NITROGEN AND NITROGENOUS SUBSTANCES. 1397 



contained in meat, it is believed that the results of the method are 

 approximately correct. It is now the practice of this laboratory, how- 

 ever, to precipitate proteoses and gelatin with zinc sulphate, washing 

 the precipitate with a saturated solution of zinc sulphate and deter- 

 mining the nitrogen in the precipitate by means of Gunning's method. 

 The filtrate is then diluted with an equal amount of water and the pep- 

 tones (including gelatin-peptone) determined by means of bromin, as 

 directed above. 



It is found that proteoses and peptones are completely precipitated 

 from a half -saturated solution of zinc sulphate, though, as stated 

 above, the precipitation from aqueous solution is not complete. 



GELATIN. 



If desired, gelatin may be determined in a portion of the filtrate 

 from the coagulated proteids by the method suggested by Stutzer a for 

 the examination of meat extracts. The following modification of this 

 method has proven satisfactory in this laboratory in the hands of Mr. 

 Chace and the writer, and is much simpler: 



The portion of the filtrate from coagulated proteids which is to be 

 used for the determination of gelatin is evaporated in a porcelain 

 dish of about 10 cm. diameter, after the addition of about 20 grams of 

 sand which has been freed from dust by sifting and thoroughly ignited. 

 The residue is exhausted with four 50 cc portions of absolute alcohol, 

 and the supernatant liquid, which is somewhat turbid, filtered through 

 an asbestus filter, care being taken to transfer as little as possible of 

 the insoluble residue to the filter. The residue is repeatedly extracted 

 with 50 cc portions of a mixture containing 100 cc of 95 per cent 

 (by volume) alcohol, 300 grams of ice, and 600 grams of cold water, 

 care being taken that the temperature shall not be above 5 at any 

 time. The extraction is continued until the various portions of sol- 

 vent used are entirely colorless. The extract is passed through an 

 asbestus filter which rests on a porous plate in a funnel of about 7 cm 

 diameter. The funnel is surrounded by pounded ice and attached to 

 an aspirator by which gentle and gradually increasing suction may be 

 applied. Finally the asbestus filter is returned to the beaker which 

 contains the exhausted residue, and the whole thoroughly extracted 

 with boiling water. The hot water extract is placed in a Kjeldahl 

 flask, evaporated to dryness, and used for the determination of nitro- 

 gen by the Kjeldahl or Gunning method. 



MEAT BASES. 



The sum of the nitrogen contained in coagulated proteids, proteoses, 

 peptones, and gelatin deducted from the total nitrogen and multiplied 

 by 3.12 gives the percentage of meat bases. 



a Ztschr. anal. Chem., 1895, 34, 568. 

 12249 No. 1302 3 



