IOWA ACADEMY OF SCIENCES 
237 
colleagues at the Bureau of Standards, and due to the fact that the won- 
derful facilities of this institution were placed at my disposal, I was 
able to obtain results, which I consider accurate within 1 in 10,000, an 
accuracy which I believe has not been obtained before in measurements 
of this kind. 
My final results are the following: 
A. Standard cells with electrolytically prepared HgaS 04 . 
Clark cells^ at 25'-^ C. 
E. M. F. = 1.42040 volts. 
Cadmium cells at 25° C. 
Acid solution stronger than normal, 
(F series) E. M. F. =: 1.01827 volts. 
Acid solution weaker than normal, 
(E, K and O series) E. M. F. = 1.01833 volts. 
B. Standard cells with chemically prepared Hg 2 S 04 . 
Cadmium cells at 25° C. (C series) 
E. M. F. = 1.01857 volts. 
This shows that the cells with electrolytic Hg 2 S 04 have an electro- 
motive force 0.0003 volt lower than those with chemically prepared Hg 2 S 04 
Reducing to 20° C, we obtain for the Cadmium cells, 
F. series, E. M. F. = 1.01847 volt. 
E, K and O series, E. M. F. = 1.01853 volt. 
C series, E. M. F. ~ 1.01877 volt. 
Reducing to 15° C, we obtain for the Clark cells, 
E. M. F. =: 1.43296 volt. 
By this investigation I have therefore fully corroborated the results 
of our former work, namely that the correct value of the Clark standard 
cell at 15° C is nearer 1.433 volt and not 1. 434 as legalized in the United 
States. 
The electrochemical equivalent of silver as determined by the porous 
cup coulometer is 1.11773 milligrams per coulomb. 
The following tabli gives a comparison of the results obtained by 
former investigations. The values of the electrochemical equivalent are 
reduced to the porous cup coulometer. The values of the E. M. F. of the 
Clark cell are given for 15°C, that of the Cadmium cell for 20°C. 
A. 
ELECTROCHEMICAL EQUIVALENT OF SILVER. 
Observer Date Coulometer Method Found Corrected 
Mascart 1884 — Usual type. . . .Current balance . . . .1.1156 1.1158 
Fr. andW. Kohlrausch 1884 — Usual type. .. .Tangent galvanometer 1.1183 1.1177 
Rayleigh and Sidgwick 1884 — Usual type. .. Current balance 1.1179 1.1176 
Gray 1886 — Plate Coulom’r Sine galvanometer ..1.1183 1.1178 
K,oepsel 1887 — Usual type. ... Current Balance ....1.1174 1.1169 
Pellat and Potier 1890 — Usual type. ... Current Balance ....1.1192 1.1189 
Patterson and Guthe..l898 — ^Sil’r-oxide type Electro-dynamometer 1.1192 1.1177 
Pellat and Leduc 1903 — Leduc’s type. .. Current balance ....1.119i5 1.1190 
Van Uijk and Kunst. .1904 — Usual type. .. .Tangent galvanometer 1.1182 1.1178 
Outhe 1905 — Porous cup .... Electro-dynamometer .1.1177 1.1177 
