52 HANDBOOK FOE BIO-CHEMICAL LABORATORY. 



and allow it to stand in a cold place for several days, when 

 allantoin and magnesium phosphate crystallize out, with ge- 

 latinous magnesium urate. Now dilute with water, stir, and 

 decant the liquid from the allantoin and magnesium-phos- 

 phate crystals. Eepeat this several times, and boil the crystals 

 with water after having added some animal charcoal; filter 

 while hot; faintly acidify the filtrate with HC1, which keeps 

 the phosphates in solution, and allow to crystallize. Purify 

 by recrystallization from water. ( W'ohler.) 



2. Make a thin paste of uric acid and water, heat nearly to 

 boiling, and add in small quantities a thin paste of finely 

 ground lead peroxide with water, continually stirring until 

 the chocolate-brown color of the mixture just disappears. 

 (Care must be taken not to have an excess of lead peroxide.) 

 If the mass has become too thick, some water may be added 

 during the operation; now filter while hot, and allow to cool. 

 After crystallization the mother-liquor is concentrated by 

 evaporation so as to obtain more allantoin. The preparation 

 is purified by repeated crystallization from small amounts of 

 boiling water. (K. Hoffmann.) 



3. Treat 3 mols. uric acid, subdivided in water, with 1 mol. 

 potassium permanganate, taking care that the mixture does 

 not get warm. Filter quickly, supersaturate with acetic acid 

 and allow to stand 24 hours, when crystals of allantoin will be 

 formed. (K. Hoffmann?) 



Properties. Allantoin is a colorless substance, often crys- 

 tallizing in prisms, or, when prepared from calf urine, as small, 

 thin columns. It is soluble in 160 parts cold (20 C.) and 30 

 parts boiling water. It is insoluble in cold absolute alcohol 

 and ether. Allantoin combines with acids and bases, forming 

 salts. "With silver oxide and mercuric oxide it forms im- 

 portant combinations. Allantoin reduces Fehling's solution 

 on continued boiling. 



