RESULTS OF EXPERIMENTS ON THE DEPOSITION 

 OF OTHER METALS AS COATINGS. 



Coating with Platinum. This metal has never yet been success- 

 fully deposited as a protecting coating to other metals. A solution 

 may be made by dissolving it in a mixture of nitric and muriatic 

 acids, the same as is employed in dissolving gold ; but heat must be 

 applied. The solution is then evaporated to dryness, and to the 

 remaining mass is added a solution of cyanide of potassium ; next, 

 it must be slightly heated for a short time, and then filtered. This 

 solution, evaporated, yields beautiful crystals of cyanide of platinum 

 and potassium ; but it is unnecessary to crystallize the salt. A very 

 weak battery power is required to deposit the metal : the solution 

 should be heated to 100. Great care must be taken to obtain a 

 fine metallic deposit : indeed, the operator may not succeed once in 

 twenty times in getting more than a mere colouring of metal over 

 the surface, and that not very adhesive. The causes of the diffi- 

 culty are probably these : the platinum used as an electrode is not 

 acted upon ; the quantity of salt in solution is very little ; it requires 

 a particular battery strength to give a good deposit, and the 

 slightest strength beyond this gives a black deposit ; so that, were 

 the proper relations obtained, whenever there is any deposit, the 

 relations of battery and solution are changed, and the black pulveru- 

 lent deposit follows. 



We have occasionally succeeded in obtaining a bright metallic 

 deposit of platinum, possessing the qualities of adhesion and dura- 

 bility: some of the articles thus covered presented no signs of 

 change at the end of seven years : but we have never been so for- 

 tunate as to get a platinum deposit that could protect any metal 

 from the action of acids, or other fluids by which the metal could 

 be effected. "We have covered iron, such as the end of a glass- 

 blower's blow-pipe, so that it could be made red hot without the 

 iron rusting, but rather taking the characteristic appearance of pla- 

 tinum; but even that did not protect the iron from rusting when it 

 was put a short time into water, or kept exposed to moist air. 



