446 SCIENCE AND PRACTICE OF CHEESE-MAKING 



especially under proper instruction, no difficulty should 

 be found in recognizing quickly when the casein is 

 separated so as to give satisfactory results. 



(5) Titration with alkali. After filtration is com- 

 pleted, one measures 100 cc. of the filtrate with the 

 pipette into a cup and then runs into this from the 

 burette the standard alkali until a faint but distinct 

 pink color remains clearly marked throughout the 

 solution for half a minute or longer before beginning 

 to fade. The number of cc. of alkali used is noted and 

 this result is recorded as B. 



The last portions of the alkali must be added care- 

 fully, a drop at a time, agitating the mixture well after 

 each addition. The exact neutral point is not perfectly 

 sharp on account of the presence of phosphates, and 

 the appearance of the desired coloration is, therefore, 

 not as sudden and pronounced as might be desired. 

 With experience one should have no difficulty in get- 

 ting within one drop of the correct amount of alkali. 

 The chief precaution to be observed is to have the same 

 shade and duration of color every time. Thus, one 

 should not in one titration add alkali until a deep pink 

 coloration appears, lasting for some minutes, and in 

 another a coloration that disappears within 5 seconds. 

 In the case of milk rich in phosphates, the solution 

 usually grows quite turbid as the neutral point is ap- 

 proached, making it necessary to use more care in ob- 

 serving the color of the end-point of the reaction. 



If one desires to make a second titration of the same 

 filtrate, one can use 50 cc. of the remaining portion, 

 multiplying the result by 2 and recording this as B. 



(6) Calculation of results. The calculation of the 

 percentage of casein from (i) the amount of acid 

 used (A) in precipitating casein and (2) the amount 



