58 Medway — Further Work with the Rotating Cathode. 



In the usual method of electrolysis with stationary electrodes, 

 it lias been found that, when the attempt is made to remove 

 the zinc from the platinum upon which it has been deposited, 

 there is a coating of platinum black, some of the zinc presum- 

 ably having amalgamated with the platinum. Only by dis- 

 solving the zinc, heating the crucible to redness and finally 

 making another application of acid can this black coating be 

 conveniently removed, there being a loss of platinum due to 

 this removal. In order to avoid this formation it has been 

 found necessary to coat the platinum with copper and deposit 

 the zinc upon this. The zinc and copper may then be easily 

 removed together by acid. 



In depositing the zinc upon a rotating cathode it was found 

 to be unnecessary to coat the platinum with copper, since the 

 zinc could be removed without any appearance of platinum 

 black, thus avoiding the second treatment by acid, with the 

 attendant loss of platinum. 



Gold. 



The apparatus was next applied to the determination of gold. 



A solution of auric chloride was made of 25 cm 3 volume. 

 Potassium cyanide was then added in considerable excess and 

 about 30 drops of strong ammonia. The electrolysis was carried 

 on in the usual manner. 



The results are given below : 



Gold 



Gold 











taken 



found 



Error 



Current 



N. D. 



Time, 



grm. 



grm. 



grm. 



Amp. 



100. 



min. 



0-0695 



0-0694 



— o-oooi 



2' 



6-6 



30 



0-0695 



0-0696 



+ 0-0001 



2- 



6-6 



30 



0-0598 



0-059,8 



±0'0000 



0-5 



1-8 



30 



0-0598 



0-0598 



±0-0000 



0-5 



1-8 



30 



0-0598 



0-05915 



— 0-00005 



1- 



3-3 



25 



No attempt was made 

 for these depositions. 



to find the minimum time required 



