56 METHODS FOR THE ANALYSIS OF URINE 



etc. When poorly dissociated acids, e.g., some fatty acids, are pres- 

 ent, these will in part be included in the result and lead to values 

 which are too high. Certain of the amino-acids when present in large 

 amounts will give erroneous results, but in the ordinary urine or 

 digest these errors are either negligible or compensate each other. 

 In the titration of colored solutions the control solution which is 

 necessary in this method must be colored to correspond with the 

 color of the unknown solution. 



Procedure. The determination of the amino-acids is carried 

 out as follows: The solution to be analyzed, if carbonates, phos- 

 phates and ammonia are absent, is made neutral to litmus (paper) 

 and the solution titrated with formaldehyde. In case carbonates, 

 phosphates or ammonia are present a preliminary treatment is 

 necessary which will vary according to the quantity of ammonia 

 present. 



(a) For Small Amounts of Ammonia. Applicable to most 

 urines. Fifty c.c. of the material under examination is pipetted 

 into a 100 c.c. measuring flask and 1 c.c. phenolphthalein solu- 

 tion and 2 gms. of solid barium chloride are added; the whole 

 is shaken, to saturate the solution with barium chloride ; saturated 

 barium hydroxide solution is added until the red color of the 

 phenolphthalein develops and then an excess of 5 c.c. is added. 

 The flask is filled to the graduation mark with water, shaken 

 and permitted to stand for fifteen minutes, after which it is filtered 

 through a dry filter. Eighty e.c. of the clear red filtrate (which 

 corresponds to 40 c.c. of the liquid under examination) are placed 

 in a 100 c.c. measuring flask, neutralized to litmus and diluted 

 to 100 c.c. with freshly boiled water. Equal portions of this 

 solution, 40 c.c. (equivalent to 16 c.c. of the original solution), 

 may be taken for analysis, one for the formol titration and the 

 other for the determination of ammonia nitrogen. 



(6) For Large Amounts of Ammonia. After the treatment 

 with phenolphthalein, barium chloride, and barium hydroxide, 

 and the solution has been diluted to 100 c.c. as in (a) above, 

 the ammonia is distilled off, in vacuo. 



In case the solution is deeply colored, as in protein digests, 

 it may be necessary to decolorize before the titration is attempted. 



Final Titration. For the final titration a volume of from 

 20 to 40 c.c; which contains approximately 0.0125 gm. of nitro- 

 gen is the most desirable. A control solution is run composed 



