THE ACTION OF HEAT, ALKALIES AND ACIDS 



265 



precipitate of calcium oxalate would form and the system as regards the 

 introduction of neutral salts would be unaffected. The prepared juices 

 were then heated in an autoclave for thirty minutes at a temperature of 115° C 

 corresponding to a pressure of 10 lbs. per square inch. The results were as 

 below : — 



The Action of Alkalies on Reducing Sugars. — If a solution of reducing 

 sugars, whether all dextrose or all levulose, or a mixture of these in any 

 proportion, be left for a sufl&ciently long time in contact with even very 

 dilute alkaU, a material is eventually obtained which is almost optically 

 inactive. At higher temperatures the change takes place ver\' rapidly. 

 On anal5''sis it will be found that the reducing power has also slightly de- 

 creased. This behaviour, which was first observed by Dubrunfaut^^, has 

 been explained by Lobry de Bruyn and Van Ekenstein^^ who have shown 

 that it is due to an isomeric change, the final position of equihbrium being 

 obtained with a mixture of glucose, fructose, mannose and glutose. Glutose 

 which has not been obtained in a crystalline state is said to have only half 

 the reducing power of the other sugars, and to its presence is due the major 

 part of the reduction in reducing power. It is to be observed that with dilute 

 alkah there is no actual destruction of sugar, but onl}' an isomeric change. 

 In cane juices the combination of reducing sugars present nearly always 

 is levo-rotatory. In the process of manufacture part of this levo-rotation 

 is destroyed so that the net dextro-rotation of the juice increases, and a 

 fictitious and unreal rise in purity may often be observed under conditions 

 where no purification is possible, and this change in rotation is accompanied 

 by a fall in the reducing power pointing to a loss of " glucose." The extent 

 of this rise in purity will depend on the alkalinity of the juice, the temperature, 

 and the duration of exposure. It ma}- easily reach one unit, and can be 

 observed between defecated juice and s\Tup, under conditions where the 

 only material removed is w-ater. The following observations were made by 

 the writer^* on juice with an acidity of about 0-5 c.c. normal per 100 c.c, 

 referred to phenolphthalein as indicator. The juice was exposed in a 

 pre-evaporator to a temperature of 110° -112° C. for from 10 to 12 minutes. 

 Each determination was made on a sample collected at intervals of 5 minutes 

 over a period of half an hour. 



Polarization gravity purit}^ before heating. Polarization gra\ity purity after heating. 

 85-22 ... 85-86 



84.97 •■• 85-99 



84-44 -•• 85-33 



85-41 ... 85-82 



85.12 ... 85.22 



83-45 ••- 84-55 



83-22 ... 83-61 



84-57 ••• 85.19 



Mean 84-55 ■•• 85-22 



