80 



does not filter clear. It is therefore advisable to keep the washing separated from 

 the iiltrate, and, if necessary, wash with sodium sulphate solution or with bromin 

 water. The nitrogen in the precipitate is determined by the Guiming-Kjeldahl 

 process as follows : 



The precipitate which has been collected on the asbestos filter, together with the 

 asbestos, is returned to the beaker in which the precipitation took place. Twenty 

 cubic centimeters of strong sulphuric acid are added, the beaker covered with a 

 watch glass and placed on a wire gauze over a lamp. When frothing has ceased 

 about 10 grams of powdered potassium sulphate are added and the liquid boiled 

 until colorless. After cooling it is diluted with water and the ammonia distilled off 

 and determined in the usual way. The percentage of nitrogen found, when multi- 

 plied by the factor 6.33, or, in the case of gelatin, by 5.5, gives the amount of pro- 

 teid matter precipitated by broinin. In the commercial gelatin above mentioned 

 the nitrogen content was found to be 14.1 and 14 per cent, respectively, on two 

 determinations. Solutions of creatinin, asparagiu, and aspartic acid w r ere found to 

 yield no precipitates with broinin, but bromiu was found to precipitate all albumin, 

 acid albumin, and all peptones formed by the digestion of albumin with pepsin. 



NITROGEN IN MEAT EXTRACTS. 



On applying the bromiii method to commercial meat extracts the following results 

 were obtained. The solutions of the Bovril preparations were not previously iiltered 

 and therefore the figures contain the nitrogen in the fiber present: 



Relative amounts of nitrogen in meat extracts. 



Koenig and Boemer have shown that the proteid nitrogen in meat extracts is 

 generally much overestimated. They found a total of 1.17 per cent of proteid 

 nitrogen in the Liebig Company's extract, which is equivalent to 7.41 per cent of 

 total proteids, mostly albumose. 



PROBLEMS SOLVED BY THE BROMIN METHOD. 



The fact that bromin completely precipitates all proteid and gelatinoid matters 

 in solution affords a convenient means of solving certain problems which have 

 hitherto presented considerable difficulty. For instance, in a solution which has 

 been subjected to digestion it may be possible to precipitate all the unchanged 

 proteids by saturation with zinc sulphate. The peptones which have been formed 

 during digestion remain in solution and can be separated by nitration. In the fil- 

 trate the peptones can be completely precipitated by bromin, and thus the total 

 quantity of these bodies formed during digestion can be accurately determined. 



Allen and Searle applied this method to an examination of the Liebig Company's 

 extract, 5 grams of which were dissolved in 100 c. c. of water and the solution satu- 

 rated with zinc sulphate. After filtering, bromin water was added to the filtrate 

 and a precipitate produced which redissolved on diluting with water and the addi- 

 tion of hydrochloric acid. When the filtrate from the saturated zinc sulphate was 

 previously diluted with water and acidulated no precipitate was formed on the 

 addition of bromiu. This reaction shows that no considerable quantities of real 

 peptones exist in Liebig's extract. 



o 



