THE VOLATILE PAET OF PLANTS. 75 



starch Tvitli a little ivater, and pour the mixture into the hot liquid, drop 

 by drop, so as not to interrupt the boiling. The stai'ch dissolves, and 

 passes first Into dextrin, and finally into glucose. Conthiue the ebul- 

 lition for several hours, replacing' the evaporated water I'rom lime to 

 .time. To remove the sulphuric acid, add to the liquid, wliich may he 

 still milky from impurities in the starch, powdered chalk, until the sour 

 taste disappears ; filter from the snljihate of lime, (gypsum,) that is 

 formed, and evaporate the solution of glucose* at a gentle heat to a 

 syrupy consistence. On long standing it may crystallize or granulate. 



By this method is prepared the so-called potato-sugar, or starch-sngar 

 of commerce, which is added to grape-juice for making a stronger wine, 

 and is also employed to adulterate cane or beet-sugar. 



In the sprouting and malting of grain, glucosef is like- 

 wise produced from starch. 



Even cellulose is convertible into glucose by the pro- 

 longed action of hot dilute acids, and saw-dust has .thus 

 been made to yield an impure syrup, suitable for the pro- 

 duction of alcohol. 



In the formation of glucose from cellulose, starch, and dextrin, the 

 latter substances take up the elements of water as represented by the 

 equation 



Starch, &c. Water. Glucose. 



CjsHmOio + 2H2O — CijHjiOij 



In this process, 90 parts of starch, &c., yield 100 parts of glucose. . 



Trommerh Copper test. — A characteristic test for glucose and levulose 

 is found in their deportment towards an alkaline solution of oxide of 

 copper, which readily yields up oxygen to these sugars, being itself re- 

 duced to yellow or red suboxide. 



Exp. si. — Prepare the copper test by dissolving together in 30 e. c. of 

 warm water a pinch of sulphate of copper and one of tartaric acid ; add 

 to the liquid, solution of caustic potash until it feels slippery to the 

 skin. Place in separate test tubes a few drops of solution of cane-sugar, 

 a similar amount of the dextrin solution, obtained in Exp. 28 ; of solu- 

 tion of glueose, from raisins, or from Exp. 30 ; and of molasses ; add to 

 each a little of the copper solution, and plaee them in a vessel of hot 



* If the boiling has been kept up but an hour or so, the glucose will contain 

 dextrin, as may be ascertained by mixing a small portion of the still acid liquid 

 with 5 times its hulk of strong alcohol, which will precipitate dextrin, but not 

 glucose. 



+ According to some authorities, the sugar of malt is distinct from glucose, 

 and has been designated maltose. Probably, however, the so-called maltose is a 

 mixtore of glucose and dextrin. 



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