1908-9.] 
The Atomic Weight of Platinum. 
745 
The Analysis of Potassium Bromoplatinate. 
It was found that the potassium bromoplatinate was even more stable 
than the chloroplatinate. It could be heated for an indefinite length of 
time, in pure dry air, at as high a temperature as 400° C. without under- 
going the least decomposition. Consequently, all but inappreciable amounts 
of water must have been expelled from the salt before it was weighed. 
This salt was somewhat more difficult to decompose in hydrogen than the 
chloroplatinate, and the reduced platinum had to be washed many times 
with the occluded hydrogen, as described above, before all the hydrobromic 
acid was expelled. The method of analysis was very similar to that used 
for the other compounds. The bromine remaining as potassium bromide 
was estimated separately from that forming hydrobromic acid. Here, too, 
the silver required for the precipitations, as well as the amount of silver 
bromide produced, was determined. 
The advantages of silver bromide as an ideal precipitate to work with 
are well known. Its low solubility in water allows one to estimate the 
amount dissolved by the wash water even more accurately than in the case 
of the chloride. 
The results obtained, together with the ratios which may be found 
from these, are set forth below. 
Table IX. — Results of the Analysis of Potassium Bromoplatinate. 
Experi- 
ment. 
Sample 
of Silver 
used. 
Weight of 
K 2 PtBr 0 
in vacuum. 
Weight of 
Platinum 
in vacuum. 
Weight of 
4AgBr 
in vacuum. 
Weight of 
2AgBr 
in vacuum. 
Weight of 
4Ag 
in vacuum. 
Weight of 
2Ag 
in vacuum. 
22 
II. 
2T9076 
0-56779 
2-18543 
1-09273 
1-25544 
0-62770 
23 
2-42094 
0-62766 
2-41510 
1-20758 
1-38761 
0-69378 
25 
55 
1-78705 
0-46344 
1-78284 
0-89156 
1-02416 
0-51214 
26 
I. 
1-81840 
0-47156 
1-81430 
0-90703 
1-04228 
0-52105 
27 
55 
2-47056 
0-64063 
2-46507 
1-23246 
1-41572 
0-70800 
28 
55 
2-19017 
0-56787 
2-18525 
1-09260 
1-25530 
0-62756 
