ON MILK AND MILK-TESTING 5 



What is the theory of an envelope surrounding fat- 

 globules? 



Some chemists have been unable to find any such 

 covering, but Storch says he has found it to exist, 

 and that it is composed of 94 per cent water and 64 

 per cent proteids. 



How is the acid in milk, cream starters, or butter- 

 milk measured? 

 By an acidimeter. 



Describe an acidimeter and the method of testing. 



There are several tests for measuring acid, and 

 sold on the market under different names, such as 

 Publow's, Mann's, Farrington's, and Marshall's, but 

 the principle is the same in all of them. An alka- 

 line solution of known strength and an indicator 

 called phenol-phthalein are the reagents used. The 

 purpose of the indicator is to indicate the reaction 

 of the milk or cream ; that is, it shows whether the 

 milk or cream is acid, alkaline, or neutral. The 

 indicator has no color effect in an acid solution, 

 but it turns an alkaline substance red. . When the 

 neutral point is reached, the faintly pink color is 

 barely distinguishable. 



To make the test: A known qtfantity of the 

 milk or cream to be tested is placed in a white cup. 

 To this a few drops of indicator are added. An 

 alkaline solution of known strength is then allowed 

 to run in, drop by drop, from a graduated burette 

 until the milk or cream assumes a faintly pink 

 color, which signifies that all the acid in the milk 

 or cream has been neutralized by the alkali used. 

 The amount of alkali used can be read on the 



