282 BURGESS AND SALE: PURITY OF PLATINUM WARE 



construction. Great dijfficulty is experienced, however, in making 

 accurate comparisons of working standards against Hefner lamps 

 because of the very low intensity (0.9 candle) and the red color 

 of the flame. 



It is believed to be possible to apply the principle of the 

 present pentane lamp in specially made, accurately specified 

 lamps with interchangeable parts, and thus to obtain a closer 

 agreement between lamps. Then by operating the lamps under 

 definite conditions one should be able to obtain sufficient pre- 

 cision with either the Hefner or the pentane lamp to give a 

 valuable check on the electric standards now in use. 



PHYSICAL CHEMISTRY.— yl thermoelectric method for the 

 determination of the purity of platinum ware. G. K. Bur- 

 gess and P. D. Sale, Bureau of Standards.^ 



At the request of Dr. W. F. Hillebrand, Chairman of the 

 Committee on Quality of Platinum Utensils of the American 

 Chemical Society, experiments on the loss in weight due to 

 continued and repeated heating of platinum crucibles of vary- 

 ing degrees of purity have been undertaken, in continuation 

 of similar experiments carried out under the immediate super- 

 vision of members of the above-mentioned committee. 



From some of these earlier experiments, and from the work 

 of other experimenters on the evaporation of metals of the 

 platinum group, it appears to have been hoped to be able to 

 classify platinum ware as to purity in terms of its evaporation 

 at a definite temperature, say 1200°C. This seemed plausible 

 in view of the fact that the usually predominant impurity, 

 iridium, is very much more volatile than platinum. Even if 

 this method, however, would give an indication of the platinum 

 purity, which appears doubtful in the light of some of our more 

 recent experiments, it is at best a s-bmewhat tedious and delicate 

 operation to carry out. 



These experiments showed the desirability of having an ac- 

 curate and rapid method for deterixiining platinum purity and 

 one that could be applied to crucibles without defacing them. 



' Presented at American Chemical Society, April 6, 1914. 



