726 Proceedings of the Royal Society of Edinburgh. [Sess. 
precipitating from the acid solution and recrystallising from water, the 
salt was added to pure chloroplatinic acid solution. The chloroplatinate 
formed was reduced in pure hydrogen gas, and the ammonium chloride 
resulting dissolved in water. After precipitating the salt twice with 
hydrogen chloride gas and throughly washing in each case, it was ready 
to be used in the preparation of the pure ammonium chloroplatinate. 
It should be noted that the precipitation of these chlorides from a 
strongly acid solution should remove all foreign acid radicles, while other 
metallic radicles would be most effectually removed by the precipitation as 
the chloroplatinate. 
Potassium Bromide. — In preparing pure potassium bromide the method 
adopted by Richards and Mueller * was used. A specimen of potassium 
oxalate, already very pure, was four times recrystallised in platinum, the 
crystals being well washed each time. This oxalate was then converted 
into bromide by treating it with pure bromide in a quartz dish. After 
recrystallising the bromide from an acid solution, it was used in the 
preparation of the pure potassium bromoplatinate. 
Ammonium Bromide. — This salt was prepared by distilling some pure 
hydrobromic acid directly into redistilled ammonium hydroxide contained 
in a platinum vessel. 
Bromine and Hydrobromic Acid. — Chemically pure bromine of com- 
merce was redistilled three times, rejecting in each case the first and last 
portions of the distillate. This treatment would remove all but a trace of 
chlorine present. The bromine was now dissolved in pure calcium bromide 
and distilled from this solution. The solution and distillation from a fresh 
portion of the calcium bromide was carried out a second time. The hydro- 
bromic acid was prepared from this pure bromine by means of thoroughly 
washed red phosphorus. The solution of hydrobromic acid formed was 
then redistilled twice, after adding an excess of pure bromine, rejecting 
each time the first and last parts of the distillate. Every care was taken 
to exclude chlorine or hydrochloric acid from the laboratory where the 
bromine and hydrobromic acid were being prepared. 
Hydrochloric and Nitric Acids. — These acids were prepared from the 
chemically pure acids by redistilling from platinum and condensing the 
vapours in platinum. The first and last portions of the distillate were 
always rejected. The absence of chlorine from the nitric acid was further 
assured by testing a portion of each sample in the nephelometer *j* before 
using it. 
* Loc. cit ., p. 29. 
t Richards, Proc. Am. Acad., xxx. 385 (1894) ; Richards and Wells, Am. Ghem. Jour. 
xxx i. 235 (1904). 
