On some Comlinaiions of Platinum. 339 



iiig of platinum remains. It does not touch steel. It is not af- 

 fected by cold or hot water, nor by the nitrous, sulphuric, of 

 phosphoric acid at a boiling heat. It is insoluble in nitro-mu- 

 riatic acid, and in cold muriatic acid ; but it slowly dissolves in 

 this last acid by the assistance of heat. It is not acted upon by 

 a strong solution of the fixed alkalies. When the oxide is put 

 into liquid ammonia, minute globules of air are evolved from it, 

 but the quantity has been too small to admit of being examined; 

 probably it is common air, as the oxide appears to undergo no 

 change by being kept for some weeks in ammonia. When heated 

 with sulphur, the oxide yields sulphureous acid gas and a gray 

 sulphuret of platinum. When mixed with zinc filings and heated, 

 the oxide is decomposed with vivid ignition, and white oxide of 

 zinc is formed. 



When the oxide is mixed with borax, and exposed to a strong 

 red heat before the blowpipe, it forms a black glass, which be- 

 comes of a lighter colour on urging the heat to whiteness, and 

 the oxide appears to be reduced. If the oxide is mixed with 

 powdered glass and fused, a glass is obtained of a dull brown 

 colour. The oxide is readily reduced by moistening it witii oil 

 of turpentine, and heating it moderately; or by exposing it 

 to a dull red heat in the atmosphere ; but it requires a strong 

 red heat to reduce it in close vessels. Some of the oxide which 

 had been well dried, first on a hot sand-bath, and then exposed 

 to a heat just below redness, on a slip of platinum, was decom- 

 posed in very small green glass retorts, over mercury. In two 

 experiments in which I used seven grains of the oxide, I obtained 

 in each instance six grains of platinum, and 2*1 cubic inches of 

 oxygen, the thermometer being at 60° and l)arometer 30°. I 

 found also in the necks of the retorts, a slight trace of a fluid 

 that reddened litmus paper, and had an odour similar to tliat of 

 nitrous acid. Now, if six grains of platinum combine with 2'1 

 cubic inches of oxygen, 100 grains will take 34 cubic inches ; 

 and calculating from Sir H. Davy's statement, that 100 cubic 

 inches of oxygen weigh 34 grains, the gray oxide of platinum 

 will be found to consist of 



100 platinum, 1 , c 89-3G6 platinum, 



1 1 o Vox per cent., or .^ a-n .„„.. 



II*;) oxygen, J ' ' .I0'd34 oxygen. 



1 00-000 

 It will be readily seen, that I have here dediiced the compo- 

 sition of tiie gray oxide from the actual quantity of oxygen and 

 metal obtained in the experiments ; and this mode of analysis 

 seems liable to little objection, and can very rarely be resorted 

 to, in ascertaining the composition of metallic oxides On com - 

 paring my previous experiments upon the gray oxide, with the 

 U u 2 above 



