1914] ^- W' Thomas 217 



To the filtrate (35) solid barium hydroxide is added to strong 

 alkaline reaction and the precipitate thus f ormed is coUected on a filter 

 paper. If no precipitate is f ormed, a little more silver nitrate should 

 be added. The precipitate (36) is washed with barium hydroxide sol., 

 suspended in water, acidulated with sulfuric acid, and decomposed 

 with hydrogen sulfide. The sol. is boiled to expel hydrogen sulfide 

 and filtered from the silver sulfide. The filtrate is made slightly 

 alkaline with barium hydroxide (to remove sulfate) and the excess 

 of barium is removed by treatment with carbon dioxide, boiling and 

 filtration. The filtrate is evaporated to a small volume, nitric acid 

 is added and the mixture allowed to stand. Arginine,^^ if present, 

 will crystallize out as arginine nitrate in characteristic form. 



Arginine nitrate (anhydrous product) : m.p., about 175° C, 

 but not sharply ; easily soluble in water ; easily soluble in hot alcohol, 

 but with difiiculty in cold ; acid nitrate can be obtained by evaporat- 

 ing the neutral nitrate with excess of nitric acid ; crystallizes without 

 water of crystallization in long needles or plates, which melt at 

 145° C. ; free base crystallizes in rosette-like masses or plates melt- 

 ing at 207° C. 



The precipitate (37) is washed well with barium hydroxide sol., 

 suspended in water, acidulated with sulfuric acid, decomposed with 

 hydrogen sulfide and the excess of hydrogen sulfide removed by 

 boiling. The sol. is filtered, made alkaline with barium hydroxide 

 (the excess of the latter is precipitated with carbon dioxide), boiled, 

 filtered and evaporated to a small volume. Ammoniacal silver 

 nitrate sol. is added to the filtrate until precipitation is complete, 

 carefully avoiding an excess. The precipitate is collected on a filter, 

 washed well with water, and decomposed with dil. hydrochloric 

 acid sol. After filtering off the silver chloride, the Solution is 

 evaporated to a small volume and allowed to stand, when, if present, 

 histidine will crystallize out in the very characteristic form of his- 

 tidine di-chloride. 



Histidine di-chloride: m.p., 231° C. ; easily soluble in water; 

 crystallizes in characteristic glassy plates or prisms without water 

 of crystallization. The following diazo color reaction of Pauly 

 may be applied : Treat in alkaline sol. with diazo-sulfanilic acid, 



^5 Schreiner and Shorey: The presence of arginine and histidine in soils, 

 Jotirn. Biol. Chem., 1910, viii, p. 381. 



