Extraction of Platina in Russia. 239 
na from foreign substances ; the second to render this platina 
malleable. To obtain pure platina, the crude metal is dissolv- 
ed with the assistance in aqua regia, (composed of three 
parts of hydrochloric and one of nitric acid, experience has 
shown, that the most advantageous strength is 40° B. for the 
nitric, and 25 for the hydrochloric.) The solution is made in 
open porcelain capsules, holding from 25 to 35 pounds ; these 
when filled with a sufficient quantity of acid and platina, are 
placed on a sand bath capable of accommodating about 30. 
This sand bath is situated under a hood, closed on all sides 
with moveable glass windows, and openings for removing the 
capsules; from this arrangement, all the acid gasses are car- 
ried up the chimney. 
This operation lasts from eight to ten hours, or until no 
more red vapours are given off; at this time the solutions con- 
tain a great excess of hydrochloric acid, but this excess is 
indispensable to the retention of a greater part of the iridium, 
&c, when at an after part of the process the platina is preci- 
pitated. 
After the solution is effected, the liquor is decanted into 
large earthen vessels, and sal ammoniac added, the precipi- 
tates thus formed, are permitted to become deposited; they 
are then washed several times with cold water, dried, and 
heated to redness, in platina crucibles; in this manner the 
platina is obtained in a spongy state. The degree of its pu- 
rity, principally depends on two circumstances: 1st, that the 
solution contains an excess of acid, to retain the iridium : 2d, 
that the precipitate has been well washed. This last precau- 
tion, augments, it is true, the washings, and their evaporation 
is one of the longest parts of the process; but the combina- 
tion of platina and ammonia is thus perfectly freed from all 
admixture with foreign metallic chlorides, which would be 
injurious to the malleability of the platina. 
The washings are divided into two portions, and treated 
separately ; the first are poured into glass retorts, and eva- 
porated on a sand bath to one-twelfth of their original bulk ; 
on cooling, there is a deposit, of a combination of ammonia 
