CHEMIi'AL PROPERTIES OF MILK-SUGAR. 15 



solvent extracts it from aqueous solution. Tlie second compound 

 is an anlij'dride of phenyl-lactosazone, and is almost insoluble 

 in kot water ; but can be crystallised from hot alcotol in yellow 

 needles whicli melt at 223° to 224° C. Milk-sugar is distinguished 

 from other sugars by its osazone forming an anhydride. 



By treating with strong cold hydrochloric acid the phenyl- 

 hydrazine groups are removed, and lactosone is formed. 



The relation between these compounds is shown by the following 

 formulic : — 



^^6rt"- Osazone. Osone. 



-Loir I H \[ 



H— C-OU 



/w 



HO 



c=o 



HC = 



\ 

 H 

 HC = N— N'^ 



The osone is" readily riM'oiiverted into osazone bv tr<>utnient 

 with phenylhydrazine acetate in the cold. 



By reduction with sodium amaluim a mixture of mannitol 

 and dulcitol, hexahydric alcohols of the formula (',;H, ,(),;, with 

 lactic acid and methj'l, iso-propyl :ind liexyl alcohols is formed. 



(Jn heiiting with acetic anhydride and sodium ac<'tate an oet- 

 acet^'l-lactose is formed. This ei-ystallises in stout prisms from 

 a mixture of alcohol and chlorofurm, and has an ill-defined 

 melting point about 'M)'^ C. Its solution in chloroform is opti- 

 cally inactive or very slightly Ucvo-rotatory. 



Aiilk-sugar dissolves lime, baryta, lead, topper, and mcrciirii' 

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

 pound with sodium chloride is known. 



Ammoniacal lead acetate precipitates milk-sugar from an 

 acjueous solution. 



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

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

 however, an enzpiic, 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 sub- 

 stances. 



The aitiou of acids generally is to eonvert it into glucose and 

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

 without action on milk-sugar -when heated for moderate periods. 



Preparation. — ililk-sugar is prepared on a large scale by 

 e\ aporating whev ik lacuo, after neutralisation of any acid v.'ith 

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



