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On the Purification of Platina. 65 
minished to a certain point, it is more strongly retained by 
the substance, and it ceases to produce putrid gas. This sub- 
stance, which the putrid odour characterizes, seems rather to 
be a very evaporable combination, allied tu all the gases like 
the other elastic vapours, than a permanent vas. 
3d. Since the caseous part has less azote than most other 
animal substances, we may conjecture that during life this’ 
part is animalized more and more by acquiring a greater 
proportion of azote and hydrogen: this may be explained 
by the more intimate combination of oxygen and hydrogen 
which enter into its composition, and by a separation of 
the carbon by the act of respiration; so that the last term 
of chemical action during life has urea for its product, ac- 
cording to the opinion of M. Fourcroy *, 
XUL. On the Purification of Platina. By M. Descostits+. 
Tue only method hitherto known of purifying platina, is 
to dissolve it in the mitro-muriatic acid, and to precipitate 
it by ammoniacal salt. The decomposition of the triple 
salt. afterwards takes. place by. simple heat, and we obtain 
platina in the metallic state, 
This process is attended with two inconveniences :—the 
first, is the great quantity of acid necessary for the solution » 
of the platina in grains: the second, and the principal one, 
is the union which the platina contracts with iridium in its 
precipitation by ammoniacal salt. This union can no 
longer be destroyed but by repeated solutions and precipi- 
tations, which successively give a salt more and more ex- 
empt from iridium on account of the trifling action which ~ 
the acids exercise on this last metal, and of the greater so- 
lability of its saline combinations with respect to those of 
platina. We may, indeed, abridge these operations, by 
employing only the orange-coloured salt which we obtain 
from the precipitation of the solution of platina in grains a 
little diluted with water ; but then we lose a portion of the 
platina which remains in the mother waters, and this loss 
would be important if we operated on large quantities. 
I endeavoured to remedy these two inconveniences by 
introducing some modifications, founded upon properties 
already known indeed, but which had not been brought into 
play. The following are the modifications to which I 
allude : 
* Syst. des Conn. Chimie, tome x, p, 165. 
+ Mem. @’Arcueil, tome i. p. 370, 
Vol. 37. No, 153, Jun. 1811. E Tnstead 
