172 KePORT of TUK CniiMIOAL DKPAKlIUh.NT OF 'JDE 



PREPARATIOX OF CHEESE EXTRACT. 



Twonty-fivo grams of cheese are mixed witli quartz sand and 

 treated at 122° to 140° F. (50° to 60° C.) for a half hour with 

 each of several successive portions of water, decanting and 

 filtering each portion of extract until 500 cc. have been accuramu- 

 lated. Portions of the solution thus prepared are used in 

 making the various determinations. 



DETERMIXATION OP NITROGEN-COMPOTJN'DS IN CHEESE EXTRACTS. 



(a) Total icater-solnUe nitrogen is determined in an aliquot part 

 of the water extract. 



(b) Precipitation hy ahim. — To 100 cc, of water extract, 2 cc. 

 of saturated alum solution are added and digested at 104° to 

 108° F. (40° to 42° C.) until precipitation is complete. The 

 precipitate is filtered, washed and then treated by Kjeldahl 

 method to determine nitrogen. 



(c) Coagulation by neutralising and boiling. — The clear filtrate 

 from (b) is exactly neutralized by dilute fixed alkali and heated 

 on water bath until coagulation is complete. The precipitate is 

 filtered, washed and its nitrogen determined by Kjeldahl 

 method. 



(d) Alhimoses. — To the filtrate from (c) two or three drops of 

 dilute (one to three) sulphuric acid are added, and then powdered 

 zinc sulphate to saturation. The mixture is heated on water 

 bath until precipitation is complete and the nitrogen is deter- 

 mined in the precipitate washed with saturated solution of zinc 

 sulphate. 



(e) Peptones. — To the filtrate of (d) two or three drops of 

 ' strong hydrochloric acid are added and then bromine in succes- 

 sive portions of a few drops at a time, accompanied by vigorous 

 shaking until the liquid becomes super-saturated. The nitrogen 

 in the washed precipitate is determined as before. 



(f) Amides. — (1) First Method. The nitrogen in filtrate from 

 (e) is determined directly by Kjeldahl method and this, less the 

 nitrogen present as ammonia, is the amide nitrogen. 



(2) Second Method. To 100 cc. of the original cheese extract 



