THE URINE. 189 



concentrated it must be correspondingly diluted), in a meas- 

 uring-cylinder, add 50 cc. of magnesia mixture, to precipitate 

 the phosphoric acid, then dilute with water to 300 cc. and 

 filter at once through a dry filter into a dry vessel. Measure 

 off 200 cc. of the filtrate and add 10 to 15 cc. of a 3 per cent, 

 solution of silver nitrate. The precipitate must be flocculent 

 and gelatinous; if it appears white, it contains too much 

 silver chloride, then some ammonia must be added and the 

 liquid well stirred. Single white spots of silver chloride in 

 the precipitate do no harm; they are without influence on 

 the accuracy of the uric acid determination. Let the pre- 

 cipitate settle, take out a small portion of the supernatant 

 liquid with a pipette, place it in a test-tube, and acidify with 

 nitric acid. The fluid must become cloudy from the forma- 

 tion of silver chloride an indication that an excess of silver 

 is present. If it does not do this, make the test-fluid alkaline 

 again with ammonia, pour it back into the fluid containing 

 the precipitate, and then add a few cubic centimeters more of 

 the silver solution. Sometimes it is also necessary to add some 

 more ammonia. Let the precipitate settle again and repeat 

 the test. Now filter off the precipitate through an ordi- 

 nary smooth filter (e.g., Schleicher and Schull, No. 597), 

 and carefully remove the precipitate sticking to the glass 

 by means of a glass rod and water, so that none of it is 

 lost. The precipitate is washed on the filter with water 

 until a portion of the filtrate, when acidified with nitric acid, 

 remains clear (absence of silver) and also shows only a very 

 slight turbidity when silver nitrate is afterwards added 

 (small amount of chlorides). Now place the funnel in a 400- 

 500-cc. flask, pierce the filter, and carefully wash the precipi- 

 tate into the flask and shake thoroughly. The volume of 

 the mixture should amount to about 200-250 cc. Acidify 

 with a few drops of hydrochloric acid, pass in hydrogen sul- 

 phide, shaking frequently, until the fluid is saturated, then 



