348 PHYSIOLOGICAL CHEMISTRY. 



cold absolute alcohol for solution, but it is more soluble in warm 

 alcohol. It is nearly insoluble in ether. In alkaline solution crea- 

 tinin is converted into creatin very easily on warming. 



Creatinin gives an easily-soluble crystalline combination with 

 hydrochloric acid. A solution of creatinin acidified with mineral 

 acids gives crystalline precipitates with phospho-tungstic or phos- 

 pho-molybdic acids, even in very dilute solutions (1 : 10,000) (KER- 

 KEE). It is precipitated, like urea, with mercuric-nitrate solution. 

 Among the compounds of creatinin, that with zinc chloride, crea- 

 tinin zinc chloride (C 4 H 7 N 3 0) 2 ZnCl2 , is of special interest. This 

 combination is obtained when a sufficiently concentrated solution 

 of creatinin in alcohol is treated with a concentrated, faintly-acid 

 solution of zinc chloride. Free mineral acids dissolve the combina- 

 tion, but this, however, is prevented, when they are present, by an 

 addition of sodium acetate. In the impure state, as ordinarily ob- 

 tained from urine, creatinin zinc chloride forms a sandy, yellowish 

 powder which under the microscope appears as fine needles 'form- 

 ing concentric groups, mostly complete rosettes or yellow balls or 

 tufts, or grouped as brushes. On slowly crystallizing, or when 

 very pure, more sharply-defined prismatic crystals are obtained. 

 This combination is sparingly soluble in water. 



Creatinin acts as a reducing agent. Mercuric oxide is reduced 

 to metallic mercury, and oxalic acid and methylguanidin (methyl- 

 uramin) are formed. Creatinin also reduces copper hydroxide in 

 alkaline solution, forming a colorless soluble combination, and only 

 after continuous boiling with an excess of copper salts is free sub- 

 oxide of copper formed. Creatinin interferes with TROMMER'S test 

 for sugar, partly because it has a reducing action and partly by 

 retaining the copper suboxide in solution. The combination with 

 copper suboxide is not soluble in a saturated-soda solution and if 

 a little creatinin is dissolved in a cold, saturated-soda solution and 

 then a few drops of FEHLIISTG'S reagent added, a white flocculent 

 combination separates after heating to 50-60 C. and then cooling 

 (v. MASCHKE'S reaction). An alkaline bismuth solution (see Sugar 

 Tests) is not reduced by creatinin. 



If we add a few drops of a freshly-prepared very dilute sodium 

 nitroprusside (sp. gr. 1.003) to a dilute creatinin solution (or to 

 the urine) and then a few drops of caustic soda, a ruby-red liquid 



