1908-9.] 
The Atomic Weight of Platinum. 
747 
Summary. 
The results set forth in the foregoing pages may be briefly summarised 
as follows : — 
1. The platinum salts analysed by previous investigators must have con- 
tained appreciable amounts of impurities, as very divergent results are 
obtained when the weight of original salt is used in the calculation of the 
atomic weight of platinum. 
2. Very pure platinum metal can be obtained by the precipitation of 
the platinum as ammonium chloroplatinate. 
3. The platinum metal has been converted into the salts of bromo- 
platinic and chloroplatinic acid, without the introduction of any nitric acid, 
under conditions which ensure the absence of any appreciable amounts of 
impurity frorh the utensils employed. 
4. The potassium salts of chloro- and bromoplatinic acid, and the 
corresponding ammonium salts, have been heated to a temperature of 400° 
and 175° respectively, for the purpose of expelling the absorbed and oc- 
cluded moisture. 
5. Essentially the same results are obtained whether the platinum be 
heated and cooled in hydrogen and weighed at atmospheric pressure, or 
heated, cooled, and weighed in a vacuum. 
6. The ratios obtained from the analysis of samples of platinum salts 
obtained from different sources, and purified by different methods, lead to 
essentially the same value for the atomic weight. 
7. Assuming the values given by the International Committee for the 
atomic weights concerned in the calculation, the atomic weight of platinum 
cannot be far from 195*23. 
Chemical Laboratory, 
Syracuse University, 
Syracuse, N.Y., U.S.A. 
( Issued separately December 2, 1909.) 
