THE VOLATILE PAET OF PLANTS. 43 



somepfhat according to the source whence it is obtained. 

 In the air-dry state, at common temperatures, it usually 

 contains about 10 % of hygroscopic water. It has, in 

 common with animal membranes, the character of swell- 

 ing up when immersed in water, from imbibing this 

 liquid ; on drying again, it shrinks in bulk. It is tough 

 and elastic. 



Cellulose, as it naturally occurs, for the most part dif- 

 fers remarkably from the other bodies of this group, in 

 the fact of its slight solubility in dilute acids and alkalies. 

 It is likewise insoluble in water, alcohol, ether, the oils, 

 and in most ordinary solvents. It is hence prepared in 

 a state of purity by acting upon vegetable tissues con- 

 taining it, with successive solvents, until all other mat- 

 ters are removed. 



The " skeletonised " leaves, fruit vessels, etc., which compose those 

 beautiful objects called phantom bouquets, are commonly made by dis- 

 solving away the softer portions of fresh succulent plants by a hot solu- 

 tion of caustic soda, and afterwards whitening the skeleton of fibers 

 that remains by means of chloride of lime (bleaching powder). They 

 are almost pure cellulose. 



Skeletons may also be prepared by steeping vegetable matters in a 

 mixture of potassium chlorate and dilute nitric acid for a number of 

 days. 



Exp. 22.— To 500 cubic centimeters* (or one pint) of nitric acid of dens- 

 ity 1.1, add 30 grams (or one ounce) of pulverized potassium chlorate, 

 and dissolve the latter by agitation. Suspend in this mixture a num- 

 ber of leaves, etc.,t and let them remain undisturbed, at a temperature 

 not above 65° P., until they are perfectly whitened, which may require 

 from 10 to 20 days. The skeletons should be floated out from the 

 solution on slips of paper, washed copiously in clear water, and dried 

 tinder pressure between folds of unsized paper. 



The fibers of the whiter and softer kinds of wood are. now much em- 

 ployed in the fabrication of paper. For this purpose the wood is rasped 



* On subsequent pages we shall make frequent use of some of the' 

 French decimal weights and measures, for the reasons that they are 

 much more convenient than the English ones, and are now almost ex- 

 clusively employed in all scientific treatises and investigations. For 

 small weights, the gram,, abbreviated gm. (equal to 15i grains, nearly), 

 is the customary unit. The unit of measure by volume is the cubic cen- 

 timeter, abbreviated c. c. (30 c. c. equal one fiuid ounce nearly). Gram 

 weights and glass measures gn:aduated Into cubic centimeters are fur- 

 nished by all dealers in chemical apparatus. 



t Full-grown but not old leaves of the elm, maple, and maize, heads of 

 unripe grain, slices of the stem and joints of maize, etc., may be em- 

 ployed to furnish skeletons that will prove vsiluable in the study of the 

 structure of these organs. 



