22 THE CHEMISTRY OF CATTLE FEEDING 



the formula given below to indicate the constitution of 

 succrose. 



CH 2 OILC.(CHOH) 2 .CH.CH 2 OH Fructose radicle 

 CH.(CHOH) 2 .CH.CHOH.CH 2 OH Glucose radicle 



Milk sugar, lactose, or lactobiose is a normal constituent 

 of the milk of all mammals, but so far as is known it occurs 

 nowhere else in nature. It may be crystallised from the whey 

 after separation of the fat and nitrogenous compounds. As 

 compared with cane sugar it is not so sweet to taste, is not so 

 soluble in water, and it decomposes more readily on heating. 

 As regards its action on polarised light, it is dextrorotatory, 

 but it exhibits the phenomenon of birotation, i.e. when first 

 dissolved in water, [a] D = -J- 83*99, but after standing for some 

 time it falls to 5 2 '5 3. At least three different modifications 

 exist, and the birotation is probably due to the change from 

 one to the other. The common modification obtained by 

 crystallising the sugar from concentrated solutions is hydrated. 

 The other two are anhydrous. 



Lactose is split up on acid hydrolysis into dextrose and 

 galactose. As both products are dextrogyrate the rotary effect 

 is not changed in direction but is altered in degree. 



Lactose reduces Fehling's solution, and the fact is held to 

 indicate that it contains at least one aldose group unaltered. 

 The union of the two hexoses is probably effected through the 

 other. The molecular constitution may therefore be indicated 

 by the formula 



CH 2 (OH).CH(OH).CH.CH(OH).CH(OH) 



O CH.O.CH 2 .(CH.OH) 4 CHO 



(Lactose.) 



Malt sugar, maltose, or maltobiose is produced along with 

 dextrine (p. 32) by the action of diastase (p. 84) on starch 



