DEPOSITION OF VARIOUS METALS. 185 



The following is the process which he indicates as suitable 

 for depositing on copper or its alloys any quantity of platinum. 



Introduce in a long-neck glass matrass 10 grammes of 

 finely laminated, or even better, frothy or spongy platinum, 

 with 150 grammes of hydrochloric acid, and 100 grammes of 

 nitric acid at 40 degrees. Heat on a piece of sheet iron pierced 

 with a central hole so that only the bottom of the matrass 

 receives the impression of the heat. Large volumes of rutilant 

 vapours are liberated, and the platinum entirely disappears, 

 leaving only a red liquid, which must be continued to be heated 

 until it becomes so viscous that it will stick to the walls of the 

 matrass. The last part of this operation can be effected in a 

 porcelain cup, the truncated form of which is more favourable 

 to the evaporation of liquids in excess. It is then taken out of 

 the fire and allowed to completely cool, when it is afterwards 

 dissolved in 500 grammes of distilled water, and filtered if 

 required. 



At the same time 100 grammes of ammonic phosphate is 

 dissolved in a similar quantity of distilled water, and the two 

 solutions are mixed. An abundant precipitate of ammoniaco- 

 platinic phosphate is formed, upon which floats an orange- 

 coloured liquid which must not be separated. 



When in that state, a solution, prepared in advance, of 500 

 grammes of sodic sulphate in one litre of pure water is slowly 

 poured, the solution being continually stirred. 



The mixture is then brought and maintained at the boiling 

 point, the evaporated water being replaced, until, owing to the 

 escape of ammonia, which can be detected by the smell, the 

 liquor from alkaline turns sensibly acid to the litmus paper. 

 In this reaction the liquor, from yellow, turns perfectly 

 colourless, which is indicative of the formation of the double 

 salt of platinum. 



The solution is then ready to operate on copper and its 

 alloys by means of heat and a moderately powerful electric 

 current. 



AMERICAN PROCESS. Platinic chloride is prepared as above 

 described, and dissolved in distilled water ; potassic cyanide is 

 added, an excess of which will redissolve the precipitate formed. 



