THE COMPOSITION AND CHARACTERS OF THE URINE 1177 



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 strong enough, 

 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 connected with a calcium 

 chloride tube filled with cotton, and this in turn is attached to 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 .. 



FIG. 540. 



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 

 phenolphthalein are then added and decinormal sodium hydrate is run in until there is 

 a slight permanent pink colour. The amount of alkaline solution necessary to produce 

 this colour is a measure of the acidity of the urine. Ten cubic centimetres of formalin, 

 diluted with three volumes of water and previously neutralised to phenolphthalein 

 with decinormal alkali, are then added. The colour disappears owing to the setting 

 free of the acid radicals previously combined with ammonia. Decinormal alkali is then 

 run into the mixture until a permanent pink colour is again obtained. The number of 

 cubic centimetres of the decinormal alkali required in this second case corresponds to 

 the amount of decinormal ammonia previously present in the 25 c.c. of urine. 



This method gives somewhat higher figures than the method of Folin just described, 

 owing to the fact that the small traces of amino-acids, which may be present in the urine, 

 react to formalin in a very similar way. The difference does not exceed 10 per cent., 

 so that the method is amply delicate for clinical purposes. 



