124 , 
Mr. Davy on some 
be the case, as it is insoluble in aqua regia. Add to this, the 
fact, that by evaporating a common solution of platinum to 
dryness, no nitrate can be obtained, but only a muriate, or a 
compound of the metal and chlorine. 
If, according to the statements of Professors Vauquelin and 
Berzelius, the black oxide of platinum contains about 15 per 
cent, of oxygen, the grey oxide may be considered as the 
protoxide, containing 1 proportion, and the black oxide 
proportion of oxygen ; and the number representing the 
element or proportion in which platinum combines with bo- 
dies will be 126, taking Sir H. Davy's number 15, to repre- 
sent the proportion in which oxygen unites with bodies. 
Mr. Cooper states the black oxide of platinum to consist 
of 100 platinum, with only 4/317 of oxygen;* but he has, 
I think, considerably under-rated the oxygen in it. On re- 
peating his experiments on a small scale, I obtained results 
different from those he has stated. Thus, he says the powder 
obtained from the muriate of platinum by a neutral solution 
of mercury, is a compound of calomel and the protoxide of 
platinum ; but by decomposing this powder in a little retort 
over mercury, I found the neck of the retort partially lined 
with metallic mercury ; and this fact alone, I think, is suffi- 
cient to awaken suspicion as to the accuracy of his results. 
Mr. Cooper, I presume, used a nitrate of mercury to decom- 
pose the muriate of platinum, but he seems to have over- 
looked the nitrous acid in stating his results. 
The chemical history of platinum, is far from being com- 
plete. The great want of uniformity in the statements of 
* Journal of Science and the Arts, Vol. II I. 
