134 



ANALYSIS OF MILK. 



is titrated with tliis, and the number of c.c. used divided by 10 

 will give the acidity in terms of lactic acid ; this practice is, 

 however, to be deprecated, as freshly-drawn milk has a very 

 distinct acidity, though lactic acid is in all probability absent. 

 The acidity of milk to phenol phthalein is due partly to the 

 mono- and di-basic phosphates, and partly to the dissolved 

 carbonic acid. 



Soxhlet and Henkel have proposed the use of 



N 



normal 



soda solution, and use a special apparatus (Fig. ] 3) ; they express 

 the acidity as degrees ; 1 Soxhlet-Henkel degree = the number 



Fig. 12.— M'Creath Acidimeter. 



.N 



of c.c. of ^ alkali used per 100 c.c. of milk ; it is to be regretted 



that this " degree " has been introduced, as it is 2-5 times larger 

 than the ordinary degree, and has caused confusion. 



Instead of using phenolphthalein, delicate neutral litmus 

 paper may be employed; milk is practically neutral to this. 

 The acidity can be titrated with fair accuracy, though the end 

 point of the titration is not well marked. There is more justifi- 

 cation for calculating the acidity to litmus as lactic acid, as both 



