50 MILK ANALYSIS 



than 5 c.c. of water. The mass is mixed thoroughly by shaking, 

 3 c.c. of the acid mixture are introduced and the process is 

 carried out as described, taking especial care not to overheat. 

 The volume of fat multiplied by 3 gives percentage. 



Most malted cereals are easily treated by the method, but 

 some contain insoluble cellular matter. With care, this will 

 not interfere. Sometimes previous treatment with diluted sul- 

 furic acid will render the material more tractable. 



The flasks should be cleaned promptly. 



Sugars. — If regard is to be given to the presence of invert- 

 sugar, a special method must be followed. The processes 

 first given consider lactose and sucrose only. 



Lactose. — The heating employed in the manufacture of con- 

 densed milk may reduce the rotatory power of the sugar suf- 

 ficiently to cause error in the polarimetric method. The reducing 

 power with alkaline copper solutions is not seriously affected. 



Sucrose. — This determination may be made by difference; 

 that is, subtracting the sum of the other ingredients from the 

 total solids. This will serve for ordinary inspection purposes, 

 since the amount present is almost always large, generally 

 more than the total of milk-solids, and an error even of several 

 per cent, does not affect the judgment as to the wholesomeness 

 of the sample. Exact work requires, however, that the cane- 

 sugar be determined directly, and several processes have been 

 devised for the purpose. Sucrose exerts but little action on 

 Fehling's solution, but invert-sugar acts powerfully, and some 

 processes depend on determining the reducing power before 

 and after inversion. Since the polarimetric reading is also 

 markedly changed by the inversion, the difference in polariza- 

 tion may be employed. Processes of fermentation may be so 

 conducted as to remove the sucrose (also any form of glucose) 

 while the lactose is unaffected. This method is chiefly valuable 

 for recognizing invert-sugar or either of its constituents. 



When inversion methods are used, they must be such as to 



