402 



ADDITIONS. 



cubic centimetres, and from this the percentage 

 urea is calculated in the manner given below. 

 . Deficit of Nitrogen. The chief causes of variatioi 

 in the amount of nitrogen given off, have beei 

 mentioned in the text. Hiifner, Pfliiger an< 

 Schenk find with the apparatus used by them, anc 

 with a 1 p.c. solution of urea, that the deficit 

 nitrogen is very nearly 4 '4 p.c., i.e. 1 gram of ui 

 instead of giving off 373 vols. of nitrogen gives of 

 357. 



Russell and West using a 2 p.c. solution of urei 

 find with their apparatus a deficit of nearly 8 p.c., 

 i.e. 1 gram of urea, instead of giving off 373 vol 

 of nitrogen gives off about 343 vols. When th< 

 volume of the gas is measured at a temperatun 

 of 18 C., no correction being made for the tensk 

 of the aqueous vapour, the deficit of 8 p.c. is nearl; 

 corrected by the expansion of the gas, so thi 

 according to Russell and West, in making 

 approximate estimate of urea with their apparatus 

 no account need be taken of a deficit of nitrogei 

 nor any correction be made for temperature am 

 pressure. 



Correction for temperature and pressure. Ifv' be tnt 

 volume in cubic centimetres of the nitrogen obtained, 

 at temperature t C. and pressure B in mm. of mer- 

 cury, and T be the tension of aqueous vapour at t C, 

 the volume v at C. and 760 mm. pressure will 



v 



-~-. x 



B-T 



1 + '003665 t 760 ' 

 '003665 being the coefficient of expansion of gas< 



