OF METALS OF THE PLATINUM GROUP. 
649 
Methods adopted for the Analysis of the several Alloys Experimented upon. 
(Added June 13, 1892.) 
For alloys of gold 100, and platinum 900 parts.—Two carefully weighed portions 
of the alloys to be analysed were weighed and cupelled in pure lead with two and 
three-quarter times their weight of pure silver, in identically the same manner as in 
conducting the process of gold assaying; one of the buttons so obtained was then, 
after lamination and annealing, parted in nitric acid, which by two distinct treat¬ 
ments removes the whole of the silver and the platinum, leaving the gold in a 
pure state, which, when washed, annealed and weighed accurately, gives the pro¬ 
portion of pure gold in the alloy. 
The other button, after being laminated and annealed in precisely the same way, 
was parted in sulphuric acid, which removes the silver only, leaving the whole of the 
gold and the platinum intact. By weighing the gold obtained by parting in nitric 
acid against the gold and platinum left by the sulphuric acid parting, the proportion 
of platinum obtained is the difference. This is a simple but very accurate method, 
and is universally recognised and employed by professional assayers when deter¬ 
mining alloys of gold containing platinum. By working checks or standards of gold 
and platinum, made synthetically of platinum ten and gold ninety parts, any error 
which might arise is completely checked and controlled. 
In the case of the alloys of platinum 900, and gold 100 parts, the foregoing- 
process was obviously unavailable. After many different experiments, the following 
method was one which I found to be accurate and trustworthy ; and duplicate 
analyses, each on 50 grains of metal, were carefully made by this process on each of 
the portions of the hemispheres removed for examination. 
Exact weighings of fifty grains each were taken cf each of the alloys under exami¬ 
nation and treated with an excess of nitrohydrochloric acid, which gradually dis¬ 
solved the whole. The resulting solutions of platinum-gold chloride were then 
evaporated nearly to dryness to ensure the elimination of all free acid, so as to 
obtain perfectly neutral solutions. These chloride solutions were then diluted with 
distilled water to about 20 cub. centims. capacity, a degree of strength which was 
ascertained by experiment to be the best for ensuring complete precipitation of the 
gold. The metallic gold was thrown down by means of crystals of oxalic acid and 
was carefully washed, dried, and weighed. 
From the mother liquors the metallic platinum was then precipitated by means of 
pure metallic zinc, and the resulting precipitated platinum was thoroughly washed, 
and boiled in diluted hydrochloric acid. The platinum thus purified was then 
washed, dried, and weighed. 
Side by side, with each set of analyses, standards synthetically prepared were 
used, each of 37'5 grains pure platinum and 12 - 5 grains pure gold. This was 
4 o 
MDCCOXCTT.—A. 
