APPENDIX 389 



Ronchese first utilized this principle and Mathison found that pot. oxalate 

 made the end reaction sharper. Brown found that preliminary clearing with lead 

 subacetate made the end reaction still sharper and removed certain nitrogenous 

 substances which reacted with formalin making the result only about 5% higher 

 than with Schaffer's method. The technic is as follows: About 60 c.c. of filtered 

 urine are treated with 3 grams of basic lead acetate, well stirred, allowed to stand 

 a few minutes and filtered. The filtrate is treated with 2 grams of neutral potas- 

 sium oxalate well stirred and filtered; 10 c.c. -of the clear filtrate are diluted to 50 

 c.c. with distilled water; a few drops of i% phenolphthalein solution are added. 

 The mixture will be slightly alkaline or acid. Five grams potassium oxalate 

 are added and stirred. It is exactly neutralized with decinormal NaOH or H 2 SO 4 . 

 Twenty c.c. of 20% commercial formalin, previously made neutral, are added, and 

 the solution again titrated with decinormal NaOH to neutralization. Every c.c. 

 of decinormal NaOH corresponds to 0.0017 gram NHs. The quantity of ammonia 

 is then calculated on the basis of the twenty-four-hour volume. Example: The 

 10 c.c. of urine required 4 c.c. N/io NaOH to give a pink color. 4X0.0017 =0.0068. 

 Then 100 c.c. urine would contain 0.068 and 1000 c.c. (twenty-four-hour urine am- 

 ount) 0.68 gram of ammonia. 



ESTIMATION OF TOTAL NITROGEN. 



Principle. The nitrogenous material of the urine is converted into ammonium 

 sulphate on boiling with H 2 SO 4 . The ammonia is then estimated as described 

 under estimation of ammonia by the formalin method. 



Technic. Solutions required : 



1. Twenty per cent, commercial formalin previously made neutral with NaOH. 



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 

 to 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 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 original 10 c.c. 

 were diluted to 200, the 10 c.c. taken for titration would only be 1/20; hence 0.007 X 

 20 = 0.14 gram for 10 c.c or 1.4 for 100 c.c. or 14 grams for 1000 c.c. 



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 estima- 

 tion are more time-consuming than the one just given for total N. 



