734 
Proceedings of the Royal Society of Edinburgh. [Sess. 
The Analysts of Potassium Chloroplatinate. 
From a complete analysis of potassium chloroplatinate, one should be 
able to gain considerable information concerning the purity of the com- 
pound. If the salt at the beginning can be weighed free from water, and 
if, after being reduced in hydrogen, the platinum left behind can be 
weighed and the potassium chloride and the chlorine set free estimated 
separately, we can from the relations between these constituents tell which, 
if any, has been present in excess, or has been replaced by some impurity. 
Only with a pure salt, having the exact composition represented by the 
formula, will the several ratios found between these constituents give the 
same value for the atomic weight. Unfortunately, we are here confronted 
at once with the knowledge that as the salt has been precipitated from 
a water solution, it must inevitably have enclosed within the crystals some 
of the mother liquor, and complete expulsion of this water will only be 
brought about, as pointed out by Richards,* by the entire disintegration of 
the crystal. It remains to be considered whether or not the salt in question 
can be freed, before weighing, from all but an inappreciable quantity of 
moisture. 
In the first place, we are dealing here with a salt which can be obtained, 
as a precipitate, in an exceedingly fine state of division. As it is very soft, 
it can be ground to a still finer powder without danger of contaminating 
it with pieces of the pestle or mortar. After such treatment, it would seem 
as if all but the most minute of the crystal cells must be broken. Further, 
as pointed out below, we are able to heat the salt in this fine state of 
division to a temperature but little short of 400° C. and bottle it in a current 
of pure dry air. It does not seem as if, under these conditions, a very large 
amount of moisture can be left in the salt. Nevertheless, although the 
results of the weighings of the salt are given, and are useful as a check 
upon its purity, the atomic weights calculated from ratios in which the 
weight of original salt appears are not used in determining the final value. 
The analytical procedure is now about as follows : — Two weighing- 
bottles, not differing in weight by more than two or three tenths of a gram, 
and two porcelain boats fulfilling the same condition, are selected : the one 
bottle to hold the boat containing the salt to be weighed, the other bottle 
and boat to act as a tare ; thus doing away with the necessity of making 
buoyancy corrections, except for the salt weighed. We can also assume, as 
the bottles are made of the same kind of glass, that the moisture on the 
surface of one, when being weighed, is practically equal to the moisture on 
* Proc . Am . Phil . Soc xlii. 28 (1903). 
