XXIII.] URINE. 243 



the gas obtained must be corrected for this tem- 

 perature and pressure (cf. p; 402). 



When, as in medical practice, a rough estimation 

 of the percentage of urea is sufficient, the tube in 

 which the nitrogen is collected is graduated em- 

 pirically, at the ordinary indoor temperature, i.e. at 

 about 18° C. The graduation is performed by 

 mixing a known, quantity of hypobromite solution 

 with 5 c.c. of a 1 p.c. solution of pure urea, and 

 marking on the collecting tube the volume of 

 nitrogen given off. Similar observations are made 

 with 5 c.c. of a 2 p.c. and of a 3 p.c. solution of 

 urea. The tube, between each , of the marks so 

 obtained, is divided into tenths. Hence, when 

 5 e.c. of a solution of urea of unknown strength are 

 taken, and treated as the standard solution was 

 treated, the percentage of urea in it is at once 

 roughly determined by the number of divisions of 

 the tube occupied by the nitrogen given off. 



One form of apparatus of this kind is described in 

 the Appendix (cf. p. 400). 



2. Liebig's Method. (See p. 398.) 



Quantitative Estimation of Sugar. 



Fehling's fluid (cf. p. 381) contains a known amount 

 of cupric sulphate, and this, as has been seen in 

 using Trommer's test, is reduced by sugar to cuprous 

 hydroxide or oxide when boiled with it in an alka- 

 line solution. In making an estimation, 10 c.c. of 



16—2 



