On Copper Electrolysis in Vacuo. 



means of the data in Table XIII. In this table I have collected the 

 chief results of my experiments. By means of Gray's values I have 

 reduced the observed differences to a temperature of 15 C., and then 

 calculated the values in vacua. The curve thus obtained is more 

 uniform in its course than the curves for air. 



Table XIII. Summary of Experiments with fresh Acid Solutions. 

 (Tables IV XII.) 



The results of my experiments may be briefly summarised : 



1. With two copper voltameters containing freshly made neutral 

 solution of copper sulphate, one of which is under reduced pressure, 

 the copper deposit in the partial vacuum is higher (for the same 

 current, current density, and temperature) than the deposit under the 

 atmospheric pressure ; but the percentage difference is not constant. 



2. If a little free sulphuric acid be added to the air solution, the 

 percentage difference is more constant and higher than in 1. 



3. The addition of acid to both voltameters causes the percentage 

 difference to be constant within experimental errors: The experi- 

 ments conducted under this condition show that 



i. For current densities above O'Ol ampere per square centimetre 



of active cathode, there is no practical difference between the 



two deposits, 

 ii. For current densities below O'Ol ampere per square centimetre, 



the vacuum deposit is very appreciably higher than the air 



deposit, 

 iii. A curve drawn representing the deposits obtained in vacua at 



different current densities is more regular than the air curves, 



and for densities below O'Ol ampere per square centimetre is 



approximately a straight line. 



Q 2 



