731 
1908-9.] The Atomic Weight of Platinum. 
would not be dissolved by the concentrated hydrochloric acid. The cleanest 
appearing ones to which we had access, and which appeared perfectly white, 
after being boiled with hydrochloric acid for weeks, still gave off traces of 
iron to a fresh portion of concentrated acid. The porous cup diaphragm was 
therefore discarded. 
In the next place, as it seemed possible that traces of the platinum anode 
might be dissolved, along with the finely divided platinum in contact with 
it, and as this might result in the contamination of the solution, a thick 
coating of platinum was deposited electrolytically upon the anode, from a 
solution of pure platinum. 
This apparatus was steamed out for several hours before it was used. 
In order to still further diminish the action of the solution upon the glass, 
the tube, while being used, was immersed in a bath of cold water. The 
current used was a weak one, never more than 4 amperes. 
Potassium Chloroplatinate.— -After each portion of platinum had been 
separately dissolved in this apparatus, by means of the electric current, 
chlorine generated from pure hydrochloric acid and potassium perman- 
ganate was passed through each solution. If a considerable excess of 
hydrochloric acid was not already present, more was added in order to 
neutralise any tendency to hydrolyse on the part of the platinic chloride. 
The several solutions were now diluted to a concentration corresponding to 
about 1J per cent, of platinum, and each was precipitated separately by 
adding it slowly, with constant agitation, to a dilute solution of pure 
potassium chloride. The precipitates were thoroughly washed with water 
and alcohol, and after drying as completely as possible, were kept in 
porcelain over calcium chloride. In this manner samples of potassium 
chloroplatinate Nos. I., II., III., and IV. were prepared from the above 
samples of platinum. 
Ammonium Chloroplatinate. — For the preparation of the ammonium 
double salt, the platinum resulting from the analysis of samples I. and III. 
of the potassium salt was combined and dissolved in the manner described 
above ; the platinum from sample IV. was likewise dissolved separately, 
and the platinum in each precipitated in exactly the same way as in the case 
of the potassium salt. These precipitates gave the samples of ammonium 
chloroplatinate I. and II. 
Potassium and Ammonium Bromoplatinates. — The platinum which 
remained from the analysis of the chloroplatinates was used in preparing 
the corresponding salts of bromoplatinic acid. It was dissolved in pure 
hydrobromic acid, by aid of the electric current, in the apparatus described 
above. The potassium and ammonium bromide solutions used in pre- 
