134 THE SIMPLER NATURAL BASES 



composes between 200 and 240 without melting. The aurichloride, 

 C 5 H 9 N 3 . (HAuCl^, melts with decomposition at 200-210. 



The dipicrate, C 5 H 9 N 3 . (C 6 H 3 O 7 N 3 ) 2 , is the most convenient salt for 

 purposes of isolation. It forms deep yellow rhombic leaflets, melting 

 at 238-242 (corr.) according to the rate of heating. It is very spar- 

 ingly soluble in cold water and can be recrystallised from hot water. 

 The monopicrate, C 5 H 9 N 8 . C 6 H 3 O 7 N 3 , m.p. 233-234, forms bunched, 

 slightly curved, pointed needles. 



The dipicrolonate, C 5 H 9 N 3 (C 10 H 8 O 5 N 4 ) 2 , dissolves in about 450 parts 

 of boiling water, from which it crystallises in sheaves of needles, melt- 

 ing at about 264. 



Reactions of $-iminazolyl-ethylamine. In common with histidine, 

 this amine gives Pauly's reaction with p-diazobenzene sulphonate ; a 

 very distinct rose pink coloration is still obtainable at a dilution of 

 I : 10,000. It also gives Knoop's histidine reaction, a claret colora- 

 tion, on boiling with bromine water. It is precipitated by ammoniacal 

 silver oxide, by mercuric chloride in the presence of potassium 

 hydroxide, and by phosphotungstic acid. On the other hand, it is 

 distinguished from histidine in not giving the biuret reaction, nor 

 Ruhemann's reaction with triketohydrindenehydrate, and it further 

 behaves differently on benzoylation. When shaken with benzoyl- 

 chloride in potassium hydroxide solution, the glyoxaline ring is rup- 

 tured and tribenzoyl-butentriamine is formed, of the following con- 

 stitution : 



CH . NH . CO . C 8 H S 



C . NH . CO . C 8 H, 



CH 4 . CHj . NH . CO . C 8 H S . 



Histidine, on the other hand, yields a monobenzoyl derivative. 



