724 
Proceedings of the Koyal Society of Edinburgh. [Sess. 
are all average values from a number of determinations ; individual de- 
terminations would show considerably greater variation. 
In 1887 Dittmar and M‘ Arthur * published an account of a critical 
examination of potassium chloroplatinate. They concluded that the salt 
is seldom if ever prepared pure ; that hydrolysis invariably takes place, 
some chlorine being replaced by hydroxyl, and also that some potassium is 
always replaced by hydrogen. In the light of these considerations, they 
apply corrections to a number of determinations which they made of the 
ratio 2KC1 : Pt. The results which they found give a mean value of 195*50. 
These authors at the same time criticised the work of Seubert, and 
concluded that if the proper corrections were applied to his results a value 
above 195*00 would be obtained. 
Dittmar and M‘ Arthur have made some timely suggestions regarding 
the preparation of pure potassium chloroplatinate. The strong tendency of 
the salt to hydrolyse in water solutions seems to have been generally dis- 
regarded by others, while the difficulty of getting rid of nitric acid by 
evaporating with excess of hydrochloric acid after dissolving the platinum 
in aqua regia was not fully appreciated. 
Seubert f replied to the criticisms of Dittmar and M‘ Arthur, claiming 
that the close agreement of the values calculated from the different ratios 
given by his analyses showed that the impurities mentioned by these 
authors could not have been present in the material he worked with. In 
view of the values shown above, this claim should be more or less modified. 
The different investigations mentioned above give us the following 
values for the atomic weight of platinum. From the work of 
Berzelius ..... 
. 195*90 
Andrews ..... 
. 197*88 
Seubert ..... 
. 195*22 
Halberstadt .... 
. 195*05 
Dittmar and M‘ Arthur 
. 195*50 
When selecting a method for the determination of the atomic weight of 
platinum, one naturally turns to the analysis of the double salts of 
pottasium chloride, or ammonium chloride and platinic chloride. These 
salts, when pure, are among the most stable salts of platinum. From their 
analysis they allow of several ratios being formed, from which not only can 
the atomic weight of platinum be calculated, but one can at the same time 
gain a most complete knowledge of the purity of the salts. In addition to 
these points, the determination of chlorine as silver chloride is among the 
t Ber. Deutsch. Chem. Gesell . , xxi. 2179 (1888). 
* Loc. cit. 
