460 



PROCEEDINGS OP THE AMERICAN ACADEMY. 



the larger one, in which to mis the nitrate and sand ; this small cru- 

 cible was completely surrounded and covered with a layer of silicic 

 dioxide. 



If with this arrangement the heating is conducted slowly and cautiously, 

 no evidence appeared of loss by sublimation. No trace of deposition 

 was found upon the under surface of the clean cool platinum lid of the 

 crucible. 



Potassic and caesic silicate both seem to be essentially permanent and 

 non-volatile at 1000°, as far as the present experiments were concerned, 

 and constant weight was easily reached. 



The next problem to be solved was the finding of the best source of 

 heat. In the first place, in order to avoid the danger of contamination 

 from the impurities in illuminating gas, an electric furnace giving the 

 desired temperature was used. We soon found, however, that the 

 platinum heat-producing resistance was volatilized to a serious extent. 

 The fire-clay of the oven was soon partially coated by a black film of 

 sublimed platinum, and an empty crucible heated in the oven for an hour 

 gained 0.0002 gram. Qualitative analysis showed beyond doubt the 



nature of this sublimate, when 

 deposited upon pure porcelain. 

 This tendency of platinum under 

 certain circumstances to volatilize 

 has been studied by Hall ; * it 

 brought an unwelcome complica- 

 tion into the present work. Evi- 

 dently platinum cannot safely be 

 used as a resistance for obtaining 

 high temperatures in accurate 

 work ; we had almost introduced 

 a large error into the investigation 

 while trying to eliminate a small 

 one. Of course the temperature 

 of the wire in the electric drying 

 oven previously mentioned is too 

 low to cause any danger from this 

 source. 



Recourse was now had to a 

 contrivance which had been used 



Figure 2. 



* Hall, J. Am. Cliem. Soc, 22, 8, 494 (1900). 



