GUANIDINE AND ITS DERIVATIVES 171 



Properties. 



Creatinine separates from hot saturated solutions in colourless, 

 shining prisms (Fig. 36), from cold saturated solutions in plates or 

 prisms containing 2H 2 O. It has 

 a caustic taste and its solutions 

 react slightly alkaline. It is sol- 

 uble in 1 1 -5 parts of cold water, 

 more easily in hot water, in 625 

 parts of cold absolute alcohol and 

 more easily in hot alcohol. 



It behaves as a strong alkali 

 displacing ammonia from its salts. 

 It forms salts with acids and double 

 salts with salts of the heavy metals, 

 of which the zinc chloride double 



salt is the most characteristic. 



FIG. 36. Creatinine. (After Funke.) 

 Reactions. 



Creatinine has two reactions by which its presence in a solution 

 can be detected, e.g. in urine : 



(1) Sodium Nitroprusside Reaction (Weyl). 



A few drops of a dilute freshly prepared solution of sodium nitro- 

 prusside are added to a small quantity of the solution (urine) and dilute 

 sodium hydroxide is added drop by drop. The solution becomes 

 red in colour and in a short time changes to yellow. If the yellow 

 solution be acidified with glacial acetic acid and heated, the solution 

 becomes green and a deposit of Prussian blue forms on standing. 



Note. Acetone gives a similar colour reaction, but the colour 

 changes to purple on acidifying. It is advisable to remove acetone, if 

 present, by boiling the solution before testing for creatinine. 



(2) Picric Acid Reaction (JaffiT). 



To the solution containing creatinine (urine) some saturated picric 

 acid solution is added and the mixture made alkaline with sodium 

 hydrate. The solution becomes deep orange in colour which remains 

 permanent for some hours. 



One part of creatinine in 5000 can be detected by this reaction. 



Note. Aldehyde, acetone and other compounds also reduce picric 

 acid in the cold ; glucose, fructose, urea, etc., reduce it on warming 

 (Chapman). 1 The picric acid is converted into picramic acid, amino- 

 dinitrophenol and diamino-nitrophenol. 



Analyst, 1909. 



