1892.] On the Estimation of Uric Acid in Urine. 95 



precipitation, but, as stated above, two hours is amply sufficient in 

 the case of urine. (Vide note (5), infra'). 



The process of estimation in urine may be carried out as follows : 



To 100 c.c. of the urine, finely-powdered pure ammonium chloride 

 is added in excess, about 30 grammes being necessary. The solution 

 is allowed to stand for two hours, with occasional stirring, and the 

 precipitate then filtered off through a thin filter paper. 



The precipitate is then washed with a saturated solution of 

 ammonium chloride. If a few crystals of the solid salt used for pre- 

 cipitation are still un dissolved at the time of filtration, it is of no 

 disadvantage ; the light flocculent urate is easily washed first on to 

 the filter, the crystals being then dissolved in a minimum of distilled 

 water and used for washings. 



After it has been washed twice or thrice with the saturated 

 chloride solution, the urate is washed off the paper into a small 

 beaker by means of a jet of hot distilled water. 



The ammonium urate is then decomposed by boiling with a slight 

 excess of HOI, the solution concentrated, if necessary, and the uric 

 acid allowed to separate out. It may be finally determined by any 

 accustomed method. (Vide, however, note (c), infra). 



Notes. 



(a.) The ammonium chloride used must be pure. Since 30 grammes 

 are used to precipitate 100 c.c. of urine, and only some 30 40 milli- 

 grammes of uric acid finally weighed, it is obviously fatal to the 

 accuracy of the process if even a very small percentage of insolu- 

 ble matter is present in the salt. In some samples, sold as pure, I 

 have found appreciable quantities of sand, and, in others, an amount 

 of fibre from the filter used in the preparation of the salt equal to 

 2 3 milligrammes in the 30 grammes. Other mineral salts of 

 ammonia will precipitate the urate on saturation, but none are so 

 satisfactory as the chloride. 



(6.) The presence of free ammonia greatly accelerates the separa- 

 tion of ammonium urate after saturation with ammonium chloride. 



The addition of AmHO to urine obviously involves the separation 

 of phosphates. But, if the samples be first saturated with the 

 chloride, and the hydrate subsequently added, the separation of 

 urinary phosphates is greatly modified. No gelatinous precipitate 

 comes down, but only a small quantity of triple phosphate crystals, 

 such as neither adds appreciably to the bulk of the urate precipitate 

 nor increases the difficulty of filtration (this is rendered evident if 

 the precipitate produced by AmCl in an acid urine be first filtered off 

 and AmHO added to the filtrate). 



If, therefore, time is of special importance, AmHO may be safely 



