Chemical Notices : — On Nitride of Magnesium. 381 



of magnesia is formed, pyrophosphoric acid being liberated ; and 

 this was proved to be the case by dissolving pyrophosphate of 

 magnesia in nitric acid, evaporating the solution till syrupy, and 

 then placing it under a bell jar over sulphuric acid ; after a time, 

 nitrate of magnesia crystallized, and the pyrophosphoric acid 

 could be drained off. 



But although nitrate of magnesia is formed and pyrophos- 

 phoric acid set free on the addition of nitric acid to the pyrophos- 

 phate, it is probable that, when this mixture is evaporated and 

 heated, the products are not always mere mixtures of nitrate of 

 magnesia and pyrophosphoric acid, but that they are sometimes 

 compounds ; and the reasons for this opinion are, that these pro- 

 ducts are but slightly deliquescent, that nitric acid is less readily 

 expelled from them than from nitrate of magnesia, and that on 

 heating these products suddenly, pyrophosphate of magnesia is 

 volatilized, though it is not under ordinary circumstances a 

 volatilizable salt. 



In the ordinary mode of estimating phosphoric acid or mag- 

 nesia, there is great difficulty in obtaining the pyrophosphate of 

 magnesia perfectly white, except by long calcination, and unless 

 a few drops of nitric acid have been added. This plan, which is 

 often recommended and adopted, is likely, however, to lead to 

 considerable errors in the estimation both of phosphoric acid 

 and of magnesia, in consequence of the action above described ; 

 and there is no doubt that this mode of operating has been one 

 of the causes which have led to the discrepant results of analyses, 

 and the disputes that have frequently arisen as to the richness 

 of substances in phosphates. It was in the course of some 

 investigations of this kind, some considerable time ago, that the 

 peculiar action of heat upon pyrophosphate of magnesia and 

 nitric acid was first observed. 



LI. Chemical Notices from Foreign Journals. 

 %E. Atkinson, Ph.D., F.C.S. 



[Continued from p. 311.] 



BRIEGLEB and Geuther* have investigated the action of ni- 

 trogen on magnesium and some other metals. When mag- 

 nesium was heated in a current of ammoniacal gas to incipient 

 redness, its volume increased, and externally it became covered 

 with black from the reduction of silicon from the glass tube in 

 which it was heated. The product was dried over sulphuric acid, 

 and, on subsequent fusion with potash, emitted ammoniacal gas. 

 In a subsequent experiment, pellets of magnesium were placed 

 in a porcelain boat and rapidly heated to redness in a current 



* Liebig's Annalen, August 1862. 



