THE ORGANIC CONSTITUENTS OF THE UHINE. 245 



To 25 or 50 c.c. of urine, placed in an areometer cylinder about 45 

 cm. high and 5 cm. in diameter, there are added 8 or 16 grammes of 

 sodium chloride, according to the amount of urine, 5 to 10 c.c. of 

 petroleum or toluol, and 1 or 2 grammes of sodium carbonate. The 

 sodium chloride is added to prevent decomposition. A current of 

 air is driven through the urine, carrying off the ammonia set free 

 by the sodium carbonate ; this is absorbed by passing through a 

 definite amount of r ^ normal acid, the excess of which is after- 

 ward titrated and the ammonia calculated (1 c.c. of -j^ sulphuric 

 acid corresponds to .0017 gramme of ammonia. The length of time 

 necessary for the completion of the operation will depend upon the 

 amount of air passing through the liquid, as well as upon the 

 temperature. At 22-25 C. and with an air current of approxi- 

 mately 700 liters per hour, the ammonia will be completely driven 

 off from 25 c.c. of urine in an hour and a quarter, or from 50 c.c. 

 in an hour and a half. With a larger volume of urine, a smaller 

 air current, or lower temperatures of the urine, a longer time will 

 be necessary. The requisite time must be learned for each air 

 current. This can easily be done by continuing the operation, 

 until in an hour there is no ammonia given off. It is necessary to 

 pass the air through a tuft of absorbent cotton, or closely packed 

 glass wool, after it leaves the urine and before it passes through the 

 acid, in order to prevent alkali from being carried over. The air 

 current should be uniform and constant. Folin uses a specially 

 constructed tube, for the absorption of the ammonia by the acid. 

 Where this is not done, it will usually be found necessary to pass 

 the air through two successive portions of acid to prevent loss of 

 ammonia. 



Folin employs alizarin red as indicator ; 2 drops of a 1 per cent, 

 solution suffice. The titration is carried to the red point, not to 

 violet. The method as described is also applicable in the case of 

 blood. 



Estimation of the Total Urinary Nitrogen. KJELDAHL'S METHOD. 

 The method is based upon the observation that on treating urine 

 with a mixture of two parts of concentrated sulphuric acid and one 

 part of fuming sulphuric acid and boiling, the entire amount of 

 nitrogen can be transformed into ammonium sulphate. This is 

 then decomposed with an excess of sodium hydrate and the liberated 

 ammonia estimated by distilling into a known amount of dilute acid, 

 and retitrating the excess of acid. 



Five c.c. of urine are treated in a Kjeldahl digesting flask with 

 a pinch of yellow oxide of mercury (about 0.3 gramme) and 20 c.c. 

 of the sulphuric acid solution. The mixture is boiled until a per- 

 fectly colorless solution is obtained. Vigorous ebullition, how- 

 ever, must be avoided, and the flask should be placed at an angle 

 of about 45 degrees, so as to prevent loss from spurting. The milder 

 the ebullition the better. On cooling, the contents of the flask are 

 transferred to a Kjeldahl retort, with the aid of a little distilled water. 



