735 
1908-9.] The Atomic AVeight of Platinum. 
the surface of the other. After carefully drying and desiccating for a long 
time, the difference in weight between these two sets of apparatus is 
accurately determined. One boat is now filled with the salt to be analysed, 
and placed in the combustion tube of the Richards * bottling apparatus. 
The bottle and stopper belonging to this boat are also placed in position. 
A current of pure dry air (dried by passing over 18 inches of phosphorous 
pentoxide) is passed through the apparatus, and the combustion tube, which 
passes through an asbestos oven, is carefully heated. The apparatus 
through which the air passes, while being purified and dried, is entirely of 
glass, the pure air not coming in contact with any rubber whatever. 
The temperature of the asbestos oven is now gradually raised to 380°- 
400°. By passing the escaping air through a solution of silver nitrate, and 
then examining this solution in the nephelometer, it was shown that a 
little hydrochloric acid was given off between 100° and 150°. All the 
hydrochloric acid seemed to be expelled between these temperatures. The 
observation of Noyes and Weber, f in regard to the stability of pure 
potassium chloroplatinate at high temperatures was confirmed, as it was 
found that the salt could be heated to 400° in dry air without any de- 
composition taking place. The salt was kept at a temperature between 
380° and 400 for about two hours. The boat and contents were then 
allowed to cool, and with the stream of air still passing through the 
apparatus, they were bottled and transferred to the desiccator. After 
desiccating for two hours the salt is weighed in its bottle and is now ready 
to be reduced. 
In order to make sure that nothing more could be expelled from the 
salt by further heating, it was upon several occasions reheated, bottled, 
desiccated and weighed as before ; but no change in weight was found to 
have taken place. The results from one such experiment will suffice. 
Weight of salt after first heating . . . 2 20469 
„ after heating again for three hours . 2 '20468 
The silver nitrate solution, through which the escaping air was bubbling, 
showed no sign of the presence of any chlorine ions. It is evident that 
nothing appreciable is volatilised from the salt, while it is being heated at 
this high temperature. 
The weighed salt is now placed in the combustion tube of the reducing 
apparatus and carefully heated in a stream of pure hydrogen. The 
hydrogen for this purpose was prepared by electrolysing a solution of 
* Proc. Am. Acad xxxii. 55 (1896). 
t Loc. cit. 
