Shepard — New Solution for the Copper Voltameter. 49 



Art. V. — A New Solution for the Copper Voltameter; 

 by William K. Shepard. 



The importance of the convenient and accurate method of 

 measuring electric currents by the voltameter depends very 

 largely upon the construction of a voltameter which admits of 

 high current densities. 



The silver voltameter gives results of a high degree of 

 accuracy, but is not conveniently used except for small cur- 

 rents ; the copper voltameter, however, from the cheapness of 

 its materials, finds employment in the laboratory for the 

 measurement of comparatively large currents. 



As ordinarily used, the copper voltameter is subject to 

 irregularities due to the solvent effect of the solution in some 

 cases and the oxidation of the copper in others. The volta- 

 meter solution recently investigated by the writer commends 

 itself by the facts that these irregularities are avoided and that 

 approximately twice the current density permissible with solu- 

 tions hitherto in use may be employed without loss of accuracy, 

 thus allowing large currents to be measured without incon- 

 veniently increasing the size of the electrolytic cell. 



Many different solutions for the voltameter have been recom- 

 mended by various experimenters. Gray,* using a copper sul- 

 phate solution of density 1*15 to 1*18 with one per cent free 

 sulphuric acid, found that the highest current density desirable 

 was *02 amperes per square centimeter of cathode surface. 



Vannif observed that a copper sulphate solution of density 

 1*12 with one per cent free sulphuric acid dissolved copper 

 and therefore gave indications always too small. With an 

 increase of the current density the deduced electro-chemical 

 equivalent of the copper increased. A solution neutralized 

 with copper hydrate, on the contrary, yielded results in constant 

 excess, probably on account of the oxidization of the copper. 

 By adding to a liter of the normal solution one half a gram of 

 a solution which contained one per cent sulphuric acid, he 

 found neither a gain nor a loss in the weight of a piece of cop- 

 per immersed in it. . With this solution he successfully used a 



current density of -Oil --, but no experiments seem to 



have been made to determine the limit. 



Oettel % obtained smaller deposits of copper from copper 

 sulphate solutions than Faraday's law demands resulting from 



*Phil. Mag., xxii, p. 289, 1886, 



+ Wied. Annal., x, p. 214, 1891 and Phil. Mag., xxv, p. 179, 1888. 



% Chemische Zeitung, p. 543, 1893. 



Am. Jour. Sci.— Fourth Series, Vol. XII, No. 67.— July, 1901. 



