146 KREATININ. 



with acids and salts which crystallise well. Of these the most 

 important is the salt with chloride of zinc (C^TNsO^ZnCla, both 

 on account of its characteristic crystalline form and of its general 

 insolubility in comparison with the other compounds of this sub- 



FIG. 11. KREAirxiN-ziNC-CHLORiDE CRYSTALS. (Krukenberg after Kiihne.) 



stance. Hence its formation is employed not merely for the de- 

 termination of kreatinin but for its separation from solutions. It 

 crystallises in warty lumps composed of aggregated masses of 

 prisms, or fine needles. 



This compound is formed when a concentrated neutral solution 

 of the zinc salt is added to a not too dilute solution of kreainin, 

 and since it is almost insoluble in alcohol it is frequently con- 

 venient to employ alcoholic rather than aqueous solutions of the 

 two substances. 



Preparation. 1 This does not admit of any useful brief descrip- 

 tion, but the principles involved are the following : 



(i) By the action of dilute boiling mineral acids on kreatin. 



(ii) By concentrating large volumes of urine to a small bulk. 

 From this the kreatinin is obtained as a compound either by the 

 addition of chloride of zinc or by precipitation with mercuric 

 chloride. From these compounds it is then separated by boil- 

 ing with hydrated oxide of lead, and is finally purified by 

 crystallisation. 



It may also be precipitated by phospho-tungstic and phospho- 

 molybdic acids. 2 



Apart from the characteristic formation of the compound with 

 zinc chloride, kreatinin yields several well-marked reactions, of 

 which the following are the more striking. 



1 For details see Hoppe-Seyler, Phys.-path. chem. Anal. 1883, S. 182, and 

 Neubauer u. Vogel, Horn-analyse, 1890, S. 228. 



2 For recent synthesis see Horbaczewski, loc. cit. (sub kreatin). 



