117 
Ordinary Meeting, March 6th, 1866. 
R. Angus Smith, Ph.D., F.R.S., &c., President, in the 
the Chair. 
Mr. E. Sonstadt communicated the following “ Note on 
the Purification of Platinum — 
The tendency of platinum to alloy with other metals, 
at a temperature far below its fusing point, is sufficiently 
well known to every user of platinum crucibles. It is equally 
well known that iron, &c., which has been absorbed by 
platinum cannot be removed, except superficially, by the 
action of hydrochloric acid for instance, nor even by heating 
in acid sulphate of potassium. Stas, in his memoir on 
the atomic weight of silver, &c., states that he purified his 
platinum vessels from iron, by causing them to come in 
contact, at a red heat, with the vapour of chloride of 
ammonium. The process had to be repeated as often as any 
yellow sublimate was formed. This process is less effectual, 
or less conveniently and speedily effectual, than the modifica- 
tion of it that I have to propose ; because, if the vapour of 
the sal ammoniac is generated from the solid salt in the vessel 
to be purified, the heat absorbed in the vaporization of the 
salt tends to keep the vessel at a temperature below that at 
which volatile metal chlorides are most readily formed. 
Instead of chloride ot ammonium, I put dry double chloride 
of ammonium and magnesium in the platinum vessel intended 
for purification. The vessel is then heated to about the 
fusing point of cast iron for about an hour. I find a Gore’s 
furnace convenient for this purpose. In this process, not 
Pboceedings— Lit. & Phil. Society.— Foe. V. — No. 12 — Session 1865-6. 
