OF METALS OF THE PLATINUM GROUP. 
037 
with nitric acid; in the latter, the silver only separates, leaving the whole of the 
gold and of the platinum together, the proportion of platinum in the alloy being 
the difference. The two resulting products weighed against each other yield the 
gold and the platinum. This is a simple but very accurate process, and is the 
recognised method adopted by the professional assayer when determining gold alloys 
containing small proportions of platinum. 
With each set of analyses I employed standards synthetically made with ten parts 
pure platinum and ninety parts pure gold, by means of which any possible error 
which might arise was completely checked and controlled. 
In the case of the estimation of the gold in the alloys of 90 per cent, platinum, and 
10 per cent, of gold, the foregoing process was obviously unavailable, and I was com¬ 
pelled to try several methods in order to obtain trustworthy results. The following, 
however, proved to be an exceedingly satisfactory process, and was therefore adopted. 
Exact weighings of 50 grains each, in duplicate, were taken of each of the portions 
of the hemispheres removed for examination. These were dissolved in aqua regia , 
evaporated to ensure the elimination of all free acid, and then diluted with distilled 
water to about 20 c.c. capacity, which was ascertained by experiment to be the best 
for the complete precipitation of the gold; the gold was precipitated by crystals of 
pure oxalic acid, washed and weighed. All the duplicate results agreed most satis¬ 
factorily. To corroborate these gold results, I precipitated the platinum by means 
of pure zinc, boiled the precipitated platinum in hydrochloric acid, and after washing 
and drying weighed the resulting pure platinum. With every set of analyses of 
metal from their respective spheres, I made up standards synthetically, each of 
37’5 grains pure platinum and 12‘5 grains pure gold to ensure accuracy, it being 
practically impossible to extract the whole of the constituent metals within y§^ths 
per cent. I tried other known processes with a view to obtain absolutely correct 
results, but I consider that the methods employed were very accurate. 
I am confirmed in this view by the experience gained in similar experiments by 
Mr. W. Bettel, in a paper contributed to the ‘Chemical News,’ vol. 56, No. 1452, 
which is evidently the result of much careful work. 
With alloys of gold and palladium it is usual to determine the amount of gold by 
quartation with pure silver, and parting by nitric acid. 
Carefully weighed portions of the alloys are cupelled in pure lead with two and 
three-quarter times their own weight of fine silver. 
These cupelled buttons are laminated and annealed, and then treated by boiling in 
nitric acid three distinct times. By these means the palladium becomes dissolved, as 
well as the silver, leaving the pure gold, which, after washing and annealing, is 
weighed. The difference is, of course, the palladium. 
With alloys of gold and palladium, say of gold 90 parts and of palladium 10 parts 
in the hundred, it is preferable to re-cupel and re-part the gold obtained with a further 
proportion of fine silver, as sometimes, and where there is as much as 10 per cent, of 
palladium, the whole of the palladium is not removed in one parting operation. 
