combinations of platinum. 123 
6 grains of platinum combine with 2*1 cubic inches of oxy- 
gen, 100 grains will take 34 cubic inches ; and calculating 
from Sir H. Davy's statement, that 100 cubic inches of oxy- 
gen weigh 34 grains, the grey oxide of platinum will be 
found to consist of 
100 platinum! „ 80*3 66 platinum, 
1 l or per cent, of ^ 1 
11-9 oxygen J 10 034 oxygen. 
lOO'OOO 
It will be readily seen, that I have here deduced the com- 
position of the grey oxide from the actual quantity of oxy- 
gen 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 comparing my previous experiments upon the 
grey oxide, with the above results, I am most inclined to 
place confidence in the latter. There is, indeed, a near co- 
incidence between them, and the difference, which is only 
about one per cent, may be referred to the presence of a 
little more acid in my first experiments. The grey oxide is 
insoluble in aqua regia, a fact which seems to add additional 
support to Sir H. Davy's opinion respecting the action of 
aqua regia on platinum.* This menstruum, according to 
Sir H. Davy, does not oxidate platinum, but merely causes 
its combination with chlorine. Now, if the metal were oxi- 
dated previous to its solution, the oxygen, there is reason to 
think, would be derived from the nitrous acid, and the grey 
oxide formed by this acid, be produced, which can scarcely 
* Journal of Science and the Arts, Vol. I. 
