1863.] 577 



benzol (iu which it is somewhat less soluble), in well-developed white 

 plates, benzidine being always deposited from these solvents in well- 

 defined needles ; and whilst the latter is freely soluble in boiling 

 water, from which it separates on cooling in the form of a crystalline 

 mass of nacreous lustre, the former is so sparingly soluble in water 

 that it is impossible to recrystallize it from that solvent. The fusing- 

 point of hydrazobenzol is 131C., that of benzidine being 118C. 

 The basic properties of benzidine are well defined ; it dissolves even 

 in the weakest acids, such as acetic acid, in which hydrazobenzol is 

 nearly insoluble. Stronger acids, such as hydrochloric and sulphuric 

 acids, more especially on application of heat, dissolve hydrazobenzol ; 

 but the solution thus obtained contains no longer the unchanged 

 body ; the addition of alkali, fixed or volatile, produces a precipitate 

 which now possesses all the properties of benzidine. 



These characters are sufficient to individualize hydrazobenzol. 

 There is, however, another property which marks its difference from 

 benzidine in even a more conspicuous manner. Benzidine when sub- 

 mitted to a high temperature distils ; a certain portion is decomposed 

 in this process, but the larger quantity is volatilized without decom- 

 position. On heating hydrazobenzol considerably above its fusing- 

 point, a powerful reaction ensues, the heat evolved being sufficient 

 to carry over nearly the whole amount of substance in the form of a 

 deep red oil, from which, on cooling, crystals of azobenzol are depo- 

 sited. On addition of an acid the oil yields a further quantity of 

 this substance, and the acid solution is then found to contain abun- 

 dance of aniline. The reaction which occurs is simple enough. 

 2C 12 H 12 N 2 = C 12 H 10 N 2 + 2C 6 H 7 N. 

 Hydrazobenzol. Azobenzol. Aniline. 



I had hoped that among the products of the reaction paraniline 

 (C 12 H W N 2 =2C 6 H 7 N) might be met with; in this hope I have 

 been disappointed. 



The reproduction of azobenzol from hydrazobenzol may be accom- 

 plished in a variety of other ways. Nitrous acid, chlorine, bromine, 

 iodine, chromate and permanganate of potassium, and nitrate of silver 

 produce this effect in a most easy manner ; in these processes the 

 loosely adherent hydrogen is simply eliminated, no aniline being 

 formed as a secondary product. Even when moistened with alcohol 



