727 
1908-9. J The Atomic Weight of Platinum. 
Chloroplatinic Acid . — Four samples of chloroplatinic acid were prepared. 
The material for three of these was platinum scrap. The scrap was first 
boiled with hydrochloric and nitric acids separately to remove surface 
impurities. It was then dissolved in aqua regia. The nitric acid was then 
almost, if not entirely, removed by repeated evaporation with hydrochloric 
acid. The solution was now diluted to a concentration corresponding to a 
5 per cent, solution of platinum. One-third of this solution was set aside 
for separate treatment. In order to remove the iridium and any iron 
present, the remaining two-thirds were treated with enough of a dilute 
solution of pure ammonium chloride to precipitate about 98 per cent, 
of the platinum. The precipitate was thoroughly washed and dried. It 
was then reduced in a current of pure hydrogen. The ammonium chloride 
set free was washed out of the platinum black, and the latter was boiled 
with successive portions of concentrated hydrochloride acid to dissolve 
out a possible trace of iron. The platinum was now ready to be again 
dissolved in aqua regia and subjected to the above treatment a second time. 
It was found very difficult to remove the last traces of iron from the 
platinum. Treating it repeatedly with concentrated hydrochloric acid 
failed to do it, but after a number of precipitations as ammonium chloro- 
platinate, followed each time with the boiling in the presence of hydro- 
chloric acid, no iron could be found in the platinum. 
The elimination of the iridium could be plainly followed from the 
colour of the residue left upon evaporating the mother liquor from a pre- 
cipitation. The characteristic dark red colour of the iridium compounds 
is in evidence when only a very small amount of iridium is present. 
All indications of iridium had vanished after the above operations had been 
repeated three times. 
After the platinum ammonium salt had been precipitated and reduced 
in hydrogen for the fifth time, a portion of the platinum was set aside, which 
eventually was used to prepare sample I. of the potassium chloroplatinate. 
The remainder was redissolved and the above procedure of precipitation 
and reduction repeated four times more. This treatment gave the platinum 
which was used to prepare sample II. of the potassium chloroplatinate. 
The portion of chloroplatinic acid set aside at the beginning of the 
purification process was treated for the removal of other platinum metals, 
as well as any iron, according to the method of Schneider and Seubert.* 
The precipitations were carried out in very dilute solutions in the presence 
of some alcohol, the more effectually to remove any gold that might be 
present. The reductions of the platinum salt were effected in the case 
* Graham Otto’s Lehrbuch, 5th eel., iv. 1153. 
