728 Proceedings of the Royal Society of Edinburgh. [Sess. 
of this portion with ammonium formate, prepared by passing ammonia 
vapour, from a platinum still and condenser, directly into freshly distilled 
formic acid. 
This portion of platinum was subjected to five precipitations and 
reductions. It was then used in the preparation of the third sample of 
potassium chloroplatinate. 
The fourth sample of chloroplatinic acid was prepared from 150 grams 
of osmo-iridium ore supplied by Baker and Company of Newark, N.J. This 
ore contained about 35 per cent, of platinum. It was first boiled with 
concentrated hydrochloric acid to dissolve a small per cent, of iron present. 
This treatment was repeated several times. The ore was then well washed, 
and afterward boiled with successive portions of nitric acid. To dissolve 
out the free platinum, the ore was boiled with successive portions of aqua 
regia until nothing more appeared to go into solution. These several 
platinum solutions were now combined and evaporated with a large excess 
of hydrochloric acid. After the nitric acid had been expelled in this way, 
the solution was diluted to correspond to a 5 per cent, solution of platinum, 
a considerable amount of alcohol was added, and the platinum then 
precipitated with ammonium chloride. The mother liquor from this 
precipitation showed, upon evaporation, that an appreciable amount of 
iridium had been dissolved along with the platinum. The precipitate of 
ammonium chloroplatinate, after being throughly washed, was reduced 
with ammonium formate. The finely divided platinum was now boiled 
with nitric and hydrochloric acid separately to remove any metal soluble 
in these acids. It was found practically impossible to remove all 
the iron in this way, as, after being treated with eight different portions of 
50 c.c. each of hydrochloric acid, the boiling being continued for two hours 
in each case, iron was still found in the last portion. The platinum was 
now dissolved in aqua regia and subjected to the treatment recommended by 
Schneider and Seubert,* precipitated, and again reduced. The treatment 
with nitric and hydrochloride acid was now repeated. This time only a 
trace of iron was found. The process of precipitation and reduction was 
repeated until the platinum had been precipitated four times. The salt 
was then reduced and dissolved as usual in aqua regia, and this solution 
was electrolysed, at as a low a voltage as possible, until about 90 per 
cent, of the platinum had been deposited. The platinum anode used here 
was thickly coated with electrolytic platinum before being used. As, 
according to Classen, j* the iridium requires a much higher voltage for its 
* Loc. cit. 
t Ber. Deutsch. Ghem. Gesell., xvii. 2467 (1884). 
