APPENDIX. 



For full particulars relative to the general principles of the separa- 

 tion of the different forms of nitrogenous bodies the reader is referred 

 to the Principles and Practice of Agricultural Analysis, volume 3, 

 and to Bulletin No. 54 of this Division. An abstract of the literature 

 relating to the separation of flesh bases from other nitrogenous bodies 

 is given here. 



PRECIPITATION OF PROTEIDS SOLUBLE IN WATER BY CHLORIN AND 



BROMIN. 1 



Rideal and Stewart recall some of the experiments made in 1876, in which it was 

 shown that a current of chloriu gas conducted through an aqueous solution of pro- 

 teid 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 foi 

 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. in place of chlorin for the precipitation, and state that the studies of the use 

 of bromin are under way. They call attention also 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's Jahresbericht, volume 19, page 734, in 

 which he obtained results on precipitation quite similar to those secured by Rideal 

 and Stewart. 



Other references to the literature on the subject are also given, viz: De Yrij, 

 Ann. Pharm., Ixi, 248; The'nard, Mom. d'Arcueil, ii, 38; Mulder, Bulletin en Ne'er- 

 laiide, 1839, 153; and Berzelius' Jahresbericht, xix, 729. 



Allen and Searle, acting on the suggestion of Rideal and Stewart, worked out the 

 bromiu method by applying it to various soluble proteids, including the whole 

 range from albumin to peptone. In the application of this test to commercial gela- 

 tin 50 grams of commercial gelatin are dissolved in waina water and the solution 

 diluted to half a liter. In 10 c. c. of this solution, corresponding to 1 gram of the 

 gelatin, the nitrogen is determined directly by the Gunniug-Kjeldahl process. 



Another portion of 10 c. c. is treated with an excess of bromin. The solution is 

 first brought to a volume of 100 c. c. with water and placed in a conical beaker with 

 a sufficient quantity of hydrochloric acid to produce distinct acidity. A saturated 

 solution of bromin water is added in considerable excess and the liquid stirred vig- 

 orously for some time. The precipitate which separates is flocculent when first 

 formed, but becomes more viscous after stirring and adheres for the most part to the 

 sides of the beaker, which, with its contents, is allowed to stand for about half an 

 hour, or until ail the precipitate is settled. The supernatant liquor is decanted 

 through an asbestos filter. The precipitate adhering to the beaker is washed several 

 times w r ith cold distilled water and the washings poured through the filter. Occa- 

 sionally, when most of the free bromin is washed out of the precipitate, the liquid 



The Analyst, 22, pp. 228 and following; also pp. 255 and following. 



7J 



