THE VOLATILE PART OF PLANTS. 59 
Exp, 23.—To prepare parchment paper, fill a large cylindrical test tube 
first to the depth of an inch or so with water, then ponr in three times 
this bulk of oil of vitriol, and mix. When the liquid is perfectly cool, im- 
merse into it a strip of unsized paper, and let it remain for about 15 sec- 
onds; then remove, and rinse it copiously in water. Lastly, soak for 
some minutes in water, to which a little ammonia is added, and wash 
again with pure water. These washings are for the purpose of removing 
the acid. The success of this experiment depends upon the proper 
strength of the acid, and the time of immersion. If need be, repeat, va- 
rying these conditions slightly, until the result is obtained. 
Prolonged contact with strong sulphuric acid converts 
cellulose into dextrin, and finally into sugar, (see p. '75.) 
Other intermediate products are, however, formed, whose 
nature is little understood; but the properties of one of 
them is employed as a ¢esé¢ for cellulose. 
Exp. 24.—Spread a slip of unsized paper upon a china plate, and pour 
upon it a few drops of the diluted sulphuric acid of Exp. 23. After some 
time the paper is seen to swell up and partly dissolve. Now flow it witha 
weak solution of iodine,* when these dissolved portions will assume a 
fine and intense bluerolor. ‘This deportment is characteristic of cellulose, 
and may be employed for its recognition under the microscope. - If the 
experiment be repeated, using a larger proportion of acid, and allowing 
the action to continue for a considerably longer time, the substance 
producing the blue color is itself destroyed or converted into sugar, and 
addition of iodine has no effect.t 
Boiling for some hours with dilute sulphuric acid also 
transforms cellulose into sugar, and, under certain circum- 
stances, chlorhydric acid and alkalies have the same 
effect upon it. 
The denser and more impure forms of cellulose, as they 
occur in wood and straw, are slowly acted upon by chemi- 
cal agents, and are not easily digestible by most animals; 
but the cellulose of young and succulent stems, leaves, and 
fruits, is digestible to a large extent, especially in the 
stomachs of animals which naturally feed on herbage, and 
therefore cellulose ranks among the nutritive substances. 
® Dissolve a fragment of iodine as large as a wheat kernel in 20 ¢c. u. of alco- 
hol, add 100 c. c. of water'to the solution, and preserve in a well stoppered bottle. 
+ According to Grouven, cellulose prepared from rye straw, (and impure ?) 
roquires several hours’ action of sulphuric acid before it will strike a blue color 
with iodine, (2¢er Salzminder Bericht, p. 467.) 
