32 MILK AND DAIRY PRODUCTS PART 



If the amount of lactic acid corresponding to the degrees of 

 acidity is required, then it is only necessary to multiply by 

 0'0225 to get the lactic acid expressed in grams. 



In a later method by Soxhlet-Henkel, 100 c.c. of milk are 

 titrated with N/4> NaOH and 4 c.c. phenolphthalein solution, 

 and the number of cubic centimetres then gives the degree of 

 acidity. It is necessary to know, when dealing with the 

 " degrees of acidity according to Soxhlet-Henkel," whether the 

 titration has been made with 50 or 100 c.c. of milk. 



5. Thorners l Method of Titration. 



Ten c.c. are diluted with 20 c.c. of distilled water, 5 drops of a 

 5 per cent, alcoholic phenolphthalein solution added, and the 

 titration with JV/10 NaOH carried out in the usual way. The 

 number of cubic centimetres of JV/10 NaOH which are required, 

 multiplied by ten, expresses the degree of acidity for 100 c.c. 

 milk. If, for instance, 1*7 c.c. of N/10 NaOH are required to 

 neutralise 10 c.c. of milk, then the milk has 17 degrees of 

 acidity. 



This method is often preferred to the older Soxhlet method 

 because the quantity of milk required is less, and there is no 

 need to prepare a special N/4> NaOH solution ; the ordinary 

 JV/10 NaOH, which is always at hand in the laboratory, can 

 be used. 



Thorners method, however, has the disadvantage that the 

 dilution with water causes a loss of acidity, for some of the alka- 

 line calcium phosphate is brought into solution by the water. 

 This, of course, may be avoided by not adding water to the milk. 



Fresh milk has an average acidity of 16-18 degrees by 

 Thorner's method ; at 25 degrees and above the milk coagulates 

 on boiling. 



By multiplying the number of cubic centimetres of 

 N/W NaOH by 0'009, the amount of lactic acid in grams is 

 obtained. 



6. Domic s 2 Method of Titration. 



Domic uses a caustic soda solution which is somewhat stronger 

 than decinormal ; it contains 4'444 g. NaOH per litre. Nine 



1 Chemiker-Zeitung, 1892, Nos. 80 and 83 ; Milch- Zeitung, 1893, p. 58. 



2 Le Controle du Lait: Besan^on, 1897. 



