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porous cup coulometer which is somewhat more convenient for use than 
Richards’ type. The main disturbing factor in silver coulometric work 
lies in the formation around the silver anode of a complex silwer salt 
which on reaching the platinum cathode deposits too much silver. 
The introduction of a porous cup keeps the troublesome solution 
at least partly away from the cathode, if the current is not allowed to 
be closed for more than, an hour. I use in my form a platinum bowl of 
the size recommended by the Chicago congress and a closely grained 
porous cup only a little smaller in diameter. At the bottom of this cup 
some granulated silver is placed and upon this a large plate of silver, 
forming the anode, is pressed. The granulated silver partly decomposes 
the heavy solution streaming from the plate and makes the use of a 
siphon (to keep the solution inside the porous cup at a lower level than 
the outside) unnecessary.* 
Richards’ and my results w’ere corroborated by Van Dijk, namely that 
with a porous cup coulometer the silver deposit is about 3 in 10,000 
smaller than in the usual form, and that such coulometers will give re- 
sults which can be relied upon to 1 in 10,000. 
While thus the silver coulometer was improved other investigators 
attacked the problem of perfecting the standard cell. The Weston stan- 
dard cell with solid hydrated Cadmium sulphate has proved to be, in 
many respects, so far superior to the Clark cell that doubtless it will 
at the next international congress be selected as the standard cell and it 
is natural that the most recent work has been done with this type of cell 
instead of the Clark. Carhart, Hulett and Wolff* have by their researches 
upon the electrolytic preparation of 11^2^04 enabled us to construct cells 
which, when made by different experimenters, will closely agree in their 
electromotive force. According to Hulett the 11^2^04 should be prepared 
electrolytically from an acid solution of concentration larger than normal, 
so as to avoid hydrolysis. 
By these researches we have now arrived at a point where we can 
rely wuth equal confidence upon as well the indications of the silver- 
coulometer as upon an accurate reproduction of Standard cells, and the 
next question of importance was to redetermine with improved apparatus 
the absolute values of the electrochemical equivalent as determined 
by the porous coulometer, and the electromotive force of the improved 
standard cells. I have just finished this work, the experimental part of 
which was done at the Bureau of Standards in Washington. The appar- 
atus which I used was a large electrodynamometer, consisting of two 
coils, each of a single layer of wire. This allows an accurate measure- 
ment of the linear dimensions entering into the calculations. The large 
coil was wound upon a plaster of Paris cylinder while the smaller mov- 
able coil was wound upon Berlin porcelain. Two movable coils of dif- 
ferent dimensions were used, and the small difference of the two final 
results served as a valuable check upon the whole work. The torsional 
*Guthe, Bull. Bur. Standards, I, p. 349, 1905. 
♦Van Dijk, Ann. Phys. 19, p. 249, 1906. 
♦Carhart and Hulett, Proc. Am. Electroch. Soc. 5, p. 59, 1904. 
Wolff, Proc. Am. Electroch. Soc. 5, p. 49, 1904. 
Hulett, Zeitsch. Phys. Chem., 49, p. 483, 1894. Phys Rev. 22 p 321, 1906. 
