174 ESSENTIALS OF CHEMICAL PHYSIOLOGY 



LESSON XXV 

 UBIC ACID AND CREATININE 



1. Preparation of Pure Uric Acid. — If one wishes to prepare pure uric acid 

 the sohd iirine of a reptile or bird, which consists principally of the acid 

 ammonium salt, should be selected ; one has not then to separate any pig- 

 ment. It is boiled with 10 per cent, caustic soda or ammonia, diluted, and 

 then allowed to stand. The clear fluid is decanted and poured into a large 

 excess of water to which 10 per cent, of hydrochloric acid has been added ; 

 after twenty-four hours, crystals of iiric acid are deposited. These may be 

 purified by washing, re-solution in soda, and re-precipitation by acid. 



2. Estimation of Uric Acid (Hopkins's method). — The following reagents 

 are required : 



Pure chloride of ammonium, finely powdered. 



A wash bottle containing a filtered saturated solution of the same salt. 



A twentieth normal solution of potassium permanganate made by 

 dissolving 1'581 grammes of permanganate in a litre of water. 



Separation of uric acid from the urine. — Measure 100 c.c. of urine into 

 a beaker of about 150 c.c. capacity. 



Add to this 25 grammes (approximately weighed) of ammonium chloride, 

 stirring briskly till all the salt is dissolved. Now add 2 c.c. of strong 

 ammonium hydrate, and allow the mixture to stand until the precipitate of 

 ammonium urate, which rapidly forms, has wholly settled to the bottom of 

 the beaker ; its subsidence is promoted by occasional brisk stirring. 



Adjust a small filter paper (7 cm. diam.) in a funnel of such size that only 

 a small margin of glass projects above the edge of the folded paper, and 

 transfer to this the ammonium urate precipitate. 



Filtration should not be commenced until the precipitate has settled 

 satisfactorily, and the supernatant liquid is clear. The latter should be first 

 poured on to the filter, the precipitate being so far as possible retained in the 

 beaker until the greater part of the clear liquid has filtered through ; finally 

 transfer the whole to the filter with the help of a wash bottle containing 

 saturated ammonium chloride solution. After the filter has thoroughly 

 drained, wash the precipitate twice again with the same solution. 



While the last washings are running through the paper, distilled water 

 should be heated to boiling in a wash bottle provided with a fine jet. The 

 funnel containing the filter is now held horizontally over a small porcelain 

 basin (of about 50 c.c. capacity) and the precipitate washed into the latter 

 with a jet of hot water, the filter itself being afterwards opened out over the 

 basin in order that any urate adhering to ils folds can be washed off. Not 



