138 THE SIMPLER NATURAL BASES 



of meat extract, and Kutscher himself obtained 3 grm. of ignotine 

 from I Ib. of Liebig's extract. 



The free base, C 9 H 14 O 3 N 4 , crystallises in needles, soluble in 3-2 parts 

 of water at 25 and appreciably so in alcohol ; m.p. 248-5 - 250 ; [a] D 20 

 = 21, independent of the dilution. A 2-5 per cent, aqueous solution 

 gives no precipitate with platinic chloride, but it causes turbidity with 

 picric acid and a precipitate with gold chloride and potassium bismuth 

 iodide. 



The nitrate, C 9 H 14 O 3 N 4 . HNO 3 , melts at 219 and dissolves in 1^04 

 parts of water at 25; [a D 20 ] in 1-48 per cent, solution = +24*2, in 8 

 per cent, solution = +22*8; excess of nitric acid lowers the rotation 

 [Gulewitsch, 1913]. 



The copper salt, C 8 H 14 O 3 N 4 . CuO, forms deep blue six-sided plates, 

 resembling cystine crystals in shape. It is sparingly soluble in hot 

 water and results when carnosine is boiled with copper carbonate. 



Carnosine yields a sparingly soluble dipicrolonate, of which 

 Mauthner [1913] has attempted to use the mono-sodium salt as a 

 means of estimating carnosine in the histidine fraction of muscle 

 extracts. 



Carnosine resembles arginine and differs from histidine in requir- 

 ing a fixed alkali for its precipitation as silver compound from a solu- 

 tion of carnosine nitrate containing an equimolecular amount of silver 

 nitrate. With silver nitrate in excess the silver compound is also 

 precipitated by careful addition of ammonia, but is soluble in excess. 

 Demjanowski [1912, Ch. V, methyl-guanidine] gives the following 

 limits of precipitation in aqueous solution : mercuric chloride, 

 i : 2000 ; mercuric sulphate, I : 100,000 ; mercuric nitrate, I : 100,000 ; 

 25 per cent, phosphotungstic acid, I : 20,000. 



Urocanic Acid. 



Preparation. Jaff obtained the substance by a very simple 

 method. The urine was evaporated to a syrup and the latter was 

 extracted with hot alcohol ; after evaporation of the alcohol the 

 residue was acidified with sulphuric acid ; after washing with ether to 

 remove impurities the urocanic acid crystallised from the aqueous 

 layer. Hunter used phosphotungstic acid for the isolation of urocanic 

 acid and this is probably also the most certain method of obtaining 

 it from urine. The amount when present in urine is not inconsider- 

 able; Jaffe obtained '2-3 grm. per day and Siegfried found the urine 

 to contain O'i8 per cent, of the substance. 



Jaffe gave the formula C 12 Hi 2 O 4 N 4 , 4H 2 O to the free acid, but this 



