242 ELEMENTARY PHYSIOLOGY. [XXIII. 



12, Bile-acids. Use Pettenkofer's test (Lesson xvii. 

 B, § 4). 



Or — Soak a small piece of white blotting paper in a 

 syi'up of sugar, and allow it to dry. Let fall on it a 

 drop of the urine supposed to contain, bile-aoids, and 

 near it a drop of strong sulphuric acid, so that the 

 two drops run into oue another. If bile-acids are 

 present, there will be a purple colouration at the 

 junction of the drops. If the quantity of bile-acids 

 present is small, the urine must be concentrated, but 

 in such cases it is best to test in the ordinary way. 



Quantitative Estimation of Urea. 



Knop-Hiifner Method. {Hypobromite Method) 

 When sodium hypobromite in an excess of alkali 

 is added to a urea solution nitrogen is given off, 

 thus, 



CO (NH2)2 + 3Na Br O + 2Na HO = 3Na Br + NaaCOg + SH^O + Ng. 

 According to this equation I gram of urea gives off 

 very nearly 373 c.c. of nitrogen. In fact, however, 

 the decomposition of urea is not complete, the 

 amount of the deficit depends chiefly upon the 

 amount and strength of the hypobromite solution, 

 and on the percentage of urea in the urea solution. 

 In making an accurate estimation of urea, the 

 deficit of nitrogen under the conditions of the 

 observation, (determined beforehand) must be 

 allowed for; and as the theoretical amount of 

 nitrogen is estimated at a temperature of 0° C. and 

 a pressure of 760 mm. of mercury, the volume of 



