THE VOLATILE FART OF PLANTS. 50 



EXP. 23. To prepare parchment ^oper, fill a large cylindrical ttst tubft 

 first to the depth of an incli or so with water, then pour 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, aud 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.&quot; 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 test for cellulose. 



EXP. S4. Spread a slip of unsized paper upoij 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 with a 

 weak solution of iodine,* when these dissolved portions will assume n&quot;- 

 fine and intense blue color. This deportment is characteristic of cellulose, 

 and may be employed for its recognition underlie microscope. If the 

 experiment be repeated, using a larger proportion^ acid, and allowing 

 the action to continue for a considerably longer\Kie, the substance 

 producing the blue color is itself destroyed or converted^ato sugur, 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 upontt: 



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. c. of alco 

 hol, add 100 c. c. of vrater to the solution, aud preserve in a well stoppered bottle. 



t According to Qrotiven, cellulose prepared from rye straw, (and impure ?) 

 requires several hours action of sulphuric acid before it will strike a blue colot 

 with iodine, (%er Salznrtnder BerlcM, ~ 467.) 



