CHEMICAL PRINCIPLES. 
359 
black, and the alkali abstracts the muriatic acid from it ; the Oxides oC pla- 
decomposition, however, proceeds but slowly. If the alkali 
be in excess, this will dissolve a small quantity of the oxidule 
and assume in the first place a dusky-green colour, changing 
afterwards to the blackness of ink. On boiling the mixture a 
part of the oxidule is decomposed, and there are formed 
metallic platina, a double sub-muriate of the oxide of platina, 
and kali which is dissolved in the fluid. Theoxidum plati- 
nicum, when freed as far as possible from the muriatic acid and 
the alkali, forms a black powder, which suffers no alteration 
from being dried. If the black ley wliich is above the 
oxidulo be neutralized by the sulphuric acid, the oxidum 
platineum is precipitated of a brownish colour, but which 
appears black when taken on the filtre. If the black oxide 
be heated till it becomes quite dry, it then gives out 
w'ater in the first place, and afterwards oxigen gas, leaving 
as a residuum metallic platina. It is, therefore, an hy- 
drate of the oxidum platineum. By cold digestion with the 
muriatic acid, the hydrate undergoes no alteration ; But if 
they are boiled together, the hydrate is decomposed and pro- 
duces murias platinicus and metallic platina. The sulphuric 
acid does not combine with the oxidum platineum in a dry 
state j but if the solution of the oxidule in an alkali be precipi- 
tated by the sulphuric acid in excess, a blackish solution is then 
formed,which appears to oxidate by degrees in the air, and then 
becomes of a more red colour. The concentrated nitric acid 
dissolves the oxidule not yet dried, the solution being of 
greenish brown, and when evaporated black. It contains a large 
portion of the oxide of platina. The concentrated acid also 
dissolves the oxidule in a moist state. Ihe fluid is of a 
greenish brown, and affords on evaporation a gummy mass of 
the same colour, which 'is soluble in water, but does not deli- 
quesce. The oxidum platineum does not combine with the 
carbonic acid, for the alkalized sub-carbonates decompose the 
murias platineus with effervescence. With the muriatic 
acid and ammonia the oxidum platineum produces a double 
muriate. I have not been able to produce it by a direct com- 
position^ 
