GENERAL CHARACTERISTICS OF THE URINE. 215 



of albumins and alkaline salts present, or of salts which can be trans- 

 formed within the body into alkaline carbonates, it follows that a 

 highly acid urine must also result when an increased destruction of 

 tissue-albumins is taking place from whatever cause. We accord- 

 ingly find a very acid urine in various pathological conditions, nota- 

 bly in fevers. 



An alkaline urine will similarly result when, as in pneumonia and 

 in diseases in which large accumulations of fluid occur in the 

 serous cavities of the body, and where a certain amount of alka- 

 line salts has thus been withdrawn from the circulation, absorption 

 subsequently occurs. Alkaline salts are, however, retained from 

 the ingested food, and an increased elimination occurs when the addi- 

 tional supply finds its way into the plasma from these various sources. 

 A notable change in the normal alkalinity of the blood can hence 

 scarcely occur so long as a sufficient amount of alkali is furnished in 

 the food. 



In order to decide whether the alkaline reaction of a specimen of 

 urine is due to the presence of fixed or volatile alkali, a strip of red 

 litmus-paper is clamped in the cork of the bottle, and so arranged as 

 not to touch the liquid. If free ammonia is present, the red color 

 changes to blue, while fixed alkali is indicated only when the paper 

 comes into contact with the urine. 



Determination of the Acidity of the Urine. As the acidity of the 

 urine is almost exclusively due to the presence of acid phosphates, its 

 determination resolves itself into the estimation of these salts. The 

 resulting values are expressed in terms of hydrochloric acid, of which 

 102.8 mgrms. correspond to 100 mgrms. of the diacid sodium salt. 

 Negative values are similarly expressed in terms of sodium 

 hydrate. 



FRETJND'S METHOD. The total amount of phosphoric acid is first 

 determined as described on page 220). In a second portion the 

 monacid phosphates are then estimated as follows : 50 c.c. of 

 urine are precipitated with a normal solution of barium chloride, 10 

 c.c. being added for every 100 mgrms. of the total amount of phos- 

 phoric acid that has been found. The mixture is diluted with water 

 to lOOc.c., filtered, and the phosphoric acid determined in 50 c.c. of 

 the filtrate. But as barium chloride precipitates not only the mon- 

 acid phosphate, but also a small amount of the normal phosphates, 

 with the simultaneous formation of a small amount of diacid phos- 

 phates, which latter pass into solution, an error is thus incurred. 

 This, however, remains constant, and amounts to 3 per cent, in favor 

 of the diacid phosphates. It is deducted from the latter, and the 

 total amount of acid salts is then determined by calculation. The 

 result is expressed in terms of hydrochloric acid. 



If relative values, on the other hand, are desired, the percentage 

 of the diacid salts is ascertained and compared with the total amount 

 of phosphoric acid, as shown in the following example: 



The total amount of urine is 2000 c.c., and the total amount of 



