METHODS FOR THE DETERMINATION OF UREA. 689 



Recently FOLIN and FARMER 1 have suggested a method for the estima- 

 tion of the total nitrogen in very small quantities of urine, 1 cc. dilute 

 urine. After hydrolysis with acid the ammonia formed is colorimetrically 

 determined by means of NESSLER'S reagent. 



Among the methods suggested for the special estimation of urea, 

 that of MORNER-SJOQVIST, in combination with FOLIN'S method, is the 

 one that is generally used. 



Principle of Mvrner-Sjdqyist's Method. 2 According to this method 

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

 ammonia, hippuric acid, creatinine, and traces of allantoin, 3 are pre- 

 cipitated by a mixture of alcohol and ether after the addition of a solu- 

 tion of barium chloride and barium hydroxide, or in the presence of sugar 

 with solid barium hydroxide. The urea is determined in the concentrated 

 filtrate, after driving off the ammonia, by KJELDAHL'S nitrogen estima- 

 tion. The slight error due to the presence of hippuric acid and creatinine 

 can be prevented according to MORNER by a combination of his method 

 with FOLIN'S method. 



Principle of Folin's Method. 4 On heating urea with hydrochloric 

 acid and crystalline magnesium chloride, which melts in its water of 

 crystallization at 112-115 C. and then boils at about 150-155 C., the 

 urea is completely decomposed, while no appreciable decomposition 

 of the hippuric acid and creatinine takes place. The ammonia produced 

 from the urea is distilled off and determined by titration. The amount 

 of ammonia previously existing in the urine must be specially determined. 



Determination of Vrea by the Morner-Sjoqvist and Folin Method. 5 

 Five cc. of the urine are treated with 1.5 grams of powdered barium 

 hydroxide, and when as much of this is dissolved as possible by gently 

 mixing, it is precipitated by 100 cc. of the alcohol and ether mixture 

 (J vol. ether). On the following day it is filtered and the precipitate 

 washed with the alcohol and ether mixture. The alcohol and ether 

 are distilled off from the filtrate at about 55 C. (not above 60 C.). The 

 remaining liquid is treated with 2 cc. of hydrochloric acid of sp.gr. 

 1.124 (for 5 cc. urine), and carefully transferred to a flask of 200 cc. 

 capacity, and evaporated to dryness on the water-bath. Then add 20 

 grams of crytalline magnesium chloride to the contents of the flask 

 and 2 cc. of concentrated hydrochloric acid, and boil on a wire gauze 

 over a small flame for two hours, making use of a proper return cooler. 



1 Journ. of biol. Chem., 11. 



2 Skand. Arch. f. Physiol., 2, and Morner, ibid., 14, where the recent literature 

 may also be found. 



3 According to Wiechowski, Hofmeister's Beitrage, 11, the quantity of allantoin 

 is so great iji urine that it must be considered in this method. 



4 Zeitschr. f. physiol. Chem., 32, 36 and 37. 

 6 See Morner, Skand. Arch, f . Physiol., 14. 



