60 HOW CEOPS GEOW. 



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,„ 0„. In 100 parts it contains 



Carbon, 44.44 

 Hydrogen, 6.17 

 Oxygen, 49.39 



100.00 



3Iodes of estimating cellulose.— In 6tatements of the composition of 

 plants, the ievms fiber, woody fiber, and crude cellulose, are olten met with. 

 These are applied to more or less impure cellulose, wliich 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. Tlie methods formerly employed, and 

 those by which most of our analyses have been m:ide, are confessedly 

 imperfect. If the 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 unattached. The 

 method adopted by Henneberg, {Versuchs Statiotien, 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. o. of water, and this operation is repeated a 

 second time. The residual substance is now boiled half an hour witli 

 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 etiier, as long as these 

 solvents take up anythin^^ 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, aa is usually indicated by its appearance and its 

 composition. While, according to V. Hofmeister, tiie 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 celluloBO 

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

 Salzmiinder Bericht, p. 456.) 



Digitized by Microsoft® 



