PRACTICAL EXERCISES 



481 



volume of nitrogen by multiplying by $1$. Since the volume of 

 a gas is inversely proportional to the pressure, we must further 

 multiply by |$. Thus we get 10 x Sji x f;^ = W(/f = 9'29 c.c. 

 as the volume of the nitrogen reduced to"o C. and 760 millimetres of 

 mercury. Multiplying this by 0*00268, we get 0*0249 gramme urea 

 for i c.c. urine, which for a daily yield of 1,200 c.c. would correspond 

 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 

 of giving off 373 c.c. of nitrogen, 

 gives only 354 c.c. at o C. and 760 

 millimetres pressure. We must 

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

 sponding to 0*00282 gramme, in- 

 stead of 0*00268 gramme urea. But 

 it is affectation to make this correc- 

 tion if, as is constantly done in 

 hospitals, the temperature is not 

 taken into account. 



A convenient apparatus is shown 

 in Fig. 178. In B, place 10 c.c. 

 of a solution made by adding bro- 

 mine to ten times its volume of 

 40 per cent, sodium hydroxide solu- 

 tion. 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 the water in the burette is 

 read off. The pinchcock having 

 been closed, the bottle B is now 

 tilted so that the urine in the 

 thimble is gradually mixed with the 

 hypobromite solution, and the nitro- 

 gen given off is added to the air in 

 the burette and its connections. 

 The level of the water in the burette 



and immersed in water contained in 

 the glass cylinder E. 



FIG. 178. HYPOBROMITE METHOD 

 OF ESTIMATING UREA. 



A, glass thimble ; B, bottle, 

 through the rubber cork of which 

 pass two short glass tubes, one con- 

 nected by the rubber tube C with 

 a burette D, and the other armed 

 with a short piece of rubber tube F. 

 F is provided with a pinchcock. 



is therefore depressed. When gas The buret te is supported on a stand, 

 ceases to be given off, and a short 

 time has been allowed for the whole 

 to cool, the tube is raised till the 

 level of the water is once more the same inside and out. The 

 level is again read off ; the difference of the two readings gives 

 the volume of nitrogen at the temperature of the air and the 

 barometric pressure. In order that the temperature of the water 

 may be the same as that of the air, the cylinder should be filled a 

 considerable time before the observations are begun. 



For clinical purposes sufficiently accurate results may be very 

 easily obtained with the so-called ureometer of Doremus (Fig. 179). 

 A little urine is poured into the side-tube A, the stopcock C being 

 closed. The stopcock is then opened for an instant, so as to fill 



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