44 Determination of Ammonia in Urine [Oct. 



sium Oxalate and one gram of carbonate are added to twenty-five 

 c.c, and the aeration process carried out as usual. This procedure 

 will prevent reformation of the triple phosphate. Folin preferred 

 this procedure to that suggested by Steel because he believes that 

 carbonate is a far safer alkali to employ than is hydroxide. If, 

 however, as we have pointed out above, a method should be em- 

 ployed which will prevent interference by magnesium ammonium 

 phosphate in all urines, the addition of the large quantity of Oxalate 

 (seven to ten grams) in every determination, is somewhat of a 

 draw-back. We are inclined to regard Steel's modification as a 

 safe procedure until someone shows that it actually decomposes 

 other urinary constituents to yield ammonia. We feel that it is 

 distinctly preferable to carbonate alone, as advised in the original 

 Folin process. 



We may add that in his latest " microchemical " processes for 

 ammonia, Folin and his collaborators^ have provided for the addi- 

 tion of Oxalate in all instances. The small volumes dealt with keep 

 down the quantity of Oxalate necessary. The figures reported by 

 Folin and Macallum by the colorimetric method for ammonia in 

 urine do not seem to us very satisfactory. While in many instances 

 the agreement between the figures obtained by the old process and 

 by the new is very close, in several cases the colorimetric values ex- 

 ceed the others by from five to twelve percent of the total ammonia 

 present. Folin and Macallum State that "a trace of something 

 capable of giving a color with Nessler's Solutions continues to come 

 long after all the ammonia has been removed," but that "the effect 

 of this substance in actual ammonia determinations is so small as to 

 be hardly, if at all, perceptible." So long as this substance capable 

 of giving a color with Nessler's Solution remains an unknown factor 

 and where results may be as much as twelve percent higher by the 

 colorimetric procedure, we should hesitate to regard this latter proc- 

 ess as of equal accuracy with the older. 



* Folin and Macallum: Jour. Biol. Chem., ii, p. 523 (1912). Folin and Denis: 

 Ibid., II, p. 532 (1912). 



