740 Proceedings of the Royal Society of Edinburgh. [Sess. 
the precipitate must be determined. The silver chloride in the wash water, 
as well as the excess of silver over that required for the precipitation, was 
estimated by means of the nephelometer. The instrument used in this 
research was supplied by Kny & Scherrer (and proved very satisfactory). 
Particular attention was paid to having the standard solution correspond as 
nearly as possible, in every particular, to the solution that was being 
analysed, and sufficient time was always allowed to elapse before the 
opalescence of the two solutions was finally compared. 
In order to reduce the weights of the different substances to the vacuum 
standard, the specific gravities must be known. For silver, silver chloride 
and bromide, these constants have been determined with sufficient accuracy. 
The specific gravity of platinum sponge was redetermined, and a slightly 
lower value than those already recorded was obtained. In the case of the 
platinum salts, new measurements were made using toluol as the liquid to 
be displaced. Kahlbaum’s toluol was dried over sodium and redistilled. 
2T5570 grams of this liquid at 24° C. were found to occupy the same volume 
as 25’0120 grams of water at 4° C. This gives a specific gravity of (18618 for 
the toluol at 24° C. referred to water at 4° C. It was shown by digesting a 
portion of each salt with the toluol, and evaporating some of the liquid in a 
platinum dish, that the salts were not at all soluble in the toluol. The 
values found are tabulated below, together with the correction to be applied 
for all the substances weighed. In the case of the platinum salts, each 
result is the mean of two determinations. 
Table I. — Specific Gravities. 
Salt. 
Weight of 
Salt. 
Weight of 
Toluol 
displaced. 
Sp. Gr. of 
Salt. 
Correction to 
be applied to 
1 gram, of Sub. 
K 2 PtCl 6 . . . 
1-6712 
0-4116 
3-499 
+ 0-00020 
(NH 4 ) 2 PtCl 6 . . 
1-4563 
0-4137 
3-034 
+ 0-00026 
K 2 PtBr fi 
1-4787 
0-2736 
4-658 
+ 0-00012 
(NH 4 ) 2 PtBr 6 
1-3210 
0-2669 
4-265 
+ 0-00015 
Pt 
21-16 
- 0-00009 
■Ag .... 
10-49* 
- 0*00003 
AgCl .... 
5‘55t 
+ 0-00007 
AgBr .... 
6-473J 
+ 0-00004 
The results from the analysis of potassium chloroplatinate, together 
with the ratios obtained from these data, are set forth in the tables below. 
These are all the analyses made of the potassium salt, after the preliminary 
* Richards and Wells, Jour. Am. Chem. Soc., xxvii. 459 (1905). 
t Richards and Wells, ibid. t Baxter and Hines, Amer. Chem. Jour., xxxi. 220 (1904). 
