TESTS USED IN CHEESE-MAKING 443 



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 pinkish coloration 

 appears. This can be more readily perceived by plac- 

 ing beside the flask another flask half full of uncolored 

 diluted skim-milk. The coloration must be as slight 

 as possible and yet be appreciably distinct when com- 

 pared 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, especially when exposed to 

 light, and with others it may fade. If any deepening 

 of color is observed at any time, addition of dilute 

 skim-milk will reproduce the proper shade; in case of 

 fading, the addition of one or more drops of carmine 

 ink is called for. Skim-milk is used because, in case 

 of normal milk, the fat separates on standing, adheres 

 to the sides of the flask, and obscures the color. 



(b) Use of color-standard. — In neutralizing a 

 sample of milk, the color-standard is placed beside the 

 sample under examination for constant comparison 

 after each addition of alkali. The flasks should be 

 placed on a white surface and in a good light. In fresh 

 milks, it is usually found that 3 or 4 cc. of alkali is 

 sufficient to neutralize the milk. One can add 2 or 3 

 cc. of alkali at the start and then add it in smaller por- 

 tions, until the milk begins to show signs of neutrality, 

 after which the alkali is added drop by drop. 



(3) Precipitation of casein.- — (a) Addition of acid. 

 Into the neutralized sample of diluted milk, which 

 should be at a temperature of 65° to 75° F., one now 

 runs from a burette some of the standardized acetic 

 acid, adding the acid approximately in 5 cc. portions 



