733 
1908-9.] The Atomic Weight of Platinum. 
followed also by fusion in hydrogen on a lime boat under a pressure of 
40 mm. 
The treatment of the third portion of silver nitrate solution was the 
same in principle as in the case of the second sample, but here the silver 
solutions were not allowed at any time to come in contact with glass 
vessels. The reductions were carried out in a silver dish, while the 
electrolysis was effected in a quartz basin. The final fusion took place 
under the same conditions as in the above cases. 
The pellets of silver resulting from the fusions in hydrogen were now 
scrubbed with sand and cut into pieces of the proper size with a clean 
piece of hard steel. They were then warmed with diluted nitric acid until 
well etched. After washing and drying, they were kept in a desiccator 
until used. The above preparations gave samples of silver Nos. I., II., 
and III. 
The arc spectrum, from the orange to the ultra-violet, of a portion of 
sample II. of the silver, has also been photographed by Professor Saunders, 
under very favourable conditions, using the concave grating. The results 
indicate the entire absence of copper and iron from this sample of 
silver. 
Considerable attention was paid to the water used in this research. It 
was twice distilled, the second time in the presence of a trace only of 
sodium hydroxide and potassium permanganate. It was condensed in 
block tin, received and stored in Jena glass stoppered bottles. Every care 
was taken to exclude dust, and it was always used soon after distilling. To 
make certain of the absence of chlorine ions, every sample was tested in the 
nephelometer before using. 
The balance used was made by Christian Becker of New York. It was 
procured especially for this work, and was not used for any other purpose. 
It is a gold-plated short-arm balance sensitive to 002 mg. with a load of 
40 gms. This was looked upon as being quite accurate enough for the 
purpose in hand. It cannot be too strongly emphasised that even in 
atomic weight work the errors of a chemical nature are likely to 
far exceed the errors made in weighing. There is little to be gained 
in weighing to a few thousandths of a mg., when there may be several 
hundredths of a mg. of unknown impurity in the portion of substance 
weighed. 
The weights used were new ones of the Sartorius make, gold-plated. 
They were standardised according to the method suggested by Richards,* 
and have not been used in any other work. 
* Jour. Am,. Ghem,. Soc ., xxii. 144 (1900). 
