88 PROPERTIES OF CERTAIN AMINO-ACIDS. [CH. IV. 



(v.) Add more hot water to make the volume up to about 2 

 litres and shake vigorously. 



(vi.) Adjust the reaction to P H = about 8-1. 10 cc. of the 

 mixture is taken, treated with about 10 drops of cresol 

 red and titrated with 0-2 N.NaOH from a microburette 

 (or a i cc. pipette graduated in i/iooth cc.) until a 

 reddish purple colour is obtained. The bulk is then 

 treated with the corresponding amount of N. soda (i.e. 

 100 times the amount of 0*2 N. used). Should the 

 volume required exceed 100 cc., 40 per cent, soda can 

 be used, this being 10 N. The mixture is well shaken 

 at frequent intervals after the addition of the soda. 

 The reaction should now be alkaline to cresol red and 

 acid to phenol phthalein. 



(vii.) Add 15 cc. of toluol (to prevent putrefaction) and 2 grams, 

 sodium fluoride dissolved in about 10 cc. of hot water 

 (to decrease the action of oxidases). Shake well. 



(viii.) Add 70 cc. of the pancreatic extract described on p. 212, or 

 a corresponding amount of a commercial preparation of 

 trypsin (" liquor pancreaticus ") and mix well. 



(ix.) Clean the inside of the neck of the bottle with a cloth, insert 

 a cork, shake again, and stand the bottle in a water bath 

 or air thermostat at 37 to 40 C. for 4 days, shaking the 

 bottle every day without removing the cork. 



(x.) After 4 days add another 50 cc. of the pancreatic extract, 

 and allow the digestion to proceed for another 4 days, 

 making 8 days in all. 



(xi.) Remove the bottle from the incubator, and allow it to 

 stand at room temperature for 24 hours or longer. 



B. Filtration and acidification. 



(i.) Filter off the precipitate, which consists of tyrosine, un- 

 digested casein, etc., reserving it for the separation of 

 tyrosine described in Ex. 89. 



