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necks of these flasks should have an internal diameter of at least three- 

 fourths of an inch. The reason for this diameter is accessary if the milk 

 is neutralized in the Mask. This neutralization can be done in the beaker 

 into winch the milk is weighed, if weights are taken. Third, pipetfr -. a 

 Babcock milk pipette accurately graduated to deliver 17.5 ce. of milk, 

 when 17.5 cc. or 18 grams of milk are used. When 22 cc. or 22.6 grains of 

 milk are used it will be necessary to have a volume pipette graduated to 

 deliver the above amounts or a 25 cc. Mohr pipette graduated into 1/10 cc. 

 will be required, fourth, one 100 cc. pipette or a volumetric flask graduated 

 to hold 100 cc. Fifth, beakers of convenient sizes holding at least 200 cc. 

 Sixth, if standard solutions are to be made, measuring cylinders or volu- 

 metric flasks holding 1,000 cc. are needed. 



In regard to the making of the solutions it is best to prepare both the so- 

 dium hydroxide and the acetic acid as tenth normal. The accuracy of the 

 succeeding work depends primarily on the correctness of the standard 

 alkali and acetic acid. When it is desirable to make dilutions for different 

 quantities of milk it can be made from the tenth normal stock solution. 

 The phenol pthalein solution is prepared by dissolving one gram of phenol- 

 pthalein powder in 100 cc. of 50 per cent, alcohol. This should be neutralized 

 by the use of a few drops of ^ NaOH to a very slight pink color. 



Carrying out the operation. Weigh out 22.66 grams of milk, or measure 

 out 22 cc, neutralize in the beaker in which the weighing has been made, 

 using only enough alkali to give a very faint pink, then transfer to a 200 cc. 

 flask and wash out beaker with 75 to 80 cc. of distilled water, free from 

 carbon dioxide, shake and warm to 22° to 25° C. At this point observe 

 the color of the diluted milk. Frequently on dilution the pink color becomes 

 quite pronounced; if so, add a few drops of ^ acetic acid to a light pink. 

 Run in from a burette 25 cc. of a f acetic acid, frequently shaking, for milk 

 rich in casein it would require 30 to 40 cc. of acid. Then fill up to the 200 

 cc. mark, insert stopper and shake thoroughly. After standing for 5 or 

 10 minutes, filter, after filtration pipette or measure 100 cc. of the filtrate 

 into a 250 ce. or 300 cc. beaker and titrate to a permanent faint pink color, 

 record the cc. used. Since 25 cc. were added to the total volume and only 

 one-half titrated, we only take 12.5 cc. into consideration. From what has 

 been said a portion of the 25 ce. ~ acetic acid has been used in forming 

 free casein, therefore the difference between 12.5 cc. and the amount of 

 ^ NaOH used to neutralize the acid in the 100 cc. filtrate equals the number 



