COMPOSITION AND CHARACTERS OF URINE 



1127 



prepared solution of sodium hypobromite, and the nitrogen evolved is collected in a 

 graduated tube over water. 



Folin's Method. In Kjeldahl's method all the nitrogenous constituents of the urine 

 are converted into ammonia by boiling with strong sulphuric acid. This conversion 

 occurs with extreme readiness in the case of urea, so that by using a weaker acid and 

 carefully regulating the temperature the hydrolysis may be confined practically to the 

 urea itself. This is the principle of Folin's method of estimating urea. 



Five cubic centimetres of urine are measured into a 200 c.c. Erlenmeyer flask. Five 

 cubic centimetres of concentrated hydrochloric acid, 20 grm. crystallised magnesium 

 chloride, a piece of paraffin the size of a small hazel nut, and finally 2 or 3 drops of a 

 1 per cent, solution of alizarin red in water are added. A special safety tube is then 

 inserted into the neck of the flask and the 

 mixture boiled until each returning drop from 

 the safety tube produces a very perceptible 

 bump. The heat is then reduced somewhat, 

 and the heating is continued for a full hour. The 

 alizarin red is used in order to ensure that the 

 contents of the flask do not become alkaline. At 

 the end of an hour the contents of the flask are 

 put into a litre flask with about 700 c.c. water 

 and 20 c.c. of a 10 per cent, sodium hydrate, 

 and the ammonia is then distilled off into a 

 measured quantity of acid. The results obtained 

 in this way will give us the total amount of 

 urea together with any ammonia which was 

 preformed in the urine. It is therefore neces- 

 sary also to determine the amount of this pre- 

 formed ammonia. 



ESTIMATION OF AMMONIA. In Folin's 

 method for the estimation of ammonia, this is 

 set free by the addition of weak alkali (sodium 

 carbonate) and is then removed from the urine 

 at ordinary room temperature by passing a strong 

 current of air through the liquid. The issuing 

 current of air carrying the ammonia passes 



through a measured quantity of decinormal acid. If the air current be sufficiently 

 strong, one and a half hours is sufficient to remove the whole of the ammonia from 25 c.c. 

 of urine. The decinormal acid is then titrated and the amount of the ammonia reckoned. 

 In carrying out the method 25 c.c. of urine is measured into a cylinder 30 to 40 cm. 

 high and about a gramme of sodium carbonate and some petroleum (to prevent foaming) 

 are added. The upper end of the cylinder is then closed by a doubly perforated rubber 

 stopper through which pass two glass tubes, only one of which is long enough to reach 

 below the surface of the liquid. The shorter tube, about 10 cm. in length, is con- 

 nected with a calcium chloride tube filled with cotton, and this in turn is connected 

 with a glass tube extending to the bottom of a wide-mouthed bottle, capacity about 

 500 c.c., which contains 20 c.c. decinormal acid in 200 c.c. of water. 



A more convenient method for the estimation of ammonia is that originally pro- 

 posed by Schiff and recently worked out by Malfatti. It depends on the fact that when 

 a neutral solution of an ammonium salt is treated with formaldehyde, combination 

 occurs with the formation of hexamethylene tetramine (urotropine) and the liberation 

 of a corresponding amount of acid, which can be estimated by titrating with decinormal 

 alkali. The reaction which occurs is as follows ; 



6CH 2 + 2(NH 4 ) 2 S0 4 = 6H 2 O + N 4 (CH 2 ) 6 +' 2H 2 S0 4 . 

 Formaldehyde Hexamethylene tetramine 



In carrying out this method 25 c.c. of urine are measured by means of a pipette into a 

 flask or beaker and diluted with five times its volume of water. Four or five drops of 



FIG. 527. 



