ADDITIONS. 401 



sodium hydrate solution should be kept ready, and 

 bromine added just before the mixture is required. 

 It is convenient to have thin glass capsules, each 

 containing 2"3c.c. of bromine, if one of these be 

 placed in 25 c.c. of the hypobrpmite mixture 

 broken by a sharp shake, the proper amount of 

 hypobromite solution for a single observation is 

 obtained. 



Method of using Gerrard's apparatus. In this, as 

 in many other forms of apparatus, the collecting 

 tube is graduated so as to show percentages of urea 

 when 5 c.c. of a urea solution are taken. 



Raise the tube (a) to about the height shown in 

 the figure, pour water into it until the tube (6) is 

 filled with water to the zero mark. Pour 25 c.c. of 

 hypobromite solution into the bottle (c), measure 

 from a burette 5 c.c. of urine into the tube (d). 

 With the aid of a forceps, place the tube (d) in the 

 bottle, being careful not to spill any of the urine. 

 Fit the cork, with the tube attached to it, tightly 

 into the bottle, and clamp the tube (e). Fill up 

 and gently shake the bottle so that the urine and 

 the hypobromite solution mix. Place the bottle 

 in a basin of water. Lower (a) until the level of 

 the water in it is the same as that in (b). Leave 

 for about five minutes, re-adjust the level of the 

 water in the two tubes, and note how much 

 nitrogen has been given off. 



An estimation of urea should also be made, using 

 two burettes instead of the tubes (a) and (&). 

 The volume of nitrogen evolved is measured in 

 I- 26 



