18 PROVISIONAL METHODS FOE ANALYSIS OF FOODS. 



and determine nitrogen in an aliquot portion of the filtrate; then deduct the per- 

 centage of nitrogen in the total filtrate from the percentage of total nitrogen for the 

 percentage of nitrogen in meat fiber. Multiply the percentage of nitrogen by 6.25 

 for the percentage of meat fiber. 



(c) DETERMINATION OF COAGULABLE PROTEIDS. 



Make the filtrate (as large an aliquot portion as practicable when the nitrogen of 

 meat fiber has been determined by difference) from meat fiber slightly acid (if not 

 already acid), adding acetic acid or sodium hydroxid as may be required, boil for 

 two or three minutes, cool to room temperature, dilute to 500 cc and filter through 

 a fluted filter. a 



Determine nitrogen in 50 cc of the filtrate by means of the Kjeldahl or Gunning 

 method. Ten times the nitrogen so obtained deducted from the percentage of soluble 

 nitrogen (which in turn is obtained by deducting percentage of nitrogen occurring as 

 meat fiber from the total nitrogen) gives the percentage of nitrogen contained in 

 albumin and globulins. Multiply this figure by 6.25 for the percentage of coagula- 

 ble proteids in the sample. 



(d) DETERMINATION OF SYNTONIN. 



Exactly neutralize the filtrate from the determination of coagulable proteids 

 with sodium hydroxid, using litmus as indicator, and allow to stand until the precipi- 

 tate settles. If only a small amount of syntonin is precipitated, it may be separated 

 with an ordinary filter, washed with water, and its nitrogen content determined by 

 means of the Kjeldahl or Gunning method. If present in any considerable quantity, 

 dilute to a definite volume, filter through a fluted filter, and determine nitrogen in 

 50 cc of the filtrate. 



The nitrogen thus obtained (calculated to total volume) is deducted from the 

 nitrogen in the filtrate from the globulins for the syntonin nitrogen. This multi- 

 plied by 6.25 gives syntonin. 



(e) DETERMINATION OF PROTEOSES, PEPTONES, AND GELATIN. b 



If it be desired to group these bodies together, proceed as directed under (e), page 

 11, unite the two precipitates and make a single determination of nitrogen. The per- 

 centage of these bodies can not be determined by using aliquot parts and deducting 

 the nitrogen content of the filtrate from the bromin precipitate from that of the 

 filtrate from the determination of syntonin, because of the decomposing effect exerted 

 by bromin on nitrogen compounds. Experiments in this laboratory also indicate 

 that the aliquot portions of the filtrate from the determination of syntonin can not 

 be used separately for the zinc-sulphate precipitate and the bromin precipitate for 

 the same reason. Although bromin precipitates peptones and zinc sulphate does 

 not, Trescot found, in the examination of a large number of meat extracts when 

 working with aliquot portions of the same solution, that more nitrogen was precipi- 

 tated by zinc sulphate than by bromin. 



(f ) DETERMINATION OF PROTEOSES AND GELATIN. 



Evaporate the filtrate from the determination of syntonin (as large an aliquot por- 

 tion of the filtrate as is practicable when the percentage of syntonin is determined 



The filtering and washing of coagulated proteids are always tedious and unsatisfactory and some- 

 times almost impossible. The work is greatly simplified, therefore, bypassing through a fluted filter 

 and employing aliquot parts of the filtrate, as by this means the complete filtration and washing of 

 precipitates is made unnecessary. 



b Allen, The Analyst, 1897, 22, 258; Com. Org. anal., 2d edition, vol. 4, p. 325. 



Bomer, Ztschr. anal. Chem., 1895, 5, 562; also Mallet, U. S. Dept. Agr., Div. of Chem., Bui. 54. 



