On Copper Electrolysis in Vacuo. 67 



this paper), an inspection of which shows that the deposit is heavier 

 the higher the current density and the lower the temperature. 

 (" Current density " is defined as the ratio of the value of the current 

 in amperes to the total immersed surface of the cathode plate.) A 

 very possible explanation of this anomaly is furnished by the work 

 of Gore* and Gray,f who independently found that copper dissolves 

 to a very appreciable, though variable, amount in solutions of copper 

 sulphate. 



The secondary chemical reactions which follow chiefly the forma- 

 tion of basic salts complicate the electrolysis. This corrosion of 

 copper plates in the sulphate solution is much diminished if a little 

 free sulphuric acid is present, with the result that the electrolysis of 

 acid solutions yields more consistent results than are obtainable with 

 nearly neutral solutions. Now, Schuster J found thab the loss in 

 weight of copper plates in a solution of copper sulphate does not 

 occur if the air be removed from the solution. It is therefore very 

 probable that it is the oxygen of the air present in the solution that 

 causes this chemical corrosion ; and hence it was of interest to 

 examine if any difference could be found between the weights of the 

 deposits of two copper voltameters, one of which would be placed in 

 vacuo. Schuster and Crossley showed that the silver deposit is 

 slightly greater in vacuo than in air ; and the experiments tabulated 

 in this paper point out, with certain limitations, a similar result. 



The plan of these experiments was simple. The same current 

 passed through two voltameters connected in series, one being under 

 the ordinary atmospheric pressure and the other in a partial vacuum. 

 The voltameters, in most of the experiments, consisted of ordinary 

 glass beakers, containing the solutions of copper sulphate, into which 

 dipped three parallel copper plates of the same size, the centre one 

 acting as the cathode, and the side ones forming a double anode. 

 The plates were held in position by means of German silver clips 

 pressing against vertical brass supports which were attached to an 

 ebonite framework. One voltameter was placed in an inverted bell- 

 jar, into the neck (lower part) of which was fitted an india-rubber 

 cork. Through the cork, which was coated with Faraday cement, 

 passed three glass tubes, one connected with an exhaust pump and 

 the remaining two containing the leads. In some of the experi- 

 ments another tube was introduced, through which was passed into 

 the jar a stream of nitrogen gas previous to exhaustion ; but as this 

 did not give any better results, it was discarded. At the bottom of the 

 bell-jar inside was a support for the beaker, and on the latter rested 



* ' Nature,' vol. 25, p. 473. 



t ' Phil. Mag.,' vol. 22, p. 400, 1886. 



See " Note " at end of this paper. 



' Koy. Soc. Proc.,' yol. 50, pp. 344358. 



F 2 



