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 13 H 30 O 10 . 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 alternate 

 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 made, are confessedly 

 imperfect. If the solvents are too concentrated, or the temperatuie at 

 which they act is too high, cellulose itself is dissolved ; while with too 

 dilute reagents a portion of other matters remains unattacked. Tho 

 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 1} 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 1% 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 th 

 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 ia 

 brown, and that from rape-cake is almost black in color. 



Grouven gives the following analyses of two samples of crude cellulost 

 obtained by a method essentially the same as we have described. (2to 

 t, p. 456.) 



