ADDITIONS. 403 



Calculation of percentage of urea. Theoretically 

 373 c.c. of nitrogen are given off by 1 gram of 

 urea, if then v c.c. of nitrogen, after correction 

 for temperature and pressure, are obtained in 

 an experiment, this will have been given off by 



^r grams of urea, that is there are ^r- grams of 



01 o 



urea in the 5 c.c. of urea solution taken, so that 

 the percentage of urea in the solution is -^-5- . 



But since in practice the whole of the nitrogen is 

 not given off, the deficit must be allowed for, if wu 

 take Hiifner's estimate of the deficit of the volume 

 of the nitrogen, viz. 4'4p.c., the percentage will be 

 20 y 

 357' 



Sources of error in estimating urea in urine. Nitro- 

 genous bodies other than urea are partially decom- 

 posed. Further certain substances increase and 

 others decrease the completeness of the decom- 

 position. 



2G 2 



