30 



NA TURE 



[December io, 1891 



by means of fused calcium chloride, after treatment with 

 which pure anhydrous azoimide distils over. 



Azoimide is a clear, colourless, mobile liquid, which 

 boils without decomposition at 37''. It is endowed with the 

 same intolerable odour as the solution. Its most charac- 

 teristic property, however, is its frightful explosiveness. 

 It explodes in a most erratic manner— sometimes, without 

 the least apparent provocation, at the ordinary tempera- 

 ture. Its distillation is an operation attended with great 

 danger ; Prof. Curtius and his assistant have succeeded, 

 as above described, in isolating it and determining its 

 boiling-point several times ; but upon other occasions, 

 under apparently the same conditions, the experiment 

 has ended with a disastrous explosion. When suddenly 

 heated, or touched with a hot body, it always explodes. 

 The explosion is accompanied by an intensely vivid blue 

 flame. The damage wrought by the explosion of very 

 minute quantites is most surprising. The thousandth 

 part of a gram, placed upon an iron plate. and touched 

 by a hot glass rod, is sufficient to produce a loud de- 

 tonation, and considerably distort the iron plate. The 

 twentieth part of a gram was found sufficient to completely 

 pulverize a Hofmann "density" apparatus, when an 

 attempt was made to determine its vapour-density in the 

 Torricellian vacuum at the ordinary temperature. Upon 

 another occasion, seven-tenths of a gram, contained in 

 a closed glass tube, upon removal from the freezing 

 mixture in which it had been immersed exploded with 

 such immense force as to shatter every piece of glass 

 apparatus in the laboratory. It was upon this occasion 

 that Prof. Curtius's assistant was so seriously injured as 

 to cause the temporary abandonment of the work The 

 aqueous solution is almost as explosive as the anhydrous 

 liquid, the explosion of two cubic centimetres of a 27 per 

 cent, solution upon one occasion shattering the glass tube 

 into dust so fine that Prof. Curtius, who was attempting 

 to seal it, escaped uninjured. 



The anhydrous liquid readily dissolves in water and 

 alcohol. The aqueous solution is strongly acid to litmus. 

 Magnesium, aluminium, zinc, iron, and even copper are 

 rapidly attacked by it, hydrogen being evolved. Gold 

 and silver are likewise attacked, although not so rapidly. 

 In the case of gold a red solution of the gold salt is 

 formed ; the silver salt being insoluble soon prevents 

 further action in the case of silver. 



The anhydrous compound appears to be decomposed 

 by concentrated sulphuric acid. 



• Other Metallic Salts of Azoimide. 



The silver salt, Ag — NC I, is obtained in the form of 



a white precipitate whenever a soluble silver salt is added 

 to azoimide, its aqueous solution, or solutions of its salts. 

 It resembles silver chloride very closely in appearance, 

 but is not darkened by the action of light. There is very 

 little difficulty in distinguishing between the two salts, 

 however, inasmuch as the silver salt of azoimide partakes 

 of the frightfully explosive properties of the free acid. It 

 is the most dangerous of all the salts to handle. In spite, 

 however, of this explosiveness. Prof. Curtius has once., 

 and only once, succeeded in obtaining a determination of 

 its nitrogen content, by combustion in a long layer of 

 copper oxide. The number obtained was 27'65. The 

 value calculated from the formula AgN, is 28'oo. In 

 every other experiment the tube was shattered into 

 fragments, notwithstanding the finest subdivision and 

 distribution among the copper oxide. 



Theprecipitated silver salt is soluble, like silver chloride, 

 in ammonia. Upon evaporation of the solution, however, 

 instead of obtaining an ammoniacal double compound, 

 the silver salt itself crystallizes out in almost colourless 

 crystals half an inch long. These crystals, as may be 



NO. II 54, VOL. 45] 



imagined, are most delicate objects to handle ; they 

 explode even upon breaking the prisms across. They 

 are almost perfectly insoluble in water. 



The me? citrous salt, HgNg, is likewise insoluble in 

 water, and may be leadily obtained by precipitation of 

 the free acid or its soluble salts with mercurous nitrate. 

 It has the advantage of being more safely handled than 

 the silver salt, and is less sensitive to percussion. It also 

 requires a higher temperature to bring about explosion 

 by heating. It is usually obtained by precipitation in 

 the form of microcrystalline anisotropic needles. It 

 becomes coloured yellow when exposed to light. Like 

 mercurous chloride, it forms a black compound with 

 ammonia. 



The lead salt, PbNy, resembles lead chloride very closely. 

 It is insoluble in cold water, but dissolves somewhat in 

 boiling water, though not to such an extent as lead 

 chloride, about half a gram dissolving in a litre of boiling 

 water. Upon cooling, brilliant colourless needles, attain- 

 ing sometimes the length of half an inch, separate out. 

 It may be best obtained by precipitating the solution of 

 the sodium or ammonium salt with lead acetate. The 

 precipitate is soluble in excess of lead acetate. The 

 crystals of the lead salt explode with fearful force when 

 slightly warmed. By long boiling with water this lead 

 salt appears to be decomposed, anon-explosive lead com- 

 pound separating, and free azoimide escaping. Warm 

 acetic acid also dissolves it, with gradual decomposition 

 and liberation of azoimide. 



The barium salt. BaN^, is readily obtained by neutraliz- 

 ing the acid with baryta, and crystallizes from solution in 

 large lustrous crystals. It is likewise a highly explosive 

 salt, and the explosion is accompanied by the production 

 of a brilliant green flame. 



Ethereal Salts of Azoimide. 



The metallic salts of azoimide may be readily converted 

 into ethereal salts by reacting upon them with haloid 

 ethers. The phenyl ester has been prepared by Prof. 

 Curtius, and is found to be identical in every respect with 



.N 



the long known diazobenzene imide, CgH^N 



A 



The 



^N 



aromatic esters are generally remarkably stable substances, 

 and it was consequently found impossible to obtain azo- 

 imide by the direct saponification of diazobenzene imide 

 with soda. Within the last few months, however, Drs. 

 Noelting and Grandmougin,of Miilhausen.have succeeded 

 in preparing azoimide indirectly from diazobenzene imide, 

 by first diminishing somewhat the stability of the com- 

 pound by introducing two nitro groups into it. Upon 

 treating dinitro- diazobenzene imide with alcoholic potash, 

 the potassium salt of azoimide was at once formed. Upon 

 distilling this with dilute sulphuric acid, an aqueous solu- 

 tion of azoimide was obtained, and eventually anhydrous 

 azoimide itself, identical in all respects with that obtained 

 by Prof. Curtius. 



Hydrazine Salt of Azoimide, N3H . N2H4. 



This interesting substance, formed by the union of equal 

 molecules of the two remarkable compounds, hydrazine 

 and azoimide, whose isolation we owe to Prof. Curtius, is^ 

 a solid substance forming large well-defined crystals. It 

 is obtained when one molecular equivalent of hydrazine 

 hydrate (the preparation and properties of which were 

 described in Nature, vol. xliii. p. 205) is added to the 

 ammonium salt of azoimide, and the mixture, placed in a 

 shallow dish, is allowed to evaporate in a desiccator. It 

 is curious, also, that by adding a very concentrated aqueous 

 solution of azoimide, obtained by distilling 60 grams of 

 the lead salt with dilute sulphuric acid, to hydrazine 

 hydrate, until litmus is turned strongly blue by the mix- 



