50 Shepard — New Solution for the Copper Voltameter. 



the formation of oxygen compounds such as HS0 4 . By the 

 addition of alcohol these losses were avoided. He advised as 

 the best solution : 



150 



gms 



. CuS0 4 



50 



it 



H 2 S0 4 



50 



a 



Alcohol 



000 



it 



H s O 



Beach* investigated the use of copper nitrate in the volta- 

 meter. His solution after neutralization had a density of about 

 1*53 and contained one drop of a saturated solution of NH 4 C1 

 to lOOcc. of the nitrate. The NH 4 C1 was added to prevent the 

 oxidization and consequent excess of deposit which occurs 

 when a neutral solution is used alone. He found that he could 

 use a much higher current density with this solution than with 

 the copper sulphate solutions commonly used. But as copper 

 nitrate is relatively expensive in comparison with the sulphate, 

 it is not so well suited for general laboratory use. 



It seemed to the writer of interest to attempt the use of a 

 neutral solution of the sulphate in the same manner, with the 

 aim of increasing the allowable current density. The solution 

 was prepared as follows: A saturated solution of copper sul- 

 phate was boiled for a short time to expel the air and then 

 kept at 100° C. for about an hour in contact with metallic copper 

 in order to neutralize the solution. The density was then 

 about 1*20. A very small amount of NH 4 C1 was added, about 

 •05 of one per cent. 



Two voltameters were used in the investigation. They 

 were connected in series in order to see how the different 

 solutions would agree when using exactly the same current. 

 Each voltameter consisted of three anode and two cathode 

 plates, the cathode plates being placed alternately between 

 the anodes at distances of about 2 centimeters. The plates 

 were 10"5xl9cm., of which a working cathode surface of about 

 600cm 2 was employed. The voltameters were used in 

 battery jars 20cm. high and 15cm. in diameter. 



The method used in the preparation of the cathode plates 

 was that given by Gray.f The edges and corners were well 

 rounded and the plates polished with sand paper. They were 

 next placed in water slightly acidulated with sulphuric acid for 

 a short time to remove any trace of oxide, rinsed in clean water, 

 dried with filter paper and then over a gas flame. After cop- 

 per had been deposited, the plates were not exposed to the air 

 for a time longer than absolutely necessary before the copper 

 sulphate solution had been completely washed off. The reason 



* This Journal, xlvi, p. 81, 1893. 

 fPhil. Mag., xxii, 1886. 



