CHEMICAL PROPERTIES OF MILK-SUGAR. 33 



On heating with acetic anhydride and sodium acetate 

 an oct-acetyl-lactose is formed. This crystallises in stout 

 prisms from a mixture of alcohol and chloroform, and 

 has an ill-defined melting point about 90 C. Its solu- 

 tion in chloroform is optically inactive or very slightly 

 Isevo -rotatory. 



Milk-sugar dissolves lime, baryta, lead, copper, and mercuric 

 oxides, and probably forms compounds with them. No com- 

 pound with sodium chloride is known. 



Ammoniacal lead acetate precipitates milk-sugar from an 

 aqueous solution. 



It is not fermentable by ordinary yeast, and is unacted on by 

 invertase, diastase, rennet, pepsin, and trypsin. There exists 

 however, an enzyme, which has been called lactase, which is 

 found in fresh kephir grains, which hydrolyses it to glucose 

 and galactose. The enzyme does not appear to be present 

 in dried kephir grains, but is probably found in other 

 substances. 



The action of acids generally is to convert it into glucose and 

 galactose. Some organic acids, such as citric, are, however, 

 without action on milk-sugar when heated for moderate 

 periods. 



Preparation. Milk-sugar is prepared on a large scale by 

 evaporating whey in vacuo, after neutralisation of any acid with 

 lime and clarification with alum or other means, and allowing it 

 to crystallise. The product is purified by re-solution, treatment 

 with animal charcoal and re-crystallisation. In countries where 

 alcohol used for manufacturing purposes is free from duty the 

 sugar is precipitated from solution by this means instead of 

 being crystallised from water. 



On a small scale it is best to precipitate the protein 

 from milk or whey by as small a quantity of acid mercuric 

 nitrate as possible. The clear filtrate is neutralised with dilute 

 caustic soda solution till a very faint tinge is given with phenol - 

 phthalein ; it is filtered from the precipitate thus produced, 

 which consists of mercury salts. Sulphuretted hydrogen is 

 passed through the clear solution to remove the mercuric oxide 

 dissolved by the sugar, and, after filtration from mercuric sul- 

 phide, the sulphuretted hydrogen is expelled by boiling. On 

 evaporating the solution, milk-sugar crystallises out ; crystallisa- 

 tion may be hastened by vigorous stirring of the concentrated 

 solution while it is being rapidly cooled. 



Glucose and Galactose. These are two isomeric sugars of 

 the monose type. Both are aldoses or aldehydrols, and have 

 been obtained in three modifications (a- and /^-modifications, 

 and a stable equilibrium form). 



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