LESSON XXV 

 URIC ACID AND CREATININE 



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

 the solid urine 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 uric 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 dis- 

 solving 1-581 grammes of permanganate in a litre of water. 



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 

 ammonia, 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. The precipitate should be as 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 its folds may be washed off. Not 

 more than 20-30 c.c. of water need be employed in this transference : if much 

 more has been used the liquid should be concentrated over the water-bath at 



