W, Gibbs on the Platinum metals. 59 
The nitrite of ruthenium and potash may then be treated in the 
manner already described and the ruthenium brought into the 
form of the double salt of mercury and ruthendiamin, from 
which the pure metal is easily obtained. This method of sepa- 
rating the platinum metals gives excellent results, but is not free 
from objection. In the first place it will be remarked that it 
does not dispense with the employment of the alkaline nitrites, 
although to some extent it facilitates their use. But the chief 
objection is found in the necessity of employing very large quan- 
tities of chlorid of luteocobalt, a salt which is not to be had in 
commerce and which must therefore be specially prepared for 
the occasion, 
hydric acid. The precipitate on the filter consists chiefly of the 
H,.Co,Cl,+Rh,C 
of the corresponding iridium salt. 
by aleohol, and the iridium and rhodium separated by nitrite of 
soda and sulphid of ammonium in the manner already pointed 
out. ; 
The filtrate from the insoluble rhodium and iridium salts con- 
tains the ruthenium as RuCl, KCl and Ru,Ci, 2KCI, together 
Usually with a small quantity of the double salt 6NH, .Co,Cl, 
+8RuCl, and of PtCl, KCl. The platinum and ruthenium are 
then to be separated with nitrite of potash and alcohol by the 
Process already described. This method of employing the 
