CREATININE. 661 



with zinc chloride, creatinine-zinc chloride, (C-jH^NaO^ZnC^, is of special 

 interest. This combination is obtained when a sufficiently concentrated 

 solution of creatinine in alcohol is treated with a concentrated, faintly 

 acid solution of zinc chloride. Free mineral acids dissolve the com- 

 pound, hence they must not be present; this, however, may be prevented 

 by an addition of sodium acetate. In the impure state, as from 

 urine, creatinine-zinc chloride forms a sandy, yellowish powder which 

 under the microscope appears as fine needles, forming 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. The compound is slightly soluble in water. 



Creatinine acts as a reducing agent. Mercuric oxide is reduced to 

 metallic mercury, and oxalic acid and methylguanidine (methyluramine) 

 are formed. Creatinine also reduces cupric hydroxide in alkaline solution, 

 forming a colorless soluble compound, and only after continued boiling 

 with an excess of copper salt is free suboxide of copper formed. Creat- 

 inine interferes with TROMMER'S test for sugar, partly because it has a 

 reducing action, and partly by retaining the copper suboxide in solution. 

 The compound with copper suboxide is not soluble in a saturated soda 

 solution, and if a little creatinine is dissolved in a cold saturated soda solu- 

 tion and then a few drops of FEHLING'S reagent added, a white flocculent 

 compound separates after heating to 50-60 C. and then cooling (v. 

 MASCHKE'S 1 reaction) . An alkaline bismuth solution (see Sugar Tests) 

 is not reduced by creatinine. 



An aqueous solution of creatinine is precipitated by picric acid. 

 The precipitate consists on recrystallization from hot water, of thin, 

 silky, pale yellow needles (JAFFE). If the urine is treated with picric 

 acid (20 cc. of a 5-per cent solution in alcohol for each 100 cc. urine), 

 then a double picrate of creatinine and potassium is precipitated (JAFFE). 

 If a solution of creatinine in water (or mine) is treated with a watery 

 solution of picric acid and a few drops of a dilute caustic-soda solution, 

 a red coloration, lasting several hours, immediately occurs at the ordinary 

 temperature, which turns yellow on the addition of acid (JAFFE's 2 reac- 

 tion). Acetone gives a more reddish-yellow color. Dextrose gives 

 with this reagent a red coloration only after heating. 



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

 prusside solution (sp.gr. 1.003) to a dilute creatinine solution (or to the 

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

 which quickly turns yellow again (WEYL'S S reaction). If the cold 

 yellow solution is neutralized and treated with an excess of acetic acid, 



1 Zeitschr. f. analyt. Chem., 17. 



2 Zeitschr. f. physiol. Chem., 10. 



3 Ber. d. deutsch. chem. Gesellsch., 11. 



