72 9 
1908-9.] The Atomic Weight of Platinum. 
deposition than the platinum, this treatment should free the platinum most 
effectually from iridium. That the pure metal might not again he con- 
taminated with iridium or iron from the electrode only about 75 per cent, 
of the deposit was dissolved off. This was again precipitated as the 
ammonium double salt, and after being reduced, was ready to be used in 
preparing sample IV. of potassium chloroplatinate. 
Professor F. A. Saunders has very kindly photographed the arc spectrum 
from the orange to the end of the ultra-violet of a portion of sample No. I. 
of the platinum, using a concave grating, and finds no indication of the 
presence of iridium, osmium, palladium, Rhodium, Ruthenium, or iron in the 
platinum. The strongest lines of iridium are entirely absent, as indicated 
in a portion of the spectrum, enlarged and reproduced below. If the iridium 
has been so effectually removed from this sample of platinum, we are surety 
warranted in assuming the other samples which were subjected to even more 
severe treatment for purposes of purification to be equally pure. I wish 
here to record my appreciation of the kindness of Professor Saunders in 
making this test. 
Small part of platinum arc spectrum (in ultra-violet) photographed with 
concave grating. Enlarged x 2. Place marked : strong Ir line might 
occur ; | Pd line ditto, but does not. 
It has been shown by Precht,* that it is almost impossible to remove 
the last trace of nitric acid from a solution of chloroplatinic acid prepared 
by dissolving platinum in aqua regia. This point has also been emphasised 
by Noyes and Weber,]* and, according to the latter’s statement, they never 
succeeded in preparing perfectly pure potassium chloroplatinate from acid 
made by this method. It was thought safer, in the present instance, to avoid 
the use of nitric acid altogether in the preparation of the chloroplatinic acid, 
from which the potassium chloroplatinate for the analyses was to be prepared. 
In order to dissolve the platinum, recourse was had to the electrolytic method 
described by Weber. J According to this method, the platinum to be dissolved 
rests upon the platinum anode B in the tube A, fig. 1 ; the anode being in 
* Loc. cit. t Jour. Am. Ghem. Soc ., xxx. 13 (1908). 
| Jour. Am. Ghem. Soc., xxx. 29 (1908). 
