52 Shepard — New Solution for the Copper Voltameter. 



The results are not given, as different values of the current 

 being used they included the errors of the instrument. 



Having now performed these preliminary experiments show- 

 ing that the solution could be employed for large current 

 densities without loss of accuracy and having obtained a fair 

 idea of the working of the solution, experiments were begun 

 with the aim of eliminating the error of the instrument. 



Another Weston ampere-meter was obtained which read only 

 to 15 amperes, each ampere division being divided into ten 

 parts. So that with this instrument the current could be 

 measured with an error in the reading of less than -^-th. °^ an 

 ampere. The instrument was not assumed to be correct, but 

 after the experiments had been finished the results were aver- 

 aged, and taking the electro-chemical equivalent of copper to 



2fm. 



be '000329 — the true value of the current at the division 



amp. sec. 



used on the instrument was obtained. 



Only one point on the ampere-meter was used, namely, the 

 one which gave the nearest value to 15 amperes. Thus with 

 the same division and changing the current density, by raising 

 the immersed surfaces of the voltameter plates, the error of the 

 instrument was eliminated. 



From what has just been said, it will be plain that the 

 results given below are not presented as determinations of the 

 electro-chemical equivalent of copper ; the experimental data 

 are reduced to that form simply for convenience in comparing 

 them. 



The current was obtained from a storage battery of 50 cells, 

 and was kept constant by means of a copper sulphate resistance 

 which could be varied at will by varying the distance between 

 the copper plates. 



An auxiliary circuit was arranged whose resistance was 

 equal to that of the two voltameters. The current was thrown 

 by means of a switch first through the auxiliary circuit to the 

 ampere-meter and resistances included in the circuit. These 

 were allowed to heat up until everything became constant and 

 the resistance adjusted so as to give the desired reading of the 

 ampere-meter. Then the current was thrown through the 

 voltameters and assumed the desired value instantly. 



The duration of an experiment was 20 minutes, so that a 

 deposit of about 6 grams was obtained. This deposit showed 

 no oxidization even up to the highest current density used 



which was greater than *07 — ~- . 



cm 2 



The results are arranged in series according to their respec- 

 tive current densities, as follows : 



