462 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



VI. The Analysis of Potassic Nitrate. 



The details of experimentation having heen mastered, three careful 

 analyses of potassic nitrate were made. 



The salt lends itself easily to purification by recrystallization, on account 

 of the great temperature coefficient of its solubility; it was recrystallized 

 eight times in Jena glass vessels and four more times in jilatinum. The 

 product thus obtained was carefully dried and fused in a platinum dish at 

 the lowest temperature possible, in order to avoid the formation of even 

 a trace of nitrite. The pure white solid was finely powdered and again 

 dried. Although, as Hempel has shown,* a hard mineral causes con- 

 siderable abrasion in an agate mortar, a soft substance like potassic 

 nitrate may be powdered safely in one. 



In every case at least five times as much of the silica by weight was 

 used as of the nitrate. 



In order to reduce the observed weights to the vacuum standard, the 

 specific gravity of the potassic nitrate was taken as 2.09. f It was 

 assumed that the contraction which takes place when potassic oxide com- 

 bines with silica is negligible as far as the reduction to vacuum is con- 

 cerned, and hence that the specific gravity of potassic oxide may be taken 

 as 2.65, according to Karsten. $ 



Following are the results of the three consecutive determinations of 

 the atomic weight of potassium, using the nitrate prepared in the manner 

 described above. 



Results of Analysis of Potassic Nitrate. 

 O = 16.000 ; N = 14.040. 



* Hempel, Chem. Centralis, 2, 719 (1901). 

 t Landolt and Bornstein, Tabellen (1894), 134. 

 average of many determinations. 



| Karsten, Schweigger's Ann., 65, 419 (1832). 



This is the most probable 



