 has been unsteady since its arrival, and has

a relative value, with respect to L 17, larger by more than 20

millionths than before leaving Teddington. L 87 is a strip coil of

manganin capable of carrying a current of 10 amperes, and was

brought to the Bureau of Standards for inclusion in voltameter

circuits, and not primarily as a resistance standard.

The sealed coil L 17 is steady and indicates a difference in the

values of resistance at the two laboratories of

NPL - NBS =+12 millionths.

The value found in the intercomparisons of November 1908, to

May, 1909, was about

NPL- NBS = +25 millionths.

The National Physical Laboratory standard is that obtained

from the NPL mercury standards of resistance. No resistance

coils are assumed constant except over a short period of time.

TABLE IV

Laboratoire Central d'Electricite Coil

Measured values LCE value— NBS value Date Temp.

Potential terminals Current

terminals

LCE value Mean

No. 3961

1910 Apr. 6 25° + 104.0 +122.0 +234 + 112. 7 20 + 27.5 + 45.5 +151 + 105.5

11 25 + 101.0 + 119.0 +234 + 115.0 19-20 25 + 96.0 +114.0 +234 +120. + 117 30 25 + 94.0 + 112.0 +234 + 122.0 May 7 25 + 95.0 +113.0 +234 + 121.0 14 25 + 93.5 + 111.5 +234 +122.5

This coil has also been measured at the Reichsanstalt and at the National Physical Laboratory, and these determinations are given in the following table for comparison with those just made:
International Electrical Units 93

Date Place Temperature Value

Millionths

Apr., 1909 NPL 20° +15.5

July, 1909 PTR 20° +32.4

Apr., 1910 NBS 20° +27.5

Assuming that the coil has remained constant over this period,

this would indicate a value NPL-PTR = — 17 millionths, whereas

the value derived from the comparisons on the Bureau coils

November, 1908, to May, 1909, was NPL — PTR = about + 20,

that is a value of about the same magnitude but with the opposite

sign. The values in each case are for the resistance between the

potential terminals.

This coil showed relative changes, as did the other open coils

with respect to the Bureau of Standards basis of reference.

The measurements on 141 7-K are:

Coil Apr. 11 Apr. 20 Apr. 21

1 +438. +433 +436. 5

2 +443. +448 +450. 5

3 + 13.0 + 13.0

4 +312.0 +309 +310.5

5 + 83.5 + 82 + 84.5

These measurements were made at 20 between potential ter- minals. For the most part these coils, which are of bare wire on

porcelain, have remained very steady during the intercomparisons.

Bureau of Standards Coils

In the above comparisons the standard of reference was the

mean of five of the sealed standard unit coils of the Bureau.

There has been no change in their relative values greater than

one-millionth during these intercomparisons, and no relative

change greater than three millionths during the last year, except

in the case of No. 3. The following table gives an idea of their

relative constancy during this period:
94 Report on Concrete Standards

TABLE V

The Bureau of Standards Coils

1909

Coil January February March April May July October

3 +45 44 46 46 47 48 49

7 +53 54

" 54 54 54 55 55

8 +61 62 62 61/ 61 62 62

3939 3940 | Sealed June, 1909

f +89

I +88

1910

Coil February March Apr, 6 Apr. 7 Apr. 11 Apr. 20 Apr. 30 May 7 May 14 May 23

3 50 52 52 52 52 52 52.0 52.5 52.5 .53

7 54 56 56 56 56 56 55:5 55.5

~ 55.5 55

8 60 62 62 62 62 62 61.0 62.0 61.5 61 3939 89 91 90 91 91 91 91.0 91.0 91.0 91 3940 88 89 «9 89 89 89 89. 5 89.0 89.0 89

If we assume that the Physikalisch-Technische Reichsanstalt

corrections to coils No. 2836 and No. 2838 correspond to the

mean values obtained in the seven comparisons, we have the

difference between the values of these coils, as measured at the

Physikalisch-Technische Reichsanstalt and at the Bureau of

Standards, equal in the case of one coil to —2, and for the other

+ 6 millionths. Taking the mean of these and the results on the

sealed National Physical Laboratory standard L 17, we have

Millionths. PTR-NBS + 2 NPI,-NBS ... +12

Mean ' + 7 This is the correction recommended by the subcommittee to be

applied to the values given in the above tables and expressed in

terms of the Bureau of Standards basis of reference. The new

unit thus defined is intended to represent the mean values of the

Physikalisch-Technische Reichsanstalt and the National Phy-
International Electrical Units 95

sical Laboratory mercury units as represented by the coils submitted.

The following table gives the values of the coils referred to the

new unit

:

TABLE VI

Coil

2836 2838 L 17 L87

3961

Type

jopen.

Sealed

Open.

Apr. 6, 25°

+ 163.5 + 153.0 +120.

+334. 5 + 129.0

Apr. 7, 20°

+114.0 + 108.5 + 29.5 +285. + 52.5

Apr. 11, 25° Apr. 19-20, 25"

+157.5 + 150.0 + 151.0 +144. 5 +118.0 + 118.0 +349. +341.

5

+ 126.0 + 121.0

Coil Type Apr. 30, 25° May 7, 25° May 14, 25°

2836 2838 L 17 L87

3961

jopen

Sealed

Jopen

f +146.0

1 +141.5 + 117.5

J +341.0

I +119.0

+147. +142. 5 + 119.0 +348. + 120.0

+ 146.5 +140. 5 +117. 5 +354. + 118.5

Coil of 1417-K Type Apr. 11, 20° Apr. 19-20, 20° Apr. 21, 20"

Number 1 Number 2 Number 3 Number 4 Number 5

iOpen

+445. +450. + 20.0 +319. + 90.5

+440

+455 + 17 +316 + 89

+443. 5 +457. 5 + 20.0 +317.5 + 91.5

Coil Type Apr. 6, 25° Apr. 7, 25° Apr. 11, 25° Apr. 19-20, 25°

3

78 ! 3939 3940

Sealed

+59 +63 +69 +97 +96

+59 +63 +69 +98

+96

+59

+63

+69 +9

8 +9

6

+59 +63

+69

+98

+96

Coil Type Apr. 30, 25° May 7, 25° May 14, 25°

3

78 3939 3940

iSealed

[ +59. +62.5

+68. +98.0

+96.5

+59.5 +62.5 +69.0

+98.0

+96.0

+59.5 +62.5

+68.5

+98.0 +96.0

No. 3961 measurements include resistance between current terminals. 22451 —12 7
96 Report on Concrete Standards

2. STANDARD CELL COMPARISONS

Each of the delegates brought with him a considerable number

of cells, which have been repeatedly compared, under the most

favorable conditions, with those of the Bureau of Standards, thus

furnishing a basis for expressing the results of the voltameter

work undertaken at Washington, as well as for further work in

the home laboratories. In addition, this made possible the direct

comparison of the standards of electromotive force employed in

the four institutions, and furnished data of value on the accuracy

attainable in the reproduction of the Weston Normal Cell. Further

data on the last question were obtained from 48 cells 7 set up in

Washington, with four samples of mercurous sulphate representing the methods of preparation adopted in the four institutions.

Portions of each sample were washed according to the procedure

followed in the four laboratories, and three cells were set up with

each washed sample as stated below. In addition, two cells were

set up with each of four samples of cadmium sulphate submitted;

comparative tests were also made of four samples of mercury and

of cadmium or cadmium amalgam.

The comparisons were made in a basement room especially

fitted up for such work. Fig. 2 shows the general arrangement of

the apparatus. No important modifications of the installation

have been made since 1907, when a full description was published. 8

All cell comparisons are made in automatically controlled

petroleum baths, each of which is provided with coils for electric

heating, a cooling coil for water circulation when operating at

temperatures below that of the room, an efficient stirrer and means

for directing the circulation in the bath, and a sensitive thermoregulator, in addition to a rack for mounting the cells. The cells are mounted on wooden strips and held in place by

sheet metal clips. The strips were supported by a metal frame

work so that the cells were 3 or 4 cm above the level of the thermo

regulator grid and several cm below the surface of the oil. Between the cells were mounted hard rubber blocks, carrying, near the ends, copper blocks provided with a pair of holes for

7 Four additional cells were also set up by Mr. Smith. These are not included in the report, since it was previously agreed that each delegate should set up only 12 cells.

8 Wolff and Waters, Bulletin, Bureau of Standards, 4, p. 1; 1907. (Reprint No. 70.)


International Electrical Units 97

mercury cups, one pair serving for the cell terminals and the other

pair for external connections. The holes for the latter purpose were spaced at equal distances so that the cells could be put in

circuit by inserting a pair of stiff contact wires mounted in a hard

rubber block.

Connections to the potentiometer were made by the aid of three

insulated line wires extending over the baths, and to which the

leads from the contact wires and the potentiometer terminals

could be connected in any desired manner by the aid of copper

clips.

The Electrical Measurements

The measurements given below were all made by means of a

5 -dial "Wolff potentiometer of the usual construction having a

resistance of 10 ooo ohms per volt, the units of the tenth ohm dial

corresponding therefore to 10 microvolts. The potentiometer

current was furnished by a storage cell of ample capacity, which was continuously left in circuit and covered with sheet asbestos

to reduce temperature variations. Under these conditions the

current, regulated by a manganin rheostat, was sufficiently constant for all purposes.

A high sensibility D'Arsonval galvanometer, made by the Cambridge Scientific Instrument Co., was employed throughout. A

difference of 10 microvolts produced a deflection of several milli- meters, so that the values could be readily measured to microvolts, even with the high resistance potentiometer employed.

The comparisons of the cells were made by the differential

method, each cell being measured in opposition to one of the lot taken as a standard of reference. As the differences measured

were small, no errors are introduced by possible variations of the

potentiometer current likely to occur during a complete set of

measurements. From the differences thus measured, the results

could be expressed in terms of any particular cell or the mean

value of certain selected cells, by applying a suitable correction.

Sources of Error

Errors due to temperature measurement may be considered as

practically eliminated on account of the very small temperature
98 Report on Concrete Standards

coefficient of the Weston Normal Cell, about 50 microvolts per

degree at 25 °. The error made in the employment of a carefully

calibrated mercurial thermometer graduated to tenth degrees can

hardly exceed 0.01 under the very favorable conditions here met.

The perfect regulation of temperature also reduced the effect of

hysteresis to negligible proportions, except in the case of a very

few of the cells which seemed to show an abnormal hysteresis.

On account of the differential method employed in the standard

cell comparisons and the small differences in electromotive force

found, errors due to variation in the potentiometer current, and

errors in the calibration of the potentiometer, are also practically

eliminated. Care must, however, be taken to keep the switch

contacts of the potentiometer in good working order, as some

trouble has been occasionally found owing to a gradual yielding

of the hard rubber blocks carrying the contact brushes. Thermoelectromotive forces were practically absent, as shown by occasional tests, made in the customary way by reversals of both the

potentiometer battery and the connections to the cells compared.

Measurements had previously been made of all insulation resist- ances, including the resistance between cell terminals in the bath on a blank cell with the cross arm sealed off, but in every case the

resistances were found so high that this error could not exceed one

microvolt.

In view of the constancy of the results given below, as shown

by this agreement of measurements on successive days, the errors

in the relative values of the cells can hardly exceed one or two

microvolts.

The Cells and their Relative Values

The standard cells submitted by the four laboratories (types of

which are shown in Fig. 3) , and others included for various reasons

in the comparisons, are listed in the following tables which give

details concerning the source and the methods of preparation or

purification of the various materials employed, the washing of the mercurous sulphate, the date of setting up, and other information

which may be of interest.
D E

Fig. 3.

Types of Standard Cells A, National Physical Laboratory; B, Physikalisch-Technische Reichsanstalt; C, Bureau of Standards; D and E, Laboratoire Central d'Electricite

International Electrical Units 99

The tables also give the results of the comparisons made at the

Bureau of Standards, for the most part by Mr. M. P. Shoemaker.

For the older cells these include, for completeness, data obtained

before the comparisons made under the auspices of the International Committee. In all cases the values are expressed in terms

of the basis of reference adopted by the Bureau of Standards, and

originally defined as the mean value of twelve cells set up with mercurous sulphate prepared by various methods. Unfortunately, seven of these cells were accidentally short-circuited in 1908 during the determination of the temperature coefficient of the Weston

Normal Cell, and subsequently showed considerable relative

changes. They were, therefore, replaced by seven other cells, set up by Wolff and Waters, which had previously shown exceptionally uniform differences with respect to the first reference set though differing from them in the mean by approximately 14

parts 9 in 1 000 000. To preserve the continuity of values, this

difference has since been applied as a correction to the measurements.

TABLE VII

Bureau of Standards Reference Cells

Data

Cell Date Hg2 SO< Method of washing Remarks

20

21

June, 1906 ...do

bis

bio •

bJ5 bis

Acid, alcohol, CdSO< .

.

do

JtJntreated sol CdSO< used.

7 ...do do fCdSOi shaken with Cd amalgam, cloudy

10 ...do do | solution. Basic CdSO* or Cd(OH)2

[ formed; filtered solution used.

23 ...do bis do CdSO< sol. unsaturated, shaken in atmosphere of C. P. nitrogen 48 hours.

25 ...do b,s do CdSOi sol. unsaturated, shaken in atmosphere of C. P. hydrogen 48 hours.

13 ...do b» do CdSO) sol. saturated, shaken with Cd

amalgam in vacuo 48 hours.

9 In most of these cells, the CdSOi solution had been shaken under various conditions, for 24 hours or more, with Cd amalgam before it was used, to determine whether any change ensued which might affect the electromotive force.
ioo Report on Concrete Standards

TABLE VII—Continued

Bureau of Standards Reference Cells—Continued

Differences, at 25° C, in Microvolts, from Bureau of Standards Basis of Reference

Cell Feb. 7 Mar. 1 Mar. 18 Apr. 6 Apr. 7 Apr. 8 Apr. 11 Apr. 15 Apr. 22 Apr. 29 May 10 May

16

20 -27 -25 -26 -25 -25 -24 -24 -26 -25 -25 -25 -24

21 -16 -15 -14 -13 -14 -13 -13 -12 -14 -15 -13 -13

7 - 1 - 1 — — 1 - 2 - 1 - 1 - 1 - 1 - 2 - 2 - 1 10 - 4 - 3 - 3 — 4 - 5 - 4 - 4 - 4 - 4 - 5 - 5 - 4

23 -20 -21 -22 -22 -22 -22 -22 -22 -23 -23 -24 -24

25 -14 -14 -13 -12 -13 -12 -12 -12 -11 -11 -11 -10

13 -21 -21 -21 -21 -22 -21 -21 -22 -21 -22 -22 -23

Untreated CdS04 solutions were used in making up all pastes; 12.5 per cent cad- mium amalgam was employed.

TABLE VIII

Differences, in Microvolts, between Cells Employed in Voltameter Work

and the Bureau of Standards Basis of Reference. Temperature, Approximately 25° C.

Date No. 37 No. 180 No. 109 No. 56

Apr. 9 -15 -5 +3 + 7 13 -14 -2 +4 + 8 14 —14 -4 + 4 +8 15 -14 -4 +4 +8 20 -14 -5 + 2 +6 26 -15 -4 + 3 + 7 28 ' -16 -4 +4 + 6 29 -15 -4 + 3 +6 30 -15 -7 +2 +5 May 2 -15 -5 +3 +7

3 -14 -4 + 4 +7

5 -15 -4 + 3 + 7

7 -15 -4 +3 +7

9 -15 -4 +4 +7

12 -15 -5 + 2 + 5 17 -18 -7 +4

19 -20 -8 +3

-15.2 -4. 7 + 2. 8 +6.4
International Electrical Units 101

TABLE IX

Cells Submitted by the Physikalisch-Technische Reichsanstalt

Differences, at 25° C, in Microvolts, from Bureau of Standards Basis of Reference

Cell Date HgsSOi Apr.

6io Apr. 6"

Apr.

7 Apr.

8 Apr.11 Apr.15 Apr.22 Apr.

29 May

10 May16

Di [+24 +21 +17 +22 +21 +21 +21 +21 + 19 + 19 D2 [Oct. 29, 1909 xm

I 17 16 15 18 19 17 17 16 14 15 D3

1 9 12 15 16 15 15 15 15 12 13 D< [ 22 26 28 29 28 28 28 28 28 29 Eu

En

E12

El3

Oct. 30, 1909 +13 + 17 +17 +18 +18 + 18 + 18 +17 +15 +16

Jdbc. 3, 1909 ym ] 6

1 15

817714

8

15

8

16

8

15

8

15

8

15

7

13

713

I 16 18 15 15 16 15 15 15 14 14 F, [+37 +43 +44 +44 +44 +42 +43 +43 +42 +41 F8 Dec. 1, 1909 zm

I 40 43 44 44 44 42 43 43 42 42 F9 | 36 41 41 42 42 41 41 41 41 40

Fio 1 134 59 43 . 42 42 41 42 41 40 40 Hi [+37 +34 +33 +32 +32 +31 +31 + 29 +28 +27 H2 joec. 2, 1909 0m 43 37 35 36 36 35 35 33 31 31 Hj [ 36 31 29 29 29 28 28 27 25 25

Mean +26 +26 + 27 + 27 +26 +27 +26 +25 +25

Average deviation from mean ±12 ±11 ±11 ±10 ±10 ±10 ±10 ±10 ±10

10 Cells measured five to twelve minutes after putting in bath.

11 Cells measured one hour after putting in bath. FURTHER DATA SUPPLIED BY THE REICHSANSTALT.

The mercury was taken from a specially purified supply prepared for ohm work. The remaining materials (CdS04 +8/3 H2

, Cd , H2 S04) H2 and HNOa) were obtained from Kahlbaum, and are to be considered, according to tests made in the chemical

division, as the purest. The Cd was nevertheless examined by the Mylius test for zinc, and found to be free from zinc; the mercurous nitrate was recrystallized once;

the cadmium sulphate employed was also recrystallized, that for the preparation of the saturated cadmium sulphate solution once and that for the crystals twice.
102 Report on Concrete Standards

The four samples of mercurous sulphate employed were prepared by slowly adding

a solution of mercurous nitrate and nitric acid to a warmed solution of sulphuric acid

(r: 6 by volume). After settling, the precipitate was washed, by decantation, about

three times with i: 6 sulphuric acid, and then washed in portions with about 150 cc H2 on a large Gooch filter. Finally it was washed several times with small quantities of saturated cadmium sulphate solution and preserved under saturated cadmium

sulphate.

The cadmium amalgam was prepared by melting together the calculated quantities

of Cd and Hg, and contained 12.5 per cent Cd. The paste for the cells, set up the same day, was prepared in sufficient quantity for

all of them by lightly mixing the ingredients to form an easily flowing paste. Both

electrodes were finally covered with a layer of CdS04 +8/3 H2 crystals. The following table gives further data for the four samples of Hg2 S04

:

Designanation Date of preparation HgN03 HNOj H2O H2S04 H2O

Time of precipitation

Q <7 V g Minutes zm Oct. 26, 1909 150 15 150 77 100 5 ym Oct. 28, 1909 150 15 150 77 150 5±

Nov. 12, 1909 150 15 300 75 300 3.5

(sm Nov. 27, 1909 150 24 276 75 150± 1.3

The cells had not shown any appreciable relative changes before they were taken

to Washington.
International Electrical Units 103

TABLE X

Cells Submitted by the National Physical Laboratory

Differences, at 25° C, in Microvolts, from Bureau of Standards Basis of Reference

Hg2 SOi (by chem- Apr. Apr. Apr. Apr. Apr. Apr. Apr. Apr. May May

Cell Date

ical precipitation) 6

12 g 13 7 8 11 15 22 29 10 16

Ai + 9 + 9 + 11 + 15 + 15 + 14 + 15 + 15 + 14 + 13 A2 + 9 + 7 + 9 + 13 +12 + 13 + 15 + 15 + 14 + 12 A3 Sample 1 + 7 + 7 + 10 + 13 + 13 + 12 + 14 + 13 + 12 + 12 Ai + 4 + 3 + 2 + 6 + 7 + 6 + 7 + 6 + 6 + 6 As + 4 + 1 + 5 + 4 + 4 + 4 + 4 + 4 + 3

Oct., 1909 Bi r+ 7 + 5 + 5 + 9 +10 + 9 + 9 + 9 + 8 + 8 B2 Sample 2 + 9 + 8 + 8 +10 + 10 + 9 + 9 + 9 + 7 + 6 B3 1+ 4 + 4 + 1 + 5 + 6 + 3 + 3 + 3 + 1 - 1 Ci r+i7 +12 + 13 + 19 +20 + 20 +20 +20 + 20 + 19 C2 1+9 +11 + 9 + 14 + 16 + 17 + 16 + 16 + 17 + 15 Di r+29 +31 + 28 +32 +32 +31 +31 +31 +31 +29 D2 Sample 4 +31 +31 +28 +31 +32 +31 +31 +32 +32 +30 D3 1+34 +29 +25 +27 + 28 +28 + 27 +28 +27 +25

Ei f+29 +31 +25 +29 +30 +29 +29 +30 +29 +27

Ea +31 +29 + 27 +30 +32 +31 +31 +32 +31 +29 E3 Nov., 1909 1+31 +29 + 28 +31 +32 +31 +30 +31 +30 +28 E4 1+29 +36 +32 +35 +37 +35 +33 +34 +33 +30

Fi +27 +29 +26 +29 +32 +30 +29 +29 +30 +29 F2 +33 + 25 +22 +25 + 27 +26 +26 + 25 +25 +25 F3 +29 + 27 + 20 + 27 + 29 +28 +26 + 25 +25 +25 F< +41 +31 + 28 +31 +35 +33 +33 +34 +35 +34

Gi +37 +36 +33 +37 +39 +38 +36 +35 +35 +33 G2 +35 +39 +35 +40 +41 +40 +37 +38 +36 +35 G3 Sample 7 +33 +36 +32 +36 +38 +36 +35 +35 +34 +32

Ga + 29 + 30 + 28 +31 +33 +32 + 30 +31 +30 + 29 G5 +29 +35 +31 +35 +36 +34 + 32 +32 +31 +30

Hi

Jan., 1910 +34 +36 +33 +37 +38 +37 +35 +35 +34 +34 H2 +36 +37 +32 +36 +37 +36 +35 +35 +35 +33 H3 Sample 8 ' +37 +37 +34 +38 +39 + 38 +36 +35 +34 +33 Hi +31 +32 +30 +34 +35 +35 +34 +35 + 33 +32 H5 1+37 +31 +27 + 29 +31 +31 +31 +31 +30 +29

Ki r+22 +22 + 18 +21 + 22 +20 +19 + 18 +17 +16 K2 jpeb., 1910 Sample 9 |+25 +27 + 23 +26 + 27 +27 + 26 +25 + 24 +23 K3 1+22 + 22 + 17 + 19 + 21 + 19 + 18 + 18 + 17 + 16 Mean _ _ _ + 24 + 22 + 25 + 26 + 25 +25 + 25 +24 + 23

±10 ± 9 ± 9 ±10 ± 9 ± 9 ± 9 ± 9 ± 9

12 Cells measured five to twelve minutes after putting in bath.

13 Cells measured one hour after putting in bath. The following additional data were supplied by the National

Physical Laboratory:

The mercury for all cells was distilled twice, and electrolytically purified before

distilling for some of the cells.
104 Report on Concrete Standards

The cadmium sulphate was recrystallized from slightly acid, pure commercial salt. Most of the cadmium amalgam was prepared by depositing cadmium into mercury by electrolysis. All the cells contained 10 per cent amalgam.

The methods of washing the mercurous sulphate, preparing the paste, etc., were

in the main identical with those described in the appendix to the report of the London

Conference. The same paste mixture was used in setting up cells designated by the same letter. TABLE XI

Cells Submitted by the Laboratoire Central d'Electricite

Differences, at 25° C, in Microvolts, from the Bureau of Standards Basis of Reference

Cell Apr

6"' Apr

6

ii' Apr.

7 Apr.

8 Apr.

11 Apr.15 Apr.22 Apr.29 May10 May

16

E» -74 -41 -17 -12 -19 -18 -21 -23 -29 - 3 En -46 -31 - 2 — 1 - 2 —11 -14 -12 -19 -21

E13 -16 + 2 + 6 + 4 - 9 -15 -19 -22 -31 -33 En - 3 +15 +27 +29 +20 +19 +15 + 14 + 8 .+ 8

T>i +73 +79 +45 +49 +49 +49 +49 +49 +52 +55 D3 +68 +78 +46 +49 +50 +48 +48 +47 +45 +45

Pi +72 +61 +65 +67 +67 +64 +64 +63 +61 +62 Pi +62 +63 +68 + 69 +69 +68 +68 +67 +67 +67 P3 +79 +67 +68 +69 + 69 +68 +68 +68 +67 +65 Sj — 1 +16 +27 +31 +34 +35 +43 +53 +80 +98

s, + 9 +17 +27 +31 +34 +34 +33 +31 +28 +26 s5 +37 +35 +26 +27 +26 +24 +23 + 18 + 14 +11 Sr +39 +47 +55 +57 +55 +53 +53 +52 +48 +46 S8 +11 + 17 +30 +35 +38 +38 +37 +37 +31 + 29 Zs +56 +61 +66 +69 +68 +67 +66 + 65 +64 +64 Mean +35 +38 +37 +35 +34 +34 +32 +35

Average deviation from mean ±22 ±22 ±23 ±21 ±25 ±26 ±30 ±30

14 Cells measured five to twelve minutes after putting in bath.

15 Cells measured one hour after putting in bath. The following additional data concerning the above cells were

submitted by M. Laporte

:

Cells designated by the same letter were made of the same materials and at about

the same time. The methods of preparation and purification of the materials were the same as those described in the paper by Janet and Jouaust. (Bull. Soc. Int. des Elect., 8, 409;

1908.) The washing of the Hg2S04 was always done at the time of making up the cells. Concentrated CdS04 was used for this purpose and continued until congo paper showed no blue color after 10 minutes contact with the nitrate. The Hg2 S04 sample in the D and S cells was prepared by D. C. electrolysis. The

sample for the P and Z cells, as also a second sample for the E cells, was made by

A. C. electrolysis.
International Electrical Units 105

TABLE XII

New Cells Submitted by the Bureau of Standards

Data

CeU Date Hg2SOJ Method of washing Remarks regarding Hg2SOi, etc.

222 1 b 61 A. E. V.

226 b 61 A. E. V. 3 samples mixed after washing and exposed to air 2 days.

228 b 61 A. E. V. Exposed to air for 1 day.

230 b 60 A. E. V. 90% saturated solution of CdSOi used in paste.

231 b 58 A. E. V.

232 b 59 A. E. V. (Flooded with alcohol and let stand 1 hour.

233 b 60 A. E. V. J 240 b61 A. E. V. Duplicate of cell 222. 241 b44 A. E. V. Washed 1908; materials mixed dry; cell exhausted and

242 243b 61 b 61

A. E. V. A. E. V.

CdSOj solution admitted.

[Duplicates of cell 222.

J 244 Feb., 1910 b61 A. E. V. Materials introduced dry; cell exhausted and CdSO*

solution admitted.

245 b 44 A. E. V. "W/a^hpH ,v aaucu lQnS* 17UO, Tflfltprialc 1UO.IG1 laia> intrnrluppH 11111 uuul~cu da \v\ 111 ppll I.C11 ?dd 246 b 61 A. E. V. F. ISame paste; Hg2 SOj washed and digested with alcohol 247 b 61 A. E. V. F. and ether. 248

249 b 61 b 61

A. E. V. F. A. E. V. F. [Same paste; same materials as in cells 246 and 247.

J 250 b 61 A. E. V. F. Two pastes for cells 246-249 mixed and let stand 1 hour.

251 b 44 A. E. V. Washed 1908; rewashed 1909; ingredients of paste not mixed dry. 252 b 44 A. E. V. "V^ashed 1903; rewashed 1909; ingredients of paste mixed

dry. 257 b 44 A. E. V. Q,itid oil matori^l oo i« i»olle 9^1 anil 9^9. i_i rr„a~i . otffro/1 lie IlldLclldl da 111 (.Glib CJl dud Irig .OUi Sliteu through Pt. gauze.

259 b 67 A E V Exposed to air 5 hours altogether; sealed in vacuo.

275

nr 1010 b 67 A. E. V. HgsSOi sealed in vacuo; sifted through Pt. gauze before

using.

276 0/ A. Ejt V . Duplicate of cell 275. 277 b 67 A. E. V. Exposed to air 1 month; sifted through Pt. gauze. B22 b 62 A. E. V. F. B24 b 63 A. E V F Hg:SO i also digested with alcohol 1 hour, and rewashed B25 b 64 A. E. V. F. I and dried. £26 b 67 A. E. V. F. B27

Feb., 1910

b 61 A. E. V. ngSDLfi lei MdllU in dir dnu reuigesiea 111 C01Q 1U L. 4 washed as in B22. B29 b 43 A. E. V. After washing, Hg2SOi kept in sealed bottle 1 year; re- washed as B22. B32 Chem. F. A. E. V. Hg2SOj made according to NPL specifications. B38 b 67 A. E. V. Washed as in B22. B39 Chem. F. A. E. V. Same as in B32. B40 b 67 A. E. V. Under house vacuum 4 hours after washing. B41 b 67 A. E. V. Hg2SO< exposed to air several days, and then kept under

vacuum. B43 Mar., 1910 b 61 A. E. V. Hg2SC>4 let stand in air for several weeks. B45 b 67 A. E. V. Same as cell 259. B49 b61 A. E. V. Hg2 SO< exposed to air of basement 1 month. B50 b 67 A. E. V. Same as B45.
io6 Report on Concrete Standards

TABLE XII—Continued

New Cells Submitted by the Bureau of Standards—Continued

Differences, at 25° C, in Microvolts, from Bureau of Standards Basis of Reference

Cell

1-4 days9-20 days Apr. 7 Apr. 8 Apr. 11 Apr. 15 Apr. 22 Apr. 29 May 10 May 16

222 226 +28 +72 +44 +36 +37 + / +37

-1- + 7/ +38 + o +36 + / +34 +

+33 + 3 +31

228 230

231 232

233 240

241

+71 + 27 +20 + 16 + 18

+ 14

+46 + 20 +19 + 18 + 17

1 1 Q + 6

+38 + 15 + 19 +24 +21 + 16 + 8

+39 + 17 +21 +27

+23

lie +13 + 9

+38 +17 + 21 +26 +22

_t_1(» +10 + 12

+38

+17 +20 +25 +22 +16 + 9

+36 +17 + 21 + 26 + 22 +10 + 10+34

+16 +20 +25 +22

_l_1ft + 10 +10

+33 + 16 + 19 +25 +22 +17 + 9+33 +18 +20 +26 +24 +17 + 9

242 243

244

+ 29 +26 + 14

+17

+12 + 8

+ 16 + 11 + 10

+16

+12 + 9

+17 + 13 +12

+ 15 +11 + 10

+ 16 + 12 + 11

+16 +11 +10+ 15 + 10 + 10

+15 + 10 + 10

245

246

247 248

249

250

251

+53 +30 +42

+32 +30 +53 +41

+29 + 18 + 28 +22 + 19 +39 +22

+24 + 15 +21 + 14 +15 +30 +17+25 + 15 +22 + 14 + 15 +31 + 19+ 28 + 17 +22 + 16 +16 +32 +19+25 + 15 + 19 + 15 + 15 + 29 + 17+24 + 14 + 18 + 15 + 14 +27 + 16

+22 +13 + 17 + 14 + 14 +26

+16

+22 +13 +16 + 14 + 13 +25 + 16+ 21 + 11 +15 +13 +12 + 24 +15

252 + 28 + 17 + 14 + 16 +17 + 15 +15 + 15 + 13 + 13

257 +37 +27 + 24 +25 +27 + 24 + 24 +23 + 20 +21

259 275 + 17 + 13 + 15 + 4 +11 + 4 + 12 + 5 +12 + 7 + 12 + 6 +12 + 6 + 10 + 6 + 7 + 3 + 7 + 4

276

277 B22

B24 B25

B26

B27

+12 +35 + 21 + 22 +25 + 14 + 29

+ 2 +24 + 22 + 20 +18 + 14 +24

+ 2 +24 + 20 + 19 + 11 + 11 +20

+ 4 + 26 + 21 +19 + 12 + 11 + 19

+ 5 +27 + 22 +20 +13 +12 +20+ s +25 + 22 + 20 + 14 + 13 + 20

+ 5 +26 +22 + 20 + 13 + 13 + 19+ 5 +26 + 21 + 19 +13 + 13 + 18

+19 + 19 + 18 + 12 + 12 + 17

+ 10 +20 + 19 + 13 +13 + 17 B29 +12 + 10 + 10 +10 + 10 + 11 + 11 +11 + 10 +10 B32

B38

B39 B40

B41

+37 +14 +39 +32 +38

+ 12 +36 +25 +32

+22 + 14 +28 +23 +30

+ 20 +13 + 28 + 22 +29+21 +15 +29 +23 +29

+ 20 + 15 + 28 +22 +29+ 20 + 16 + 28 +23 + 29

+19 + 17 +27 + 22 +28+ 18 + 17 +25 +20 +27

+19

+18 + 26 +21 + 27 B43

B45

B49 B50

+20 + 13 +20 + 10+ 17 + 9 + 19 + 10+20 + 8 + 18 + 9+ 18 + 7 +18 + 11+20 + 8 + 18 + 9+19 + 7 + 18 + 10

+ 20 + 7 + 19 + 10

+ 20 + 7 + 18 + 10

+ 18 + 6 + 18 + 9

+ 19 + 7 + 19 + 9 Mean + 29 + 20 + 17 +18 +19 + 18 + 18 + 17 + 16 + 16 Average deviation from mean ±11 ± 7 ± 7 ± 6 ± 6 ± 6 ± 6 ± 6 ± 6 ± 6
International Electrical Units

METHOD OF WASHING AND DRYING THE MERCUROUS SULPHATE A indicates washing with, absolute alcohol. E indicates washing with anhydrous ether. V indicates drying in vacuo. F indicates that material was flooded with the wash liquid and allowed to stand one

hour or more. The general procedure was the same in other respects as described elsewhere except

that 10 per cent cadmium amalgam was employed throughout. The cells were set up by F. A. Wolff and E. C. McKelvy.

Discussion of the Results

It will be seen from the foregoing tables that the relative values

of the same cell, as obtained in the various comparisons, show,

with few exceptions, a most excellent agreement which must be

attributed in great part to the very perfect temperature regulation

maintained throughout the whole period of the measurements.

Bureau of Standards Reference Cells.—The constancy of the rela- tive values of the reference cells used by the Bureau of Standards,

as shown by Table VII and by measurements extending over a long

period, led to the provisional adoption of the Bureau basis of refer- ence for expressing the results of all the measurements, particularly as no decision could be reached in advance as to any other

basis for expressing the results. Bureau of Standards Cells employed in Voltameter Work.—Table

VIII shows the relative constancy of W 109, the cell employed

throughout in the voltameter work, and that of three others maintained in the same bath. These cells were selected from a large

number employed in the determination of the temperature coeffi- cient of the Weston cell in 1908, 18 on account of the small hysteresis shown. Slight differences are in part due to the temperature not having been exactly 25 throughout. Xo correction is

; however, required for this, as the cells were compared with the

reference cells at 25 and were used at the temperature of the bath.

The measurements made by the aid of a special line, highly

insulated, are in almost exact agreement with check comparisons

made on transferring one of the cells to the bath containing the

reference cells.

16 Wolff . Bulletin, Bureau of Standards, 5, p. 309; 1908.
io8 Report on Concrete Standards

The Cells Submitted by the Four Laboratories.—The relative

values of the separate cells constituting four groups (Tables

IX-XII) show changes from their means which do not exceed

±3 microvolts except in a few instances, excluding the first two

sets of comparisons made ten minutes and one hour after they were placed in the comparing baths.

From the tables it appears that the mean values of the normal

cells submitted by the four laboratories are in most excellent

agreement, and, also, that the average deviations of individual

cells from their respective group means are quite small.

The values of the French mean and the average deviation of

the individual cells from the group mean may, as suggested by

M. Taporte, be affected in part by the cells of high value, set up

with mercurous sulphate prepared by alternating current electrolysis, since similar high values have been found at the National

Physical Laboratory and at the Bureau of Standards with a sample of mercurous sulphate prepared by this method at the

Laboratoire Central, and also with the French sample employed

in Washington. Moreover, the values of some of these cells show

relative changes from the comparisons previously made in the

home laboratory, thus increasing the average deviation from the

group mean. As indicated by M. Taporte, most of the French

cells are several years old, as it was impossible to set up new cells before the Washington meeting, since arrangements for the participation of the Taboratoire Central d'EUectricite were not completed until shortly before the meeting.

Summary

From Table XIII, which shows the values of the separate group means for eight series of comparisons (the first two series being

excluded for reasons stated above), it is seen that the average

variation of any of the group means hardly exceeds ± i microvolt, and that the average deviation of all of the groups from the

mean of the group means is approximately ±5 microvolts, which

may, indeed, be considered as a most excellent agreement.

For this reason, it was decided by the committee that the

voltameter results should be expressed in terms of the mean of

the group means of the four sets of cells, thus necessitating a
International Electrical Units

correction of +26 microvolts to the results expressed in terms of

the basis of reference of the Bureau of Standards. Assuming,

further, that the cells now set up have the same value as the

cells which formed the original basis of reference of the Bureau,

it would appear from Table VII that these reference cells have

decreased by approximately 2 parts in 100 000 since 1907.

The mean value of W 109 employed in the voltameter work,

after applying the above correction of 26 microvolts, is equal to the mean value of the group means less 23 microvolts. This

correction has been applied in the tables below giving the results

of the voltameter experiments.

TABLE XIII

Differences, in Microvolts, between Separate Group Means and the Bureau

of Standards Basis of Reference

Group Mean—NBS Basis of Reference

Number of cells Apr.

7 Apr.

8 Apr.11 Apr.15 Apr.

22 Apr.

29 May10 May16 Means

Means

minus

group mean

Average

deviation

of individ- ual cells from separate group means

PTR 15 +26 +27 +27 +26 +27 +26 +25 +25 +26 ±10 NPL 34 +22 +25 + 26 +25 +25 +25 + 24 +23 +24 -2 ± 9 LCE 15 +35 +38 +37 +35 +34 +34 +32 +35 +35 +9 +25 NBS 40 +17 + 18 + 19 +18 + 18 +17 + 16 + 16 +17 -9 ± 6 Mean of group means + 25 +27 +27 +26 +26 +26 +24 +25 +26

New Cells set up at Washington by the International Committee

In order to determine the effect of different methods of preparation and of washing the mercurous sulphate, it was agreed

by the committee (see minutes of the seventh meeting) "that

representatives from each of the four laboratories receive samples from representatives of each of the other laboratories, and

that with this material and his own he make up 12 cells—three

from each of the samples, using the method of preparation which

he chooses." It was further agreed that the mercury, cadmium

amalgam, cadmium sulphate crystals, and solution, should be
I IO Report on Concrete Standards

taken from a common supply furnished by the Bureau of Standards.

In addition it was agreed to permit the representatives of the

Bureau of Standards to set up eight cells—two each with the

samples of cadmium sulphate from the four institutions, the other

materials being the same, and to compare the mercury and cadmium amalgams brought to the Bureau with those used in setting

up the 48 cells. This program was carried out in so far as time permitted.

Owing to the numerous voltameter experiments made, and the

sessions of the committee, and the impracticability of more than

one person setting up cells at the same time, the operation of

washing the mercurous sulphate by M. Laporte, was done under

most unfavorable conditions, and extended over a number of days.

Prof. Jaeger washed only his own sample of mercurous sulphate,

Mr. McKelvy washing the remaining samples in accordance with

the instructions furnished, preparing the pastes, and setting up

the 12 cells representing the Physikalisch-Technische Reichsanstalt procedure.

The Mercurous Sulphate

Three samples of mercurous sulphate were prepared in Washington by the following methods:

1. By the precipitation method, by Prof. Jaeger.

2. By the precipitation method, by Mr. Smith.

3. By direct current electrolysis, by Mr. McKelvy.

Three samples of mercurous sulphate were made, using a cur- rent density of 4.7 amperes per dm 2 for 5.5 hours. The sulphuric

acid used was J. T. Baker's best, diluted to 1 : 6 by volume (23.5

per cent H2S04 or 2.8 N). The mercury used was the same as that used in constructing the cells. The three samples were mixed

thoroughly and kept under 1 : 6 acid. The sample was separated

from the excess metallic mercury by decantation.

An apparatus was also constructed for preparing mercurous

sulphate by alternating current electrolysis, as prepared by the

Baboratoire Central d'EUectricite. With the particular apparatus,

the yield was so small, using a 60-cycle current, that no solid mercurous sulphate had been precipitated at the end of two hours.
International Electrical Units in

With a frequency of 42 cycles per second, the yield with a current

of 5 amperes was insufficient after 24 hours' continuous operation

to set up the 12 cells agreed upon. A sample prepared by the same method at the Laboratoire Central d'^lectricite, by M. R.

Jouaust, was therefore used instead. This sample had been prepared in 24 hours. The more rapid production of mercurous

sulphate is attributed to a stronger agitation of the surface of the

mercury.

The Washing of the Mercurous Sulphate

Physikalisch-Technische Reichsanstalt.—The white sample precipitated chemically by Dr. Jaeger was washed with water three

times by decantation, then five times with small portions of a satu- rated CdS04 solution in a Gooch crucible provided with a filter paper disk as filtering septum. The PTR sample was kept under

saturated CdS04 solution until used. The three other samples were used immediately after washing.

Bureau of Standards.—The four samples used in making up the

12 cells representing the Bureau of Standards procedure were washed twice with pure absolute alcohol in a Gooch crucible, then

let stand under alcohol in a beaker for an hour. On again transferring to the crucible, they were washed twice with alcohol and

then twice with anhydrous ether. These samples were then

placed in a high vacuum and so kept until used.

Laboratoire Central d'Electricite.—The washing of the four samples was made in a Gooch crucible using a disk of filter paper. It was washed twice with H2S04 of spec. grav. 1.15, then several

times with a concentrated solution of CdS04) until a piece of

congo paper placed in contact with the last wash water showed

only a slight tendency to become blue. As a result of the meetings and other circumstances, the washing was interrupted several

times, and lasted several days. The cells were then set up under

very unfavorable conditions.

National Physical Laboratory.—The sample precipitated chemically by Mr. Smith was washed with dilute H2 S04 (1 to 6) twice

by decantation. The precipitate was then filtered, washed three

times with dilute H2 S04 and afterwards 6 times with a neutral

saturated solution of cadmium sulphate to remove the acid. The

22451 —12 8
112 Report on Concrete Standards

mercurous sulphate was then flooded with cadmium sulphate

solution and left for one hour. It was then washed twice more

with cadmium sulphate solution.

The Remaining Materials

The Mercury.—All the Hg used in this investigation was first subjected to a preliminary purification by electrolysis. It was

then further purified by distilling it at least twice in a current of air

under greatly reduced pressure, according to Hulett and Minchin.17 The essential feature of this method is the oxidation of any

metals, that may distill with the mercury, by means of a slow cur- rent of air, admitted through a tube drawn out at one end to a very fine capillary extending almost to the bottom of the distilling bulb.

The Cadmium Amalgam.—The 10 per cent amalgam was made up

by direct weighing from Kahlbaum's electrolytic cadmium and

the purest mercury. The thin film of oxide on the surface of the

cadmium was removed by means of dilute sulphuric acid. This was removed by thorough washing with pure water, the amalgam

then being dried before weighing.

The Cadmium Sulphate.—Kahlbaum's cadmium sulphate, prepared especially for standard cells, was treated in the manner

prescribed by Wolff and Waters. The final product was crushed

and thoroughly mixed to give a uniform sample. This cadmium

sulphate was used for this entire series of cells. The Cadmium Sulphate Solution.—The cadmium sulphate described above was added in excess to the purest water, and the whole

rotated at 25 ° in liter bottles for at least a day. The solution was

then filtered. This solution was used in washing the mercurous

sulphate, and in constructing the cells by all the representatives,

and was made in such quantity as to cover these operations for

all the cells set up, where it was desired to keep the cadmium sul- phate constant.

Setting up the Cells

All the cells were set up in the manner described in the appendix to the report of the London Conference.

17 Physical Review, 21, p. 388; 1905.
International Electrical Units "3

Sealing

All the cells were hermetically sealed in glass without overheating the cell contents in any case. The Results

The differences, at 25 C, found between these 48 cells and the

mean of the group means, used as the basis of the voltameter

experiments, are given in the following Table XIV:

TABLE XIV

Cells set up by the International Committee

Set up by Dr. Wolff and Mr. McKelvy, May 9, 1910

Cell Hg2 SO< May 12 May 14 May 16 May 24 May 27 May 31 June 6 June 14 June 20

301 - 8 -10 -13 -15 -16 -16 -17 -18

302

| NBS - 8 -10 -14 -17 -17 -17 -18 -18

303 { + 1 - 3 - 5 -10 -13 -14 -13 -14 -15

304 f +15 + 14 +15 + 16 +15 +15 + 18 +19 +19

305 J LCE | +13 + 13 +14 + 16 + 16 + 16 + 18 + 18 +18

306 I +17 + 17 + 18 + 18 +17 +17 +19 + 19 +20

307 ( -26 -30 -30 -34 -35 -36 -35 -35 -34

308 J NPL | -39 -41 -42 -40 -41 -41 -39 -39 -38

309 I -25 -29 -31 -33 -35 -36 -34 -35 -34

310 r +12 + 9 +10 + 11 + 9 + 9 +12 +12 +12

311

| PTR | +12 +

9' + 11 +10 + 9 + 9 + 11 +11 + 11 312 1 +11 +10 + 10 + 10 + 8 + 8 + 10 +10 + 10 Mean -1.6 -3.9 -4. 2 -5.2 -6. 8 -7.2 -5.5 -5.8 -5.6

Average deviation from mean. ±15.4 ±16.

1

±17.2 ±18.8 ±19.2 ±19. 5 ±20.2 ±20.6 ±20.6

Set up by Mr. Smith, May 13, 1910

313 -15 -27 -29 -31 -32 -31 -31 -31

314

J NBS - 5 -23 -31 -34 -35 -35 -35 -36

315 - 4 -10 -14 -18 -18 -20 -21 -21

316 +34 +29 +22 + 18 +17 + 18 + 16 + 16 317

| LCE

1

+27 +22 +19 + 16 +15 + 17 + 16 +16

318 +50 +42 +31 +29 +26 +26 +23 +23

3f9 +44 +22 + 8 + 2 + 1 - 1 - 5 - 6 320

| NPL

1 +34 +17 - 2 - 9 -10 -13 -18 -18

321 +33 + 13 + 3 - 3 - 4 - 7 -11 -12

322 + 8 + 6 + 5 + 2 + 3 + 3 + 3 + 2 323

J PTR + 2 + 3 + 3 + 2 + 2 + 2 324 + 18 + 13 + 10 + 8 + 8 + 9 + 7 + 6 + 18.8 +8. 9 +2.

1

-1.7 -2.4 -2.7 -4. 5 -4.9

Average deviation from mean ±18.2 ±15.9 ±14.

1

±14.5 ±14.4 ±15.5 ±15.7 ± 14.9
114 Report on Concrete Standards

TABLE XIV—Continued

Cells set up by the International Committee—Continued

Set up by M. Laporte, May 24, 1910

Cell Hg2 S01 May 12 May 14 May 16 May 24 May 27 May 31 June 6 June 14 June 20

325

326

327

328

329 330

331 332 333

334

335

336

NBS

LCE

NPL

PTR

Mean

Average deviation from mean

.

+ 163 +199 +236 - 26 + 91 + 92 + 171 +200

+208 +165 + 105 +171

+ 157 +182 +214 + 22 + 84 + 85 +163 +179 +193 +162 + 130 +154 +147. 9 + 143.8

±54.9 ±42.2

+154 +172 + 199 + 48 + 80 + 81 + 157 + 166 + 179 +150 +131 +143+ 144 +158 + 183 + 49 + 75 + 76 + 143 + 150 + 164 +138 + 124 + 133

+132 + 143 +166 + 46 + 69 + 71 + 134 +139 + 153 + 127 +114 +123 + 138.3 + 128. 1 + 118.1

±35.7 ±31.4 ±28.8

Set up by Mr. McKelvy for Dr. Jaeger, May 26, 1910

337

338 339 340

341 342 343

344

345

346 347

348

NBS

LCE

NPL

PTR

Mean

Average deviation from mean

—32

-15

-41 + 16 +29 + 14 + 4 + 3 + 8 +39 +65 +35 + 10. 4

-38

-29

-48 + 11 + 17 + 7 —12

-12 - 9 +25 +40 + 15

-2. 8

; 21. 9

-37

-32

-41 + 13 + 17 + 10 -15

-14

-13 +25 +34 + 12

-3. 4

±21.9

-36

-33

-38 + 13 + 16 + 10 -18

-17

-15 +24 +30 + 11

-4.4

±21. 8

-35 -32

-36 + 15 + 18 + 12 -18

-17

-15 +23 +27 + 8

-6. 7

±21.3
International Electrical Units "5

The agreement of the separate cells of each group of three is quite close, as might have been expected, since the same paste

mixture was employed.

The average deviations from the respective group means of the

separate cells in each group of 12, representing the four samples of mercurous sulphate washed by the same method, are, however, considerably larger than were found in the case of the

cells submitted by the four laboratories, where each group was

set up according to the same specifications. The means for the

groups, with the exception of the cells set up by M. Laporte,

which, as already explained on p. 111, were constructed under

abnormal conditions, are, however, practically identical with the

mean of the group means given in the main body of the report,

thus indicating apparently that no differences are introduced by

the differences in procedure followed.

TABLE XV

Group Means for New Cells set up in Washington by International Committee

Hg2 SO<

Set up by

Means

omitting LCE NBS LCE NPL PTR

NBS -17 +19

-35 +11

+ 147 + 62 +142 + 121

-29 +18

-12 + 3

-34 + 15 -17 +19-27

+17

-21 + 11

LCE

NPL

PTR

Means - 6 +118 - 5 - 4 - 5

The comparison of the separate means for the four samples of mercurous sulphate, as shown by the values given on the same

horizontal line, Table XV, is also fairly satisfactory, omitting the

cells set up by M. Laporte for the reasons stated above. Differ- ences are, however, indicated, by the means given in the last column, between the four samples of mercurous sulphate, the

NBS and NPL samples both giving, respectively, values 27 to 21
1 1 6 Report on Concrete Standards

parts in i ooo ooo lower than the mean of the group means

adopted by the committee, and the LCE and PTR samples higher

values by 1 7 and 1 1 parts in i ooo ooo. To establish these as

real differences considerable more investigation would be required.

In particular, the fact that the mercurous sulphate prepared by

alternating current electrolysis gives cells whose emf is a little higher than usual, has been observed by several experimenters.

This is not to be explained by the dimensions of the crystals of

the Hg,S04. Measurements made at the IXE have shown that

the crystals have a magnitude of from 3 to 6 thousandths of a mm to more than .02 mm. This corresponds closely with the

dimensions given by Mr. Smith for crystals prepared by other

methods.

Other Cells set up

It was agreed by the committee to permit representatives of

the Bureau of Standards to set up two cells with the four samples

of cadmium sulphate submitted by the four laboratories, using

the same sample of mercury and cadmium amalgam as used in

the 48 cells, and a common sample of mercurous sulphate. The

latter was prepared by the electrolytic method, and washed with

alcohol and ether, and since preserved in a highly evacuated

glass tube, thus eliminating sources of error due to washing. The

dry sample was freed from lumps by sifting through platinum

gauze, and was then thoroughly mixed.

The cadmium sulphate samples, except in the case of the

Bureau of Standards, do not represent the stock employed in

setting up the main group of cells. Samples of crystals and

saturated solutions were submitted by three of the laboratories,

but only crystals were submitted by the Laboratoire Central

d'PJectricite. From the latter a saturated solution was made.

The results on the cells set up in this manner are given in Table

XVI.
International Electrical Units 117

TABLE XVI

Cells set up with Different Samples of CdS04

Differences, in Microvolts, from Mean of the Group Mean

CeU CdSd May

10 May12 May14 May16 May

24 May

27 May31 June6 June14 June

20

349 1 NBS

-14 -16 —19 -21 -23 -25 -25 -22 -25

350 —11 -12 -15 -19 -20 -22 —22 -21 -23

351 Jlcef -27 -29 -28 —29 -29 -30 -30 -28 -27 -28

352 1 -27 -29 -29 -30 -30 -31 -30 -29 -28 -29

353 |npl -19 -21 —22 -23 -24 -25 -25 -25 -23 -24

354 I -14 -20 -21 —22 -23 -24 -24 -23 -21 -23

355 |pTR r+u - 1 - 3 — 4 -12 -14 -19 -20 -22 -25

356 1 +10 - 2 — 4 - 5 -12 -15 -19 -20 -23 -28 Mean - 9 -16 -17 -18 -21 -23 -24 -24 7/i -26

Average deviation from mean_. . ±13 ± 9 ± 8 ± 8 ± 5 ± 5 ± 3 ± 3 ± 2 ± 2 !

From Table XVI it will be seen that at the last measurement

the cells are in practical agreement ; the initial difference between

them has been steadily decreasing. Their mean value is now less than the mean of the group means adopted as a basis of refer- ence. It is particularly noteworthy that the two cells set up

with the Laboratoire Central d'ETectricite sample attained their

normal value immediately after they were set up. As this is one

of the principal objects sought, it is felt that further investigation

of the CdS04 solutions is highly desirable. Three other cells,

since set up with the same sample of CdS04 , also showed an exceptionally small hysteresis.

Two four-limb cells were set up to compare the samples of

mercury and cadmium or cadmium amalgam with those employed

in setting up the Bureau of Standards cells and the cells set up

by the committee in Washington. Here, again, the samples submitted, except in the case of the Bureau cells, did not represent

the materials employed for the particular cells submitted by the

respective laboratories. It was, however, thought that a comparison might be interesting.

The samples of mercury compared were the following:

(a) Purified at Bureau of Standards by Hulett's method.

(6) Purified at Bureau of Standards by making the mercury the

anode in electrolysis.
1 1 8 Report on Concrete Standards

(c) Purified at Physikalisch-Technische Reichsanstalt.

(d) Purified at National Physical Laboratory.

The samples were covered with the same paste mixture. The

differences in electromotive force, in microvolts, are given in the

following table, from which it appears that, although one of the

samples differed by 17 microvolts initially, all the samples were

in practical agreement after six weeks.

TABLE XVII

Comparison of four samples of Mercury

Differences, in Microvolts

Sample May 10 May 11 May 12 May 14 June 20

(b)-(a) - 1 - 1 (c)-(a) +17 +16 +13 +12 +4

(d)-(a) + 3 + 3 + 3 + 4 +2

The cadmium amalgam samples, all containing 10 per cent

cadmium, were the following:

(a) Prepared at Bureau of Standards from Kahlbaum's best

electrolytic cadmium.

(b) Prepared at Laboratoire Central d'filectricite by electrolysis (originally 12.5 per cent).

(c) Prepared at Physikalisch-Technische Reichsanstalt.

(d) Prepared from sample of 15 per cent amalgam submitted

by the National Physical Laboratory.

The amalgams were introduced into the cell, covered with

CdS04 crystals and saturated CdS04 solution, and the cell sealed.

The differences, in microvolts, are given in the following table:

TABLE XVIII

Comparison of four samples of Cadmium Amalgam

Differences, in Microvolts

Sample May 10 May 11 May 12 May 14 June 6

(b)-(a) - 3 - 3 - 3 - 3 —.3

(c)-(a) - 3 (d)-(a) -36 -36 -37 -37 -37
International Electrical Units 119

The National Physical Laboratory amalgam is one of a series

investigated by Mr. Smith in 1908, 18 and showed surface change

which reminded one of tin " plague." It was taken to Washington

to point out this appearance to the committee. It was made from

electrolytic cadmium and originally the amalgam had been completely melted and chilled by sudden cooling to — 30 . In making

up the 10 per cent amalgam, it was heated with the required

amount of mercury until the whole was melted and then filtered

through a capillary to remove the surface contamination, and

introduced into the cell on remelting. This should, however, have

given normal values, since any effect of chilling the original

amalgam should have been eliminated by diluting and remelting.

It is suggested that in the future international cooperative

work the cells submitted by each laboratory be set up from the same supply of mercury, amalgam, and cadmium sulphate, and

that samples be preserved for subsequent comparison.

Report on Measurements made on the Cells submitted for Comparison to determine the Magnitude of the Hysteresis following

Temperature Changes

After the 10 measurements above discussed, supplementary

observations were made at 30 , 20 , and 25 , to determine whether

there were any marked differences between the cells with respect

to the rapidity with which they adjusted themselves to temperature changes.

The baths were first regulated at 30 by increasing the electrical

heating, and this temperature was maintained within 0.02 for

48 hours. The temperature was then reduced to 20 by ice water

circulation, the regulation being effected by the method which had

been found most satisfactory in the determination at the Bureau

of the temperature coefficient of the Weston Normal Cell. 19 As was there pointed out, the difficulty of regulating and maintaining a small steady flow of ice water through the coils of two or

18 Phil. Mag., 19, p. 250; 1910.

19 Bulletin, Bureau of Standards, o, 316; 1908. (Reprint No. 104.)
120 Report on Concrete Standards more tanks in parallel, due to the separation of air bubbles in the

pipes, was overcome by the use of an auxiliary water tank provided with an overflow and maintained at a temperature of 17-18

C by regulating the flow of ice water admitted to it. The water

from this tank was circulated through the cooling coils of the two

tanks containing the cells by the aid of a rotary pump, the water

being returned to the auxiliary tank, thus forming a closed system.

No difficulty was found except from an inadequate supply of ice. In the following tables are given the differences between the

observed values of the separate cells and the values found in the

last series of observations at 25 °. For comparison, it will be noted

that the 25°-3o° difference, according to the formula of Wolff

adopted by the London Conference, is 266 microvolts, and the

corresponding 20 —25 difference is 226 microvolts.

TABLE XIX

Cells submitted by the Physikalisch-Technische Reichsanstalt

Differences, in Microvolts, from 25°

Cell 24 hours

30°

48 hours

30°

24 hours

20° 48 hours20°

24 hours

25°

4 days

25°

10 days

25°

18 days

25°

35 days

25°

36 days

25°

D, -255 -260 +254 +253 +5

D2 -261 -264 +218 +221 -3

Hi -260 -262 +233 +229 -2 -3 -2 -4 -5 -5

D< -265 -269 +220 +230 —1

Eio -263 -263 +221 +221 -2 En -264 -263 +221 +222 -1 -1 -1 -2 —2 -1

Eia -265 -263 +220 +220 -2

E13 -266 -264 +220 +221 -2

F, -261 -263 +223 +226 -2

F» -261 -263 +225 +228 —1

F9 —263 -263 +224 +225 -2 -2 -3 -5 —4 -5

Fio -261 -262 +216 +220 -3

Hi -264 -263 +216 +216 -4 H2 -264 -263 +220 +219 -4 H3 -262 -262 +221 +221 -4 -4 -5 -6 -2 -6

Mean... -262. 3 —263.

1

+223. 5 +224.8 -2
International Electrical Units 121

TABLE XX

Cells submitted by the National Physical Laboratory

Differences, in Microvolts, from 25°

Cell 24 hours 48 hours 24 hours 48 hours 24 hours 4 days

25°

10 days

25°

18 days

25°

35 days

25°

36 days

30° 30° 20° 20° 25° 25°

Ai —262 -261 +225 +225 -2

A» -260 -260 +229 +228 -3

As -262 -262 +226 +225 -4

At -262 -262 +224 +223 -5 -2 +2 -3 —1 -1

A; -262 -263 +224 +223 -5

B, -262 -262 +229 +229 -2 B2 -262 -263 +245 +243 +6 B3 -262 -263 +223 +224 -4

Ci -262 -262 +229 +228 -2

Cj -261 -262 +234 +233

Di -261 -262 +225 +225 -2 D2 -261 -263 +225 +226 -4

D3 -261 -263 +224 +225 -2

Ei -262 -263 +228 +228 -1

E2 -262 -262 +226 +226 —2 -1 -1 -4 -2 E3 -26i -261 +226 +226 E4 -262 -262 +221 +222 -1

Fi -262 -260 +222 +222 -3

F2 -261 -261 +222 +222 F3 -259 -260 +222 +222 +1

Fi —262 —262 +222 +222 Gi -263 -263 +219 +223 -4 G2 —261 —262 +221 +223 -3 G3 -265 -262 +224 +225 -3 -2 -2 —4 -1 -3

G* -259 -262 +222 +224 -1 G5 -263 -263 +220 +225 -2

Hi -265 -264 +220 +222 -3 H2 -262 -263 +221 +223 -2

Ha -263 -264 +223 +224 -3 -3 -3 -6 -2 -4 H4 -263 -264 +218 +222 -3 H5 -262 -262 +219 +222 -2

Ki -262 -262 +223 +222 -1 K2 -262 -262 +223 + 223 -1 K3 -262 -261 +210 +211 -2

Mean. .

.

-261. 8 -262.

1

+223. 9 +224. 6 -2
122 Report on Concrete Standards

TABLE XXI

Cells submitted by the Laboratoire Central d'Electricite

Differences, in Microvolts; from 25°

Cell 24 hours

30°

48 hours

30°

24 hours

20°

48 hours

20°

24 hours

25°

4 days

25°

10 days

25°

18 days

25°

35 days

25° 36 days

25°

E9 -183 —228 +644 +587 + 59 E]2 —203 —222 +460 +445 + 33 El3 -162 -194 +676 +630 + 62 En — 197 —218 +514 +495 + 75 D2 -261 -261 +209 +218 + 18 +28 +32 +41 +68 +69 D3 -251 -254 + 235 +241 + 12 Pi -261 -261 + 214 +214 - 5 P2 -260 -260 +227 +222 - 2 - 1 - 1 - 2 — 1 - 3 P3 -263 -264 +229 +224 - 3 S2 -261 -261 +410 +417 +129 s4 -246 -250 + 274 +275 + 20 Ss -241 -247 +235 +249 + 11 + 10 + 9 - 9 - 7 S; -235 -239 +273 +284 + 51 Se -240 -245 +199 +228 + 12 Z2 -253 -258 +290 +284 + 11 + 9 + 4 — 1 - 1 - 3

Mean... -234 -244 +339 +334 + 32
International Electrical Units 123

TABLE XXII

Cells submitted by the Bureau of Standards

Differences, in Microvolts, from 25°

Cell

24

30°

48

30°

24

20°

48

20°

24

25°

4 days

25°

10

25°

18

25°

35

25°

36

25°

222 264 — 265 -f247 +247 + 6 + 5 +4 +3 +2 +2 226 267 268 +268 +268 + 6 + 4 +2 o 3 3

228 —269 270 +266 +266 _i_ 3 + 2 _2 —6 5

230 —269 —269 +243 +246 — 1 _ i _1 _1 o I 231 265 —265 +232 +236 I _ i o _1 1 232 —268 —268 +230 +234 — 5 — 3 —2 —2 —2 3

233 —268 —268 +229 +233 3

240 —270 —270 +224 +233 — g 241 —262 —263 +221 +226 _ 5 242 —262 —264 +227 +228 — 3

243 —263 —263 +227 +227 _ 2 244 —263 —263 +222 +225 5

245 —264 265 +234 +239 _i_ i + 4

_i_3 j-2 _j_l 246 —261 —263 +220 +223 4

247 —262 —264 +220 +223 5

248 —263 265 +218 +223 7

249 —263 —265 +221 +225 _ 5

250 —263 —263 +229 +232 3 3 3 4 4 4 251 —262 263 _j_ 233 +236 I _ 1 _1 _1 1 1 252 —262 —264 +230 +233 2 _ 2 1 _2 1 I 257 —264 —264 +234 +235 2 2 1 —2 2 1 259 —267 —267 +227 +231 5 275 —263 264 +209 +216 10 — 6 5 _5 _5 —8

276 —263 —265 +217 +221 + 2 277 —268 —269 +203 +218 18 — 12 _g _g „ _9

B22 —262 —262 *+230 +230 o o _2 _4 _4 4

24 -260 -261 +235 +233 + 2 + 1 —1 -3 -3 -3

25 -260 —262 +240 +239 + 2 + 2 —2 —4 —5 -5

26 -262 —262 +231 +231 -1 -3 -3 -3

27 —262 -263 +255 +253 + 6 + 5 +1 —2 —1 -2

29 -261 —261 +239 +236 + 3 + 2 +2 -1 —1 -2

32 -250 -255 +255 +252 + 3 + 1 -3 -4 —4

38 -264 -255 +237 +237 + 2 + 2 +2 -1

39 -259 -261 +226 +224 «- 1 -3 -3 -2

40 -263 -264 +227 +228 - 3 - 3 -5 -6 —

7

-6

41 -262 -263 +237 +236 + 1 + 1 -1 -3 —5 —4

43 -262 -263 +226 +226 — 1 - 1 —1 -3 -3 —3

45 -262 —262 +239 +238 + 3 + 1 +1 -3 -3 -4

49 -262 -263 +242 +243 + 4 + 4 +3 —1 —1 50 -264 —264 +243 +241 + 5 + 1 -1 -2 -3 Mean —263. 2 —264. 2 +232.

3

+234. 3 - 2
124 Report on Concrete Standards

TABLE XXIII

Cells Set up by the International Committee

Differences, in Microvolts, from 25°

Set up by Dr. Wolff and Mr. McKelvy, May 9, 1910

Cell

301 302

303

304 305

306

307 308

309 310

311 312

Mean.

Hg2SO<

NBS.

LCE.

NPL.

PTR.

24 hours

30°

-269 -270

-269

-266 -265

-266

-267 -267

-267

-265

-265

-265

-267

48 hours

30"

-269

-271 -270

-266

-266

-266

-268

-268

-268

-267

-267

-266

-268

24 hours

20°

+266 +266

+266 +231 +231 +230 + 231 + 240 +244 +235 +235 +234 +242

24 hours

20°

+255 +256 +255

+224

+225

+224 +232 + 231 +234 +228

+228 +230 + 235

48 hours

25°

+ 5 + 4 + 4 - 4 - 4 - 4 - 3 - 3 - 3 - 3 - 2 - 1

5 days

25°

+ -1

- 1 - 3 - 3 - 4 - 5 - 4 - 5 - 2 - 1 - 1

6 days

25°

+ 1 - 1 - 2 - 2 - 2 - 2 - 2 - 3 - 1 - 1

1

Set up by Mr. Smith, May 13, 1910

313. 314

315

316

317 318

319

320

321

322

323

324

Mean.

.

NBS.

LCE.

NPL.

PTR.

-272

-271

-271 -276

-269

-269 -268

-273 -275

-276

-277 -277

-267

-272

+303 +310 + 291 +245 +245 +247 + 291 +298

+293 +242 +237 + 244

+270

+288 +290 +274

+233

+232 +229 +267 +274 +268 + 234 +230

+236

+255

+20 + 20 + 13 - 3 - 3 - 3 + 16 + 7 + 5 - 1 - 2 - 1 + 8+ 12 + 11 + 7 - 3 - 3 - 3 - 1 - 3 - 4 - 2 - 2

+ 1

+ 12 + 11 + 6 - 3 - 2 - 2 - 2 - 3

+ 1
International Electrical Units 125

TABLE XXIII—Continued

Cells Set up by the International Committee—Continued

Set up by M. Laporte, May 24, 1910

Cell HgjSO,

24 hours

30°

48 hours

30°

24 hours

20°

24 hours

20°

48 hours

25°

5 days

25°

6 days

25°

325

326 327

328

329

330

331 332

333 334

335 336 Mean.

.

NBS.

LCE.

NPL.

PTR.

-296 -280

-280

-249

-265

-266 -280

-283

-286

-276

-269 -283

-294

-281

-281 -248

-267

-266

-283 -285

-287

-279

-271 -282

+452

+435

+462 +216 +269 +264 +368 +423

+438

+387

+353 +389

+368 +353 +374 +204

+249 +247 +315

+350

+362

+314

+290

+317

+ 14 + 10 + 13 - 1 - 2 - 2 + 12 + 16 +17 + 4 + 9 + 1 -276 -277 +372 +312 + 8

-16 -10

-12 - 1 - 4 - 4 -13

-11 - 9 -13 - 6 - 9

Set up by Mr. McKelvy for Dr. Jaeger, May 26, 1910

337

338

339 340

341

342 343

344

345 346

347

348 Mean.

.

NBS.

LCE.

NPL.

PTR.

-270

-269

-269

-270

-270

-269 -268

-269

-269

-279 -272

-272

-270

-270

-269 -269

-270

-270

-268 -270

-269 -270

-277 -273

-271

+254 +262 +256 +246

+245 +247 +254 +254 +254 +282 +279 +293 +260

+245 +251 +254 +236

+235 +241 +243 +240 +241 +259

+258 +268 +248

+ 1 + 3 + 6 - 7 - 6 - 3 - 2 - 2 - 1 - 1 + 3

1

+ 2 + 4 + 6 - 7 - 5 - 3 - 1 - 3 - 3 - 3 - 4+ 3 + 6 + 7 - 5 - 4 - 1 + 1 - 2 - 3 - 2 - 2 + 2

TABLE XXIV

Cells Set up to Test Different Samples of Cadmium Sulphate

Differences, in Microvolts, from 25°

Cell

349 350

351 352

353 354

355

356 Mean

CdSO,

NBS.

LCE..

NPL.

PTR.

24 hours

30°

-263

-264 -264

-263 -264

-265

-272 -270

48 hours

30°

-263

-264 -264

-264 -265

-265

-273

-270

-266

24 hours

20°

+ 243 +241 +125 +227 +241 +241 +285 +288 +236

24 hours

20°

+237 +235 + 217 + 227 +235 +237 +266 +268 +240

48 hours

25°

+2

-5

+2+2+ 5 +9+2

5 days

25°

+2

-2

+ 1 +2 -4

-2

6 days

25°

+ 2 +1 -1+1 +2 +3 -1+1 + 2
126 Report on Concrete Standards

3. DESCRIPTION OF THE EXPERIMENTS ON THE VOLTAMETER

The persons who took part in the voltameter experiments were: Mr. Smith of the National Physical Laboratory, Dr. Jaeger of the

Physikalisch-Technische Reichsanstalt, M. Laporte of the Laboratoire Central d'Electricite, and working under the direction of Dr.

Rosa, Messrs. Vinal, McDaniel, Post, Grover, Dellinger, and McBride, of the Bureau of Standards.

General Arrangement of the Apparatus.—The general arrangement of the circuits and the apparatus used is shown in Fig. 4

and the photograph (Fig. 5) . The current was taken from a 1 20-

volt storage battery, no one else using the battery at the same

time. After the first experiment of this series, a special fine was

120 VOLTS

EARTH Fig. 4.

The Voltameter Circuit

Before beginning the experiment, the current flows through a resistance B approximately

equal to the resistance of the voltameters

run from the battery to the voltameters to guard against troubles

due to uncertain contacts and plug resistances, such as might arise at the switchboard, and the connections between the separate cells of the battery were investigated and found satisfactory. The

voltameter circuit included five manganin coils of 40 ohms, and

one of 20 ohms in an oil bath A (Fig. 4) , which coils constituted the

main portion of the resistance in the voltameter circuit. In series

with these was a variable rheostat B of 30 ohms range, which

could be substituted in the circuit in place of the voltameters

before the beginning of the experiment by means of the main

switch. From the latter the current passed through a Weston


International Electrical Units 127

ammeter of 1.5 amperes range, a resistance standard of 2 ohms, a

rheostat D of 15 ohms, variable in steps of less than one-tenth ohm,

to a rheostat C of 25 ohms, variable in steps of one-half ohm.

Arrangement for Holding the Current Constant.—Before the beginning of the experiment, the resistance of the rheostat B was

set to a value which past experience would indicate as the probable resistance of the voltameters. With this resistance in the

circuit, the current was adjusted to approximately the desired

value, by means of the rheostats C and D. For the fine regulation

of the current, two circuits were arranged in parallel with a portion of the manganin resistance A of 60 ohms resistance. One of

these circuits consisted of a variable rheostat E of about 2000

ohms, while the other contained a Kelvin rheostat F having a

total resistance of 580 ohms, in series with a variable rheostat G

of about 230 ohms. Before an experiment, the current was al- lowed to flow for some time with the rheostat B in place of the

voltameters. The current having been found to be satisfactorily

steady, and having been adjusted to the proper value, the main

switch was thrown to its other contacts, thus introducing the

voltameters into the circuit in place of the rheostat B. The

change in the current (usually small) due to the difference between

the actual and the predicted resistance of the voltameters, was in a very few seconds corrected by rapidly sliding the contact of the

rheostat D in the direction indicated by the deflection of the galvanometer, the correct current being quickly attained by oscillations of rap; dly decreasing amplitude about the correct value.

The current was then maintained constant by means of the Kelvin

rheostat.

The Adjustment of the Value of the Current.—The current was

adjusted to the desired value by means of a Wolff potentiometer

and standard cell. The connections are shown in Fig. 6. The

potentiometer was of the Wolff form as modified for the Bureau of

Standards, according to suggestions of Mr. H. B. Brooks. The

main circuit of the potentiometer includes eighteen 1000-ohm

coils, nine 100-ohm coils, nine tens, nine units and ten tenths, and,

in addition, fixed coils of 800 ohms and 190 ohms, together with an extra dial A of ten i-ohm coils. The total resistance in the
128 Report on Concrete Standards

main circuit is therefore 20 000 ohms plus a variable external

resistance depending on the voltage of the storage cell, and the

usual Wolff arrangement of double dials, as shown in the figure,

provides that the total resistance shall be independent of the set- ting of the dials. Permanent connections are made to the end of

the eighth 1000-ohm coil, and to the sliding contact of the extra

dial of units, so that by placing the switch on' the points N, the

standard cell may be placed across a resistance of 10 190 ohms

plus the resistance up to the contact on the extra unit dial A.

For example, a cell having a value of 1.0195 volts can thus be

instantly placed across 10 195 ohms, and the main current adjusted by means of the external resistance, without disturbing

the setting of the dials. The current was held at such a value that the drop of potential over the 2-ohm resistance standard, Fig. 4, was equal to the elec- tromotive force of the standard cell used. To correct, however,

for errors in the potentiometer, such as errors in the adjustment of

the relative values of the coils, thermoelectromotive forces', changes

in the potentiometer current and the like, a control circuit was

arranged as shown in Fig. 6. The cell No. 109, whose value was to

be determined by means of the voltameters, was joined in series

with a sensitive galvanometer, so that by depressing a key the

drop of potential over the standard resistance could be opposed

directly to that of the standard cell. This circuit served as the

ultimate control for the current. The procedure adopted was as

follows: While one observer adjusted the current until the elec- tromotive forces in the circuit just described were balanced, a

second observer at the potentiometer took note of the resting place

of the potentiometer galvanometer which corresponded to this

balance. The reading of the potentiometer galvanometer was

then held at this point, by means of the Kelvin rheostat, with an

occasional check on the correct resting point by the method just

described. This procedure not only allows the errors of the

potentiometer to be eliminated, but permits a second observer to

judge of the steadiness of the current at the same time.
International Electrical Units 129

The sensibility of the arrangement adopted was such that a change of current of one part in a hundred thousand produced a

deflection of 6 mm in the potentiometer galvanometer, while the

STORAGE CELL

2 OHM

RESISTANCE STANDARD

Fig. 6.Diagram of Potentiometer

The small dial marked A enables the observer to place the standard cell across the proper

resistance so that the battery current may be checked without changing the setting of the dials.

deflection corresponding to the same lack of balance in the control circuit galvanometer was 2 cm. Under normal conditions the

current could be held so close that the potentiometer galvanometer
13° Report on Concrete Standards

uffered no deflection, positive or negative, as great as half a centimeter. As a rule, no correction is applied for these small fluctuations of the current since special experiments, in which a record has

been taken of the deflections of the galvanometer during the entire

experiment, have shown that the integrals of the positive and

negative deflections over the duration of the experiment balance one another very completely.

The Standard Resistance was an open 2 -ohm manganin coil by

Otto Wolff, No. 2342, kept in an oil bath which was stirred by a motor, the temperature of the bath being taken both at the beginning and end of an experiment. No attempt was made to control

the temperature of the bath. The following determinations of the

resistance of this coil will give an idea of its constancy. The values

observed are here corrected by 7 millionths to conform to the basis

of reference adopted by the committee.

Dat3 Resistance at 25°

Ohms

1909: Feb. 8 2. 000124 Mar.12 134 Apr. 5 136 July 21 132 Aug. 30 150 Oct. 2 150

1910: Mar. 2 150 Apr. 8 134 May 2 136

The resistance at any other temperature is given by the formula

. ^=i?25 [i+ 7 .4 m (t-2 5 )-o.4m (t-25) 2] The Standard Cell used was a Weston cell, No. 109. This, with

three others, was kept in an oil bath whose temperature was automatically maintained at 25° by a thermostat regulating to o?oi.

Previous to this series of experiments, this cell had, with others,

been carried downstairs for occasional comparisons with the refer- ence cells of the Bureau of Standards. At the beginning of this

series of experiments a specially insulated line was run from the
International Electrical Units 131

laboratory on the second floor through a shaft to the standard cell room. The insulation resistance was found to be greater than

1000 megohms, so that no error as great as one microvolt could

have been introduced. As a further check, one of the cells was

transferred to the reference bath, and the measurements repeated.

The difference, after reduction to exactly the same temperature, was found to agree with that found with the special line to within

2 microvolts. This arrangement was found very convenient,

allowing as it did measurements of the cells to be made in place.

Accordingly, frequent comparisons of these four cells with the

reference cells of the Bureau of Standards were made during the

course of the series of voltameter experiments. The results of

these comparisons have already been given in Table VIII, p. 100. It was there shown that the variations of cell No. 109 with respect

to the standard of reference were less than 2 microvolts, the mean

value being equal, on the scale adopted by the committee, to — 23 microvolts.

Measurement of the Time.—The connections used are shown in

Fig. 7. A chronograph, with two pens, was used. One of the

pen magnets was placed in series with the secondary of a relay,

which received a signal once a second from the standard Riefler

clock. The other pen magnet was joined to one set of blades of

the main switch.

This was a double-pole, double-throw switch, whose blades were

so shaped that when thrown in either direction contact was made

on one side just as it was being broken on the other. One side of

this switch was used to throw either the voltameter or an equivalent resistance into the circuit as already described ; the other side was connected to the time circuit. When this switch was to be

thrown up, to insert the voltameters in the circuit, the single pole

double-throw switch B was previously thrown up, so that at the

instant the current was made through the voltameters the pen

magnet was energized. At the end of the experiment, the switch

B was thrown down, so that at the instant when the main switch was thrown in the same direction to break the current through

the voltameters, the pen magnet was energized exactly as before.

Thus, any possible inequality in the working of the magnet on
132 Report on Concrete Standards

make and break circuit was avoided by recording both the beginning and the end of the experiment by means of closing the circuit

of the pen magnet.

The chronograph used was made by the Societe Genevoise.

The speed of the electrical driving motor is controlled by a centrifugal governor which acts on the field circuit of the motor.

Three speeds of the drum may be obtained. That used in these

Fig. 7.

Arrangement for Time Measurement

The main switch of the voltameter circuit, Fig. 4, is mechanically joined to the main switch of the time circuit so that they act simultaneously, the latter operating one pen of the chronograph,

the other being operated by a standard clock.

experiments was one revolution in 10 seconds, a distance of 5 cm

on the record corresponding to one second, thus allowing one hundredth of a second to be easily read with certainty. As the

duration of an experiment was about two hours, the determination of the time correctly to one part in a million should not be a

difficult matter. Evidence on this point was obtained in an ex- periment, previous to those of this series, in which the current was

started and stopped nine times, so that any systematic error in
International Electrical Units 133

the measurement of the time should be magnified and detected in

the weight of the deposit, as compared with that obtained under

otherwise the same conditions but with no interruption during

the experiment. From this experiment it seemed probable that no systematic error in the determination of the time greater than

a few parts in a million is to be expected.

Dimensions of the Cathodes and Anodes Used.—These are given,

roughly, in the tables below, together with the approximate capacity of the cathodes in cc. Photographs of these have also been

made.

TABLE XXV

Dimensions of the Cathodes

Laboratory Designation of cup Material Shape Diam. at top Depth Capacity

LCE

LCE. PTR

PTR

NPL

NPL

NBS

NBS

NBS

NBS

LC

SCB

I....

Ill A

B

92, 93, 95.

127, 128...

27, 28

125, 126...

Platinum

.

....dodo

do

do

do

do

dodo Gold

Hemisphere

...do

Cylinder

....do Nearly cylinder. do

....do Hemisphere

Crucible do

cm

10.0 9.0

5.0

5.0

10.0

10.0 10.0

7.5 6.0

6.0

cm

4.5 4.0

6.0

6.0

9.0

9.0

7.5 5.0 8.0

8.0

cc

250

200

120

120 400

400

350

165

125

125

TABLE XXVI

Dimensions of the Anodes

Laboratory Form Diameter or transverse dimension Axial dimension

LCE

LCE

Hemisphere

Disk

cm

4.0

5.0

1.0 S.0

1.5 3.0

cm

0.3 3.0 1.0 « 3.0

0.3

PTR Rod NPL Disk NBS Rod NBS Disk
134 Report on Concrete Standards

Description of the Voltameters

Form used at the Laboratoire Central d'Electricite.—The platinum

cup rests on a ring of sheet copper, a projecting lug and binding

post serving to lead in the current. The ring and cup are contained in a cylindrical glass vessel, and to insure good contact

between the ring and cup the latter rests on sheets of tin foil wrapped on the ring. A vulcanite cross arm, sliding on an

upright, carries the anode. Connection is made to the latter by

a screw connector soldered to a flexible cord, which terminates in a second binding post on the vulcanite base. The filter paper,

used as septum, is formed by the aid of sealing wax, into a cylinder

closed at the bottom, and is suspended by silk threads from the

cross arms. The general arrangement is shown in the photograph (Fig. 8).

Form used at the Physikalisch-Technische Reichsanstalt.—The

top edge of the cylindrical platinum cup is turned over to form a

flat rim, which is made fast by winged nuts to a metal holder

partly embracing the cup. The cylindrical anode is held by a

metal cross arm provided with adjustments for centering the

anode, and for holding it at the height desired. When silk is employed as a septum, two layers are generally used, the silk

being wrapped completely about the anode and tied around the

supporting rod with a silk thread from the same sample of silk. Whether used with silk or without a septum, a little hemispherical

glass dish is supported below the anode by three glass rods, bent

to hang from the top edge of the cup. The assembled voltameter

is shown in the subjoined photograph (Fig. 9)

.

Form used at the National Physical Laboratory.—This is referred to in presenting the results of the experiments as the "new form."

In this the platinum cup rests on a ring of brass, attached to the

vulcanite base, and joined to a binding post. The large disc

anode is supported by an eccentrically placed rod, protected from

the action of the current by a glass tube. The anode rests in a shallow glass cup provided with a ground edge. This glass cup

is supported by a glass rod, fused to its center and passing through

a hole in the center of the anode. The supporting rods of both

anode and cup are held by a metal cross arm, adjustable on a

metal upright. A cylinder of glass, about 7 cm in diameter and
Fig. 8.

The French Voltameters

Fig. 9. —The German Voltameters


Fig. 10. —The English Voltameters

Fig. 12.

The American Voltameters. No septum form
International Electrical Units 135

7 cm axial length, is ground to fit over the edge of the glass cup.

This cylinder is embraced by a metal collar carried by a piece of

brass, which is in turn borne on an adjustable clamp on a second

metallic upright. The cylindrical piece is first adjusted to rest on the edge of the glass cup, the whole being centered in the

platinum cup. The inner and outer chambers thus formed are next filled with electrolyte to the same level in both, and the glass

shield raised until its lower edge is just below the surface of the

electrolyte. After the deposit has been made, the cylindrical

shield is again lowered to close the anode chamber, and the whole

system, filled with electrolyte, is removed from the platinum

cup. An assembled view is given in the subjoined photograph

(Fig. 10).

The Porous Pot Voltameter as used at the Bureau of Standards.—

The platinum cup is held by gold-plated spring clips, mounted on

a vulcanite base and screwed to a gold-plated strip bearing a

binding post. The porous pot is held in a friction ring of vulcanite, which sets on a second vulcanite ring of somewhat larger

aperture, carried by a metal arm terminating in a sleeve which is adjustable on a metal upright. The anode is carried by another

metal arm, with adjustments both in a vertical and in a horizontal

plane. The porous pots are cylindrical, those used in the smaller

platinum cups being 3.5 cm in diameter and 5 cm deep, and those

used in the largest cups 4.2 cm in diameter. (See photograph

Fig. 11.)

The no-septum form as used at the Bureau of Standards.—When no septum is used, the disk anode rests in a glass cup 5 cm in diameter

and 2.5 cm deep, which is suspended from two glass rods bent to hook

over a strip of vulcanite carried on the supporting arm. A glass

ring is fused to the supporting rods about 2.5 cm above the cup,

and the position of the latter is so adjusted that the ring lies in

the surface of the electrolyte. This prevents any anode slime,

which may rise to the top of the solution, from reaching the

cathode. (See Fig. 12.) If silk is to be used as a septum, the supporting rod of the

anode is slipped through a small hole in the silk, and the latter is tucked between the anode and the cup. The anode then holds

the silk in place by its weight.
136 Report on Concrete Standards

Methods of Washing and Drying the Cathodes and of Preparing

Them for the Next Experiment

Procedure at the Laboratoire Central d'Electricite. —At the end of

the experiment the electrolyte is removed from the cathode by

means of a pipette, taking care not to remove any loose particles

of silver. Any particles which may be drawn into the pipette are

carefully replaced. The wash water is renewed eight times, the

deposit ordinarily being left several hours, or over night, in the

fifth wash water. The electrolyte and all the wash waters are

carefully examined for particles of silver, and any which may be

found are replaced in the cathode. The latter is then dried at about 140 before weighing.

After weighing, the voltameter is assembled and a small current

is sent through in the opposite direction so that at the same time

in which the deposit is removed from the cup, an adherent deposit

is laid down on the anode. When the deposit has been entirely

removed, the cup is washed out, first with nitric acid, and then

with a concentrated solution of caustic soda and with distilled

water, and dried at 140 . Procedure at the Physikalisch-Technische Reichsanstalt.—At the

end of the experiment, the electrolyte is first poured out, the

deposit is rinsed several times with distilled water, after which

the cathode is submerged in a beaker of distilled water for an hour

or more. The cathode is then rinsed off, both inside and out,

into the beaker, to collect any loose silver, and the cup is dried

in an oven at a temperature of from 120 to 140 . The electrolyte, as well as all the wash water, is then filtered in a Gooch crucible (covered with a hard filter) in order to collect all the silver

particles. This crucible is then set in a porcelain crucible without

holes, and dried in the manner described above. The silver particles are added to the deposit before weighing. After weighing,

the deposit is removed by electrolysis as already described, or simply dissolved by nitric acid, and the cup washed and dried.

Procedure at the National Physical Laboratory.—For the usual

procedure, see page 18 of the appendix of the report of the London Conference. The procedure adopted in this series of experiments was somewhat modified. The solution was first removed
International Electrical Units 137

from the bowl, which was then nearly filled with distilled water

and allowed to stand for at least an hour. This wash water was

then removed and the deposits washed eight times with small

quantities (about 50 cc) of distilled water. The bowl was dried

in an electric oven at about 160 . If any loose silver was observed

in the solution or in the wash waters, these liquids were filtered,

the filter paper dried, and the loose silver added to the bowl after

drying the deposit. The bowl was cooled in a dessicator and

weighed.

After weighing, the deposit is removed by passing a current

through the voltameter in the opposite direction (a small current

density being used in order to obtain an adherent coating of silver on the anode), and the cup was washed with strong nitric acid

and distilled water and dried in an electric oven. Procedure at the Bureau of Standards.—The electrolyte is drawn

off by means of a small siphon or pipette, care being taken not to remove all on account of the danger of losing particles of loose

silver. The amount of electrolyte left in the bowl will depend on

the quantity of loose silver present, which is usually very small.

Four wash waters are successively poured into the cup from an

Erlenmeyer flask, which eliminates the danger of splashing. The

wash waters are each drawn off by means of the siphon into large

beakers, and these wash waters are examined for loose silver by

placing the beakers on black paper in a strong light, the inspection being aided by stirring the liquid in order that any particles

present may collect in the center of the beaker. In case any

particles are found, they are entrapped in a pipette and replaced

in the cathode. Four more wash waters are then added, if necessary, the number depending on the amount of electrolyte left orignally in the cup. The final wash water is not entirely removed

from the cathode, but a few cc are left, the quantity depending on

the amount of loose silver. The cup is then dried in an oven for an hour at about 150 , then cooled and weighed. After weighing, the deposit is removed by electrolysis, the cup soaked in

strong nitric acid, washed with caustic soda, dil. HN03 , and

distilled water, and then dried in the oven. Treatment of the Porous Pots.—These are removed from the

electrolyte after an experiment, and kept in silver nitrate until the
138 Report on Concrete Standards

# next experiment. If they are not to be used again for a long time,

they may be kept in distilled water or may be washed and dried.

Description of the Balances Used.—The balances used were four

in number. The larger cups, 92, 93, 95, A and B, were weighed on

an Oertling balance, those of medium size, 127, 128, LCA and SCB

, on one by Rueprecht, and the smaller cups, I, III, 27, 28, 125, and

126, on a balance by Stiickrath. The latter was arranged so that

the cups could be transposed and the sensibility could be determined without opening the balance case. These-three balances are

set up on piers in a vault 3 m by 3.5 m, provided with a double

wall, access being possible through a double door in the two walls.

The deflections of the balances are observed from outside by

telescope and scale. The temperature and humidity conditions

in this room, with a single observer present, have been very satisfactory. If care be taken to keep the doors closed, and to remain

in the room no longer than is necessary,20 the temperature rise

during a day's weighing is rarely more than a tenth of a degree,

and the change in humidity not more than 1 per cent. In practice it was found necessary to wait at least 15 minutes

after the balance case had been closed before a reading of the

balance could be made. With the Stiickrath balance, where it was not necessary to open the case so often, and where the vibration of the small pans is not important, weighings could be made

more rapidly.

After the first experiment the Physikalisch-Technische Reichsanstalt cups were weighed on a second Rueprecht balance, similar

to that already mentioned, but situated in the room where the

regular precision measurement and adjustment of weights by the

Bureau of Standards is carried on. The constancy of temperature and humidity in this room (which has several windows and

walls of a single thickness only), while good, is naturally not as good as is attainable in the vault when only one observer is present.

Description of the Methods of Weighing.—Since the methods used

by the delegates had to be, in some cases, somewhat modified from

those previously used to conform with the conditions existing at

the Bureau of Standards, and the nature of the balances, the

20 This room was intended for use by only one observer at a time. When several observers were present the conditions were naturally not so favorable as just described.
International Electrical Units 139

method used in weighing the Bureau of Standards cups will first be indicated, and the deviations in the practice of the other delegates noted.

The cups are weighed in pairs against a counterpoise, the

weights of the two cups and the counterpoise being adjusted very

closely to the same value, the differences being in every case less than a milligram and for the most part less than 0.5 mg, except

in the case of Nos. 127 and 128, which are, respectively, 2 mg and

3 mg lighter than the cup No. 25, used as counterpoise. The cups

92, 93 and 95 were weighed against a platinum cup, No. 94, while

for the small cups, 27, 28, 125, and 126, a square of sheet platinum

had been adjusted to serve as counterpoise.

For weighing the cups after an experiment, an additional

weight, closely equal to the weight of the silver, was added to the

counterpoise. The weights used for this purpose on the Oertling

and Stuckrath balances, which weights will be referred to as S and

S, are of silver, gold-plated. Their values, 4098.26 and 4098.36

milligrams, respectively, were originally adjusted to be as closely

equal as possible to the normal deposit in one hour, with a current

of 1 ampere. With the voltameters as now used, it is found neces- sary with a current of half an ampere (potential drop on the 2 -ohm

standard equal to the emf of the Weston cell) to let the current

flow for about 2 seconds more than two hours, in order that the

deposit may be sensibly equal to these weights. Since they are of

silver, no buoyancy correction has to be applied. For weighing

the deposit in the cups 127 and 128, a weight of platinum, designated as 2, and having a weight of 4095.23 milligrams, was used.

This was purposely made lighter than S and S on account of the

fact, already mentioned, that these cups 127 and 128 are 2 to 3

milligrams lighter than their counterpoise. A buoyancy correc- tion of 0.24 mg had to be applied to the weight of the deposit in

this case because 2 is of platinum instead of silver. With the counterpoises and cups adjusted as described, the

process of weighing is very much simplified, and the necessity for

introducing the hand into the balance case is very much decreased,

with an increase in accuracy and saving of time, which amply

justify the labor of the adjustment.

The following examples will illustrate the method of making the

weighings and recording the results:
140 Report on Concrete Standards

[Test, Large Cups, Empty; Date, April 13, 1910; Temperature, 2291; Balance, Oertling; Humidity, 51%;

Observer, F. W. G.]

Pans Readings

Equilib- rium

reading

Differ- ence Computation Observed

Left Right Left Right

differ- ence

93+A

(A=0.4mg)

94 22.93

22.98

25.70 25.62

25.53

22. 96 25.62

(1) 95-94= t|?X 0.399=

(2) 9.95=^X°f?=

(3) 93-94=^||x0.399=

mg

-0.322

+0. 224

Aremoved 94

25. 17

25. 28

29. 06 28.94

28.84

48.58

25. 22 28.95

-0. 063

93 95 23. 13

23. 22

(26. 56) 26.47

54.17

26. 47 23.18

5.59

4. 52

= sensibility for 0.4 mg

From (1) and (3) 93-95=0.259 mg (calculated)

93-95=0.224 (observed)

Discrepancy= 0. 035 mg

95 93 26.99

27.05

(28. 97) 28.90

49. 65

27.02

28. 90

55.92 6.27

95 94 27.39

27.43

29.44

29. 38

29.32

27.42

29.38

56.80 0.88

Here the weight A, used in determining the sensibility, was a

rider whose effect, when applied to the fourth division of the

beam, was the same as 0.399 mS on the pan.

It will be seen that the differences of the individual cups and

the counterpoise are determined by substitution. The difference

between the weights of the two cups is determined by transposition. No discrepancy greater than 0.04 mg between the value

thus measured and the value calculated from the two measure- ments by substitution was tolerated. The average value of this

discrepancy, with this balance, was about 0.02 mg or five parts in a million of the weight of the deposit.

From the above measurements we find by least squares adjustment

93-94= -0.075 mg

95-94= -0.310 mg
International Electrical Units 141

The cups were then used in the third international experiment

and, on weighing, the adjusted values were

(93 + Deposit) - (94 + S) = +0.333 mg

(95 + Deposit) — (94 + S) = +0.091 mg

from which we find

Deposit on 93 = S +0.408 mg = 4098.67 mg

Deposit on 95 = S + 0.401 mg = 4098.66 mg

With the Stuckrath balance the procedure was a little different, as is shown in the following example. The discrepancy here in

the observed and calculated values of 28-27 is only 0.01 mg.

[Test, Small Platinum Cups, Empty; Date, April 22, 1910; Temperature, 2391; Balance, Stiickrath; Humidity, 60%; Observer, G. W. V.]

Pans Readings

Equilib- rium

reading

Differ- Computation Observed

Left Right Left Right

Difference

27 C (124.6) 104.7 124.

3

27— C= =

mg

000 124.3 105.0 104.9 «-SH— 0. 619

C 27 (130. 7) 130.2

98.7

99.2

229.2

130.2 99.0

28 -27=

3X-6 X

^ mg=

28—27 calculated= Discrepancy=

0.609

0. 619

0. 010

229.2 0.0 c added (116.8) 74.0 116.2 A=l mg 116.2 74.6 74.3

190.5 38.7 = sensibility for 1 mg

c 28 ( 97.9) 98.1

108.0

107.8

107.9 98.1

206.0

28 C (102. 8) 103.4

150.8

150.0

103.4

150.4

253.8 47.8

28 added A=l mg(100.3) 100.5

114.8

114.6

100.5 114.7

215.2 38.6 = sensibility

28 27 (110.2) 110.7

141.9 141.4

110.7

141.6

252.3

27 28 (108.3) 108.2

97.0

97.1

108.2 97.1

205.3 47.0
142 Report on Concrete Standards

The adjusted values were 27— C = +0.003 mg

28 — C = +0.616 mg

These cups were then used in the sixth experiment, and re- weighed on April 25th, the values found being

(27 + Deposit) - (C + S) = +0.458 mg

(28 + Deposit) -(C + S) = +1.151 mg

which give

Deposit on 27 = 8 + 0.455 mg = 4098.82 mg

Deposit on 28 = 8 + 0.535 mg = 4098.90 mg

The National Physical Laboratory cups were weighed on the

Oertling balance against 94. To do this, a small platinum weight

of about o. 1 14 gram was added to 94, whenever these cups were to

be weighed, and the difference between A and B (about 0.496

gram) necessitated the preparation of a second weight equal to

this difference, to be added to B. Otherwise, the weighings of

these cups were made exactly as in the example already given.

At the suggestion of Mr. Smith the weighings were made by

Dr. Grover or Mr. Vinal and occasionally checked by himself.

The Daboratoire Central d'Blectricite cups were weighed against a set of brass weights, NBS 6550, which were calibrated at the

beginning of the experiments. The following example will make

clear the method of procedure

:

[I, Weight of Cathode A, Empty; Date, April 19, 1910; Balance, Rueprecht; Observer, Laporte]

Pans Readings Means Computation

Left Right Left Right

Tare

(100 g)

A+10. + 1+0.5

+0.1. +0.005

. +0.002. + 0.002..

22.51

22.52

22.75

22.73

22.71

22.51 22.73

This gives

„, 10.69 Tare=A+11.619-j2-73mg

Tare

(100 g)

50+ 20+ 10. + 10.. +5+2. +2..+1

45.24

26.34

29.59

= A+11.61815g

Tare

(100 g)

Added 1 mg

55.93

19.87 23.33

1 mg on right gives— 12.73 divi- sions.

43.20
International Electrical Units 143

[II, Weight of the Cathode A with the Deposit]

Pans Readings Means Computation

Left- Right Left Right

18.04 Tare A—Deposit 19.20 Tare=A+Deposit+7.520—^jjX

-f-5+2.+0.5+0.02 19.40

2 mg=A+Deposit+7.51853 g

38.60 Tare 5C-r20+10. +10.. 24.97 +5+2.+Z..+1 31.67

56.64 2 mg on right gives —24.51 divi- Tare Added 2 mg 13.75 sions. 18.38

32.13

[HI, Weight of Deposit] Tare = A + Deposit + 7.51853

Tare = A +11.61815

Deposit = 4.09962 g

Cor. of Weights = 8

Cor. for Buoyancy = — 8

4.09962

Result given 4.0996 g

For weighing the PTR cups, a platinum counterpoise of about

60 g was used, various small weights of a fraction of a mg being

used to bring the equilibrium nearer the center of the scale. For

weighing the silver, the Bureau of Standards gold-plated silver

weight S was used.

The following example will serve to show the method of weighing and the form of record:

2245

1

—12 10
144 Report on Concrete Standards

[Weighing No. 9; Date, April 14, 1910; Cup I, Empty; P=Cup I; G=Bi+0.5 mg; Balance, Stiickrath Bi= Counterpoise; Observer, Jaeger]

Pans

Readings Position Mean

Left Right

G P 106.2 106.4 120.15 GP= 119.5 Zero position= 121.1 134.0 PG= 122.7 P G 104.3 105.0 122.72 P-G=+3.2

140.8 Correction to 0.5 mg= +0.009 mg G P 104.6 105.0 118.9

133.0 |l8.4 G P+l 122.8 121.8 100.5 mg 78.2 Sensibility= 0.0543 mg

P = G + 3.2 x

0-0543

2 = G + 0.087 mS

P = B! 4-0.509 +0.087 = Bi + 0.596 mg

[Weighing No. 11; Date, April 16, 1910; Cup I, with Silver of Experiment No. 3; P=Cup I+Deposlt; Balance, Rueprecht; G=B]+S+(0.5+0.3) mg correction of 0.5+0.3 mg=+0.015 mg]

Pans

Left Right

Readings

87.3 87.7 100. 75 114.0

107.2 107.0 101. 75 96.4

91.2 91.6 101.25

111.1 116.4 116.9 109.5

102.3

Position Mean

G

P

P+0.4 mg

GP= 101.0 PG= 101.75 Zero= 101.4 P-G=+0.75

8.25= 0.420 mg

0.420 Sensibility= -g^j=0.051 mg

0.05I

P = G+o.75 x —— =G + 0.019 mg = Bi + S + 0.815 +0.019 mg = B 1 + S + 0.834 mS

Therefore,

Cup I + Deposit = B! + S + 0.834 mS

Cup I =Bt +0.596

Deposit = S + 0.238 mg

= 4098.602 mg
International Electrical Units 145

APPENDIX D. TABLES OF RESULTS OF THE EXPERIMENTS WITH THE

SILVER VOLTAMETER

INDEX OF EXPERIMENTS

TABLE XXVII

April 9, 1910 (Experiment No. 1

21

)

No. of deposit Laboratory Cup Weight Weston cell at 20° Type of voltameter Electrolyte Remarks

mg LCE

LCE

PTR

PTR

NPL

NPL

NBS

NBS

NBS

NBS

LC

SC"

III AD

93

95

2728

Filter paper

.

4021. 3

4017. 04

4011. 36

4017. 2

4017. 4

4016. 95 4019.91

4017. 16

4016. 61

do No septum.

Silk New form.. ....do Porous pot. ....do ...do

....do

Per cent

15 B

15 B

20 C

20 C

11 A

11 A

10 D

10 D

10 D

10 D

Filter paper touched bowl

Good deal of anode

slime

Lost some silver

Black band around top

of deposit

April 15, 1910 (Experiment No. 3)

15 LCE LCA

4098. 8 1. 01842s Filter paper 15 B

16 LCE SCB4098. 8 842s do 15 B

17 PTR I 4098. 58 8373 No septum 20 C

18 PTR III 4098. 30 8304 Silk 20 C

19 NPL A 4098. 27 831o New form 10 A

20 NPL B 4098. 20 828. do 10 A

21 NBS 93 4098. 67 8397 Porous pot 10 D

22 NBS 95 4098. 66 8394 do 10 D

23 NBS 127 4098. 40 8328 Glass and silk 10 D

24 NBS 128 4098. 18 8274 do 10 D

Anode slime in cup

April 20, 1910 (Experiment No. 5)

29 LCE LCA

4099. 6 1. 01853s Filter paper 15 B

30 LCE SCB

4099. 1 841 4 do 15 B

31 PTR I 4098. 54 8275 Double silk 20 C

32 PTR III 4098. 95 8378 do 20 C Good deal of loose sil- ver 33 NPL A 4098. 68 831o New form 10 A

34 NPL B 4098. 57 8283 do 10 A

35 NBS 93 4098. 94 8375 Porous pot 10 D

36 NBS 95 4099. 01 8392 do 10 D

37 NBS 127 4098. 23 820i Glass and silk 10 D Silk became detached

38 NBS 128 4098. 59 8288 .....do 10 D

21 The current was interrupted for is seconds or more. Values are comparative only.
146 Report on Concrete Standards

TABLE XXVII—Continued

April 26, 1910 (Experiment No. 7

22

) No. of deposit Laboratory Cup Weight Weston cell

at 20° Type of voltameter Electrolyte Remarks mo Per cent 43 LCE LCA

4099. 3 1. 01846a Filter paper 15 B

44 LCE SCB do 15 B Contaminated

45 PTR I 4098. 36 823e Double silk 20 C

46 PTR III 4098. 25 820, .....do 20 C

47 NPL A 4099. 06 8415 New form 10 A

48 NPL B 4099. 10 842 do 10 A

49 NBS 93 4099. 29 846s Porous pot 10 D

50 NBS 95 4099. 29 8468 do 10 D

51 NBS 27 4098. 82 8352 do : 10 D

52 NBS 28 4098. 87 8363 do 10 D

May 2, 1910 (Experiment No. 10)

LCE

LCE

PTR

PTR

NPL

NPL

NBS

NBS

NBS

NBS

LC

SC*

I III A

B

127 128

125

126

4098. 25

4099.

1

4098. 77

4098. 34

4099. 17 4098. 41

4099. 48

4098. 40

4099. 71

1. 018246 845?

8376

827

8473 828s 8552 828j

New form

Filter paper

[Filter paper {Double silk New form

Filter paper Porous pot Glass and silk Porous pot Silk on porous pot .

15 B

15 B

20 C

20 C

10 A

10 A

10 A

10 A

10 A

10 A

Mean of the two deposits

More silk than usual

100 sq. cm of silk on pot May 7, 1910 (Experiment No. 13)

86 LCE LCA

4098. 28 1.018196

87 LCE SCB

4098. 95 8362 88 PTR I 4099. 44 8482 89 PTR III 4098. 48 8246 90 NPL A 4098. 66 829

91 NPL B 4098. 96 8363 92 NBS 92 4098. 72 8304 93 NBS 93 4098. 96 836s 94 NBS 27 4098. 78 8319 95 NBS 28 4098. 30 820o

Filter paper. do Double silk. Silk New form

Glass and silk. Porous pot Silk Porous pot

15 B

15 B

20 C

20 C

10 A

10 A

10 A

10 A

10 A

10 A

Electrolyte A was 2 in

106 alkaline

One layer of sSlk (Jaeger) Two layers of silk

100 sq. cm of silk on pot Very small porous pot May 14, 1910 (Experiment No. 16)

116 LCE LCA

4202. 59 117 LCE SCB

118 PTR I 4201. 58

119 PTR III 4200. 19 120 NPL 95 4202. 99

121 NPL A 4202. 77 122 NPL B 4201. 29 123 NBS 92 4202. 70

124 NBS 93 4203. 19 125 NBS 128 4202. 77

126 NBS 127 4202. 90

127 NBS .27 4202. 50

128 NBS 28 4202. 60

Porous pot.

.

Silk Double silk. do New form... dodo Porous pot .

.

do

Glass

do Porous pot .

.

do

15 B

15 B

10 C

10 c

10 A

10 A

10 C

10 A

10 A

10 A

10 A

10 A

10 A

Very small anode

Neutralized

Made 2 in 10" alkaline No septum

Do. Made 10 in 10" acid Made 5 in 105 acid

22 The current in this experiment was unusually unsteady. Error perhaps i-nriffff.
International Electrical Units 147

INDEX OF EXPERIMENTS OF THE SUBCOMMITTEE

TABLE XXVIII

April 14, 1910 (Experiment No. 2)

No. of deposit Cup Weight Weston cell at 20° Type of voltameter Electrolyte Remarks

1112

1314

125

•126

2728

mg

4098. 36

4098. 16

4098. 40

4098. 50

1. 018256 8206

826a 8288

Porous pot do

dodo

Per cent

10 A

10 B

10 D

10 c

April 18, 1910 (Experiment No. 4.)

2526

27

28

125

12627

28

4098. 84

4098. 61

4098. 86

4098. 80

1. 018292 823<

8296

828i

Porous pot do

do

do

10 D

10 c

10 B

10 A

April 22, 1910 (Experiment No. 6)

39

40

41

42

125

12627

28

4098. 72

4098. 73

4098. 82

4098. 90

1. 01827e 8278 830o

832o

Porous pot do

do

do

10 c

10 D

10 A

10 B

April 28, 1910. (Experiment No. 8)

53

5455

56

125

126

27

28

4098. 58

4098. 61

4098. 79

4098. 97

1. 01827;

828, 8328 837,

Porous pot do

do

.....do

10 B

10 A

10C

10 D

April 30, 1910. (Experiment No. 9)

5758

5960

61

92

93

95

27

28

4098. 19

4098. 73

4098. 29

4098. 15

4098. 62

1. 01828: 842

831i 8275 839a

Porous pot do

New form Porous pot do

10 A

10 D

10 A

10 A

10 D

Glass shield under por- ous pot
148 Report on Concrete Standards

TABLE XXVIII—Continued

May 3, 1910. (Experiment No. 11)

No. of deposit Cup Weight Weston cell

at 20° Type of voltameter Electrolyte Remarks mg Per cent

72 92 4099. 60 1. 018543 Porous pot 10 B

73 93 4099. 33 847s do 10 C

74 95 4098. 59 829; do 10 A

75 27 4098. 57 828; do 10 c

76 28 4098. 26 8209 do 10 A May 5, 1910. (Experiment No. 12)

77 92 4099. 22 1. 01845; Porous pot 10 B

78 93 4098. 99 840, do 10 C

79 95 4099. 16 844i New form 10 c

80 27 4098. 33 823s Porous pot 10 c

81 28 4098. 54 8286 do 10 A

82 A 4099. 30 847e New form 10 B

83 B 4098. 50 8279 do 10 A

84 I 4099. 19 844„ Filter paper 20C

85 in 4098. 25 8216 Double silk 20C May 10, 1910. (Experiment No. 14)

96 92 4096. 32 97 *93 4096. 10 98 125 4095. 84 99 126 4096. 70 100 28 4095. 16 101 27 4094. 78 102 A 4095. 16 103 B 4094. 66 104 I 4093. 41 105 in 4093. 62

Siphon ...do

....do ...do

do Porous pot .

.

Siphon New form. .

.

Double silk. do

10 B

10 old Baker

10 B

10 old Baker

10 A

10 A

10 A

10 A

10 C

10C

Current not held except approximately and time not measured.

May 12, 1910. (Experiment No. 15)

106 IC'A

4098. 35 1. 0182U Porous pot 15 B Very small anode

107 95 4098. 51 825, New form 10 A

108 A 4098. 26 8193 do 10 A Made 1 in 10< acid

109 B 4100. 50 8753 do 10 A Made 10 in 10« alkaline 110 93 4099. 34 8462 Porous pot 10 Recovered

111 92 4099. 17 842 do... 10 Recovered

112 127 4099. 82 858i do 10 Recovered Made 5 in 10« alkaline

113 128 4098. 00 8129 do 10 Recovered Made 1 in 10* acid

114 27 4098. 18 8174 do 10 Recovered

115 28 4098. 72 830, do 10 Recovered May 19, 1910. (Experiment No. 17)

129 92 4098. 39 1. 01826s Porous pot 10 E (new)

130 95 4098. 30 8249 do 10 E

131 27 4098. 40 827s do 10 E

132 28 4098. 37 8265 do 10 E
International Electrical Units

COMPLETE TABLES OF EXPERIMENTS

TABLE XXIX

First Experiment, April 9, 1910

149

No.

Laboratory

LCE

LCE

PTR

PTR

NPL NPL

N3S

NBS

NBS

NBS

Cup

LC*

SC'

Im

AD

93

95

27

28

Type

Filter paper...

....do No septum

.

Silk New form.. do Porous pot.. ....do

....do

....do

Anode

He m i sphere

Bisk

Cylinder.

..do Disk

..do Rod

Disk Rod

..do

Electrolyte

Per cent Twice re- crystallized

C 20 C 20 A 11 A 11 D 10 D 10 D 10 D 10

cc 250

200 110

110 350

350

300

300

9090

Weight

of silver

mg

4021. 3

4017. 04

4011. 36

4017. 2

4017. 4

4016. 95

4019.91

4017. 16

4016. 61

Remarks

Filter paper touched bowl

Anode slime

Lost some silver Black substance near

upper boundary

Black substance near upper boundary of deposit

The current was interrupted during this experiment so that no calculation of the value of the Weston cell could be made.

The filter paper in cup LCA touched the cathode, causing discoloration of the

deposit. The twice recrystallized electrolyte used in the LCE cups was believed

to be contaminated on the journey from Europe, and was not used in the other experiments.

The PTR Cup III met with an accident, and silver was lost, and there was a good deal of anode slime in Cup I. The deposits in the NPE and NBS cups were abnormal, in the opinion of Messrs. Smith and Rosa, a black substance being deposited with the silver near the upper boundary of the deposit. It was observed that on heating this black deposit became

white, and Dr. Rosa suggested the possibility that it was colloidal silver.
Report on Concrete Standards

TABLE XXX

Second Experiment, April 14, 1910

Experiment of Subcommittee [Room temperature, 2195; time, 7202.24 seconds; standard resistance No. 2342, at 2290,= 2.000090 ohms;

standard cell No. 109 was 23 microvolts lower than the group mean of the cells of the four laboratories; the

current was estimated as correct within ± Wq QQq except during the first 20 minutes, giving an average

deviation of not more than ±

3 "1

No. Cup Type Anode Electrolyte Vol- ume

Weight of silver Weston cell

at 20°

11

1213

14

125 126

27

28

Porous pot Rod

Per cent A 10 B 10

r> 10 C 10

cc

95

95

95

95

mg

4098. 36

4098. 17

4098. 40

4098. 50

1. 018256

820a 8265 828s

do do

do do

do do

This experiment had for its object the comparison of the deposits obtained with the

electrolyte of the various laboratories. The solutions were electrolyzed in cups of the same size and shape, and with porous cups of the same size, treated in the same

manner. The anodes were all of the same shape and practically identical in size. Cups 27 and 28 are of platinum, cups 125 and 126 of gold. TABLE XXXI

Third Experiment, April 15, 1910

[Room temperature, 2299; time, 7201.86 seconds; standard resistance No. 2342, at 2396,= 2.000112 ohms;

standard cell No. 109 was 23 microvolts lower than the group mean; the current was estimated as correct to within± iooVo]

No. Laboratory Cup

15 LCE LCA

16 LCE SCB

17 PTR I

18 PTR III 19 NPL A

20 NPL B

21 NBS 93

22 NBS 95

23 NBS 127 24 NBS 128

Type Anode Electrolyte Vol- ume

Weight

of silver Weston

cell at 20° Remarks

Filter paper... ....do No septum . .

.

Silk New form

....do Porous pot ....do Glass and silk ....do

Hemisphere. Disk

Cylinder

....do. Disk..

....do.

....do. Rod... Disk . .

.

...do.

Per cent B 15 B 15 C 20

C 20 A 10 A 10 D 10 D 10 D 10 D 10

250

200

110

110 370

370

300

300

175

175

mg

4098. 8

4098. 8

4098. 58

4098. 30

4098. 27

4098. 20

4098. 67

4098. 66

4098. 40

4098. 18

1. 018428 842, 837s

830< 831o

828o

839;

839< 8328 8274

Anode

slime in cup.

There was a good deal of anode slime in Cup I, some of which reached the bottom of the cup. All the wash waters and filtrates were free from dissolved silver. The deposits in Cups A and B were free from striae, and were very fine and adherent. There was no loose silver at all in Cup A, and only a few crystals in B.
International Electrical Units 151

TABLE XXXII

Fourth Experiment, April 18, 1910

Experiment of Subcommittee [Room temperature, 239; time, 7202.89 seconds; standard resistance No. 2342, at 2393, =2.000108 ohms;

standard ceil No. 109 was 23 microvolts lower than the group mean; the current was estimated as correct

to within : 1 "I 000 J

No. Cup Type Anode Electrolyte Volume We.i

,Eht ofi Wesft0" CeU

silver at 20

125 126

2728

Porous pot Rod

do do. do ! do. do do.

Per cent cc mg

DIO . 4098.84 1. 01829s C 10 95 4098. 61 823< B 10 95 4098. 86 8295 A 10 4098. 80 828i

This experiment was for the purpose of comparing the four different electrolytes, and differed from Experiment 2 only in that the porous pots and the cups were inter- changed among the electrolytes.TABLE XXXIII

Fifth Experiment, April 20, 1910

[Room temperature, 2295; time, 7202.47 seconds; standard resistance No. 2342, at 2392, =2.000105 ohms;

standard cell No. 109 was 24 microvolts lower than the group mean; the current was estimated as correct

to within ±—? | 100 000 J

No. Laboratory Cup Type Electrolyte Vol- Weight oi Weston cell Remarkg ume silver at 20

29 LCE LCA

30 LCE SCB

31 PTR I 32 PTR m

33 NPL A

34 NPL B

35 NBS 93

36 NBS 95

37 NBS 127

38 NBS 128

Filter paper.

.

do Double silk.

.

do

Per cent Hemisphere B 15 Disk

Cylinder... do

New form Disk

do do

Porous pot ' do

'

do do

Glass and silk. do

.do. .do.

B 15 C 20 C 20

A 10 A 10 D 10 D 10 D 10 D 10

250

200 110 110

370 370

300

300

175

175

mg

4099.6

4099.

1

4098. 54

4098. 95

4098. 68

4098. 57

4098. 94

01 4098. 23

4098. 59

L 01853,

841i 827s 837s

831g 8283 837s 8393 820j

828a

Loose sil- ver

Silk detached

The deposit in Cup I was much more adherent than that in III, where there was a

good deal of loose silver. The same silk was used in I and III as in the third experi- ment. The same silk was used in the cups 127 and 128 as in the third experiment. Since

that time the silk had been kept in weak AgX03 solution, being washed just before the experiment. The silk in 127 became detached during the experiment, and consid- erable anode slime escaped.
152 Report on Concrete Standards

TABLE XXXIV

Sixth Experiment, April 22, 1910

Experiment of the Subcommittee [Room temperature, 22°; time, 7202.72 seconds; standard resistance No. 2342, at 2294, =2.000090 ohms; cell No. 109 was 23 microvolts lower than the group mean; the current was estimated as correct to within ±

100 000 ]

No. Cup Type Anode Electrolyte Volume Weight of silver Weston cell

at 20"

39

40

4142

125 126

27

28

Porous pot ...

.

do Rod

Per cent C 10 D 10 A 10 B 10

cc

95

9595

95

mg

4098. 72

4098. 73

4098. 82

4098. 90

1. 01827s

827g 830

832

do

do do

do do

This experiment was similar to Experiments 2 and 4, the only difference being that the cups and porous pots were still further interchanged.

TABLE XXXV

Seventh Experiment, April 26, 1910

(Room temperature, 2295; time, 7202.41 seconds; standard resistance No. 2342, at 2299=2.000100 ohms;

cell No. 109 was 23 microvolts lower than the group mean; the current was unusually unsteady, the possible

1

~] error being estimated at ±

10 000.

No. Laboratory Cup Type Anode Electrolyte Vol- ume

Weight

of silver Weston

cell at 20' Remarks

LCE

LCE

PTR

PTR

NPL

NPL

NBS

NBS

NBS

NBS

LCA SCB

I

III A

B

93

9527

28

Filter paper. ....do

Double silk. do New form. .

.

....do Porous pot... ....do ....do

....do

Hemisphere.. . Disk

Cylinder. do... Disk

do... Rod

do...

do... do...

Per cent B 15 B 15

C20

C20 A 10 A 10 D 10 D 10 D 10 D 10

cc

250

200

110

110 370

370

150 330

90

90

mg

4099. 3

4098. 36

4098. 25

4099. 06

4099. 10

4099. 29

4099. 29

4098. 82

4098. 87

1. 018469 Contaminated.

8236 820o

841s 842

8468 8469 8352 8363

The Cup SCB was soiled externally by a drop of AgN03 on the tin foil. The deposits in the NPL bowls were absolutely free from striae, and were very

firm, there being no loose silver. Cup 93 was used with only half the usual quantity of electrolyte.
International Electrical Units 153

TABLE XXXVI

Eighth Experiment, April 28, 1910

Experiment of Subcommittee [Room temperature, 22°; time, 7202.47 seconds; standard resistance No. 2342, at 2294=2.000090 ohms;

standard cell No. 109 was 22 V microvolts lower than the group mean; the current was estimated to be

correct to within ± I^ob]

No. Cup Type Anode Electrolyte Vol- ume

Weight

of silver Westoncell at 20°

53

54

55

56

125

126 27

28

Porous pot .i...do Rod

do

Per cent B 10 A 10 C 10 D 10cc95

9595

95

mg

4098. 58

4098. 61

4098. 79

4098. 97

1. 018277 8284 832s 837<

do do

do do

This was the fourth experiment where the four electrolytes were compared in the

small porous pot voltameter. Each electrolyte has now been measured in each of the platinum cups and the porous pots. TABLE XXXVII

Ninth Experiment, April 30, 1910

Experiment of the Subcommittee [Room temperature, 2395; time, 7201.90 seconds; standard resistance No. 2342, at 2595=2.000138 ohms;

standard cell No. 109 was 24 microvolts lower than the group mean; the current was estimated as correct towithm± iooVo]

No. Cup Type Anode Electrolyte Vol- ume

Weight

of silver Westoncell at 20° Remarks

57

58

59

60

61

9293

95

27

28

Porous pot do

New form Porous pot do

Per cent A 10 D 10

A 10 A 10 D 10

cc 300

300

320

95

95

mg

4098. 19

4098. 73

4098. 29

4098. 15

4098. 62

1. 01828?

842o

831i 8275 839a

Glass shield under po- rous pot
154 Report on Concrete Standards

TABLE XXXVIII

Tenth Experiment, May 2, 1910

[Room temperature, 24°; time, 7202.26 seconds; standard resistance No. 2342, at 2496,= 2.000133 ohms;

standard cell No. 109 was 23 microvolts lower than the group mean]

No. Laboratory Cup

62 LCE LCA

63 LCE SCB

64 PTR I 65 PTR m

66 NPL A

67 NPL B

68 NBS 127

69 NBS 128

70 NBS 125

71 NBS 126

Type

New form. .

.

Filter paper.

....do Double silk.

New form

Filter paper... Porous pot Glass and silk.

Porous pot. Silk on pot.

Anode

Disk.

..do..

Cylinder

.

..do

Disk.

..do.. Rod.. Disk.

Rod...

..do...

Electrolyte

Per cent B 15 B 15

C 20 C 20

A 10 A 10 A 10 A 10

A 10 A 10

Vol- ume

250

200

110

110

350

400

150

175

90

90

Weight

of silver

mg

4098. 25

4099.

1

4098. 77

4098. 34

4099. 17

4098. 41

4099. 48

4098. 40

4099. 71

Weston

cell at 20° Remarks

1. 01824s 8457 [M e a n of

8376 J silk and

1 filter pa-

[ per

827o

847s

828a 855 2 More silk than usual

828< 860s 100 sq cm

silk on pot

The silver particles from Cup III were added to those from Cup I by mistake. The

combined particles were weighed by themselves. The weight found was 1.585 mg,

but "after scraping out some of the finer particles 1.858 mg." This last weight was

used and the mean of the two cups found. On first weighing cups 125 and 127, the weights 4098.68 and 4098.74, respectively, were found. It was then noticed that there was on the outside of each a white spot which, on being removed and tested, was found to be crystallized AgN03 , probably

spattered from a pipette On rebaking the cups and reweighing, the weights given

in the table were found. The silk in Cup 128 and Cup 126 was pure raw silk which had been thoroughly

washed, but had been kept dry for about two months, and was washed just before the experiment.
International Electrical Units 155

TABLE XXXIX

Eleventh Experiment, May 3, 1910

Experiment made by the Subcommittee [Room temperature, 24°; time, 7202.56 seconds; standard resistance No. 2342, at 2594,= 2.000142 ohms;

standard cell No. 109 was 22 microvolts lower than the group mean; the current was estimated as correct

2 1

to within ± 100 000.

Cup

92

93

9527

28

Type

Porous pot. do

do

do

do

Anode

Rod...

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

..do... Disk .

.

Electrolyte

Per cent B 10 C 10 A 10 C 10 A 10

Vol- ume

300

300 300

95

95

Weight of silver Weston

cell at 20° Remarks

mg

4099. 60 1. 01854s

4099. 33 8476 4098. 59 8292

4098. 57 828;

4098. 26 8209 Porous pot 4.3 cm diam. 5.5 cm deep

The porous cup in Cup 28 in experiment 76 was prepared by Mr. Smith who first boiled it in strong HN03 and then in several lots of distilled water. The pot was

afterwards baked in an electric oven to drive off any remaining acid and was then

soaked in several lots of distilled water. TABLE XL

Twelfth Experiment, May 5, 1910

Experiment made by the Subcommittee [Room temperature, 21"; time, 7202.26 seconds; standard resistance No. 2342, at 2195,= 2.000074 ohms;

standard cell No. 109 was 23 millionths lower than the group mean; the current was estimated as correct towitnin± ToTooo]

Cup

9293

95

2728A

B

IIII

Type

Porous pot . .

.

do New form Porous pot do New form do

Filter paper.. Double silk

.

Anode

Rod...

do. Disk.. Rod...

do. Disk..

do.

Cylinder.

....do....

Electrolyte Vol- ume

Weight of silver Weston

cell at 20°

Per cent cc mg

B 10 325 4099. 22 1. 01845? C 10 315 4098. 99 840 C 10 315 4099. 16 844i C 10 90 4098. 33 823s A 10 90 4098. 54 823,, B 10 350 4099. 30 8476 A 10 350 4098. 50 8279

C 20 110 4099. 19 8448 C 20 110 4098. 25 821 6

Remarks

After removal of spot of AgNOj on

outside of cup

The same silk was used in Cup III which has been used in the PTR cups in the previous experiments. A washed filter paper tube was used in Cup I.
156 Report on Concrete Standards

TABLE XLI

Thirteenth Experiment, May 7, 1910

[Room temperature, 23°; time, 7202.58 seconds; standard resistance No. 2342, at 2393, =2.000109 ohms;

standard cell No. 109 was 23 microvolts lower than the group mean; the current was estimated as correct

2

to within ±

100 000

It was unusually unsteady during the last 10 minutes]

No. Laboratory Cup Type Anode Electrolyte Vol- ume

Weight of silver Weston cell

at 20 Remarks

Per cent cc mg

86 LCE LCA New form... Disk B 15 230 4098. 28 1. 018196 87 LCE SCB Filter paper.. ...do B 15 160 4098. 95 8362 88 PTR I do Cylinder.

.

C 20 110 4099. 44 8482 89 PTR III Double silk. ...do C 20 110 4098. 48 8246 90 NPL A Silk Disk A 10 370 4098. 66 829o One layer of silk 91 NPL B New form..

.

...do A 10 370 4098.96 8363 92 BS 92 Glass and ...do A 10 315 4098. 72 830t Two layers silk

silk 93 BS 93 Porous pot..

.

Rod A 10 315 4098. 96 8363 94 BS 27 Silk and po- ...do A 10 95 4098. 78 8319 Silk on porous

rous pot pot 95 BS 28 Porous pot..

.

Small rod. A 10 95 4098. 30 820« Porous pot 1J cm diam, 4 cm deep

The same filter paper tube was used in Cup I as in the experiment of May 5. The silk in Cup A was some of that used by Dr. Jaeger which had been soaked during

the preceding experiments. The silk in cups 92 and 27 was the same as that used on May 2, and had been kept in weak AgN03 solution since that time. TABLE XLII

Fourteenth Experiment, May 10, 1910

Experiment of the Subcommittee In this experiment with the siphon form of voltameter, the current was held only

approximately constant and no accurate measurement of the time was made. The

results are therefore only relative.

No.

96

98

97

99 102

100

101 103

104

105

Cup

92

125 93

126 A

28

27B

IIII

Type

Siphon

....do

....do

....do

...dodo Porous pot .

.

New form... Double silk

.

...do

Anode

Hemisphere

.

Ring

do

do

....do ....do Rod

Disk

Cylinder

....do

Electrolyte

Per cent B 10 B 10 Old Baker 10 Old Baker 10 A 10 A 10 A 10 A 10 C 10 C 10

Vol- ume

435

195 400

195 480

195

95 400

110 110

Weight of silver

mg

4096. 32

4095. 84

4096. 10

4096. 70

4095. 16

4095. 16

4094. 78

4094. 66

4093. 41

4093. 62

Relative weights

1. 00028

1. 00014

1. 00023

1. 00037

1. 00000

1. 00000

0. 99990

0. 99988

0. 99957

0. 99962
International Electrical Units 157

The volumes of the electrolyte were taken as the sum of the volume of the cathode

liquid+one-half the volume of the siphon.

The relative values are referred to the mean of all as unity. The following table gives the difference obtained with each electrolyte:

Electrolyte

A

A

AA

BB

Old Baker Old Baker C

C

Type

New form Porous pot. .

.

Siphon, small

Siphon, large Siphon, small

Siphon, large. Siphon, small

Siphon, large. Silk ....do

Differences, parts in 100 000

+ 2 +12 + 12 +26 +40 +49 +35 -31 -26

TABLE XLIII

Fifteenth Experiment, May 12, 1910

Experiment of the Subcommittee [Room temperature, 2295; time, 7202.54 seconds; standard resistance No. 2342, at 2298, —2.000100 ohms;

standard cell No. 109 was 24 microvolts lower than the group mean]

Cup Type Anode Electrolyte Vol- Weight of silver Weston cell

at 20° Remarks

95A

93

92 127

128

2728

Porous pot. New form

.

....do....

....do....

Porous pot. .....do ....do

.do.

.do.

.do.

Small rod. Disk

....do....

do

Rod....

do. Disk...

.do.

Rod.

.do..

Per cent B 15 A 10 A 10

A 10

Recovered

Recovered

Recovered

Recovered

Recovered Recovered

cc

230 300

350

300 300

150

150

95

95

mg

4098. 35

4098. 51

4098. 26

4100. 50

4099. 34

4099. 17

4099. 82

4098. 18

4098. 72

1.0182U

825j 819s

8753

8462 842,

858i

812,

817( 8307

Made 1 in 10< acid Made 10 in 10« alkaline

Made 5 in 10s alkaline Made 1 In 10' acid

The electrolyte designated as "recovered" was obtained from impure Baker AgN03 by repeated fusion and recrystallizations. The salt was tested after this experiment

and found to contain a very appreciable amount of reducing agents. The alkaline solutions were made so by the addition of NaOH in the quantities recorded in the table. The solutions were opalescent. The acid solutions were

obtained by adding i part in io ooo of HN03.
158 Report on Concrete Standards

TABLE XLIV

Sixteenth Experiment, May 14, 1910

The current was interrupted during the experiment by the failure of the supporting rod of the anode in Cup SCB . The values are therefore relative only.

No. Laboratory Cup Type Anode Electrolyte Vol- ume

"Weight

of silver Relative weights Remarks

116

117

118

119

120

121 122 123

124

125 126

127

128

LCE

LCE

PTR

PTR

NPL

NPL

NPL

BS

BS

BS

BSBS

BS

SCE

I m

95 A

B

92

93

128

127

27

Porous pot. SilkRod..

..do.

Double silk . . . Cylinder .

.

do New form do

do

Porous pot do

Glass.. do.

..do.... Disk...

..do....

..do.... Rod....

..do....

Disk.

...do..

Per cent B 15 B 15

C 10 C 10 A 10 A 10 C 10 A 10 A 10

A 10 A 10 Porous pot Rod ' A 10

cc 230 200

110

110 270

350

350 300

300

175

17595

mg

4202. 59 0. 99995

4201. 58

4200. 19

4202. 99

4202. 77

4201. 29

4202. 70

4203. 19

4202. 77

4202. 90

4202. 50

28 do .do... A 10 90 4202. 60

0. 99971

0. 99938

1. 00004

0. 99999

0. 99964

0. 99997

1. 00009

0. 99999 L 00002

0. 99993

0. 99995

Anode 2 cm

long 0.5 cm

diam

Neutralized

Made 2 in 10« alkaline No septum

Do. Made 10inl0»

acid Made 5 in 10' acid

The relative weights are referred to the mean of the deposits with electrolyte A as unity.

The "neutralized" electrolytes •were first made 2 in io6 alkaline with NaOH, which

was then neutralized by the addition of HN03

. The anodes used in Cups 127 and 128 were prepared by the deposition of a coating

of electrolytic silver, using a small current, as is always done with the anode in the "new form.

TABLE XLV

Seventeenth Experiment, May 19, 1910

Experiment of Subcommittee [Room temperature, 22?5; time, 7202.21 seconds; standard resistance No. 2342, at 2299=2.000101 ohms;

standard cell No. 109 was 23 microvolts lower than the group mean; the current was estimated as correct

to within less than ± A, ~|

No. Cup Type Anode Electrolyte Vol- ume

Weight of silver Weston cell at 20'

129 130

131 132

9295

27

28

Porous pot do Rod

do

Per cent E 10 ElO

ElO E 10

cc 315

31595

95

mg

4098. 39

4098. 30 4098.40

4098. 37

1. 018269 824, 827j

826s

do do

do do

The electrolyte E used in this experiment was made from AgN03 recently purified

by Dr. ilcDaniel from Merck's salt.
International Electrical Units 159

APPENDIX E. REPORTS OF SUBCOMMITTEES

(The reports of the subcommittees on resistances and standard cells have been

incorporated in the Appendixes C, 1 and C, 2.)

1. SUBCOMMITTEE ON WEIGHTS

By E. B. Rosa and F. Laporte The following weights were brought by the different members

of the committee -

One gold-plated brass weight of 10 g from the Laboratoire Central d'Electricite. Four brass weights of 1, 1, 2, and 3 g, together with 12 platinum and aluminum

weights of values ranging from 1 mg to 400 mg from the Physikalisch-Technische

Reichsanstalt. Two gold-plated brass weights of 2 g and 5 g from the National Physical Laboratory.

The results of the comparisons of the above weights with the

standards of the Bureau of Standards are given below, together

with the values to the same standard of reference of the principal

Bureau of Standards' weights used in the voltameter experiments.

Laboratoire Central d'Electricite

Correction found= —0.19 mg. The following is taken from the certificate of the Bureau International des Poids et Mesures. Mass of the weight=9990.863 mg+1.2 094Awhere A is the difference between the

real and the assumed volume.

Volume assumed (density taken as 8.5) = i.iy64 ml at o°. Physikalisch-Technische Reichsanstalt

Corrections Found

Nominal value PTR, July-Aug., 1909 NBS, Apr., 1910

g mg mg

3 +0. 117 +0. 116

2 +0. 046 +0. 049

1 +0. 020 +0. 020

1 +0. 027 +0. 024

0.4 -0 009 -0. 004 0.3 + 064 +0. 061 0.2 -0. 005 -0. 009

0.1 +0. 041 +0. 040 0.04 -0 004 -0. 005 0.03 +0. 001 +0. 001 0.02 +0. 005 +0. 002

0. 01 +0. 028 +0. 030

0. 004 + 020 +0. 020

0. 003 +0. 025 +0. 023

0. 002 -0. 001 -0. 004

0.001 -0 006 -0. 009

22451° 12 —II
i6o Report on Concrete Standards

National Physical Laboratory

NBS values 5 g + 0.055 mg

2 + 0.003

Sum 7 g + 0.058 mg

The value certified by the National Physical Laboratory was

7.00000 g in vacuo. The difference may be, perhaps, explained

by the fact that one of the weights had in some way become con- taminated by a minute spot of mercury.

Bureau of Standards Weights Employed in the Voltameter

Experiments

The following weights, which had been adjusted to be closely

equal to the mass of silver deposited by a current of one-half

ampere in two hours, had in terms of the NBS standards the val- ues below:

Designation Material Mass

S mg

Gold-plated silver 4098. 262 S do » 4098. 364 2 Platinum 4095. 232

23 On Apr. 21, 1910, this weight was checked against the PTR weight by Dr. Jaeger using the Rueprecht

balance and the value 4098.388 mg. was found.

Besides these, determinations of the corrections of a box of

weights, NBS 6550, used by M. Laporte in the voltameter experiments, were made with the appended results taken from the

certificate.
International Electrical Units 161

Nominal value Correction Distinguishing marks

g mg

100 +0.02

50 +0. 12 20 -0.02

10 -0. 04 One dot

10 -0. 04 Two dots

5 -0. 006

2 -0. 124 One dot

2 -0. 005 Two dots

1 -0. 003 mg

500 +0.018

200 +0. 005 100 +0. 012 One dot

100 Two dots

50 -0.011

20 +0. Oil 10 -0. 004 One dot

10 +0. 005 Two dots

5 +0. 006

2 +0. 001 One dot

2 -0. 012 Two dots

1 +0. 008 One dot

1 +0. 007 Two dots

6 (rider) + 0.011 Shape

6 (rider) +0. 017 Shape

6 (rider) + 0. 006 Shape

The last figure in a number of the corrections is only approximate, but is given for the sake of greater accuracy in using the

corrections.

2. REPORT OF COMPARISONS OF FOUR DIFFERENT ELECTROLYTES IN SMALL

POROUS CUP VOLTAMETERS

By E. B. Rosa On April 12 the committee authorized some special experiments to be made by the Bureau of Standards under Dr. Rosa's

direction, to compare four different electrolytes submitted to the

committee by the four delegates, using the smallest sized porous

cup voltameters. Four such experiments were made, using four

voltameters each time (two platinum and two gold crucibles),

and it was so arranged that each electrolyte was used in each of

the four crucibles, and with each of the four porous cups. The
Report on Concrete Standards

results are exhibited in the accompanying table. The electrolytes were as follows:

A. Three times recrystallized silver nitrate, prepared at the National Physical

Laboratory.

B. As purchased from Poulenc Freres.

C. As purchased from the Gold-und Silber-Scheide-Anstalt, Frankfurt, being fused by the manufacturer. D. As purchased from same firm, not fused. The three samples of silver nitrate, B, C, and D, were used as supplied by the manufacturer, without further purification.

In the column headed "Means" are given the mean values

obtained in four experiments with each salt. These agree remarkably well, so well that one might infer either that all samples of

silver nitrate are pure, or that the impurities present are negligible. Other experiments with larger volumes of these electrolytes show very considerable differences in the weights of deposits

with these same electrolytes. One may conclude from these and

other experiments that when the electrolytes are not quite free

from organic impurity, the excess above the normal deposit is very slight in so small a voltameter (100 cc of electrolyte), the

excess being not greater (and possibly less) than one-third as much as in a voltameter of 300 cc capacity.

TABLE XLVI

Gold Platinum Porous cups

Electrolyte Means

125 126 27 28 2 3 5 6

A 8256 828< 830t 828i 828» 830t 828, 828i 8256 B 827; 8208 829s 832» 8274 8277 8208 832« 8295 C 8276 823( 832 3 828s 8283 8234 8278 8288 8328 D 8292 8278 8265 8374 8302 826,; 8292 8374 827s Mean . .

.

8275 825» 829, 831 6 826s 826, 8316 8289

1. 01828* 1.018284

Mean=i.018285 for Weston Normal Cell: First experiment, mean equals 1. 018254 Second experiment, mean equals 8277 Third experiment, mean equals ^ 8294 Fourth experiment, mean equals 83ifl

1. 018285
International Electrical Units

The mean of the deposits in the gold crucibles is equal to that

in the platinum (within experimental error) and the average deposit, using each of the four porous cups, is also sensibly the same. The mean of all values obtained in these experiments is 1.018285,

in close agreement with the values obtained using other electrolytes believed to be pure. (See Table XI/VII in the report of the

subcommittee on the investigation of special questions, etc.)

3. REPORT OF SUBCOMMITTEE ON THE INVESTIGATION OF SPECIAL QUESTIONS

REGARDING THE SILVER VOLTAMETER

By F. E. Smith and E. B. Rosa The subcommittee of two, appointed April 29 to investigate

certain special questions concerning the silver voltameter, have

conducted six sets of experiments, and have made chemical tests to study the following questions

:

1. The volume effect, or the difference in deposit in large and

small voltameters with different electrolytes.

2. The comparison of the siphon form of voltameter with others,

with three different electrolytes.

3. The effect of silk as used in the voltameter, on the weight of

deposit.

4. The effect of acid and alkali in the electrolyte on the deposit.

5. The relation between chemical tests for impurity and the

evidence of the deposits concerning impurity of electrolyte. The

deposits are in runs No. 9, 11, 12, 14, 15, and 16. Runs 10 and 13,

made according to the decision of the committee April 29, to compare the various forms of voltameter, have afforded some additional information. Most of the information we have obtained is presented in a series of tables.

Our object in compiling these tables is to present the results in a form convenient for discussion. We suggest that other tables be

added, and the present ones modified if such a procedure renders

the results more intelligible.

1. The Volume Effect.—Table XLVII gives a summary of 24

deposits made between April 1 5 and May 1 2 in the new form, and

in the porous cup form of voltameter, using three sizes of the latter,

using the same AgN03 in all, namely, that prepared by Smith at
164 Report on Concrete Standards

the National Physical Laboratory by recrystallizing three times

and fusing. It is now neutral when tested by iodeosine, and shows no reaction when tested by potassium permanganate, after fusing,

for the presence of organic matter or other reducing substances.

It was the purest AgN03 , judged by this chemical test, that was

available.

The conclusion seems justified, that at least for the porous cup

voltameter, the volume effect, which is pronounced in the case of

impure electrolytes, is entirely absent in this electrolyte, which is neither acid nor alkaline, and seems very pure.

Table XLVIII gives the differences obtained with three electrolytes which are not pure according to the test described above.

These three electrolytes have all been employed in the international experiments. It was shown by experiments Nos. 2,4, 6,

and 8, that these electrolytes agree very closely when used in the

small porous cup voltameters, but previous work had shown that

the differences in deposits of different electrolytes due to varying

impurity is exaggerated in larger voltameters, so it was deemed

necessary to try all the various electrolytes that showed reduction

of potassium permanganate in large voltameters. The unrecrystallized AgN03 from Frankfurt, that had been used by the

Bureau of Standards, requires 2 cc of permanganate solution; the

fused AgN03 from same manufacturer (used by PhysikalischTechnische Reichsanstalt) and the crystallized salt from Poulenc

(used by Laboratoire Central) before fusion required 0.5 cc and

after fusion required 5 or 6 cc of permanganate solution, showing

in the latter case a higher percentage of reducing agents present.

Table XI/VIII shows that the first named electrolyte gives 8.5

in 100 000 heavier deposit in the large porous cup voltameter than

in the small one, the second 16.4 in 100 ooo, and the third 21.7 in

100 000 greater, according to the deposits 72, 77, and 82. But,

according to the deposits 62, 86, and 106, the volume effect is negative, that is, minus 5.6 in 100 000. The last experiments are made with different sized cups of intermediate values. These

iesults would seem to show the advantage of purifying by successive recrystallizations the AgN03 until the products are pure as
International Electrical Units 165

tested by permanganate of potash, and as further tested by giving

identical deposits in large and small voltameters. More evidence on this subject is furnished by the experiments with the siphon

voltameter.

2. The Siphon Voltameter.—On May 14 we used six siphon

voltameters in series with four others, there being three large and

.three small voltameters, and three different electrolytes. The

latter included the NPL. pure electrolyte, the IXE slightly impure,

being the third in Table XLVIII, and an electrolyte made from

Baker AgN03 , supposed to be more impure than the others, as judged by chemical tests. The results obtained are as follows:

Taking the mean of all the deposits as 1. 00000, in the small

porous cup voltameter the deposit is 1. 00001, and the new form

is 0.99988, the English electrolyte in two siphons averaged

1.00000, the French electrolyte in two siphons averaged 1.00021,

and the Baker electrolyte in two siphons averaged 1.00030. In

the voltameters using silk the mean was 0.99960.

It is evident from the table that the deposits with the siphon

voltameter are in every case the heavier, the excess being greater,

the more impure the electrolyte, but from these experiments no

precise relation can be drawn as to the relation between the excess and the volume of the electrolyte. Whether the excess of 11 in

100 000 with the NPL is due to very slight impurities, or due to the mere fact that a siphon was used, or is purely accidental, can- not be decided without further experiment.

3. The Effect of Silk.—The experiments of May 2 (deposits 69

and 71) appear to show that silk can greatly increase the deposit.

If it is washed and soaked long enough to avoid giving an excess

of silver it may cause too small a deposit, perhaps because of the

acidity which develops in the electrolyte. Pure washed silk appears to produce two effects of quite different character. According as one or the other predominates, the deposit may be too

heavy or too light. Every test of electrolyte that has been made

when silk is used, shows a pronounced acidity at least five or ten

times as great as should, in our opinion, be permitted in a normal

voltameter.
Report on Concrete Standards

In Table L a comparison is made between the deposits in the

five different experiments with and without silk. In two experiments, the value of the standard cell is not determined, and the

results are relative. The differences, however, are expressed in

parts in 100 ooo in all cases.

4. The Effect of Acid and Alkali.—This was tested in the deposits

made May 12, the results of which are shown in Table LI.

Five or ten parts in a million of alkali produces a large excess, and two parts in a million an appreciable excess, in the weight of

the deposit. The effect of acid appears not to be proportional to the quantity of acid, one part in 10 000 not reducing the deposit

much more than one part in 100 000 of acid. More information on this subject seems to be needed.

5. We present in a separate paper a report prepared by Dr.

McDaniel on the chemical testing of silver nitrate. We have discussed above the effect of acid and alkali, and the volume effect

which we have attributed to impurity other than acid. Tests by

permanganate seem to show that the impurity which produces

the volume effect may be detected by the permanganate reaction.

The evidence is that the electrolyte which seems to be fully free

from volume effect shows no permanganate reaction, and the

three or four different samples of silver nitrate which show the permanganate reaction to a greater or less degree also show a slight

volume effect.
International Electrical Units

TABLE XLVII

Experiments Using National Physical Laboratory Electrolyte

167

No. of deposit 24 New form voltameter Small porous cup

voltameter Large porous cup

voltameter ftledium-size porous cup voltameter

1. 01831o

28

31o

283

1. 01825s

28i 30a

28i *M15

25 42

1. 01828?

31i 275 27o

1. 01828s

284 292 » 209 28c 279 «363

27 363

28 20o 25!

1. 01828? 1. 01828i 1. 01829o 1. 01828s

1920

33

34

1128

4154

47

4857

5960

66

68

70

74

7681

8391

93

95

107

Mean..

2< Deposits included in braces are deposits in the same experiment.

25 Current unusually unsteady.

25 The porous cup was a larger one than usual, 4.3 cm. diameter, and the deposit had the appearance of one from an impoverished electrolyte.

27 Different solution from the others, 2 in 10 e alkaline.

23 A porous pot only i]4 cm. in diameter was used in this experiment. The electrolyte became 10 in a

million acid during the experiment. Omitting 47, 48, and 91, new form gives 1. 018287. Omitting 76, 93, and 95, porous cup gives 1. 018284. The NBS value with small cups, and using German salt not recrystallized, was 1.018 27.
1 68 Report on Concrete Standards

TABLE XLVIII

Tests of Volume Effect on Three Electrolytes

Size

(1) NBS—From crystals of AgNOs from

the Gold-und Silber- Scheide-Anstalt

(2) PTR—From fused AgNOs from Gold-und

Silber-Scheide-Anstalt

(3) LCE—From crystals of AgN03 from Poulenc

No. of deposit Value for cell No. of deposit Value for cell No. of deposit Value for cell

Small voltameter

(Volume approxi- mately 100 cc)

1325

40

5152

56

61

1. 01826s

292 27s

35s 363 37j 392

1426

39

55

7580

1. 01828s

23 t 27s

328 288 233

12

27

42

53

1. 018206 29s

32a

27T

Mean 1. 01833i 1. 018275 1. 01827s

Large voltameter

(Volume 300ccexcept where noted)

212235

36

49SO

58

1. 01839? 394 37j

392 46s 468 42c

73

78

79

1.018477 (p. C.)

40o(p. C.) 44,(Sm.)

72

7782(370 CC)

62(250 CC) 86(230 cc) 106(250 cc)

1.018543(p.c.) 457 (p. C.) 476(Sm.)

24s

19s 21s

Mean 1. 01841s

33i

1. 018439 27s

1.018492 219 27s 27s

Differences . 000085 . 00016( . 000217 -. 00005s
International Electrical Units 169

TABLE XLIX

Comparative Results, with and without Silk

The two deposits of each, pair below were with substantially the same volumes,

except where noted as large and medium

:

No. of deposit Type of voltameter Electrolyte With

silk Without

Differ- ence,

parts in 100 000

90

91

18

17

23

2124

2237

35

38

36

69

68

71

70

92

93

94

95 Mean.

With new form ...do :.. With Jaeger form ...do With NBS glass cup and silk (medium) With NBS porous cup (large) With NBS glass cup and silk (medium) With NBS porous cup (large) With NBS glass cup and silk (medium) With NBS porous cup (large) With NBS glass cup and silk (medium) With porous cup (large) With NBS glass and silk (double)

.

(medium)

With NBS porous cup (medium).

.

With NBS porous cup and silk (double) With NBS porous cup With glass and silk (same as before) (large) With porous cup (large) With porous cup and silk (small) .

.

With porous cup—acid electrolyte.

.

NPL electrolyte

. ...do Frankfurt, fused (PTR)

...do

Frankfurt, not fused (NBS).

.do.

.do.

.do.

.do.

.do.

.do.

.do.

.do.

.do.

.do.

....do NPL electrolyte.

.do.

.do.

.do.

29

30,

323

27,

552

30,

363

373

397

375

392

28

1

363

30 20

- 73

- 69

-12,

-17,

-10,

29+26,

29+32,

- 69

•o+lls - 9:

29 Striated deposits. The silk was thoroughly washed, but had not been soaked in water a long time. The same silk gave a negative difference the next time, after having been soaked for several days.

30 The electrolyte in the porous cup voltameter was acid by 10 in io6 at the end of the run, and we suppose

this accounts for the light deposit, which makes the difference positive instead of negative as in the other

pair of deposits. In four pairs the voltameters were larger with the porous cup than with the silk, so that the difference is larger than otherwise, due to whatever "volume effect" (if any) there may be.
1 70 Report on Concrete Standards

TABLE L

Comparisons of Deposits with and without Silk

Different Electrolytes

Experi- No. ot Small porous No. ot New form No. of PTR voltameDifferences, parts in 100 000 ment

31 deposits cups deposits deposits ters (with silk) From new

form From por- ous cup

3 2 1. 018295 1 1. 01830j

32; 223

+ 0.9 + 3.0 -19.5

5 2 297 41a

2 7 2 1. 01835? 2 2 -13.5

12 2 26, 1 27s 1 216 -6.3 - 4.4

14 1 0. 99990 1 0. 99988 2 0. 999595 -28.5 -30.5

16 2 M 1. 00000s 1 0. 99999 2 0. 99954s -44.5 -46.0

31 The experiments 14 and 16 did not allow of calculating the value of the cell. The relative values of the

weights of the deposits are given for these experiments.

32 In experiment 16 the value 1.000005 was obtained when no septum was used. TABLE LI

Effect of Acid and Alkali

No. of deposit Notes

Alkaline Neutral Acid

Cell values

Differ- ence in weight,

parts in

100 000

108

107

109

113

112

121 125

126

127

124

128

123

120

NPL electrolyte neutral. NPL electrolyte alkaline New NBS electrolyte acid New NBS electrolyte alkali

100 000 ••

1 10 000"

106""

1.018753

1.01858i

1.01825(

1.018193 61

1.018129

+499

+45j

Weight of deposit

NPL electrolyte neutral, mean of 3.

NPL electrolyte acid 106" NPL alkaline 106- 4203. 19

NPL alkali and acid to neutralize (mean).

4202.82

4202.50

4202.60

+ 9 - 5 + 1
International Electrical Units 171

TABLE LII

Value of Deposits with Filter Paper

Number of deposit Value for cell Laboratory

15 1. 018428 LCE

16 428 LCE

29 538 LCE

30 41< LCE

43 46s LCE

63 457 LCE

83 64 376 PTR

67 475 NPL

84 448 PTR

87 36s LCE

83 482 PTR

Mean 1. 01845o

33 The value with this deposit is the mean of the two deposits in the German cups with filter paper and

silk. It has been excluded in taking the mean.

4. METHODS OF TESTING FOR VARIOUS IMPURITIES IN SILVER NITRATE

By A. S. McDaniel Free Acid or Alkali.—The usual methods of testing the neutrality of salts do not apply to silver nitrate solutions. Thus, toward

litmus, silver nitrate solutions react alkaline even after the addition of 1 part in 100 000 of nitric acid, while the same sample will

show an acid reaction toward methyl-orange even after the addition of an unhmited amount of alkali, so long as any undecomposed

silver nitrate remains (i. e. so long as the Ag is not completely

precipitated as AgOH)

.

If, however, the Ag be precipitated as AgCl by means of neutral

KC1 or NaCl solution, and the AgCl filtered off through asbestos,

the filtrate shows a neutral reaction toward all indicators if the

original AgN03 contained no acid or alkali. Samples of silver

nitrate purified by repeated recrystallization have been obtained

which show a neutral reaction toward iod-eosine when tested in

this manner, whereas if so little as 1 part in 1 000 000 of nitric acid

(or alkali) be added to the original solution it can be detected in the

filtrate from the precipitated AgCl. In testing for amounts of

acid less than several parts in 100 000, the AgCl must be filtered

off by means of asbestos instead of filter paper, for the reason that pure distilled water extracts a small amount of cellulose
172 Report on Concrete Standards

hydrates from filter paper which show an alkaline reaction toward

both iod-eosine and methyl-orange.

N N By the use of standard HNO, and NaOH with iodIOOO IOOO

eosine indicator the amount of free acid or alkali in a solution of

silver nitrate may be determined to within one part in one million.

The procedure is as follows

:

10 cc of a 10 per cent solution of AgN03 in a beaker are treated

with just sufficient of 20 per cent solution of carefully purified

and neutral KG to completely precipitate the whole of the silver as AgCl. The precipitated AgCl is filtered off through asbestos,

N and the whole of the filtrate titrated with standard NaOH

IOOO

(or HNO3) using iod-eosine as indicator. The titration is carried

out in a 25 cc glass-stoppered cylinder. The indicator must be

used in an aqueous-ether solution. An aqueous layer and an

ethereal layer must always be present. The iod-eosine is soluble

in the ether without coloration, whereas the alkaline compound

of iod-eosine is soluble in water with a pink color. Two cubic

centimeters of the ethereal solution of iod-eosine (5 to 10 mg per

liter) are used for each titration. Before adding the solution to

be titrated, the iod-eosine, in presence of % cc of water, is first

neutralized with ^ acid or alkali. The solution to be tested is 1000

then added and the whole brought back to the neutral point. A

blank determination is carried out in the same way, except that no silver nitrate solution is used; and the solution is not filtered. The reading obtained for the blank is subtracted from that obtained in the titration. Each cc of NaOH for a 10 cc sample

1000

of silver nitrate solution represents approximately 4 parts in

1 000 000 of free HN03 in the original solution; and each cc of

HNO, represents 6 parts of NaOH in 1 000 000 in the original

1000 r

solution. The results are expressed in terms of HN03

. N

Reducing Agents.—These are tested for by means of

KMn04 solution in the following manner:
International Electrical Units 173

10 cc of a 66.6 per cent solution of AgN03 to be tested are placed in a 25-cc glass-stoppered cylinder and made acid by the

addition of 1 cc of concentrated nitric acid free from reducing

substances. This mixture is then titrated with the standard

permanganate solution. The permanganate is added in /x 2 cc portions until the pink color persists for one minute. Each cubic

centimeter of permanganate solution is equivalent to approximately 2 parts of metallic silver, 4 parts of AgN02) or 0.4 parts of

furfural in 1 000 000 parts of dry AgN03

. One-half cc of the permanganate solution is required to give a permanent color to 10 cc

of distilled water, hence this amount is subtracted from the value

obtained in any titration. H2 S04 may be used in place of HN03

. Carefully recrystallized samples of AgN03 have been prepared

which show no permanganate reduction, whereas samples which

during their preparation have come in contact with filter paper or unwashed silk reduce from 2 to 70 cc of the permanganate solution.

Also, concentrated solutions of pure recrystallized AgN03 to

which colloidal metallic silver has been added reduce appreciable

amounts of permanganate. Likewise, silver nitrite or hyponitrite dissolved in concentrated silver nitrate solutions also reduce

permanganate. In fact, any strong reducing agent capable of

reducing a neutral solution of AgN03 to metallic silver, when

added to concentrated silver nitrate solutions causes the latter to

reduce permanganate, whereas the addition of certain other

organic substances of a mild reducing character such as cane

sugar, do not appreciably modify the amount of permanganate

reduced by the solution (except after fusion of the solid AgN03)

.

We have previously stated in detail our explanation of the

action of strong reducing agents (derived from filter paper, silk or other source) in producing abnormally heavy deposits in the silver

voltameter on account of their precipitation of colloidal silver. The test with permanganate is a sure method for detecting the presence

of such strong reducing agents, and hence a sample of silver nitrate

which is intended for use in the voltameter should fulfill this test. It is true that other milder reducing agents may reduce permanganate and their presence may not appreciably affect the electrochemical equivalent of silver, but the only safe course is to prove
174 Report on Concrete Standards

the entire absence of any substances capable of reducing permanganate. In other words, no safe method for differentiating the

strong and harmful from the weak and harmless reducing agents

is known to us. Besides, the AgN03 used should approach the

state of absolute purity as nearly as possible.

Some samples of carefully recrystallized AgN03 upon fusion, at a temperature as little above the melting point as possible, showed

no permanganate reduction after such treatment whereas other

samples, in the preparation of which organic material had not

been carefully excluded, showed considerable permanganate reduction after fusion. We, therefore, conclude that this method of

testing AgN03 for reducing substances (i. e. fusion and subsequent

titration with permanganate) is the most efficient. If the fusion

be carried out at a temperature of about 50 , or more, above the

melting point, for a half-hour or longer, a pure sample of AgN03 will afterwards show permanganate reduction. Prolonged fusion

at very high temperatures results in the complete reduction of

AgN03 to metallic Ag, hence in applying the above test care must

be exercised not to raise the temperature above 250 C (the melting point is about 208 C) and not to heat the salt longer than

necessary for its complete fusion. The crystals of silver nitrate

to be tested must show an acid reaction toward iod-eosine in 10

per cent solution.

Summary of the Action of the Various Septa used in Voltameter

Work upon Silver Nitrate Solutions as Shown by the Tests just

Described

Filter Paper.—Filter paper (or aqueous extract of filter paper)

precipitates colloidal metallic silver of varying color. This col- loidal silver can be coagulated and collected, and is easily con- verted into ordinary metallic silver by heating to 150 C or by

long contact with very dilute HN03

. This reduction of AgN03 to

metallic silver by filter paper is due to the decomposition of the

cellulose of which the filter paper is composed into strongly reducing aldehydes, consisting chiefly, if not entirely, of furfuraldehyde

(see previous reports)

.
International Electrical Units 175

This precipitation of metallic silver is accompanied by the

liberation of free nitric acid, which can be detected after the solution has stood for a considerable time, varying from a few hours

to several days, depending upon the amount of cellulose used.

The reason that this HN03 can not be detected immediately' is because it is neutralized by the excess of basic cellulose hydrates

present; until these cellulose hydrates are completely neutralized

or decomposed the solution reacts alkaline. As already stated,

aqueous extracts of filter paper show a basic reaction toward iodeosine and methyl-orange. The rate of formation of HN03 , due

to the reduction of AgN03 by filter paper, may be determined by

determining from time to time the decrease in the basicity due to the cellulose hydrates.

Silk.—Unwashed raw silk (or aqueous extract of silk) precipi- tates colloidal metallic silver from silver nitrate solutions. This

colloidal silver may be collected and converted into ordinary

metallic silver, as already described, under "filter paper" or its presence in concentrated solutions may be shown by its reduction

of permanganate solution.

This reduction of AgN03 to metallic silver by unwashed silk we

believe to be due to the partial decomposition of the latter into

strongly reducing aldehydes. Very strong evidence for this ex- planation is found in the fact that such unwashed silk is actually

decomposed into aldehydes by a solution of nitric acid containing

only a few parts of acid in 100000. Now, 10 per cent of silver

nitrate solution contains about this amount of nitric acid, due to

the hydrolysis of AgN03 into AgOH and HN03 as determined

colorimetrically by means of methyl-orange.

Thoroughly washed raw silk does not reduce AgN03 solution to

metallic Ag, at least to any considerable extent, as shown by the

absence of any color which might be due to colloidal silver. Also,

further evidence on this point is furnished by the fact that such

washed silk does not yield aldehydes upon treatment with very

dilute nitric acid, as is the case with unwashed silk. However, thoroughly washed silk and silver nitrate solutions

do act upon each other chemically in some way. This is con22451 —12 12
176 Report on Concrete Standards

clusively proven by the fact that neutral silver nitrate solutions

become distinctly acid after contact with thoroughly washed

silk. We believe that this acid results from the hydrolysis of the

protein material of the silk into amino-acids. The evidence so

far accumulated, which favors this explanation of observed fact,

is that the AgN03 solution is slightly acid (due to hydrolysis)

and it is well known that protein materials, in general, are hydrolyzed by dilute acids into a class of substances known as aminoacids. But further evidence must be accumulated on this point

before such an explanation can be established. However, there is ample experimental proof that there is some kind of a chemical

reaction between thoroughly washed silk and silver nitrate which

results in this solution becoming acid, and, so far as our present

knowledge goes, no treatment of the silk renders it inactive.

Unglazed Porcelain Pots.—These can be cleaned and treated in

such a manner that they are without action upon silver nitrate

solutions so far as the chemical tests already described are capable of showing. This method of treatment consists in first filling

the pot with about 10 per cent HN03 and allowing it to filter through the pores. The strength of acid required, and the number of filtrations necessary, depend upon the previous treatment

of the pot. This treatment is continued until the pot is free from

stains. If necessary the pot is first heated to 6oo° or 1000 C

before treatment with acid. This effectually removes all stains.

Successive portions of distilled water are now allowed to filter through until the nitrate is neutral toward iod-eosine.

Pots have been prepared in this manner which were so insoluble

that the conductivity of water having a specific conductivity of

1.2 x io-6 reciprocal ohms was not appreciably altered by filtra- tion through them. Successive portions of silver nitrate solution are now filtered through the pot until the filtrate is again neutral

toward iod-eosine; about three filtrations are usually necessary.

The pot is then ready for use in the voltameter.
International Electrical Units

5. NEUTRALITY TESTS OF ELECTROLYTES (USED IN EXPERIMENTS)

TABLE LIII

177

Date Experi- ment

Apr. 14 2 14 2 15 3 15 3

15 3

18 4 20 5 20 5 20 5 20 5 20 5 30 9 May 3 11

5 12

5 12

7 13

7 13 7 13 7 13

7 13

7 13 10 14 10 14 10 14 10 14

12 15 12 15

12 15

12 15

12 15

12 15 14 16

14 16

14 16

14 16 14 16

14 16

14 16

NPL electrolyte

Notes Acid(parts in

106)

Alkaline

NBS electrolyte

Notes Acid(parts in

106)

Before experiment. Porous pot 3.5

Porous pot Before experiment. New form1.4

New form Porous pot ...do New form

Before experiment New form

Silk (large cup) Very small porous pot Double silk (Kohlrausch,

large cup)

Silk on porous pot (small cup)

.

Siphon Porous pot Siphon New form

do

Solution made 10 in 10s alkaline Made acid 1

10 000 Made 10 in 106 alkaline

0.9

5.0

10.8.4

19. 2

1.2

109. 2

Neutralized

....do Made 10 in 106 aci(j Made 2 in 106 alkaline

.

New form

0.3

0. 3 6.6

0. 6 0.6

2.0

1.2

0.6

0. 3

0. 6

0. 6

1.5

Before experiment.

.

Porous pot do Glass and silk do Porous pot Before experiment

.

Porous pot do

Silk (Kohlrausch)..

....do Porous pot

Old Baker (siphon). ....do

New electrolyte (before). Porous pot

New Merck (before)

.

Porous pot, large ....do Porous pot, small do

0.6

3.4 1.3

14.4 12.0 1.3 0.6

0.6

1.0

84 15 M 210.9

1.2

1.2

0.5

0.6

0.9

2.4

2. 7

st The silk itself gave wash waters which were alkaline. There is probably hydrolysis of the silk to form amino acids. The values in the table all refer to the end of the experiment unless expressly stated

otherwise.
i?8 Report on Concrete Standards

TABLE LIII—Continued

Experi- ment

LCE electrolyte

Notes

Before experiment. Porous pot

Porous pot Before experiment. .

.

Filter paper

do New form

Filter paper

Before experiment. .

.

Porous pot (anode)..

.

Porous pot ( cathode )

.

Porous pot

.

New form.

Siphon. .

.

do... Anode . .

.

Cathode.

Acid

(parts in

10«)

3.6

30.6

(Alk.0.3) 0.6

1.8

3.5

0.9 3.3

3.6 3.0

1.2 3.0

2.4

PTR electrolyte

Notes

Before experiment. Porous pot

Porous pot Before experiment.

Silk I Silk in

Filter paper

Silk (small cup)..

.

Porous pot ....do New form Porous pot Washed filter tube

.

Double silk do

Double silk. New form. .

.

6. PERMANGANATE TESTS

Ten cubic centimeters of a 66.6 per cent solution of the salt is N

made acid with o.-;J cc of per cent H,SCX and titrated with

° ^

1 * iooo

KMn04 solution until the color remains permanent for one minute.

The precipitated Ag2S04 does not interfere with the titration.

Nitric acid may also be used (see p. 173).

N

Twenty-five cubic centimeters of KMn04 is equivalent to

0.006 per cent of Ag or 0.010 per cent of AgN02 , or 0.001 per cent

furfural in the dry salt.
International Electrical Units 179

TABLE LIV

Tests of the Permanganate Reduction of Different Samples of Silver Nitrate

Sample tested

Old Baker, not recrystallized New Baker (received Jan. 15, 1910) not recrystallized New Baker, after fusion and filtering New Baker, repeatedly recrystallized (after fusion) New German, not recrystallized New German, twice recrystallized New German (after fusion) New German, twice recrystallized (after fusion) French (crystallized) French (after fusion) German (Dr. Jaeger) fused English (fused) , " New " NBS electrolyte (more than)

7. SPECIAL TESTS ON THREE SAMPLES OF SILK

By A. S. McDaniel Three samples of raw silk, one furnished by the Bureau of Standards and two furnished by Prof. Jaeger were each treated with

portions of the same solution of silver nitrate in glass-stoppered

flasks in a thermostat kept at a temperature of 25 C. The silver

nitrate solution used was a 10 per cent solution of " New German "

silver nitrate which was tested for acid before the experiment and

found to contain approximately 1.8 parts of acid in one million

parts of solution. The silk furnished by Prof. Jaeger was rinsed once with distilled water before using. It was divided into two

approximately equal portions (200 cm2) and each portion treated

separately with the silver nitrate solution. The silk furnished by

the Bureau of Standards had been thoroughly washed with hot

HNO3 solution and rinsed until the water showed no acidity

toward iod-eosine indicator.

The amount of silk used in each test was approximately 200

square centimeters, and the volume of solution 160 cc. The

flasks were fastened in a rotating device immersed in the water

of the thermostat, and were sealed by a thin coating of paraffin over the stopper, which was further protected by a rubber cap.

After 24 hours, the flasks were removed and the solutions tested

for acid after filtering off the suspended particles of silk by means

of an asbestos filter. The results are tabulated in the accompanying table

:

KMnOi

required

cc 25.0 67.0

14.0 0.5

0.5

0.5 2.0

0.5

0.5

5.0 6.0

0.5

6.0
180 Report on Concrete Standards

TABLE LV

Sample of silk Treatment 35 Volume solution

Acidity, parts 106 (at end)

I. NBS, 200 cm' (new)

II. Jaeger, 200 cm' (old)

III. Jaeger, 150 cm2 (old)

Acid washed and rinsed free from acid As furnished, rinsed with distilled water do

160 cc 10% AgNOs (1.8 parts

10« acid) do

do

22

37

23 IV. No silk do (Alk)-0.3

35 All shaken for 2-1 hours at 25°. APPENDIX F. VARIOUS REPORTS GIVEN TO THE COMMITTEE

1. CONNECTION WITH PREVIOUS WORK

Mr. Smith thought it advisable to connect the results obtained

by this committee with the results obtained by the various delegates before meeting in Washington. Such links would be valuable, as they would serve to indicate the reproducibility of the

various forms of the silver voltameter. In connection with this

matter, he had perused the reports presented by the delegates and

believed that good agreement had been obtained. In the report

he had presented from the National Physical Laboratory, the

probable value of the Weston cells was given as i. 01827 ±0.00002

international volts at 20 C or 1.0183 international volts, if the

value be given within 1 part in 10 000.

This value is founded on the latest experiments at the National

Physical Laboratory, details of which are given in the National

Physical Laboratory report.

The mean value obtained from all the results given in Table

XLVII of the report of the subcommittee on the voltameter, is

1. 01 829 international volts, in very good agreement with the previous one. In his work of 1906, when filter paper was used, the value of the

cell at 20 C was given as 1. 01 843 volts. M. Laporte's value is

1.01844 and the value now obtained at Washington is 1. 01845.

Following are similar statements from Dr. Rosa, M. Laporte

and Dr. Jaeger.

PTR.—Dr. Jaeger communicated the results of earlier measure- ments at the Reichsanstalt on the electromotive force of the

Weston cell and on the silver voltameter.
International Electrical Units 181

According to these measurements (see Jaeger and von Steinwehr, Investigations on the Silver Voltameter, Zeitsch. f. Instrk.,

1908, p. 327) the mean value 1. 01834 international volts was

obtained for these standard cells, which were in good agreement

with those of America and England. The values obtained with

the porous pot were on the average about 5 in 100 000 lower.

Those without the porous pot, for the most part with silk, about

5 in 100 000 higher than this mean value. Further relative

measurements have, however, given the result that there is no

difference between voltameters with and without porous pot.

(Compare loc. cit., p. 366.) Likewise, later measurements, whose

results have been communicated to the committee, have shown

that no appreciable difference appears to exist between voltameters of the Kohlrausch form with and without silk. The mean values obtained with the Reichsanstalt's voltameter

in the joint work at Washington, 1. 01829 and 1.01833, as also

the mean of all the experiments —1 .01833, and, finally, the value

1. 01 83 recommended by the committee for the Weston Normal

Cell, all are in good agreement with the earlier values found at the Reichsanstalt.

At the present time, measurements of the same kind are in

progress at the Reichsanstalt, but the results are not yet at hand.

LCE.—By using at Paris the English unit of resistance and

assigning to the Weston Normal Cell the value 1.01818, adopted

in England, the result of the experiments on the silver voltameter was

1.1 1829

By calculating, however, the value of the Weston Normal Cell,

by taking 1.11800 for the electrochemical equivalent of silver, we

have

1 .01818 X

29 = 1.01845

1.11800 ^J The mean of the result obtained in the cooperative experiments at Washington, with the voltameters set up with filter paper, with four different electrolytes and four different observers, is 1.018447
182 Report on Concrete Standards

and the mean of the results obtained in the seven experiments

made with the electrolyte and the cathodes used at the Laboratoire Central d'Electricite is

i .018438

NBS.—As shown in the report of the subcommittee on the

silver voltameter, and the third report of the Bureau of Standards on work done on the silver voltameter, the value found for

the emf of the Weston Normal Cell by the Bureau of Standards

before April 1, 19 10, using the small porous cup voltameters, was 1.01824+0.00003 = 1.01827 volts. This is in very close

agreement with the mean value found in the experiments made

with two pure electrolytes, using two different types of voltameters (and both large and small sizes) as shown in Table I of the

report of the subcommittee, the latter mean being 1. 01 828 volts. As the electrolyte was not quite pure, we know the value found

with large voltameters was a little too large (see Table XL/VTII)

,

but we have shown that the different electrolytes agree very closely

when using the smallest size of voltameter, and hence the results

obtained in this form are considered most reliable.

2. INTERPRETATION OF RESULTS

By W. Jaeger

[Translation.] Dr. Jaeger submitted three tables showing the results obtained

with the silver voltameter

:

Table I/VT contains the means of all the separate experiments;

those only to be excluded in which impurities were purposely

added.

Table IyVII contains the means of the experiments which

were carried out with the voltameters of the Reichsanstalt.

Table I/VTII contains a summary of the three principal experiments in which the voltameters of the different countries were

used in the same way as usual.

The grand mean of Table I,VI is 1. 01 83 2, and if the experiments on filter paper are excluded, 1. 01 831. These numbers are

in good agreement with the value 1.0183, recommended to the

committee.

The mean of Table LVTI, using all the observations (not excepting those with filter paper) is 1. 01 833. Excluding the experi-
International Electrical Units 183

ments with filter paper, the value 1. 01827 (or 1. 01829) is obtained.

These numbers are also in good agreement with the value adopted

by the committee. From this I conclude that the use of silk is practically without influence, which is also in agreement with the

measurements at the Reichsanstalt (submitted to the committee)

in voltameters with and without silk. The summary I,VIII gives also, for the three measurements

(Nos. 3, 5 and 7) with the cups of the Reichsanstalt, very nearly

the same mean value, 1. 01 829, as with all the measurements

(Table LVII). The measurements with the cups of the National

Physical Laboratory give the mean value 1. 01 833, which is also

in good agreement with the adopted value, and also agrees well

with the experiments of the Reichsanstalt. Since, according to

the opinions of some of the members of the committee, that the

English salt is the purest and that the method used by Mr. Smith

avoids all organic septa, this agreement is, in my opinion, a

further proof that the use of silk as septum had no appreciable

influence on the silver deposit. The numbers obtained with filter paper (France) seem to indicate that filter paper, in agreement with

the opinions derived from observations of the Bureau of Standards

increases the deposit. The differences between the large and the

small cups of the Bureau of Standards appear, likewise, to indicate that under certain circumstances a difference between the

deposits of silver in large and small cups can occur. I incline,

however, to the opinion that this phenomenon, which has been

designated as the "volume effect" could be ascribed to the

influence of the porous pot.

In the 15th experiment, May 12, those electrolytes, which were made alkaline by the addition of NaOH became "opalescent,"

which appears to indicate that precipitation of silver hydroxide

took place. In such a case the weight of silver must naturally be

found too large. This measurement appears, therefore, to me to

be inconclusive with regard to the influence of alkali. The relative experiments, Nos. 14 and 16 of the 10th and 14th

of May, show such abnormal differences that one must be very

careful in drawing conclusions from these experiments. It is, indeed, not impossible that faults in the insulation were present,
Report on Concrete Standards

which influenced the distribution of current among the different

voltameters. The values found for the PTR voltameters appear

to me very improbable. Also it is not easy to see why the siphon

voltameters gave strongly varying values in experiment 14, while,

according to Mr. Smith, they gave values at Teddington, which

agreed well with those of the "new form." All these circumstances make the experiments concerned appear rather questionable, and I prefer, therefore, not to subscribe to the conclusions

drawn from them.

On the other hand, the experiments with cups of the same

kind and different electrolytes (see special table) indicate that

the different salts give the same deposit. This would have to be

interpreted that all the electrolytes used are sufficiently pure.

TABLE LVI

Mean of all the Experiments in which the Mean for each Experiment is Obtained, excluding those Deposits [Experiment 15] in which Acid was

Purposely Added to the Electrolyte

Number of experiment Date (1910) Weston cell at 20° (correctedto the mean of resistances and standard cells)

Differences, parts in

100 000

2 Apr. 14 1.01825 -7

3 IS 35 +3

4 18 27s -4.5

5 20 34 +2

6 22 29s -2.5

7 26 38 +6

8 28 32

9 30 34 +2

10 May 2 39 +7

11 3 36 +4

12 5 36 +4

13 7 31 -1

15 12 30s -1.5

17 19 26 -6

Mean, 1. 01832 ±3.5

These figures include 93 deposits, of which 10 or 11 were made using filter paper.

If the latter are excluded, the mean 1.01831 is obtained.

Probable error of a series =±2.8Xio-6 Probable error of the result=±o.8Xio-5
International Electrical Units 185

TABLE LVII

Mean of the Experiments with the Cups I and III of the Reichsanstalt

Number of experiment Cup EMF cell at 20° A37

3

T1

na 1 A1 oil *> 1. UloJ/ + 8

3 III 30 + 1

JvLean, l. uio34 + 5

5 I 1. 01827 - 2 5 III 38 + 9

Mean, 1. 01832 + 3

7 I 1. 01824 - 5

7 III 21 — 8

Mean, 1. 01822 — 7

10 I

as 1. 01838 + 9 10 III

12 I »9 1. 01845 +16

12 in 22 - 7

Mean, 1.01836 + 7

13 1 39 1. 01848 +19

13 m 25 - 4

Mean, 1.01836 + 7 Mean of all, 86 1. 01833

36 If the experiments with filter paper are excluded, the mean i. 01829 is obtained.

37 A is the difference of the individual values and the value 1. 01829.

38 Without septum.

39 With filter paper.
i86 Report on Concrete Standards

TABLE LVIII

Summary of the Results of the Three Experiments, Each with 10 Cups, in the Forms Used in the Different Countries

Experiment No. 3, April 15, 1910

Cup Germany Cup England Cup France Cup U. S. A. Cup U. S. A.

A A A A A

I 1.01837 +3 A 1.01831 +1 LC A

1. 01843 93 1.01840 +1 127 1.01833 +3

III 30 -4 B 28 -2 SC B

43 95 39 128 27 -3

1. 01834 1. 01830 1.01843 1. 01839 1. 01830

Experiment No. 5, April 20, 1910

I 1.01827 -5 A 1.01831 +1 LC A

1.01854 +7 93 1.01837 -1 127 1. 01820 —4

III 38 +6 B 28 -2 SC B41 -6 95 39 +1 128 29 +5

1. 01832 1.01829 1. 01847 1. 01838 1.01824

Experiment No. 7, April 26, 1910

I 1.01824 +2 A 1. 01841 LC A

1. 01847 93 1. 01847 127 1. 01835

III 21 -1 B 42 +1 95 47 128 36 +1

1.01822 1.01841 1. 01847 1. 01847 1. 01835 Mean

.

1. 01829 1. 01834 1.01846 1. 01841 1.01830

3. INTERPRETATION OF RESULTS

By E. B. Rosa Table LIX gives a summary of the results obtained in 14

international experiments, containing 98 deposits. Three experiments are not included in this table, two (1 and 16) because of

accidents whereby the current became interrupted, one (14)

because of the inclusion of six siphon voltameters having a total

resistance of about 200 ohms, and the current could not therefore

be maintained constant enough to permit an accurate determination of its average value. All other experiments were made

with very steady current, the average uncertainty in its mean

value in each of the 13 experiments being probably not greater

than 1 part in 100 000.
International Electrical Units 187

Twenty-four deposits were made with electrolytes which do not

reduce potassium permanganate. At the Bureau of Standards we

have found that the reaction with potassium permanganate is large with very impure electrolytes, which give striated deposits

and a large volume effect; that it is less with less impure electrolytes which give a smaller volume effect, and that there is no reac- tion with those samples of silver nitrate which give no volume

effect. We should, therefore, conclude that a small reaction with

potassium permanganate is not only an evidence of a small quantity of impurity in the silver nitrate, but that this small impurity

will increase the deposit appreciably in a large size voltameter

(300 to 400 cc), and we think this conclusion is justified by our work. In other words, the permanganate test seems to be a

searching test for reducing agents which tend to make the deposit

too heavy. Most of these 24 deposits were from silver nitrate

purified by Smith at the National Physical Laboratory, but four were from silver nitrate purified by McDaniel at the Bureau of

Standards. The deposits agree very accurately in the two types

of voltameters, and in the several sizes of the porous cup voltameters, and the average deviation of the 24 deposits from the

mean of all is a little over 1 part in 100 000. This surprising

agreement with so many deposits under so many conditions can

not be altogether accidental, but indicates the possibility of very

high reproducibility when the electrolyte is pure and all the conditions suitable, even though the size and type of voltameter be

varied, with different treatment in detail of the deposits. We

regret that only two samples of silver nitrate were available,

which were entirely pure as tested by potassium permanganate,

but we have prepared some others since the international experiments were finished, and shall be prepared to report on these

later. We may add that the purification of silver nitrate so that

it will stand this very severe test is not difficult when one knows

exactly how to proceed, and we mean to communicate the process

to some of the chemical manufacturers, so that they may supply

nitrate that will be strictly pure as tested in this way.

Ten deposits were made, using filter paper, by three experimenters, using different voltameters and different electrolytes.

The mean value is 15.1 in 100000 higher than the value with
i88 Report on Concrete Standards

pure electrolyte, using porous cups or no septum (as in Smith's

new form) . There is a very good agreement among these values,

although the mean deviation from the mean of all is about three

times as great as in the first set. It may be remarked that a

single sheet of filter paper was used in each case. If heavier paper,

or two sheets of the same, had been employed, the excess in weight

would have been greater. (See third report of the Bureau of

Standards on this subject.) As no member of the committee

favors the use of filter paper in the normal voltameter, it is not

necessary to discuss these results further.

Fifteen deposits were made with silk, by three experimenters,

in several different types of voltameters. Two deposits were made with new raw silk that had been washed thoroughly but not

soaked in water a long time before using. These two deposits

average 29.4 in 100 000 higher than the mean of the others. The

other 13 deposits were with washed silk that had been kept in

water a long time before using and then used repeatedly. Their

average is closely in accord with the results of group 1. This,

however, would seem to be largely accidental, inasmuch as silk seems to produce two disturbing effects which are in opposite

directions, as pointed out in the report of the subcommittee. The

first is to increase the deposit by producing reducing agents,

which effect is large at the start but decreases rapidly with con- tinued washing. The second is to produce acid, which decreases

the deposit. The special tests on three samples of silk (see report

by Dr. McDaniel) in which silk was placed in neutral AgN03 in a bottle for 24 hours, which was rotated to keep the liquid stirred,

show that acid is produced by silk, even outside of the voltameter, when current is not flowing. Two of these samples were

Dr. Jaeger's silk, and one was supplied by the Bureau of Standards. All tests of the electrolyte that have been made at the end

of experiments in which silk has been used, show acid in relatively

large quantities, about 20 to 40 parts in a million; enough to

reduce the deposit appreciably, according to the special tests on

the effect of acid. That, on the average, the deposits in the

above table are as high as with the pure electrolytes, in spite of

the presence of acid, shows to my mind that the silk probably is also producing simultaneously the first effect mentioned above.
International Electrical Units 189

Reference may be made also to the deposits with silk in the

Physikalisch-Technische Reichsanstalt voltameters in the relative

experiments 14 and 16. As compared with the voltameters 27

and B, of experiment 14 (in which pure electrolyte was used, and

in which a normal value of the deposit may fairly be assumed to

have occurred) the silk voltameters gave deposits 3 in 10 000 too

small; whereas the mean of the siphon voltameters was 3 in 10 000

greater than the two taken as normal. In experiment 16, the

mean of the deposits 121 , 125, and 126, was taken as normal, these

three having pure, neutral silver nitrate and no septum to con- taminate the electrolyte. Here the silk voltameters are 3 and 6

parts, respectively, in 10 000 too low, a departure from the normal

value greater than produced by filter paper in any of these experiments. Possibly these four deposits are only accidentally low ; if so, no suggestion was made as to the nature of the accidents. The

presence, however, of silk (producing 10 times as much acid in

the electrolyte as, I believe, is permissible) gives some ground at

least for suspicion, even though something else may have operated

to produce so considerable deviations from the mean value.

In the fourth group of results there are 35 separate deposits in

which various electrolytes have been employed, all of which,

judged by the chemical tests applied, were slightly impure. By

this is meant that they were, judged by ordinary standards, pure.

But, judged by the permanganate test, they carried an appreciable quantity of organic impurities or reducing substances that

result from organic impurities. Many of these deposits are the same as those given in Table XLVIII of the subcommittee, showing

the volume effect. That is, the deposit is larger from large volumes of electrolyte than from small when the electrolyte is impure.

In 13 deposits in large voltameters (2 National Physical Laboratory and 1 1 National Bureau of Standards) , the mean is 1 5 parts

in 100000 greater than for the 18 deposits in the small National

Bureau of Standards voltameters. To our view this is unmistakable evidence of impure electrolytes. If our view is correct,

all purchased samples of AgN03 which have been at the disposal

of the committee, from German, French, and American makers,

have been slightly impure, and only the two samples referred to

above, purified by Smith and McDaniel, are strictly pure. I regard
190 Report on Concrete Standards

it as a fortunate discovery by Dr. McDaniel that a comparatively

simple chemical test should show (as the potassium permanganate

test seems to do) the presence of small quantities of impurities so

difficult to detect by other means.

Faraday's law is the underlying principle of the silver voltameter. When the latter is employed as a standard for current

measurements, the quantity of the deposit should be proportional

to the quantity of electricity. If large and small voltameters do

not agree, there is something wrong with the voltameter or with

the manipulation, or with the electrolyte. We think that there

is no doubt whatever in this case as to where the trouble lies. The voltameters and the manipulation are the same (for the most

part) as in the first group of results. The electrolytes differ. We

do not need to trust the chemical test alone to prove the electrolytes are impure ; the voltameter experiments show it also. Hence

we clearly should not give the same weight to the results of the

experiments in group 4 in determining the true value of the emf

of the Weston cell in international volts, as to the results of experiments not open to these objections.

In groups 5 and 6 the results of adding small quantities of

alkali and acid are given. Very small quantities of either affect

the weight of the deposit, alkali increasing and acid reducing the

deposit. We have made other experiments on this subject at the

Bureau of Standards, and shall make still others. We can not say

precisely how much of either is safe, but a slight decrease in

weight is caused by a few parts of acid in a million, and probably one in a million of alkali, if always present, would be noticeable

in the mean of several experiments.

Finally, we call attention to the fact that many of the deposits

made by the Bureau of Standards in these investigations with

impure electrolytes were made for the purpose of demonstrating

the "volume effect " (as we have called it) as a test for impurity.

Four cups were used by the Bureau of Standards, instead of

two as the others did, in order to have two different volumes of

electrolyte (one 100 cc and the other 300 cc) to show how important it was to have silver nitrate of the highest purity, and it was

stated at the time that the salt was purchased and was not quite
International Electrical Units 191

pure, and would give a higher value in the large cups. All the

AgN03 used in these experiments was tested by the permanganate

test, and although it was considered very pure, the permanganate

reaction if trustworthy showed slight impurity in all except the

English. The representatives of the Bureau of Standards have

great confidence in this test, but as it is a new test and has not

been used before by others, its trustworthiness was not accepted

by all the delegates.

At the end of Table LIX is given a summary of the results

obtained in the 70 deposits of groups 1, 3, and 4, omitting those

made with filter paper and those in which acid or alkali was

added. There is a difference of opinion among the delegates as

to how these results should be weighted in taking the mean, but

for the purpose of fixing the value of the Weston Normal Cell to five figures it fortunately makes little difference how the

results are combined. If equal weight is given to all, the result

is nearly the same as though the weights were unequal.

TABLE LIX

Summary of Results of 89 Deposits, excluding relative values of Experiments 1, 14, and 16

1 With Voltameters Using Porous Cups or without any Septum ( with Electrolyte neutral by the

iod-eosine test and free from reducing substances by the permanganate test)

(1) Mean of io 40 deposits, NPL, new form voltameter 1. 01831! ±4. 3

(2) Mean of 4 deposits, NBS, porous cup, large voltameter 289 ±0. 7

(3) Mean of 9

deposits, NBS, porous cup, small voltameter 285 ±1. o

(4) Mean of 1 deposit, NBS, porous cup, medium voltameter 28g — o. 2 Mean 24 deposits, two types, several sizes of voltameters i. 018297 Mean excluding two determinations with unsteady current 1. 018285

2. Using Filter Paper

(6) Mean of 3 deposits, PTR, with filter paper 1. 018469 1. 7

(8) Mean of 6 deposits, LCE, with filter paper 437 4. 4

(15) Mean of 1 deposit, NPL, with filter paper 475 2. 5 Mean of 10 deposits 1.018450 ±3-4

,0 Two deposits in NPL. new form in seventh experiment, gave 1.018413- The current in this experi- ment was unusually unsteady. If these two determinations be excluded, the mean of 8 deposits is

1.018287 and the mean of 22 is 1.018285- 22451°—12 13
192 Report on Concrete Standards

3. Using Silk

(5) Mean of 6 deposits, PTR, with silk 1. 018283 ±4. o

(14) Mean of 2 deposits, NBS, with new silk 58,, (13) Mean of 6 deposits, NBS, with used silk 285 ±3. 2 (17) Mean of 1 deposit, NPL, with used silk (electrolyte slightly- alkaline) 29„ 0.4 Mean of 15 deposits 1. 018323 Mean of 13 deposits, excluding new silk 1. 018289 3. 3

4. Electrolyte indicated by the chemical tests to be Slightly Impure

(7) Mean of 1 deposit, PTR, with no septum 1. 018373

(9) Mean of 2 deposits, LCE, with no septum 22 t (16) Mean of 2 deposits, NPL electrolyte, with no septum, large voltameter 458 (11) Mean of n deposits, NBS electrolyte, with porous cups, large voltameter 43„

(12) Mean of 18 deposits, NBS electrolyte, with porous cups, small voltameter 28

(10) Mean of 1 deposit, LCE electrolyte, with porous cups, medium

voltameter 2i4 Mean of 35 deposits 1. 018335

5 Electrolyte Slightly Alkaline, NaOH added

(18) Mean of 2 deposits, electrolyte, alkaline, added 2.1/106 NaOH. 1. 018363 Mean of 1 deposit, electrolyte, alkaline, added 5/106 NaOH. . . 58 Mean of 1 deposit, electrolyte, alkaline, added 10/106 NaOH. . 75 Mean of 4 deposits 1. 018515

6. Electrolyte Slightly Acid, HN03 added Mean of 1 deposit, electrolyte acid, added 10/106 HN03

1. oi82o Mean of 2 deposits, electrolyte acid, added 100/106 HN03 i6 Mean of 3 deposits 1. 018173 Summary

Mean of 22 experiments, group 1 equals 1. 018285 Mean of 13 experiments, group 3 equals 1. 018285 Mean of 35 experiments, group 4 equals 1. 018335 Mean of 70, giving each equal weight, equals 1. 018310 Mean of 70, giving group 4 half weight, equals 1. 018302 Mr. Smith makes the following comments on Dr. Rosa's interpretation of the results:

Dr. Rosa's conclusions are naturally on very similar lines to those of the subcommittee on the silver voltameter, of which I was a member, and in consequence I am

in almost complete agreement with his conclusions.
International Electrical Units 193

The possible action of silk has been discussed by the full committee and I think it well that further experiments should be made with it and with porous pots or any

other medium which may contaminate the electrolyte. These experiments must of course be supplemented by others on the effects of small quantities of acid and alkali. The question of the purity of the electrolyte is most interesting. To obtain pure

silver nitrate very considerable care was taken in the early and recent experiments

at the National Physical Laboratory and, I believe, even greater care in the recent experiments by M. Laporte at the Laboratoire Central. In these cases I think that

there is no doubt but that very pure salt was obtained, although in the early National

Physical Laboratory experiments, and in some of the experiments at the Laboratoire

Central, the solutions were afterwards contaminated by filter paper.

It will be observed that the tests made by Dr. McDaniel on silver nitrate from the National Physical Laboratory showed the fresh electrolyte to be free from organic matter and to be never acid. On one occasion a sample of fused salt was given to Dr. McDaniel and this he found to be free from acid and alkali. I was surprised,

therefore, to find on May 7 that a solution was alkaline to the extent of 2 parts in

1 000 000 and at that time I was at a loss to explain the alkalinity. However, a re- port submitted by Dr. McDaniel shows that in 24 hours a 10 per cent solution which

was originally acid by 1.8 parts in 1 000 000 became slightly alkaline (0.3 in 1 000 000)

after agitation in a flask. As some of the bottles in which the electrolytes were stored, were fresh from the stores of the Bureau and in many cases the electrolyte remained

in the bottles for 14 days—perhaps more—the slight alkalinity observed on May 7 was probably produced by interaction with the glass. It is of interest to note that on May 7 the results obtained with the NPL electrolyte were higher than usual by about

8 parts in 100 000, and that this was the only occasion when such an abnormal value was obtained. It is true that there was one other occasion when high values resulted, but the current was unusually unsteady and the results are not therefore of much

weight. I conclude that solutions should be freshly prepared or stored in special

glass bottles. With regard to Dr. Rosa's statement to the effect that " if we were to restrict the volume of electrolyte to 100 cc, something might be said for permitting the use of electrolyte which is not quite pure," I think that the statement should refer to the degree of electrolysis and not to the volume. According to my own experiments, the

reason why, from a small volume of impure electrolyte, a lighter deposit is obtained than from a larger volume of the same electrolyte, when the two are placed in series,

is because the degree of electrolysis is greater in the first case than in the second. For equal concentrations the degree of electrolysis is inversely as the volumes. If alkali or other impurity tending to increase the deposit, is present in an electrolyte at the commencement of an experiment there is less present at the end of the experi- ment; the average quantity of impurity present during the experiment varies, therefore, with the degree of electrolysis and hence the deposit varies with the latter. It

also follows that the deposit from an impure electrolyte depends on the concentration

of the solution. 100 cc of a 20 per cent solution (impure) will give a heavier deposit than 100 cc of a 10 per cent solution of the same salt, if the two are placed in series. Hence, while I entirely indorse Dr. Rosa's remarks on the desirability of having a pure electrolyte, I suggest that the uniform results obtained with the four small voltameters were due to the high degree of electrolysis.
194 Report on Concrete Standards

4. INTERPRETATION OF RESULTS

By F. E. Smith Mr. Smith submitted the following table, which gives the

weighted means of all experiments with the forms of voltameters

stated at the heads of the columns. To obtain these weighted

means, values were assigned to the results in proportion to the

degree of accuracy with which the current was estimated to be

known. Each mean is accompanied by a number, in parentheses,

denoting the number of values from which the mean was obtained

;

the mean deviation from the mean is also given, but in calculating

this one deviation (associated with the experiment in which the

value of the current was estimated to be known with an accuracy

not greater than i in 10 ooo) has been omitted.

TABLE LX

Electrolyte New form,

370 cc Porous pot, small

bowl, 100 cc Porous pot, large bowl, 300 cc

NPL (11) 295 ± 27 (3) 29i ±108

(1) 44i

(9) 272 ±25 (4) 289 ±33 (6) 27s ±27

(9) 306 ±63

(2) 269 ±0<

(30) 285

(4) 30j ± 26 (3) 357 ±14s

(2) 43 ± 39 (9) 4U ± 23 (2) 25a ± lo (20) 38

Poulenc

Frankfurt (fused)

NBS, purified Weighted mean (15) 305

Electrolyte

Filter paper,

100 to 350 cc

Silk, 70 cc to 350 cc No septum

(Jaeger), 70 cc Weighted mean

NPL (1) 47a

(7) 438 ±39 (2) 465 ±1;

(3) 425 ±128 (28) 30a (17) 362 (19) 328 (22) 346 (4) 26

Poulenc

Frankfurt (fused) Frankfurt crystallized and recovered

(7) 283 ±46 (4) 282 ±35(1) 343

NBS, purified Weighted mean (10) 447 (14) 313 (1) 343

Weighted mean of all (89)= 1.01833o Mr. Smith stated that he would interpret the results in the table

submitted by him as showing that with some of the electrolytes a

larger mass of silver was deposited from a larger volume than from

a small volume, and his deduction from this was that some of the

electrolytes were impure. This was admitted in the case of the

two first electrolytes (Frankfurt crystallized; also recovered silver

nitrate) from the Bureau of Standards, both in the Bureau of

Standards' reports and during the experiments.
International Electrical Units 195

A further deduction from the table is that, with filter paper, a contamination of the electrolyte results which increases the mass

of the deposit.

It was worthy of notice that the results obtained (mean =

* 1.01826J with the purified salt of the Bureau of Standards agreed

substantially with those obtained (excluding filter paper and silk,

mean = i.oi8286 ) with the purified salt from the National Physical

Laboratory and these two electrolytes showed very little or no volume effect. It was also well to point out that the values

obtained with the four electrolytes in small voltameters of the

porous pot type agreed remarkably well, both among themselves

(mean = 1.018285) and with the two values stated above.

M. Laporte and Dr. Rosa expressed themselves as being in

agreement with these remarks.

5. INTERPRETATION OF RESULTS

By F. Laporte

[Translation.] Before the experiments in Washington, the results obtained in

the different laboratories for the electromotive force of the Weston

Normal Cell, as deduced from the value of the ohm and the deposit

of silver, may be considered to be as follows:

" 1908 « 1910

PTR 1. 01834 NPL 1. 01843 1. 01827 NBS fl. 01837 »L 01827

jl. 01863 LCE 1. 01879 1 01845

n Introduction, p. 6.

43 Appendix F, pp. 180 et seq.

43 The results given by the NBS relate only to deposits obtained in voltameters of small size and with

the porous pot. The results obtained at Washington, as is shown by Appendix

F, page 180, prove that the experimental conditions employed by

the different laboratories in 1910 are reproducible with precision.

This is a first important point gained. The measurements made

by the four laboratories are now comparable.

The use of filter paper as a septum has the effect of increasing

the weight of the deposit in the voltameter in question. This fact

is very strikingly established by the experiments ; however, under
196 Report on Concrete Standards

given experimental conditions, its action always appears to be the same. That is, the "Rayleigh" form is also as reproducible as the others.

One sees also that traces of alkali increase the weight of the deposit, and that free acid added to the electrolyte decreases it. The action of alkali is more distinct and more important than

that of acid. The experiments are entirely insufficient to evaluate numerically the importance of this action or to fix upon allowable limits in the specifications.

The use of silk as septum would appear to necessitate fulfilling

certain experimental conditions (nature of silk, preliminary washing). The same is probably true of the porous pot, which gave

in one or two experiments results which were too low, which

results were regarded as abnormal. But it would not appear to

me that any conclusion can be drawn.

Excepting the points just indicated, no other fact appears to

have been indubitably proved. The measurements of the acidity or alkalinity of the electrolyte, before and after the experiments, no acid or alkali having been purposely introduced, gave results

which were not markedly systematic. Even with filter paper, the

results of the tests have indicated alkalinity as often as acidity,

and it is necessary to enter into complicated chemical considerations to explain the results. As regards the volume effect and the test with permanganate of

potash, the results are not entirely conclusive.

The experiments which may be regarded as establishing it were

all made with the porous pot, the four electrolytes evidently gave

the same results in the small voltameters, the test with the larger

voltameters was not made in such a systematic manner. It can

also be seen from the table on page 1 68 that very noticeable differ- ences were obtained with voltameters of the same volume. Further, the question was not settled as to whether or not the fusion

of the silver nitrate, necessary for the test with permanganate,

has an effect on the weight of the silver deposit.

The volume effect, then, although very probable, does not seem

to me to have been indisputably established by the experiments.

I wish, however, to make clear that I consider the electrolyte of

the National Physical Laboratory as the purest of the solutions
International Electrical Units 197

employed. The voltameter without septum seems to me to offer the greatest amount of security and to be above suspicion. Accordingly, in discussing the experiments, all should be rejected

with the exception of those made with the new form, using the

National Physical Laboratory electrolyte, and in which the acidity of the electrolyte was controlled.

These experiments are as follows:

Experiment Deposit Acidity 10"6 Value of Weston cell

5 33 1. 01831o

5 34 283 9 59 0.9 31, 12 83 279 15 95 1.2 25( Mean 1. 01828?

But these experiments are truly too few to allow of taking their

mean as representing the value of the electromotive force of the

Weston cell; I think, therefore, that it will be better to take as the provisional value of the Weston cell the mean which results

from including all the deposits obtained in the experiments of the

International Committee (excepting those in which filter paper was used and those carried out under abnormal conditions). In

fact, we have just seen that if an attempt is made to discuss and

analyze all the results, point by point, difficulties or impossibilities are met with. Why, for example, should certain results a

little different from the mean (Experiments 7 and 13) be eliminated, or their importance be diminished, because the current was

noted to be unsteady or because the electrolyte was found acid

or alkaline, while other deposits of the same experiment are too

light or normal, the test of acidity not having been made systematically for all the electrolytes in all the experiments ? Taking the mean, then, of the 40 values contained in the following table, the value

1.0183!

is obtained.

I think, then, that the value to be adopted should be

1.0183
198 Report on Concrete Standards

TABLE LXI

Deposit Electrolyte Type

17

18

1920

2122

23

24

31

3233

34

35

36

3738

4546

47

48

4950

5152

6266

68

7086

8990

91

92

93

94

95

129 130

131 132

C

CA

AD

D

D

D

C

cA

A

D

D

DD

c

cA

A

D

D

D

D

BA

A

A

B

C

A

A

A

A

A

A

E

E

E

E

No septum

Silk New form

....do Porous pot ....do Glass and silk

.

...do Double silk ....do New form

....do Porous pot ....do Glass and silk. do Double silk do New form

do Porous pot dodo

do New form

do Porous pot do New form Double silk Silk New form

Glass and silk

.

Porous pot Silk Porous pot dodo

do

do
International Electrical Units 199

6. PROVISIONAL SPECIFICATIONS FOR THE SILVER VOLTAMETER

For work of highest precision. Prepared by E. B. Rosa at the request of the committee and submitted for consideration, but not acted upon

z. The electrolyte shall consist of a solution of silver nitrate in distilled water, having from 10 to 20 g of silver nitrate in 100 cc of the solution.

2. The electrolyte must be free from organic or other reducing substances, as shown

(a) by a suitable chemical test, (t>) by giving a crystalline deposit free from striations, and (c) by giving the same weight of deposit in a large and in a small voltameter.

3. The silver nitrate is purified by crystallization and fusion, and if the chemical

test for purity is omitted it should be purified until further crystallization does not change the weight of the deposit.

4. The voltameter should contain not less than 75 cc in the cathode chamber, and

the deposit should not continue long enough to reduce the mean concentration of the

electrolyte in the cathode chamber below 5 per cent. If no septum is used, no greater weight of silver should be deposited in a single experiment than is contained in the

electrolyte at the start.

5. The electrolyte when ready for use must be neutral or very slightly acid, as tested by iod-eosine. As one part in a million of alkali may increase the deposit

appreciably, it may be better to have a slight acidity (say one part in a million) than

to take the risk of slight alkalinity in attempting to make it strictly neutral. The

electrolyte must be neutral or slightly acid at the end of the experiment, no alkalinity, and only a trace of acid, if any, being present. In any case there must not be

enough acid present to affect the weight of the deposit. Any septum or other substance which contaminates the electrolyte or produces appreciable alkalinity or more

than a trace of acid must be avoided.

6. The cathode should be a crucible or bowl, preferably of platinum (although gold

may be used) of from 125 cc to 400 cc capacity. The surface should preferably be

smooth and bright and the deposited silver should be removed by electrolysis or by

acid, without scratching or marring the surface of the platinum by any instrument.

7. The anode should be of pure silver and is preferably coated with electrolytic

silver. This is conveniently done when a previous deposit is being removed from

the cathode bowl, using a relatively small current. The anode should have as large an active area as the size and type of voltameter permit.

8. The current during a deposit should be maintained constant, and is preferably not more than one ampere, and the time not less than one hour.

9. If the surface of the platinum is perfectly clean and the electrolyte pure the

silver will be adherent and there will be little if any loose silver. After thorough

washing, the cathode bowls are dried at about 150 C, preferably in an electric oven

and after cooling are weighed. In the weighing a similar platinum dish adjusted to the same weight is advantageously used as a tare.

10. The electromotive force of the standard cell employed is calculated from the weight of silver deposited, the resistance, and the time, using 1.11800 mg per second

as the electrochemical equivalent of silver.
200 Report on Concrete Standards

7. REPORT OF SUBCOMMITTEE ON THE MAINTENANCE OF THE UNITS

By F. A. Wolff and F. Laporte In the opinion of the subcommittee, it is considered of the

highest importance for the additional work outlined on the silver

voltameter and for similar international cooperative work in the

future to adopt measures which would enable such results to be

expressed in terms of the same resistance standards and standard

cells here employed.

The following are therefore recommended with regard to the

unit of resistance:

1. An intercomparison of the coils of the PTR, the NPL, and the LCE in the home

laboratories with other reference standards immediately upon the return of the dele- gates to their laboratories.

2. The periodic recomparison of the coils employed at the NBS by the aid of at

least two coils selected on account of their relative constancy and sent to each labora- tory in turn at least once a year.

3. The general adoption of sealed coils as reference coils to eliminate at least one

source of variation.

4. The early completion of primary mercurial standards in precise realization of the London specifications and the determination of their relation to the unit here employed.

Our recommendations in reference to standard cells are as

follows:

1. An intercomparison of the cells taken back to the home laboratories with the

cells serving as the previous basis of reference.

2. The periodic recomparison of the cells here employed by the aid of a number of

cells sent to each laboratory in turn.

3. The construction of new cells from time to time as a further check on the con- stancy of the reference cells. These should include cells set up with materials derived by exchange between the various laboratories.

4. Cooperative work along lines to be agreed upon to be made the basis of suitable

specifications to insure the highest possible accuracy of reproduction as well as uni- formity of procedure.

5. The completion of arrangements for the preparation of standard cell materials made according to the specifications agreed upon, and their distribution under the

auspices of the International Scientific Committee.

With regard to the silver voltameter the following recommendations are made:

1. The adoption of general specifications in so far as they may be agreed upon.

2 . Further experiments on matters not considered as settled at this conference and

as indicated in the minutes of the sixteenth meeting of May 23 to serve as a basis for

final specifications.
International Electrical Units 20I

In addition the following general recommendations are made

:

1 . That the results obtained in any of the above work by any member of this committee be promptly communicated to the other members.

2 . That every effort be made to complete the results of the silver voltameter experi- ment and the construction of mercury ohms by the spring of 1911.

3. That every assistance be given to members of the International Scientific Committee not represented in Washington who may be working or who desire to work on

the questions here taken up.

4. That researches bearing on these questions be published as soon as possible after their completion.

V. RESUME

By F. Laporte

[Translation] The state of the question of the electrical units and standards

at the time of the opening of the Conference of London, in 1908,

and in the following year (1909) was as follows:

THE INTERNATIONAL OHM

The National Physical Laboratory and the PhysikalischTechnische Reichsanstalt only had realized mercurial standards

representing the international ohm. These standards, dating as they do, from before 1908, do not fulfill all the conditions laid

down at London in the specifications for ohm standards to be

constructed later. The Laboratoire Central d'Evlectricite referred

its measurements to legal ohms, constructed in 1884, and preserved at the Post and Telegraph office at Paris. The Bureau of

Standards had, as base of reference, wire coils compared with the

German and English ohms.

STANDARD CELLS

The standard cells constructed in the different laboratories,

according to slightly differing procedures, principally as regards

the preparation of the mercurous sulphate, agreed in value, in so far as it had been possible to detect by exchanging cells and

samples. However, the cells prepared from mercurous sulphate,

obtained at the LCE by alternating current electrolysis, and constructed in this and the other laboratories, had shown a slightly

higher electromotive force than the others.
202 Report on Concrete Standards

SILVER VOLTAMETER

Adopting i.i 1800 as the electrochemical equivalent of silver,

the values found for the electromotive force of the Weston Normal Cell are as follows, each laboratory having employed different

electrolytes, voltameters, and experimental conditions:

At the NPL with filter paper 1. 01843 At the PTR with silk and porous pot 34 At the NBS with the porous pot 37 At the NBS with filter paper 63 At the LCE with filter paper 79 This statement shows that differences of several ten-thousandths

existed between the results. The London Conference recommended, subject to later experiments, as provisional value of the emf of the Weston cell, 1.0184

at 20 C. Following a vote of the International Committee on the proposition of Mr. Stratton, a technical committee was formed and met

at Washington to make joint experiments. The aim of this work

was to determine what value should be recommended for the emf

of the Weston Normal Cell at 20 C as determined from measure- ments made by means of the silver voltameter.

This committee was composed of Messrs. Rosa, of the Bureau

of Standards, chairman; Jaeger, of the Physikalisch-Technische

Reichsanstalt ; Laporte, Laboratoire Central d'Electricite; Smith,

National Physical Laboratory; and Wolff, Bureau of Standards.

The work continued from April 4 to May 25, 19 10. The delegates made and had made, during this time, numerous experiments and comparisons of the silver voltameter, resistance coils,

and standard cells. The results of the experiments were presented in the reports of

the subcommittees and discussed in the meetings of the technical

committee.

The work of the committee may be summarized as follows:

RESISTANCES

The resistance coils, which were brought by the delegates, were

intercompared. The experiments were made at two temperatures,

20 and 25 C. The numerous comparisons made have led to the

following conclusions-:
International Electrical Units 203

The Technical Committee decides to choose, actually and until new mercury ohms

shall have been constructed, as the value of the international ohm, to be recommended

to all countries, the mean of the values of the units realized at the PhysikalischTechnische Reichsanstalt and National Physical Laboratory. Although the inter- national ohm, as defined by the London Conference, has not been strictly realized, the committee believes that its value has been obtained in two independent laboratories, with a good degree of precision, and that future work will not change its value by more than 2 or 3 in 100 000. The committee expresses the hope that new international ohms, fulfilling all the

specifications of the London Conference, may be realized as soon as possible in dif- ferent laboratories. The results of the comparisons of the different metallic resist- ances have been as follows (see p. 94)

:

From these can be deduced that the differences between the

values of the ohms in use in the different laboratories and the value

adopted by the Technical Committee, are as follows:

The relative measurements of the metallic resistances seem to

show that the resistances inclosed in sealed boxes gave, during the

experiments in Washington, results more regular than have the

metallic resistances for which this precaution had not been taken.

Standard cells constructed in each laboratory were brought by

the delegates. From the point of view of the methods of preparation of the mercurous sulphate, the following differences exist

among the cells. At the PTR, by precipitation by adding hot sulphuric acid to

acid mercurous nitrate, or the reverse. At the NPLo by precipitation by adding mercurous nitrate to

sulphuric acid.

At the NBS, by electrolysis with direct current. At the LCE, part by electrolysis with direct current, the rest by

alternating current electrolysis.

Ohm PTR - Ohm NBS = + 2X10"'

Ohm NPIv - Ohm NBS = + 1 2 X 10-

For the PTR ohm

For the NPIv ohm

For the NBS ohm

For the LCE ohm

- 5 X 10-

+ 5 - 7 + 1 10

WESTON STANDARD CELL
204 Report on Concrete Standards

All these cells were compared at different times during the work

of the delegates (for the results, see p. 96 et seq.). As a result of

these comparisons, the Technical Committee has decided to choose

as "value of the Weston Normal Cell, the mean value of the cells submitted by the delegates of the four laboratories. This mean

has been calculated in the following manner: The mean of the

values of the standard cells, presented by each delegate, has first been taken, and then the mean of the four numbers thus found."

The results are summarized in Table XIII, page 109.

TABLE LXII

CeUs Mean of group minus general Average deviation of single

cells from mean of group No. Laboratory mean; difference in 10~6

15 PTR ±10

34 NPL -2 ± 9

15 LCE +9 ±25

40 NBS -9 ± 6

The committee expressed the opinion that new experiments were

necessary for the completion or modification of the specifications

of the London Conference on the subject of the standard cell, and

that the time was not sufficient to enable them to carry these out

during their stay in Washington.

The delegates had, however, carried out at the Bureau of

Standards the following work:

Each delegate prepared mercurous sulphate according to the

method of preparation used in his own laboratory. And then each

delegate constructed three standard cells with each of the four

samples of mercurous sulphate thus obtained; that is, 12 cells in all. The results given by these 48 cells are given in Table XV,

page 115. They show that excepting several abnormal cells, the

cells are in very good agreement.

During the work of the committee at Washington, members of

the Bureau, under the direction of Dr. Wolff, carried out a sys- tematic series of researches, having for their aim the comparing

of the materials brought by the different delegates. The results

given in the report (pp. 116 to 119) show that the different materials
International Electrical Units 205

are equivalent in their effects on me emf of the cell, but the

Technical Committee has been able to discuss neither the results

of this research nor that following.

An important investigation was made on a large number of

cells to throw light on the anomalies, which certain of them present, when their temperature is changed, and to study the lag

exhibited by the cell in taking up the value given by the formula

connecting the variation of the emf with the temperature.

THE SILVER VOLTAMETER

The delegates have sought to determine the value of the emf

of the Weston Normal Cell in international volts by joint experiments on silver voltameters connected in series, the standard cell and the international ohm being defined as has been done above.

In all the experiments with the silver voltameter, the strength

of the current was maintained constant at the value of approximately 0.5 ampere, the length of time of its passage being two

hours, and the weight of silver deposit being slightly greater than

4 grams.

The delegates have employed the silver nitrate and the voltameters which they brought with them. They carried out the

work under experimental conditions similar to those used by

them ordinarily in their respective laboratories.

In the greater part of the experiments Dr. Jaeger used a form

of voltameter, employing silk and a glass cup to separate the

anode from the cathode.

Mr. Smith employed the arrangement designated by him by the

name of " the new form."

Prof. Rosa made use ordinarily of the porous pot of porcelain.

M. Laporte employed filter paper and the so-called Rayleigh

form.

In certain experiments, certain of the delegates have exchanged

materials and have used the apparatus of one another.

While the delegates carried out their experiments, members of

the Bureau of Standards, under the direction of a subcommittee,

made other experiments on the silver voltameter, with the end in

view of studying the different electrolytes and forms of voltameter

used.
206 Report on Concrete Standards

The results have shown that voltameters in which filter paper

is used as septum lead to results which are too high. The delegates were unanimously of the opinion that the results of experiments

made under these conditions should not be used for the determination of the value of the emf of the Weston Normal Cell. The committee is of the unanimous opinion that "the mean of

the results which they have obtained will not be modified by more

than several parts in one hundred thousand when the specifications shall have been completed.

"The committee decides to recommend to the International

Committee for Electrical Units and Standards the following value

for the emf of the Weston Normal Cell: E = 1.0183 international volts at 20 C

"

The results of all the experiments are given in the tables of

Appendix D (p. 145) , and in Appendix F will be found the remarks

of each of the delegates.

Although the experiments on the silver voltameter have been

numerous, the committee (owing to the opposition of Dr. Jaeger

and of M. I,aporte) "thought best not to complete the specification of the silver voltameter until new experiments have been

made by the members of the committee in their respective laboratories on those points which are not considered as actually settled,

and that the committee shall complete the general specifications

after these experiments."

These electrolytes rendered acid or alkaline by the addition of a certain quantity of free acid or alkali have given rise to deposits

different from that corresponding to a neutral electrolyte. Acidity

brings about a diminution of the deposit, and alkali an augmentation; the effect of alkali is more important than that of acid. Messrs. Jaeger and Daporte have called attention to the fact

that the precision of the methods for testing the acidity or alkalinity had not been sufficiently investigated to allow of fixing the

limits permissible in the electrolyte.

The electrolytes used by the four delegates were tested comparatively in voltameters of small dimensions (volume about

100 cc and the porous pot form), and in voltameters of more than
International Electrical Untis 207

double the volume of the first (porous pot and new form). The

four electrolytes give the same weight of deposit in the small

voltameters; they give different results in the larger voltameters.

One only of the electrolytes, that of the National Physical Laboratory, and, later, an electrolyte obtained from a nitrate purified

by the labors of members of the Bureau of Standards, have given

with certainty the same results in both small and large voltameters. The volume effect obtained in these experiments has not

been admitted as certain by Mr. Jaeger, and the correspond- ence of these results with those obtained by the permanganate

test for organic material has not been considered as definitely

established by both Messrs. Jaeger and Laporte.

Although in a large part of the experiments the silk used as septum gave normal values for the silver deposit, there is a possibility, as some of the experiments show, that under certain conditions the weight of the silver deposit can be changed. Dr. Jaeger

is of the opinion that pure silk, if sufficiently washed, can be used

as septum without error. Experiments with siphon voltameters were also carried out. They were only comparative owing to the variations of resistance

which this form of voltameter introduces into the circuit. They

gave deposits heavier than those of the other forms. Mr. Smith

calls attention to the fact that at the National Physical Laboratory the siphon and the new form have given identical results.

J*

22451°—12 14