250 M. Stahlschrnidt on Nitride of Iron, 



If nitride of iron is heated to a high temperature in hydrogen, 

 or even in ammonia, it loses nitrogen. The percentage of one 

 specimen thus heated in ammonia was reduced from 9*3 to 4*9 

 per cent. The discordant results which various experimenters 

 have arrived at as regards the composition of nitride of iron are 

 explained by the remarkable property it has, that its decom- 

 position takes place at a temperature close to that at which it 

 is formed. 



In its formation ammonia is first decomposed, 



NH 3 = N + H 3 , 

 while the hydrogen decomposes protochloride of iron, 



3FeCl + 3H=3Fe + 3HCl. 

 The hydrochloric acid unites with a corresponding quantity of 

 ammonia to form sal-ammoniac, while the porous iron unites- 

 with free nitrogen to form nitride of iron. 



Nitride of iron was also prepared by heating iron in ammo- 

 niacal gas at just that temperature at which the gas is decom- 

 posed; the iron used was some which had been prepared from 

 nitride of iron by heating in hydrogen. 



" According to Fremy, nitrogen gas unites directly with iron, 

 though with difficulty; more readily when nitrogen is passed 

 over a mixture of oxide of iron and charcoal. The results of 

 Stahlschmidt' s experiments lead him to the conclusion that free 

 nitrogen does not unite directly with iron. 



Nitride of iron, according to the mode of its preparation, 

 appears either as a grey powder, or as a more or less compact 

 silver-white mass; it is extremely brittle, and easily pulverizable. 

 When projected into a gas- or spirit-flame, it burns with brilliant 

 sparks. When heated, it gives off its nitrogen ; iron which still 

 contained 0*9 per cent, of nitrogen was not in the least brittle, 

 but had the properties of iron free from nitrogen. 



Nitride of iron dissolves in hydrochloric and in sulphuric acids 

 with liberation of hydrogen and formation of ammoniacal salts. 

 Iodine placed in contact with nitride of iron in the presence of 

 water does not combine with it. The same is the case with 

 bromine ; but when heat is applied, bromine combines with it, 

 disengaging hydrogen, while the nitrogen can be detected in 

 the solution as ammonia. Chlorine acts in a similar manner. 



The iron prepared by heating nitride of iron in hydrogen is 

 of a silver-white colour, lustrous, and so soft that in thick pieces 

 it can be cut with an ordinary knife without much trouble. It 

 is soluble in acids without any residue, and is probably the purest 

 iron which has yet been obtained. 



Stahlschmidt finally discusses the theory of the formation of 

 steel, with especial reference to the properties of nitride of iron. 



