442 CHEMISTBY OF THE LEUCOMAINS. 



difficultly soluble in boiling water. It melts and decomposes at 

 186°- 189°. Potassium mercuric iodid alone gives no precipitate 

 but on addition of sodium hydrate a heavy white precipitate forms. 

 Potassium bismuth iodid gives a red precipitate. The picrate melts 

 at 205°. 



The addition of phosphotungstic acid to solutions of the nitrate 

 produces a pulverulent precipitate which, recrystallized from boiling 

 water, forms very small prisms or needles. It is soluble in large 

 excess of the reagent. 



Dibenzoyl arginin, Q^^^{(i^yCO)^f)^, is obtained readily, 

 though the yield is small. On treatment with benzoyl chlorid a 

 slight sticky precipitate forms and from the filtrate the dibenzoyl 

 compound is thrown down on acidulation and is separated from ben- 

 zoic acid by means of ether. From boiling water it crystallizes in 

 masses of very fine long needles or rhombic plates. The needle- 

 shaped crystals are often branched, or stellate and show split ends. 

 It is difficultly soluble in boiling water ; more readily in boiling alco- 

 hol ; easily in alkali. It melts with slight decomposition at 217°— 

 218°. This body is analogous to ornithuric and lysuric acids. 



Histidin, CgHgNjO^ . — As yet nothing definite is known regarding 

 the constitution of this base. From the small amount of hydrogen 

 present it would seem that the structure of histidin must be that of 

 a closed chain. When it is remembered that cadaverin on dry dis- 

 tillation yields piperidin (p. 273), it does not seem improbable but 

 that arginin, the parent substance of cadaverin, may in a similar 

 manner, by closing the chain yield histidin. The change in the case 

 of cadaverin is represented thus : 



NH,.CH,.C!H,.CH,.CH.,CH,.NH, = g X 6h "^ ^^'" 

 Cadavbbin. Piperidin. 



The transformation of arginin into histidin would in a similar way 

 be represented by the equation : 



ITT ?^H CHCOOH 



r^ 1 Aft 



■NH = I P 



[ C.NH CH, 



m.CH,.CHj.CH,.CH(NHj).COOH -^-^ ^g 



+ NH,. 



Aboinin. Histidin (?) 



If the above change is correct histidin would possess the formula- 



