402 ADDITIONS, 



cubic centimetres, aad from this the percentage of 

 urea is calculated in the manner given below. 

 Deficit of Nitrogen. ■ The chief causes of variation 

 in the amount of nitrogen given off, have been 

 mentioned in the text. Hiifner, Pfluger and 

 Schenk find with the apparatus used by them, and 

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

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

 instead of giving off 373 vols, of nitrogen gives off 

 357, 



Eussell and West using a 2 p.c. solution of urea 

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

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

 of nitrogen gives off about 343 vols. When the 

 volume of the gas is measured at a temperature 

 of 18° C, no correction being made for the tension 

 of the aqueous vapour, the deficit of 8 p.c. is nearly 

 corrected by the expansion of the gas, so that 

 according to Russell and West, in making an 

 approximate estimate of urea with their apparatus, 

 no account need be taken of a deficit of nitrogen, 

 nor any correction be made for temperature and 

 pressure. 



Correction for temperature and pressure. If i;' be the 

 volume in cubic centimetres of the nitrogen obtained, 

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

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

 the volume v at 0°C. and 760 mm. pressure will be 

 if B-T 



i + -0036651^ 760 ' 

 '003665 being the coefficient of expansion of gases. 



