ALDEHYDE VALUE 75 



for a nitrogen determination by the Kjeldahl method. Nitrogen 

 X 6.38 = Albumin. 



Total Acidity. Lactic Acid. 10 c.cms. of milk are placed 

 in a white porcelain basin, a few drops of phenolphthalein 



N 

 solution added and titrated with alkali until a faint pink 



colour is obtained. As the acidity of fresh milk is chiefly due 

 to phosphates, the expression of the acidity in terms of lactic 

 acid is somewhat misleading, although this is often done, 1 c.cm. 



N 

 of alkali being equivalent to 0.009 grm. lactic acid. It is 



preferable to express the acidity in degrees, i.e., the number of 

 cubic centimeters of normal alkali required for the neutralisa- 



N 

 tion of 1 litre of milk. The number of cubic centimeters of 



alkali required for the neutralisation of 10 c.cms. of milk, mul- 

 tiplied by 10 gives the required result in degrees. It is unfor- 

 tunate that in Germany the same term is used for a unit having 

 a very different value. The Sohxlet-Henkel degree usually 

 used throughout Germany is exactly 2.5 times greater than the 

 degree used in England and America. 



Aldehyde Value. Richmond and Miller's modification 

 (Richmond's Dairy Chemistry) of Steinegger's method is as 

 follows: 10 c.cms. of milk are made neutral to phenolphthalein 



N 

 with strontia, 2 c.cms. of 40 per cent formaldehyde addod, 



and again titrated to the same degree of neutrality. The 

 amount of the second addition of alkali less the amount re- 

 quired for the neutralisation of the formaldehyde added (pre- 

 viously determined), multiplied by 10 gives the aldehyde value. 

 This method is dependent upon the fact that the proteid 

 radicle is quantitatively converted to an acid by the aldehyde. 

 Richmond states that the strontia aldehyde figure is 1.1 times 



N 

 greater than that given with soda and that the former value 



multiplied by 0.170 will give a close approximation to the total 



