32 



SCIENCE 



[N. S. Vol. XXXTV. No. 862 



The London Conference of 1908 has declared 

 that the electro-chemical equivalent of silver is 

 1.11800 mg. per coulomb, and, therefore, using this 

 value and the international ohm and the second 

 we find the voltage of the Weston normal ceU at 

 20° C. to be 



1.01827 volts, ± .00003. 



The Chemistry of the Silver Voltameter: Dr. A. 



S. McDaniel, of the Bureau of Standards. 



The first problem in the chemical investigation 

 of the voltameter was an investigation of the 

 filter paper septum. This led to the detection of 

 the classes of impurities in the voltameter. The 

 plan of investigation of the filter paper form of 

 voltameter was outlined. In this connection 

 Smith's work at the National Physical Laboratory 

 was mentioned. He added substances to the elec- 

 trolyte to produce the observed striations in the 

 deposits, and hence concluded that the striations 

 were due to the impurities of the electrolyte. The 

 speaker had also produced the striations experi- 

 mentally. Tests were also made by the speaker 

 to test the effect of the filter paper upon the 

 striations. The striations produced by certain 

 substances added to the electrolyte were described 

 and illustrated by lantern slides. 



Experiments were tried of extracting the im- 

 purities from the filter papers by soaking them in 

 water and then dryiag them in the voltameter, but 

 it was found that the striations were still pro- 

 duced. It was concluded from this that oxieel- 

 lulose (oxidized filter paper) caused the active 

 principle of the striations. The degree of acidity 

 or alkalinity has quite an effect in determining the 

 direction of travel of the colloidal deposit or 

 particles. 



Tests were also made to account for the in- 

 crease in weight of the colloidal deposit on the 

 cathode. The effect of silk and porous pot septa 

 in voltameters was also investigated. The treat- 

 ment of the pot before use to make it sufficiently 

 resistant, and the action of the pot on the silver 

 nitrate, were briefly stated. 



The preparation of liquids for use in the vol- 

 tameter were described, and mention was made of 

 the determination of the electro-chemical equiva- 

 lent of silver nitrate. 



The Silver Voltameter as an International Elec- 

 trical Standard: Dr. E. B. EosA, of the Bureau 

 of Standards. 

 The silver voltameter has been used as the 



official standard for the measurement of electric 



current since the International Electrical Con- 

 gress which met in Chicago in 1893. The defini- 

 tions and specifications for the fundamental elec- 

 trical units recommended by the Chicago congress 

 were adopted by the United States and several 

 other countries in 1894. Germany, however, did 

 not act in the matter until 1898 aad then adopted 

 somewhat different definitions and a different 

 numerical value for the Clark standard cell which 

 resulted in a different value of the volt. Austria 

 and some other countries followed the example of 

 Germany, so that for the last twelve years the 

 ampere and volt have been slightly different in 

 one group of countries from its value in the other 

 countries. The International Congress at London 

 in 1908 came to an agreement on the definitions 

 such that there might be international uniformity, 

 but could not fix upon the value of the standard 

 cell for want of complete specifications of the 

 silver voltameter and also for want of agreement 

 among different experimenters with the silver vol- 

 tameter. It was for the purpose of clearing up 

 some of the mysteries in connection with this 

 instrument, which has been the subject of more 

 than forty scientific papers by investigators in 

 several different countries during the last thirty 

 years, that the work was taken up at the Bureau 

 of Standards three years ago and has been carried 

 on continuously ever since. One year ago an 

 international committee representing four of the 

 national standards laboratories met in Washing- 

 ton and carried out a series of investigations at 

 the Bureau of Standards chiefly upon the silver 

 voltameter. As a result of these investigations a 

 new value for the Weston cell was agreed upon 

 after recommendation to the International Com- 

 mittee on Electrical Units and Standards and that 

 value has since been adopted, so that we now 

 have in America the same value for the volt and 

 ampere as is used in the principal countries of 

 the world; this value will, undoubtedly, soon 

 become universal. There still remain some out- 

 standing questions in connection with the silver 

 voltameter which must be solved before complete 

 specifications can be agreed upon, but the investi- 

 gations at the Bureau of Standards and else- 

 where during the last two or three years have 

 cleared up many of the questions which were out- 

 standing at the time of the London conference 

 in 1908. 



(The first and last of the above abstracts are 

 by the authors of the papers.) 



E. L. Paris, 

 Secretary 



