424 



A MANUAL OF PHYSIOLOGY 



(3) Quantitative Estimation The Hypobromite Method. The 

 urea is split up by sodium hypobromite (p. 389), and the carbon 

 dioxide being absorbed by the excess of sodium hydrate used in 

 preparing the hypobromite, the nitrogen is collected over water in 

 an inverted burette. It is easy to calculate the weight of urea 

 corresponding to a given volume of nitrogen measured at a given 

 temperature and pressure. The nitrogen of urea is f f, or T 7 T of the 

 whole molecular weight. Now, i c.c. of N weighs, at 760 milli- 

 metres of mercury and o C., '00125 

 gramme. Therefore, i c.c. of N 

 corresponds to -00125 x ~T-= '00268 

 gramme urea. Suppose, now, that 

 i c.c. of urine was found to yield 

 10 c.c. of N measured at 17 C. 

 and 750 millimetres barometric pres- 

 sure. Since a gas expands Y }^- 

 part of its volume at o tor every 

 degree above o, we must correct the 

 apparent volume of the nitrogen 

 by multiplying by ||f . Since the 

 volume of a gas is inversely pro- 

 portional to the pressure, we must 

 further multiply by y. Thus we 

 get iox - 2 --- 3 - v --- 2 4 - 7 - 5 ^ n< 



2 <ny 



V _ 



x - 



n-vn 



FIG. 131. HYPOBROMITE METHOD 

 OF ESTIMATING UREA. 



A, glass thimble; B, bottle, through 

 the rubber cork of which pass two 



c.c. as the volume of the nitrogen 

 reduced to o C. and 760 milli- 

 metres of mercury. Multiplying 

 this by '00268, we get '0249 gramme 

 urea for i c.c. urine, which for the 

 daily yield of 1,200 c.c. would corre- 

 spond to 29'88 grammes urea. 



As a matter of fact, however, it 

 has been found that there is always 

 a deficiency of nitrogen, that is, a 

 given quantity of urea yields less 

 than the estimated Amount of gas 

 A gramme of urea in urine, instead 



short glass tubes, one connected by o f giving off 37 * C.C. of nitrogen, 







the rubber tube C with a burette D, 

 and the other armed with a short piece 



of rubber tube F. F is provided with 

 apinchcock. The burette is supported 



on a stand, and immersed in water 

 contained in the glass cylinder E. 



--. 



1VCS Onl y 354 



o T nnd 

 O C. a 



760 millimetres pressure. We must 

 therefore take i c.c. of N as corre- 



,. 

 spending to '00282 gramme, instead 



of -00268 gramme urea. But it is 

 affectation to make this correction if, as is constantly done in 

 hospitals, the temperature is not taken into account. 



A convenient apparatus for clinical use is shown in Fig. 131. In 

 B, place TO c.c. of a solution made by adding bromine to ten times 

 its volume of 40 per cent, sodium hydrate solution. Mix 5 c.c. of 

 urine with 5 c.c. of water. Put 5 c.c of the mixture into the 

 thimble A, which is then set in the small bottle B. The cork is 

 now carefully fixed in B, and the tube F being open, the level of 



