December lo, 1891] 



NATURE 



129 



by percussion, but do explode when heated to a tempera- 

 ture which is higher than in the case of most other salts of 

 azoimide. The explosion is accompanied by the produc- 

 tion of a brilliant yellow flame and a detonation which is 

 less loud than in the case of other salts. The salt is 

 not volatile, and is not changed by evaporation of its 

 aqueous solution. 



Preparation and Properties of the Ammonium Salt, 

 NH4— N< !| . 



The ammonium salt, which is by far the most convenient 

 salt to start with for the preparation of the free acid and 

 its metallic salts, is best prepared from the curious diazo 

 compound of the amide of hippuric acid, CoHgCO — 

 NHCH2C0—NH—N:=N— OH, before mentioned. This 

 substance is readily obtained in calculated quantity 

 by first acting with hydrazine hydrate upon the ethyl 

 ether of hippuric acid, and subsequently treating the 

 hippuryl hydrazine thus produced with sodium nitrite 

 and glacial acetic acid. Diazo-hippuramide appears to 

 be most prolific in its reactions. Prof. Curtius states 

 that it reacts with almost every class of organic and 

 inorganic bodies with which he has brought it in contact, 

 and generally without the application of external heat. 

 Thus, when treated with water, alcohol, haloid ethers 

 (alkyls), aldehydes, free halogens, or hydrazme deriva- 

 tives of organic acids, it evolves free nitrogen gas, and 

 forms compounds which are derived from hippuramide 

 by replacement of a hydrogen atom in the iN H, group 

 by the radicle of the reacting substance. On the other 

 hand, when acted upon by alkalies, ammonia or 

 substituted ammonias (amines), or by diamide (hydra- 

 zine) and its derivatives, salts of azoimide are formed. 

 Thus last reaction, when ammonia is employed, forms 

 the most convenient mode of obtaining the ammonium 

 salt of azoimide. 



About a pound of diazo-hippuramide is placed in a 

 flask of 2 litres capacity, and covered with 600 grams 

 of 85 per cent, alcohol. The flask is then placed in a 

 freezing mixture, and ammonia gas is led in until the 

 liquid is saturated with it. The flask and contents are 

 then allowed to stand twenty-four hours in order to com- 

 plete the reaction, when the diazo compound is quanti- 

 tatively converted into hippuramide and the ammonium 

 salt of azoimide : 



CgHsCO— NHCHoCO— NH— N— N— OH + 2NH3 



= CgHsCO— NHCH2CONH2 + NH4-N3 -I- H2O. 



The liquid is then boiled, the flask being fitted with an 

 upright condenser, until no more ammonia escapes, when 

 the heat is removed, and the solution allowed to cool. After 

 standing another twelve hours, the clear alcoholic solution 

 is decanted from the mass of hippuramide crystals, and 

 treated with four times its volume of ether, when 70 per 

 cent, of the total yield of the ammonium salt is precipi- 

 tated in the form of a white powder. The remaining 30 

 per cent, of the azoimide may be recovered by recrystal- 

 lizing the hippuramide from water, adding the mother- 

 liquor to the ethereal-alcoholic solution after removal 

 of the precipitated ammonium salt, and treating the 

 whole of the liquid with solutions of lead, silver, or 

 mercurous salts, when the azoimide is precipitated in the 

 form of the difificultly soluble lead, silver, or mercurous 

 salts. The hippuramide is readily converted, by boiling 

 with hydrazine hydrate, into hippuryl hydrazine, which 

 may thus be used again for the preparation of more of 

 the diazo compound. 



The precipitated ammonium salt is washed with ether 

 and dried in the air. The snow-white crystalline powder 

 thus obtained, consisting of fine anisotropic needles, 

 may be recrystallized from boiling alcohol. It is only 



NO. I I 54, VOL. 45] 



sparingly soluble in absolute alcohol, but on boiling for 

 some time in a flask fitted with inverted condenser, the 

 whole passes into solution. Upon cooling, the salt sepa- 

 rates out in large colourless crystals, tabular in form, and 

 frequently aggregated in step or fan-shaped forms. These 

 aggregates often resemble those of ammonium chloride 

 very closely, but the crystals do not belong to the cubic 

 system. The crystals are readily soluble in water, and, 

 upon allowing the aqueous solution to evaporate in vacuo, 

 large transparent prisms are obtained, which, however, 

 soon become turbid in air. 



The ammonium salt of azoimide reacts in a feebly 

 alkaline manner. It is not hygroscopic, although so 

 readily soluble in water. It dissolves easily in 80 per 

 cent, alcohol, but, as above described, with difficulty in 

 absolute alcohol. It is insoluble in ether and benzene. 

 It is distinguished by its great volatility. When the 

 crystals are allowed to lie exposed to air, they gradually 

 disappear, eventually passing away entirely in the form 

 of vapour. Upon gently warming a small quantity of the 

 salt ill a test-tube to a temperature very slightly superior 

 to 100°, it sublimes like ammonium chloride, condensing 

 again, however, in brilliant little prisms. This operation 

 requires great care, for if the heating proceeds too 

 rapidly the substance explodes with great violence. 



As may be expected, great difficulties were met with in 

 obtaining an analysis of a substance so explosive. Upon 

 attempting to determine its composition by combustion 

 with copper oxide in a stream of dry air, the apparatus 

 was destroyed upon each occasion with a fearful detona- 

 tion. Only one-tenth of a gram of the salt was em- 

 ployed, placed in a small platinum boat. At first the 

 compound sublimed out of the boat into the cooler por- 

 tion of the combustion tube ; the little sublimed crystals 

 then commenced to fuse into yellow drops, and imme- 

 diately this occurred, in each experiment, the tube was 

 shattered to fragments with a frightful report. The 

 platinum boat was in each case torn to fine splinters. 

 Eventually, however. Prof. Curtius succeeded in obtain- 

 ing a satisfactory analysis by performing the combustion 

 with copper oxide in a stream of carbon dioxide 



The ammonium salt may be readily converted into the 

 sodium salt by evaporation with caustic soda upon a 

 water- bath. 



Preparation and Properties of Free Azoimide, H — Nx" 1 1. 



N 



An aqueous solution of azoimide may be prepared by 

 distilling any of its salts, preferably the sodium or silver 

 salts, with dilute sulphuric acid. It is more conveniently 

 obtained, however, by dissolving the crystals of diazo- 

 hippuramide in dilute caustic soda, warming the solution 

 for a short time upon a water-bath, so as to insure the 

 formation of the sodium salt, and subsequently distilling 

 the liquid with dilute sulphuric acid. The latter is 

 allowed to drop slowly from a dropping funnel upon the 

 soda solution contained in a flask and maintained at the 

 temperature of ebullition. The flask is connected with a 

 condenser, and the azoimide, as it escapes, is carried 

 along with the steam, and condenses in the receiver in 

 the form of an aqueous solution. This solution may be 

 concentrated by precipitating it with silver nitrate, col- 

 lecting the insoluble silver salt, and distilling it with 

 sulphuric acid diluted with eight times its volume of water. 



The aqueous solution of azoimide possesses a most 

 intolerable odour. 



Free azoimide itself may be obtained by the fractional 

 distillation of the concentrated aqueous solution thus 

 prepared. The first fraction is collected separately and 

 refractioned. Upon repeating this process with four 

 successive first fractions, an acid containing over 90 per 

 cent, of azoimide is obtained, which distils at about 45°. 

 The last 10 per cent, of water may be completely removed 



