BY DR. LAUDER BRUNTON. 551 



* 196. Determination of the Amount of Uric Acid 

 in Urine. Uric acid is usually determined by precipitation 

 with dilute nitric or hydrochloric acid, the crystalline precipi- 

 tate being washed, dried, and weighed. 



Take 200 c. c. of the urine and add to it 5 c. c. of dilute hy- 

 drochloric acid of density 1.11. Set aside in a cellar for 24 

 hours. Collect the uric acid on a weighed filter, and wash 

 thoroughly with distilled water. Dry the filter and uric acid 

 in a water oven at a temperature of 100 C. Allow the dried 

 filter to cool under an exsiccator (in watch glasses, etc.) and 

 weigh. The weight of the filter and uric acid, minus the weight 

 of the filter paper, gives the amount of uric acid precipitated. 

 To this must, however, be added the quantity of uric acid 

 which has been held in solution by the urine and hydrochloric 

 acid, and by the washings of the filter. The whole of these 

 fluids are therefore mixed and measured, and for every 100 c. c. 

 0.0038 grammes of uric acid must be calculated (Neubauer). 

 The number thus calculated, added to that of the uric acid col- 

 lected on a filter, gives the amount of uric acid contained ^ 

 the urine. The number is, however, only an approximation co 

 the truth. 1 



**197. Determination of the Amount of Phosphoric 

 Acid contained in Urine. The phosphoric acid contained 

 in urine exists partly in a state of combination with the alka- 

 line earths, magnesia, and lime, but chiefly in combination with 

 alkalies. If we render the urine alkaline by the addition of am- 

 monia, the former are precipitated, leaving the alkaline phos- 

 phates in solution. It is customary to state the amount of 

 phosphoric anhydride corresponding to phosphoric acid in the 

 urine. In determining the quantity of phosphoric acid in urine, 

 we may merely determine the total quantity existing in the 

 fluid, or we may determine the total quantity first, and then 

 the quantity which remains after the precipitation of the earthy 

 phosphates. 



The volumetric method for the determination of phosphoric 

 acid in urine is based upon the following reactions: 



(a) When a solution of a phosphate acidulated with acetic 

 acid is treated with a solution of nitrate or acetate of uranium, 

 a precipitate falls which is composed of uranium phosphate. 



(6) When a soluble salt of uranium is added to a solution of 

 potassium ferrocyanide, a reddish-brown precipitate or color is 

 developed. 



Preparation of Standard Solutions of Uranium, etc. Before 

 preparing this solution, it is advisable to make a standard solu- 



1 The reader is referred to the recent researches of Dr. Salkowsky, in 

 Virchow's Archiv. Bd. 52, and of Maly, Pfliiger's Archiv. 1872, vol. vi. 

 p. 201. 



