154 Professor M. 0. Forster [May 5, 



position expressed by the curious formulfe, N4H4 and NjHg. Another 

 salt, that with ferric iron, provides a very delicate test for hydrazoic 

 acid, the red colour being noticeable in solutions containing only one 

 part per million. 



Hydrazoic acid, discovered in 1890, also by Curtius, may be 

 shown by experiment to follow an attempt to add another atom of 

 nitrogen to hydrazine. Whilst the action of nitrous acid on am- 

 monia causes both atoms of nitrogen to be liberated in elemental 

 form, 



HNO, + NH3 = N2 + 2H,0, 



hydrazine is converted by the same agent into hydrazoic acid, 

 HNO, + NHo-XH, = HN3 + 2H,0. 



This process, however, is not adapted to the production of hydrazoic 

 acid or its salts in large quantities. Two methods are available for 

 this purpose. One of these, due to W. Wislicenus (1892), consists in 

 passing a current of dry nitrous oxide over shallow layers of powdered 

 sodamide at about 200°, and by means of certain modifications good 

 yields of sodium azide may be obtained : 



NaNH, + X2O = NaNg + H,0. 



A later method, elaborated by Stolle and Thiele working independently 

 (1908), is* based on the experiment just mentioned, namely, the action 

 of nitrous acid on hydrazine, but instead of using free nitrous acid, 

 an ethereal nitrite, such as ethyl or amyl nitrite, is employed. These 

 materials, in presence of alkali, transform hydrazine into sodium azide, 

 the yield being excellent ; and this disco vety has resulted in the 

 commercial production of that salt, which may now be purchased at 

 less than 40s. per pound, 



NH, • NH, + Alk • ONO + NaOEt = NaNg + Alk • Oil + EtOH + H,0. 



The free acid is a dangerous and disagreeable substance to manipu- 

 late. When free from water, it condenses to a colourless mobile 

 liquid, which boils at about the same temperature as ether (o7') ; but 

 although harmless looking, it is a frightful explosive, and requires 

 but slightly elevated temperatures for the display of this property. 

 Moreover, the vapour is extremely poisonous, and when inhaled in 

 even trifling quantities causes distressing headache ; it is, in fact, a 

 powerful protoplasmic poison, its activity in this direction being 

 comparable with that of prussic acid. As might be expected, there- 

 fore, its effect on the blood-spectrura is immediate and pronounced. 



To chemists, however, the most conspicuous property of hydrazoic 

 acid is the resemblance it bears to the halogen acids, a solution con- 

 taining only one part per million giving a faint turbidity with silver 

 nitrate. The resulting silver azoimide, in common with other hydra- 

 zoic salts of heavy metals, is dangerously explosive, but the salts of 



