724 INFLUENCE OF FOOD PRESERVATIVES ON HEALTH. 



and one-half to four hours, with a proper return condenser attached. 

 At the end of this time the flask is cooled, the acid is neutralized, and 15 

 cc picric acid solution and 5 cc of the caustic soda solution are added. 

 The contents of the flask are thoroughly mixed and allowed to stand 

 for five minutes. It is now made up to mark and compared with the 

 half normal bichromate solution in a colorimeter. The Duboscq color- 

 imeter was used in this work. 



Ten milligrams of pure kreatinin treated in same way gives a depth 

 of color 8.1 mm of which corresponds to 8 mm of the bichromate 

 solution. The urine picrate solutions are all compared with 8 mm 

 of the half normal bichromate solution and adjusted till the depth of 

 color is the same as the standard. 



If the reading after adjustment of the urine picrate solution is 6.2 



8 1 

 mm, then 10 cc of the urine would contain 10 X 7^0 = 13. 06 mg of 



kreatinin. 



XANTHIN DETERMINATIONS ( KRUGER-SCHMID METHOD). 1 



Free 400 cc of urine from proteids by coagulation and filtration, add 

 24 grams of sodium acetate and 35 cc of 12 per cent sodium bisulphite, 

 heat to boiling and add 30 cc of 15 per cent copper sulphate. Boil 

 three minutes with careful watching and stirring. After cooling and 

 filtering, the precipitate is washed until colorless. The precipitate is 

 returned to the original beaker and 200 cc of water added. After 

 heating to boiling, 30 cc of sodium sulphid is added, then acetic acid 

 to acidity and the solution warmed on the steam bath until the copper 

 sulphid settles. Filter while warm and wash with warm water, add 

 10 cc of 10 per cent hydrochloric acid and evaporate in a 300 cc porce- 

 lain dish to a volume of 10-15 cc. During the process and on stand- 

 ing two hours the uric acid settles out. This is filtered on a small 

 filter paper washed with 3 per cent sulphuric acid until the total vol- 

 ume of filtrate and washings is 75 cc. The nitrogen of the precipitate 

 multiplied by 3 gives uric acid, to which add 3.5 mg. 



The uric acid filtrate is made alkaline with sodium hydroxid and 

 then acidified with acetic acid. After warming to 70, 1 cc of 10 per 

 cent acetic acid and 10 cc of potassium permanganate are added. 

 Shake one minute, treat with 10 cc of sodium bisulphite and 6 cc of 

 15 per cent copper sulphate, boil for three minutes, filter the wash 

 with dilute copper sulphate, and determine the nitrogen in the pre- 

 cipitate, which is that of the xanthin bases. 



a Hoppe Seyler's Thierf elder, 1903, p. 435. 



