and the Electro- Chemical Equivalent of Copper. 83 



Vanni* found that a solution of copper sulphate of density 

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

 while a solution neutralized with copper hydrate gave an 

 excess. Combining a liter of the normal solution with a half 

 gram of that containing one per cent of the acid neither a gain 

 nor loss could be observed in the weight of a piece of copper 

 immersed in it. 



The mean of six experiments with such a solution showed 



Cu 



— — = 0-2938, whence Cu equivalent = O000328± with a cur- 

 2Ag 



rent-density between 0011 and 0002. 



Cintolesi-r observed that the solution of a copper plate in 

 copper sulphate depends on the time and the current strength. 

 In vacuo the amount of copper dissolved is less than in air. 

 Oxygen was believed to have an essential influence on the 

 phenomenon. 



ShawJ using copper sulphate, and a current-density above 



0'025 — v found as a mean of fifteen experiments that the 

 cm" y 



ratio of — 3 was 3'39983 or Cu equiv. = 0*00032886. 

 Cu 



It thus appears that the behavior of copper sulphate had 

 been thoroughly studied ; but no quantitative determination 

 had been made with the nitrate, as far as the writer knows, 

 although it had been stated by Smee and others, that the nitrate 

 would bear a much greater current density than the sulphate. 



The apparatus used in the experiments presently to be con- 

 sidered, may be briefly described as follows : the cathode was 

 made from a piece of electrolytic copper about 2 mm thick, by 

 bending it so as to form three sides of a rectangle. This was 

 immersed in copper nitrate contained in a glass beaker. The 

 anode was usually a thin sheet of platinum though copper was 

 occasionally substituted for it. The former was much pre- 

 ferred on account of the ease with which the copper is re- 

 moved by dipping in nitric acid. After rinsing with water the 

 platinum electrode may be dried by heating to redness in a 

 Bunsen flame. The current was measured by the silver vol- 

 tameter when small, and a Thomson Balance in a few instances 

 when the total current was large. The value of the equivalent 

 of silver used in calculating the numbers hereafter given was 

 0*0011181, the mean of the value 0-0011183 found by Kohl- 

 rausch§ and 0'00111794 the one given by Rayleigh.|| 



*Wied. Annal., x, p. 214, 1891. + Beiblatter, xvi, p. 80, 1892. 



{Phil. Mag., xxiii, p. 138, 1887. § Wied. Annal., xxvii, p. 57, 1886. 



| Phil. Trans., p. 439, 1884. 



