GRAPE-SUGAR. 195 



verted, first, into dextrin, and, after continued diges- 

 tion, into sugar. 



Properties. Obtained from the aqueous solution, it 

 forms colorless, not very hard, granular, crystalline 

 masses, with 1 molecule of water of crystallization; 

 crystallizes from alcohol in fine anhydrous prisms, 

 united in compact nodular masses ; easily soluble in 

 water (in its own weight), difficultly soluble in abso- 

 lute alcohol ; fuses below 100, the water of crystalli- 

 zation being given off. 



A solution of grape-sugar rotates the plane of polari- 

 zation towards the right; reduces the noble metals 

 from their solutions ; on the addition of alkalies turns 

 bismuth nitrate a dark color; and, with the aid of 

 heat, separates copper suboxide from an alkaline copper 

 solution;* from an alkaline solution of mercury cya- 

 nide, metallic mercury. 



Grape-sugar can be mixed with concentrated sul- 

 phuric acid without discoloration, and forms with it a 

 saccharo-sulphuric acid, which gives a soluble barium 

 salt. 



It combines with bases, suffers a change, however, 

 very rapidly, particularly with an excess of alkali and 

 access of air, the solution becoming brown, and humus- 

 substances being formed. A solution of grape-sugar, 

 saturated with lime or baryta, and allowed to stand for 

 a long time without access of air, becomes neutral, the 

 sugar being converted into glucic acid C 12 H 18 9 . This 

 is amorphous, deliquescent ; tastes and reacts acid. 

 Sodium chloride and grape-sugar, dissolved together, 

 combine when the solution is allowed to evaporate 

 spontaneously, forming a very regular crystallizing 

 compound NaCI -f C 6 H 12 6 + 1JH 2 0. It crystallizes 

 sometimes from evaporated diabetic urine. It can 



* Fehling's Solution. Can be used for the quantitative estimation of 

 sugar. 1 molecule grape-sugar completely reduces 5 molecules copper 

 sulphate. For the preparation of this solution, 34.64 grm. of crystal- 

 lized copper sulphate, which is not effloresced, are dissolved in water, a 

 solution of 200 grm. Seignette salt (p. 182) or 160 grm. neutral potas- 

 sium tartrate and 600-700 grm. caustic soda of specific gravity 1.12 

 added, and the whole now diluted so as to make 1000 cc. 10 cc. of this 

 solution are completely reduced by 0.05 grm. grape-sugar. 



