te eS ee eS 
THE VOLATILE PART OF PLANTS. 75 
starcli with a little water, and pour the mixture into the ho. liquid, drop 
by drop, so as not to interrupt the boiling. The starch dissolves, and 
passes first into dextrin, and finally into glucose. Continue the ebul- 
lition for several hours, replacing the evaporated water froin 1ime to 
time. To remove the su!phurie acid, add to the liquid, which may be 
atill milky from impurities in the starch, powdered chalk, until the sour 
taste disappears; filter from the sulphate of lime, (gypsum,) that ie 
formed, and evaporate the solution of glucose* at a gentle heat toa 
syrupy consistence. On long standing it may crystallize or granulate. 
By this method is prepared the so-called potato-sugar, or starch-sugar 
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 eiements >f water as represented by the 
equation 
Starch, ce. Water Giucose. 
Cy2 Hoo Orin + 2H2O = Cig Hog Ore 
In this process, 90 paris of starch, &¢., yizid 190 parts of glucose. 
Trommer’s 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. 31.—Prepare the copper test by dissolving together in 30 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, 
»} Similar amount of the dextrin solution, obtained in Exp. 28; of solu- 
tio. of glucose, from raisins, or from Exp. 30; and of molasses; add to 
sach a little of the copper solution, and place 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 bulk 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. Provably, however, the so-called maltose is a 
mixture of glucose and dextrin. 
