combinations of platinum . 
1*5 
4. Observations, &c.on the peculiar compound. 
From the preceding experiments, the black powder obtain* 
ed by the agency of alcohol on the sulphate of platinum, 
appears to consist almost solely of platinum, with a little 
oxygen, and the elements of the nitrous acid. The very 
minute portion of carbonaceous matter it contains, is probably 
accidental. If the constitution of the powder is such as I 
have stated, a doubt may arise whether it can be considered 
as a definite compound ; but its solubility in the muriatic acid, 
the facility with which it combines with sulphur, and resists 
the action of a strong solution of potash at a boiling heat, 
and its acquiring fulminating properties in liquid ammonia, 
are all circumstances which favour the notion of its being a 
true chemical compound. It seems rather doubtful, whether 
the powder can be regarded as a sub-nitrate of platinum, or 
a combination of platinum with oxygen and nitrogen, in a 
different state from that in which they co-exist in the nitrous 
acid. On the idea that the powder is a compound of the 
metal with a little oxygen and nitrous acid, something may 
be said on the mode of its formation, and on the more re- 
markable properties it exhibits. 
From the manner in which the sulphate of platinum is 
formed, (namely, by the agenc}/ - of nitrous acid on the hydro- 
sulphuret of platinum) there can be no difficulty in accounting 
for the presence of a small portion of nitrous acid in it ; and 
my experiments incline me to the opinion, that it is scarcely 
possible to separate the last portions of nitrous acid from the 
sulphate, without entirely decomposing if. That the quan- 
tity of nitrous acid in the sulphate must, however, be very 
