28 



with brornin. The mixture is then allowed to stand overnight, by 

 which time the precipitate will have settled. The supernatant liquor 

 is passed through the filter and the precipitate in the flask washed by 

 decautation with water, the globule of undissolved brornin serving to 

 saturate the wash water so that it is unnecessary to use additional 

 bromin water for the washing. The filter containing the precipitate is 

 returned to the same flask in which the precipitation has taken place 

 and the nitrogen therein determined by the Gunning method. The 

 sum of the nitrogen in the part insoluble in water and the part precipi- 

 tated by bromiu is subtracted from the total nitrogen determined on 

 the original sample, and the difference gives the total nitrogen in the 

 flesh bases. 



FACTORS FOR CALCULATION OF TOTAL NITROGEN. 



The factors used for calculating the total nitrogenous bodies are as 

 follows : 



For the part insoluble in water, X x 6.25. 



For the part soluble in water and precipitated by bromin, X x 6.25. 



For the flesh bases, N x 3.12. 



This method is based upon investigations reported by Eideal and 

 Stewart 1 last year. 



These writers recall some of the experiments made in 1876, in which 

 it was shown that a current of chlorin gas, conducted through an 

 aqueous solution of proteid matters, produces a precipitate which is 

 of a quite constant composition, and one which can be collected, dried 

 in vacuo, and weighed. They describe particularly the use of this 

 reagent in precipitating gelatin prepared from the high-grade com- 

 mercial article. They show that the total quantity of gelatin can be 

 accounted for from the weight of the precipitate by multiplying the 

 weight of the precipitate obtained by the factor 0.78. The authors 

 also point out the possibility of using bromin for chlorin for the pre- 

 cipitation, and state that the studies of the use of bromin are under 

 way. They call attention to the fact that as early as 1840 chlorin 

 had been used by Mulder for the precipitation of soluble proteids, and 

 refer to a paper of his published in Berzelius' Jahresbericht, volume 

 19, page 734, in which he states results on precipitation quite similar to 

 those secured by Eideal and Stewart. 



At the close of their paper Eideal and Stewart mention the work in 

 this direction of De Vrij, Ann. Pharm. 61, 248; Theuard, Mem. 

 d'Arcueil, 2, 38; Mulder, Bulletin en Neerlande, 1839, 153, and Ber- 

 zelius' Jahresbericht, 19, 729, on the same subject. 



Allen and Searle, 2 acting on the suggestion of Eideal and Stewart, 

 worked out the bromin method by applying it to various soluble pro- 

 teids, including the whole range from albumin to peptone. In the 



The Analyst, 1897, 22, 228 et seq. 2 The Analyst, 1897, 22, 258-263. 



