THE ORGANIC CONSTITUENTS OF THE URINE. 231 



mixture, which contains 250 grammes of barium chloride in 1000 

 c.c. of a 5 per cent, solution of barium hydrate. To this are added 

 100 c.c. of a mixture of two parts of 97 per cent, alcohol and one 

 part of ether. After twenty-four hours the precipitate is filtered 

 off and treated with 100 c.c. of ether-alcohol. Filtrate and wash- 

 ings are then concentrated at a temperature not exceeding 60 C. 

 to about 20 c.c., or to a point where ammonia is no longer evolved, 

 which can be recognized by testing the vapor with litmus-paper. 

 A small amount of water may be added if the solution should 

 become too concentrated. It is then washed into a Kjeldahl digest- 

 ing flask with as little water as possible, to which a few drops of 

 concentrated sulphuric acid have been added. The solution is now 

 concentrated to a very small volume, upon a water-bath, and treated 

 with 20 c.c. of a mixture of two parts of concentrated sulphuric 

 acid and one part of the fuming acid. A pinch of yellow oxide of 

 mercury (about 0.3 gramme) is further added, when the process is 

 continued according to Kjeldahl, as described below. 



METHOD OF FOLIX. This is based upon the following considera- 

 tions : crystallized magnesium chloride, MgCl 2 .6H 2 O boils in its 

 water of crystallization at a temperature of about 160 C. Urea 

 is quantitatively decomposed in such a solution into ammonia and 

 carbon dioxide within one-half hour. If the process is carried out 

 in acid solution, the ammonia can subsequently be distilled off after 

 rendering the mixture alkaline, and is then titrated. The cor- 

 responding amount of urea is ascertained by calculation. At the 

 same time, however, the preformed ammonia is obtained, and it is 

 hence necessary to eliminate this source of error by a separate 

 estimation of this form. This is conveniently done according to 

 the method which has likewise been suggested by Folin (see below). 



Method. Three c.c. of urine are placed in an Erlenmeyer flask 

 of 200 c.c. capacity, together with 20 grammes of magnesium 

 chloride and 2 c.c. of concentrated hydrochloric acid. (The magne- 

 sium chloride usually contains a small amount of ammonia, which 

 must be separately determined.) The flask is closed with a per- 

 forated stopper through which a straight glass tube passes, measur- 

 ing 200 mm. in length, with a diameter of 10 mm. The mixture is 

 now boiled until the drops flowing back through the tube produce 

 a hissing sound on coming in contact with the solution. After this 

 point has been reached, the boiling is continued more moderately for 

 twenty-five to thirty minutes. The solution while still hot is care- 

 fully diluted to about 500 c.c. at first by allowing the water to flow 

 drop by drop through the tube ; it is then transferred to a 1000 c.c. 

 retort, treated with about 7 or 8 c.c. of a 20 per cent, solution of 

 sodium hydrate, and the ammonia distilled off into a measured 

 amount of a decinormai solution of sulphuric acid. The distillation 

 may be interrupted when about 350 c.c. have passed over (viz., after 

 about sixty minutes). The distillate is boiled for a moment to 

 remove any carbon dioxide which may be present in solution, and 



