723 
1908-9.] The Atomic Weight of Platinum. 
Here is a difference of one unit in the mean values. Another series of 
analyses where the total chlorine was determined as silver chloride gave : 
From the ratio (NH 4 ) 2 C1 6 : Pt . . . . 194 62 
„ „ 6AgCl : Pt . . . . 195-80 
6AgCl : (NH 4 ) 2 PtCl 6 . . 197*20 
It seems very likely that the high result in the case of the last ratio 
was due to the presence of water in the salt weighed. 
For the potassium chloroplatinate we have the following mean values: 
From the ratio K 2 C1 6 : Pt . . . . 194*81 
„ „ 2KC1 : Pt 194-82 
„ „ 2KC1 : K 2 PtCl 6 .... 195-00 
From another series of analyses, where the chlorine lost upon ignition 
was determined as well as the platinum, we have: 
From the ratio K 2 C1 6 : Pt . . . . 194-72 
„ „ 4AgCl : Pt 195 05 
„ „ 4AgCl : K,PtCl 6 .... 195-51 
In 1884 Halberstadt * published the results of a very complete study of 
the chi oroplatinates of ammonium and potassium. He also made some 
analyses of platinic bromide. The platinum was estimated both by weigh- 
ing the metal left after reducing the salt in hydrogen and by weighing 
the metal electrolytically. The mean values calculated from his ratios are 
given below. 
From 
the ratio Br 4 
Pt 
99 
„ (NH 4 ) 2 b| 6 
Pt 
99 
„ K 2 Br 6 
Pt 
99 
„ 2KBr 
Pt 
99 
2KBr 
PtBr 
99 
(NH 4 ) 2 C1 6 
Pt 
99 
k 2 ci 6 
Pt 
99 
2KC1 
Pt 
99 
„ 2KC1 
Pt 
. 194-51 
. 194*82 
. 195-05 
. 195-19 
. 195-89 
. 195-05 
. 194-75 
. 194-90 
. 195-33 
The extreme values among these results can be explained if we assume 
that the original salt in each case contained some water which had not been 
driven out before it was weighed. Thus in the ratio Br 4 : Pt any water 
in the PtBr 4 weighed makes the weight for the Br 4 too great ; likewise in 
the ratio 2KBr : PtBr 4 the water in the original K 2 PtBr 6 weighed gives 
too high a value to the PtBr 4 . It should be remembered that the above 
* Ber. Deutsch. Ghem. Gesell . , xvii. 2962 (1884). 
