ELEMENTARY PHYSIOLOGICAL CHEMISTRY 251 



accurate is that ofDuprd (Fig. 153), which consists of an inverted burette 

 (a) placed in a cylinder of water, and to the neck of which is connected 

 a T piece (/). With the side tube of this the generating bottle is 

 connected by indiarubber tubing, and the other tube is closed with a 

 piece of tubing and a clip. To make the estimation 25 c.c. of the 

 alkaline solution of NaBrO are placed in the generating bottle (o) and 

 5 c.c. urine in a small tube, which is then carefully placed in the 

 generating bottle without allowing the two fluids to mix. The cork 

 of the generating bottle is then inserted, and the water meniscus inside 

 and outside the burette brought to the same level at the zero mark, 

 the clip on the T piece being meanwhile open, and water being added 

 to, or removed from, the outer vessel as necessary. The clip is now 

 applied, and the burette raised to ascertain that no leakage exists. 

 Now readjust the two menisci, and mix the contents in the generating 

 bottle. The evolved N displaces the water in the burette. After the 

 reaction is complete immerse the generating flask in a basin of water, 

 so as to bring the temperature of the gas contained in it to the same as 

 that of the gas in the burette. After two minutes bring the two 

 menisci to the same level, and read off the number of c.c. of N. 

 Another form of apparatus is that of Gerrard (Fig. 154). 



The determination may also be made by means of the following 

 improvised apparatus (Fig. 155). 



The neck of a burette C is connected by means of a long piece of 

 indiarubber tubing with a glass tube Z), dipping under the surface of 

 water contained in a bottle B. Through the cork of this a second tube 

 E connects it with the generating bottle A, and a third tube F, closed 

 by a piece of tubing and a clip, is also inserted in the cork of -B. To 

 make the estimation the burette is raised, and water poured into it till 

 the tube D is full. It is then lowered till the water stands at the 

 lowest graduation (50 or 100) of the burette, and is on the same level 

 as the water in B. The urine and hypobromite solution are then 

 placed in the generating bottle, the cork of this inserted, the tube F 

 closed, and the solutions in A mixed. The gas pushes the water into 

 the burette, and, after the generating bottle has been cooled, the 

 meniscus of water in the burette is brought on a level with that in B, 

 either by lowering the burette or raising B. The amount of displaced 

 water is then read off, and from it the urea is calculated. 1 



The Metabolic Changes which give rise to Urea. Urea is in man 

 the chief end product of proteid metabolism, and consequently varies 

 enormously with the nature of the diet. 



EXPERIMENT VI. This can be very simply demonstrated by making 

 a determination of the percentage contained in a sample of urine passed 

 1 The corks must be of indiarubber. 



