GLUCOSE 



97 



Preparation. 



The most convenient source for the preparation of glucose 

 on a small scale is cane sugar. One hundred and twenty c.c. 

 of 90 per cent alcohol mixed with 5 c.c. of fuming hydro- 

 chloric acid are heated at 45-50° ; 40 grams of powdered cane 

 sugar are now added, the mixture being kept thoroughly 

 stirred. After two hours the solution is allowed to cool, and 

 a little anhydrous glucose is added to induce crystallization. 

 In the course of a few days the resulting crop of crystals is 

 filtered off and washed with a little dilute alcohol ; it is recrys- 

 tallized by dissolving in half its weight of warm water and 

 adding twice as much 90-95 per cent alcohol, filtering warm 

 and setting aside to cool. 



On a commercial scale glucose is best prepared by heating 

 freshly prepared potato or maize starch freed from nitro- 

 genous material with dilute sulphuric * acid in sealed copper 

 vessels under 3 atmospheres pressure for half an hour. When 

 the hydrolysis is complete, the acid is removed as calcium 

 sulphate by the addition of powdered chalk, and the filtered 

 solution, after being decolorized by means of animal charcoal 

 is evaporated in a vacuum ; a little anhydrous glucose is then 

 introduced, and the syrup is allowed to crystallize, the crystals 

 being separated from the mother liquor by means of the 

 centrifuge. 



Prepared in this way the glucose forms a rather soft 

 cake of small crystals of the hydrate CgHigOe . HgO ; it is 

 liable to contain small quantities of maltose, isomaltose 

 (p. 117), and dextrin from which it may be further purified 

 by crystallization from alcohol. 



Commercial dextrose is employed as a substitute for cane 

 sugar for the sweetening of cheap jams, etc., but its sweetness 

 is only about two-thirds that of cane sugar. 



In the United States it is used largely in the manufacture 

 of ice cream, chewing gum, etc., and owing to its high osmotic 

 pressure and low sweetening power it is recommended for 

 use in condensed milk. 



* More recently the use of hydrochloric acid has been recommended ; 

 this involves a modification of the technique for the removal of the acid. 



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