58 HOW CROPS GROW. 



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

 remains by means of chloride of lime, (bleaching powder.) They are al 

 most pure cellulose. 



Skeletons may also be prepared by steeping vegetable matters in a mix 

 ture of chlorate of potash, and dilute nitric acid for a number of days. 



EXP. 22. To 500 cubic centimeter*,* (or one pint,) of nitric acid of 

 density 1.1, add 30 grams, (or one ounce,) of pulverized chlorate of pot 

 ash, and dissolve the latter by agitation. Suspend in this mixture a 

 number of leaves, etc.,t and let them remain undisturbed, at a temper 

 ature not above 65 F., until they are perfectly whitened, which may re 

 quire from 10 to 20 days. The preparations of leaves should be floated 

 out from the solutions on slips of paper, washed copiously in clear water, 

 and dried under 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 

 to a coarse powder by machinery, then freed from lignin, starch, etc. v 

 by a hot solution of soda, and finally bleached with chloride of lime. 



The husks of maize have been successfully employed in Austria, both 

 for making paper and an inferior cordage. 



Though cellulose is insoluble in, or but slightly affected 

 by dilute acids and alkalies, it is dissolved or altered by 

 these agents, when they are concentrated or hot. The 

 result of the action of strong acids and alkalies is very 

 various, according to their kind and the degree of strength 

 in which they are employed. 



The strongest nitric acid transforms cellulose i\\\o nitrocellulose, (pyrox- 

 Iline, gun cotton,) a body which burns explosively, and has been em 

 ployed as a substitute for gunpowder. 



Sulphuric acid of a certain strength, by short contact with cellulose, con 

 verts it a tough, translucent substance which strongly resembles bladder 

 or similar animal membranes. Paper, thus treated, becomes the vegetable 

 parchment of commerce. 



On subsequent pages we shall make frequent use of some of the French dec 

 imal weights and measures, for the reasons that they are much more convenient 

 than the English ones, and are now almost exclusively employed in all scientific 

 trestises and investigations. For small weights, the gram, abbreviated gm., 

 (equal to 15*4 grains, nearly), is the customary unit. The unit of measure by voi- 

 ume is the cubic centimeter, abbreviated c. c., (30 c. c. equal one fluid ounce 

 nearly). Gram weights and glass measures graduated into cubic centimeters are 

 furnished by all dealers in chemical apparatus. 



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

 ripe grain, slices of :he stem and joints of maize, etc., may be employed to fur 

 nish skeletons that will prove valuable in the study of the structure of 

 organs. 



