THE URINE. 355 



a brownish-black or, in the presence of only 0.002 milligram uric 

 acid, a yellow spot (SCHIFF'S test). 



Preparation of Uric Acid from Urine. Filtered normal urine is 

 treated with 20-30 c. c. of 25$ hydrochloric acid for each litre 

 of urine. After forty-eight hours collect the crystals and purify 

 them by redissolving in dilute alkali, decolorizing with animal char- 

 coal and reprecipitating with hydrochloric acid. Large quantities of 

 uric acid are easily obtained from the excrements of serpents by 

 boiling them with dilute caustic potash until no more ammonia is 

 developed. A current of carbon dioxide is passed through the 

 filtrate until it barely has an alkaline reaction; dissolve the 

 separated and washed acid potassium urate in caustic potash, and 

 precipitate the uric acid by addition of an excess of hydrochloric 

 acid to the filtrate. 



Quantitative Estimation of Uric Acid in the urine. The older 

 method of HEINTZ, somewhat modified by SCHWANERT, is in its- 

 main points as follows : The filtered urine free from albumin and 

 any sediment of urates (dissolved by warming) is concentrated 

 when too dilute to a sp. gr. of 1.020, 200 c. c. measured off and 

 this treated with 10-20 c. c. hydrochloric acid of a sp. gr. of 1.12. 

 After allowing this mixture to stand forty-eight hours in a cool 

 place the precipitated uric acid is collected on a small weighed 

 filter (5-6 cm. diameter), and the crystals which have adhered to 

 the sides of the glass are removed by means of a glass rod tipped 

 with a piece of rubber tubing, using the filtrate to wash with. 

 After all the liquid has passed through, fill the filter with water 

 and allow it to run through completely before adding more water; 

 continue until the wash-water does not give a chlorine reaction, 

 then dry and weigh. A part of the uric acid always remains dis- 

 solved in the filtrate. The filtrate, including the wash-water, must 

 therefore be measured, and for each 10 c. c. of filtrate (and wash- 

 water) 0.00048 grm. uric acid must be added. With this correc- 

 tion this determination gives the same results as the following 

 more complicated method. 



In SALKOWSKI and LTJDWIG'S method the uric acid is precip- 

 itated from the urine by silver-nitrate solution, treated with 

 magnesium mixture, and the uric acid removed from the silver 

 precipitate and weighed. Uric-acid determinations according to 

 this method are often performed according to the treatment sug- 

 gested by E. LUDWIG, which requires the following solutions : 



1. An AMMONIACAL SILVER-NITRATE solution which contains in one litre 

 26 grms. silver nitrate and a quantity of ammonia sufficient to completely 

 reklissolve the precipitate produced by the first addition of ammonia. 

 2. MAGNESIUM MIXTURE. Dissolve 100 grms. crystallized magnesium chlo- 

 ride in water and add enough ammonia so^that the liquid smells strongly of it, 



