APPENDIX 



463 



2. N/io NaOH. 



3. Forty per cent. NaOH. 



Ten c.c. of filtered urine are pipetted into a Kjeldahl or Koch flask; 10 c.c. of 

 concentrated H 2 SO 4 and 10 grams K 2 SO 4 are added. The mixture is heated over 

 a free flame, gently at first to avoid foaming, and is finally brought to a boil, which 

 is continued until the mixture is perfectly clear, usually requiring forty-five minutes 

 to an hour. The contents are cooled and quantitatively transferred to a 200 c.c. 

 volumetric flask and i c.c. of phenolphthalein 

 solution added. The greater part of the 

 acidity is now neutralized by adding about 

 30 c.c. of the 40% NaOH. It is cooled 

 under a water tap and made up to the 200 c.c. 

 mark; 10 c.c. are taken, diluted in 50 c.c. with 

 distilled water and exactly neutralized with 

 N/io NaOH. Twenty c.c. of the formalin 

 solution are now added and the titration 

 again performed. The pink end reaction is 

 beautifully clear and sharp. The second 

 reading multiplied by the factor 0.0014 gives 

 the amount of nitrogen in grams in 10 c.c. 

 of the fluid. It is t then computed for the 

 twenty-four-hour volume as for N, eliminated 

 as ammonia. Example: It required 5 c.c. 

 N/io NaOH 5X0.0014 = 0.007. As origi- 

 nal 10 c.c. were diluted to 200, the 10 c.c. 

 taken for titration would onlybe^o; hence 

 0.007X20 = 0.14 gram for 10 c.c. or 1.4 for 

 100 c.c. or. 14 grams for 1000 c.c. 



UREA ESTIMATIONS 



The amount of urea, which represents from 

 85 to 90% of the total nitrogen, is usually 

 determined instead of the total N. The 

 hypobromite and hypochlorite methods are, 

 however, lacking in accuracy, and more exact 

 methods of urea estimation are more time-con- 

 suming than the one just given for total N. 



Probably the most convenient test for urea is the hypobromite method, using 

 the Doremus ureometer with a side tube connected to the closed arm of the fermenta- 

 tion tube by a glass stop cock. 



The reagent is prepared by taking 70 c.c. of a 30% stock solution of NaOH, 

 diluting it with 180 c.c. water and then adding 5 c.c. of bromine, stirring until the 

 bromine is dissolved. This solution if stored in a*cool dark place will keep about 

 one week. 



The urine to be tested must be free from sugar and albumin and contain less than 

 i% of urea. Ordinarily the urine must be diluted two to four times to obtain a 

 specimen containing less than i%. In using this improved Doremus ureometer 



FIG. 113. Doremus- Hinds Ure- 

 ometer. 



