732 
Proceedings of the Royal Society of Edinburgh. [Sess. 
cipitating the platinum were both very dilute, and the platinum solution 
was added as before to the bromide solution slowly and with constant 
stirring. 
The several solutions from which the above platinates were precipitated 
were so dilute, and precipitation took place so slowly, that it was thought 
to be impossible for an appreciable amount of potassium chloride or bromide, 
or the corresponding ammonium salt, to be occluded by the precipitate. 
That considerable amounts of these are carried down, as contended by 
Dittmar and McArthur,* when the platinum salts are formed in solutions at 
all concentrated, has been found for a number of cases. When carrying out 
some preliminary work on these salts, it was found that as much as 05 per 
cent, in excess of the potassium salt may be present in a precipitate formed 
in a 25 per cent, solution of potassium bromide. 
Silver . — The mode of preparing pure silver followed closely the 
admirable methods developed by Professor Richards, which have proved so 
satisfactory. Briefly stated, C.P. silver nitrate was dissolved in pure 
water and precipitated, from a very dilute solution, with pure hydro- 
chloric acid. This precipitate was well washed and reduced, in a strongly 
alkaline solution, with invert sugar. The sugar used here had been 
dissolved, filtered, and recrystallised in the laboratory. The caustic soda 
used had been electrolysed, in order to remove a possible trace of iron. 
The reduced silver, after a thorough washing, was dissolved in pure nitric 
acid, and this solution was divided into three portions ; these portions 
giving eventually three samples of silver. The first portion was again 
precipitated with hydrochloric acid. Reduction by means of invert sugar 
followed, and the reduced metal, after washing, was fused on pure lime 
before the blowpipe. This lime was prepared from calcium nitrate, which 
had been recrystallised several times, and then precipitated as carbonate 
with pure ammonium carbonate. The lumps of silver obtained from the 
fusion were now electrolysed, with a very weak current, in a solution of 
nitrate prepared from one of these pellets of silver and pure nitric acid. 
The crystals of silver deposited were well washed, and were then fused on 
a boat of pure lime, in an atmosphere of hydrogen, at a pressure of 
40 mm. 
The second portion of silver nitrate solution was recrystallised twice 
from platinum. It was then reduced with ammonium formate prepared by 
passing ammonia vapor, from platinum still and condenser, directly into 
freshly distilled formic acid. The reduced metal, after being washed, was 
fused on lime and electrolysed as in the case of the first portion ; this was 
* Loc. cit. 
