60 HOW CROPS GROW. 
Chemical composition of cellulose.—This body is a com- 
pound of the three elements, carbon, oxygen, and hydro- 
gen. Analyses of it, as prepared from a multitude of 
sources, demonstrate that its composition is expressed by 
the formula, C,, H,, O,,, In 100 parts it contains 
Carbon, 44,44 
Hydrogen, 6.17 
Oxygen, 49.39 
100.00 
Modes of estimating cellulose.—In statements of the composition of 
plants, the terms fiber, woody fiber, and crude cellulose, are often met with. 
These are applied to more or less impure cellulose, which is obtained as 
a residue after removing other matters, as far as possible, by nlternate 
treatment with dilute acids and alkalies, but without acting to any great 
extent on the cellulose itself, The methods formerly employed, and 
those by which most of our analyses have been mide, are confessedly 
imperfect. Ifthe solvents are too concentrated, or the temperature at 
which they act is too high, cellulose itself is dissolved; while with too 
dilute reagents a portion of other matters remains unattacked. The 
method adopted by Henneberg, (Versuchs Stationen, VI, 497,) with quite 
good results, is as follows: 3 grams of the finely divided substance are 
boiled for half an hour with 200 cubic centimeters of dilute sulphuric 
acid, (containing 114 per cent of oil of vitriol,) and after the substance 
has settled, the acid liquid is poured off. The residue is boiled again 
for half an hour with 200 c. c. of water, and this operation is repeated a 
second time. The residual substance is now boiled half an hour with 
200 c.c. of dilute potash lye, (containing 114 per cent of dry caustic 
potash,) and after removing the alkaline liquid, it is boiled twice with 
water as before. What remains is brought upon a filter, and washed 
with water, then with alcohol, and, lastly, with ether, as long as these 
solvents take up anything. This crude cellulose contains ash and nitro- 
gen, for which corrections must be made. The nitrogen is assumed to 
belong to some albuminoid, and from its quantity the amount of the 
latter is calculated, (see p. 108.) 
Even with these corrections, the quantity of cellulose is not obtained 
with entire accuracy, as is usually indicated by its appearance and its 
composition. While, according to V. Hofmeister, the crude cellulose 
thus prepared from the pea is perfectly white, that from wheat bran is 
brown, and that from rape-cake is almost black in color. 
Grouven gives the following analyses of two samples of crude cellulose 
obtained by a method essentially the same as we have described. (ter 
Salamiinder Bericht, p. 456.) 
