IQ2 MODERN METHODS OF TESTING MILK 



filled to the mark and the milk run into a 2oo-cc. flask. 

 To this is added about 80 cc. of pure, soft water, pre- 

 ferably distilled. 



(2) Neutralizing the milk. To the diluted milk add 

 i cc. of phenolphthalein solution and then run into it 

 the alkali solution from the burette, in small portions, 

 shaking vigorously after each addition, until a faintly 

 but distinctly pinkish shade of color remains even after 

 considerable agitation. Marked excess of alkali must 

 be avoided. In this connection, the preparation and 

 use of a color-standard are desirable. 



(a) Preparation of a color-standard. More satisfac- 

 tory results in neutralizing can be attained by prepar- 

 ing a color-standard for comparsion, as follows : About 

 20 cc. of fresh skim-milk and 80 cc. of water are put 

 into a 2OO-CC. flask and a small amount of corrosive 

 sublimate added to prevent souring. A few drops of 

 ordinary carmine ink are considerably diluted with 

 water and this is carefully added, a few drops at a time, 

 to the diluted skim-milk until a faint but distinct pink- 

 ish coloration appears. This can be more readily and 

 accurately perceived by placing beside the flask another 

 flask half full of uncolored diluted skim-milk. The 

 coloration must be as slight as possible and yet be ap- 

 preciably distinct when compared with uncolored milk. 

 After the color-standard has been prepared, the flask 

 is stoppered. It is well to keep this standard in a dark 

 place when not -in use. With some carmine colors, the 

 pinkish shade in the milk deepens on standing espe- 

 cially when exposed to light, and with others it may 

 fade. - If at any time a deeper shade is observed, the 

 proper shade can be reproduced by slight dilution 



