222 



MILK AND DAIRY PRODUCTS PART 



(1) The curve which gives expression to the figures obtained 

 in the distillation is characteristic of the acid in question. 



(2) A certain definite relation exists between the quantity of 

 acid which was present in the flask from the commencement 

 onwards, and the quantity which distils over at any given 

 time. It is thus possible, knowing the amount of acid in the 

 first 10, 20, 30, 40, etc., c.c. to calculate the original quantity of 

 acid in the distillation flask. 



(3) When a mixture of two acids is distilled, each acid 

 behaves as thoiigh it alone were present. 



Duclaux used lime-water for the titration, for when saturated it 

 has exactly the right alkalinity for titrating the small quanti- 

 ties of acid which occur. The strength of the lime-water is 

 first determined by titrating it against an acid of known 

 strength ; phenolphthalein being used as the indicator. If the 

 relation between the amounts of lime-water necessary to 

 neutralise the first 10, 20, 30, 40, etc., c.c., and the quantity 

 necessary to neutralise the total original amount of acid is 

 found, then there is obtained for each acid a series of numbers, 

 which may, if wished, be expressed by a curve. This curve is 

 characteristic of each separate acid. The figures obtained for 

 the ordinary volatile fatty acids are as follows : 



TABLE A. 



Instead of determining the relation between the quantity of 

 lime-water required for the whole of the acid and that used for 

 the successive fractions, it is simpler to calculate the relation 

 between the lime-water neutralised by the 100 c.c. of distil- 



