722 



INFLUENCE OF FOOD PRESERVATIVES ON HEALTH. 



METHODS OF ANALYSIS EMPLOYED AND COMPARISON OF RESULTS. 



UREA DETERMINATIONS. 



Two methods of determining- the urea, which are regarded as the 

 best of those in use, were employed, and the data obtained were com- 

 pared. These were the Morner-Sjoqvist and the Braunstein method. 

 The principle of the Morner-Sjoqvist method depends on the fact that 

 the nitrogenous constituents of the urine, with the exception of urea, 

 ammonia, hippuric acid, and kreatinin, are precipitated by means of a 

 solution of barium chlorid and barium hydroxid (50 grams Ba(OH) 3 

 and 350 grams BaCl 2 per liter) and a mixture of alcohol and ether 

 (2:1); 5 cc of urine, 5 cc of the barium solution, and 100 cc of the 

 alcohol-ether solution are mixed and allowed to stand over night. It 

 is then filtered into a beaker or porcelain dish and the precipitate 

 washed with 50 to 75 cc of the alcohol-ether mixture. The filtrate is 

 then evaporated at a temperature not exceeding 55 C., and when 

 solvents have disappeared a small quantity of water is added and about 

 0.5 gram of magnesium oxid. It is then evaporated to dry ness or till 

 the fumes are no longer alkaline. The residue is transferred into a 

 Kjeldahl flask and nitrogen determined in the usual manner. The nitro- 

 gen found is calculated to urea by multiplying by the factor 2. 1407. 



According to Braunstein the above method is inapplicable in the pres- 

 ence of hippuric acid. His modification of the method consists in 

 taking up the evaporated residue in a small quantity of water and 

 adding 10 grams of crystallized phosphoric acid and heating in an air 

 bath for four and one-half hours at 140-145 C. The residue is then 

 transferred to a Kjeldahl digestion flask and nitrogen determined. 



In the following table are given the comparative date obtained by 

 the two methods on the daily samples and the composite samples: 



TABLE III. Comparison of the two methods for the determination of urea. 



