156 CANADIAN DAIRYING. 



that is, for a certain quantity of an acid a certain quantity of a 

 base is required to effect neutralization, and vice versa. Within 

 the past few years this knowledge has been turned to practical 

 account in the manufacture of cheese and butter, the result 

 being tha a convenient and rapid method of determining the 

 acidity of milk and its products has been placed in the hands 

 of dairymen. 



" The process of estimating the percentage acidity of milk 

 and its products by means of the alkaline solution may be 

 described as follows : The necessary quantity of the substance 

 ('io c.c. is convenient) being weighed or measured, as the case 

 may be, and mixed with distilled or rain water to a proper 

 state of dilution if necessary, an appropriate indicator is added 

 (three or four drops of phenolphthalein). Standard alkaline 

 solution is then cautiously added from a burette till the change 

 of color occurs. The alkaline solution should be of such a 

 strength that I c.c. of the solution will exactly neutralize .01 of 

 a gram of lactic acid ; therefore the percentage acidity (if io 

 c.c. of the milk be used) can be read direct by noting the 

 number of c.c.'s of the alkaline solution required to bring about 

 a permanent change in color. Example : Suppose io c.c. of 

 milk are placed in a beaker, the proper indicator used, and the 

 standard alkaline solution added until the color of the contents 

 of the beaker changes. We read the burette and find that 5.7 

 c.c. of the alkaline solution have been used. The acidity of 

 such milk would be .57. Why ? Because i c.c. of the alkaline 

 solution represents .01 of a gram of lactic acid ; therefore 5.7 

 c.c.'s of the alkaline solution would represent .057 of a gram of 

 lactic acid. 



" Now io c.c. of milk contained .057 of a gram of acid. 



"Therefore 100 c.c. of milk would contain .57 of a gram of 

 acid. 



" As phenolphthalein is the best indicator to use in testing 

 the acidity of milk, the alkaline solution should contain no 

 carbonate. Carbon dioxid interferes with the detection of the 

 end-point ; therefore every precaution should be taken to pre- 

 vent the solution from absorbing this gas. The accompanying 

 diagram shows a small bottle attached to the larger one, which 



