194 ELECTROLYSIS. 



This solution must be heated to 40 C. and electrolysed by 

 a current of 4 to 6 volts. The deposited metal is white, and 

 resembles tin. It is very soft and does not offer any important 

 advantage in industry. 



DEPOSITION OF COBALT. 



A concentrated solution of the chloride, with its excess of 

 acid neutralised by the addition of caustic potash or ammonia, 

 and electrolysed by a weak current, deposits its metal in uniform 

 layers. The deposited metal is brilliantly white, hard and 

 brittle, and can be obtained in cylinders, bars, and medals by 

 using proper moulds to receive it. The deposited rods are 

 magnetic. 



With an anode of cobalt it is unnecessary to alter the solution 

 after its preparation. Kods of cobalt electrolytically deposited 

 contain as much as thirty-five times their volume of hydrogen. 



DEPOSITION OF GERMAN SILVER. 



German silver is an alloy of copper, zinc, and nickel. 



A suitable bath is prepared by dissolving German silver of 

 good quality in nitric acid, and adding to the solution a solution 

 of potassic cyanide, stirring slowly until all the metal is pre- 

 cipitated. The exhausted liquid is then poured out, the pre- 

 cipitate is washed, redissolved in .potassic cyanide, and diluted 

 with double its volume of water. 



Or 1 kilogramme of cyanide of potassium and an equal 

 quantity of carbonate of ammonium may be dissolved in 10 

 litres of water, the solution being heated to 70 C., and the 

 German silver dissolved in it by means of the electric current. 

 If the deposit becomes too red, add carbonate of ammonium, if 

 too white, add cyanide. 



All the alloys of this description require very strong cur- 

 rents to be effectively decomposed. 



