62 
PHYSICS: ROSA AND VINAL 
Another discovery of importance is the alloying effect of the silver 
and platinum when determining the inclusions of foreign matter in 
the deposits by the method of heating. After the slight alloying has 
taken place, the removal of the silver leaves a very thin layer of plati- 
num black on the inside surface of the cup. Unless this is entirely 
removed its adsorptive properties make the weight of the cup uncer- 
tain and its catalytic properties cause the deposition of hydrogen ions 
when another silver deposit is made so that the amount of silver is 
not a true measure of the electricity according to Faraday's law. 
Various observers in different countries by avoiding these sources 
of error have obtained very concordant results as the following table 
shows : 
TABLE 1 
Values for the Weston Normal Cell at 20 °C. Computed from Silv'er Voltameter 
Measurements 
COUNTRY* 
FORM OF VOLTA- 
METERt 
VALUE FOR CELL 
A 
parts in 100 000 
Smith 
1.018274 
-O2 
United States 
Richards 
1.018267 
-O9 
Japan 
Smith 
1.018269 
-O7 
RussiaJ 
Smith 
1.018296 
+ I9 
HoUand 
Smith 
1.01826 
-le 
Germany 
Kohlrausch 
1.01829o 
+ I4 
Mean 
1.018276 
=^li 
* England and France have not published any measurements of this kind since the time 
of the International Committee. The Observers are: for Japan, Obata; for the U. S., 
Rosa, Vinal, and McDaniel; for Russia, Mile. Ferringer; for Holland, Haga and Boerema; 
for Germany, von Steinwehr. 
fThe Smith form and the Kohlrausch form are similar in principle. They have no 
separation between anode and cathode except a glass trap to catch the anode slime, but the 
construction of this trap is very different in the two forms. The Richards form makes 
use of a porous cup septum. 
% This is the mean of four sets of measurements on a particular cell at different periods 
during several years. 
The average deviation from the mean result is only 0.001%. The 
experimental error involves the errors of both the cell and the standard 
resistance as well as the numerous sources of error in the voltameter 
itself. These include the errors of weighing the bowls both before and 
after the deposit, the errors of timing the deposits, the errors due to 
fluctuation in the current, and the errors in washing and drying the de- 
posits. In view of these it is remarkable how small the deviations are 
for the individual countries. These results are the work of investigators 
