PHYSIOLOGICAL CHEMISTRY 



421 



FIG. 244. Ureometer. 



graduation corresponds to grammes of urea in the quantity of urine 

 used. 



II. MSmer-Folin Method. Principle. By the addition 

 of certain reagents to a measured quantity of urine, the 

 greater proportion of the nitrogenous bodies, except urea 

 and ammonia, are precipitated. The precipitate is removed 

 by filtration, and, after expelling the ammonia by heat, the 

 nitrogen of the filtrate is determined. This, multiplied by 

 2-143, gives the amount of urea present. 



Solutions necessary. 



1. Powdered barium hydroxide (baryta). 



2. A mixture of 1 vol. ether and 2 vol. absolute alcohol. 



3. Apparatus, etc., for Kjeldahl's nitrogen deter- 



mination. 



Determination. 5 c.c. urine are shaken in a small stop- 

 pered flask with 1'5 grm. barium hydroxide until no more 

 will dissolve : 100 c.c. alcohol-ether mixture are then added, 

 whereon a copious precipitate falls down. The flask is corked 

 and left standing over night. The contents are then filtered 

 through a small filter paper (10 cm. in diameter), the filtrate being collected in a 

 Kjeldahl combustion flask of 500 c.c. capacity. When all the solution has 

 passed through, the precipitate is washed at least three times with alcohol-ether 

 mixture, and then the flask is connected with a suction pump and placed on the 

 water-bath heated to 55 C. 1 When the liquid has been reduced to a few c.c., 

 25 c.c. water and a pinch of magnesium oxide are added to the contents and 

 the evaporation continued so as to drive off the last traces of ammonia from the 

 solution. When the volume of fluid in the flask has reached about 10 c.c. 

 the urea is determined by Folin's method. 



Folin's Method. Unless reducing substances such as sugar are present 

 this method is usually applied directly to the urine without a preliminary 

 treatment by the Morner and Folin method. 



The principle of this method depends on the fact that urea becomes completely 

 hydrolysed into carbon dioxide and ammonia, when solutions of it are heated for 

 about an hour to a temperature of 150-160 C. The hydrolysis must be performed 

 in acid reaction so that no ammonia can escape. The above temperature may 

 be obtained, either by heating under pressure (in an autoclave) or, as recom- 

 mended by Folin, by heating the urine with magnesium chloride which, after 

 the excess of water has evaporated, gives a solution boiling at 160 C. 



EXPERIMENT. Place 5 c.c. urine, 5 c.c. HC1 (con.) and 20 grm. magnesium 

 chloride in a 200 c.c. Jena flask. Connect the neck of the flask with a glass 

 trap or a wide tube, and heat fairly strongly so as to drive off the water from 

 the contents of the flask. The trap prevents too much HC1 from escaping. 

 When all the water has been boiled off (10-15 minutes) the contents of the 

 flask will change in their manner of boiling (they will behave as warm water 

 does when H 2 SO 4 (con.) is dropped into it). Now lower the flame and connect the 



x To employ the suction pump in this way to accelerate evaporation at low 

 temperature the flask is closed by a doubly-bored cork; through one hole the 

 pump is connected, through the other passes a tube ending below the surface of 

 liquid in the flask in a fine capillary point. 



