46 HOW OKOPS GROW. 



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 (Ce Hm 06)n. The value of n in this form- 

 ula is not certainly known, but is at least two, and the 

 formula C12H20O10 is very commonly adopted. 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 ob- 

 ta^Tied as a residue after removing other matters, as far as possible, by 

 alvernate treatment with dilute acids and alkalies. The methods are 

 6bnf essedly im^yerfect, because cellulose itself is dissolved to some ex- 

 tent, and a portioli of other matters often remains unattacked. 



The method of Henneberg, usually adopted ( Ts. Si. , VI, 497), 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 li 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 

 dilute potash lye (containing IJ per cent of dry caustic potash), and, after 

 removing the alkaline liquid, it is boUed 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 nitrogen, for which 

 corrections must be made. The nitrogen is assumed to belong to some 

 alHumlnoid, and from its quantity the amount of the latter is calcu- 

 lated ; (see p. 113). 



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 the crude cellulose thus prepared /rom the pea is 

 perfectly white, that from wheat bran is brown, and that from rape- 

 cake is almost black iu color, from impurities that cannot be removed 

 by this method. 



Grouven gives the follO"wing analyses of two samples of crude cellu- 

 lose obtained by a method essentially the same as we have described. 

 (iter ScUsmilnder Bericht, p. 466.) 



Bye-straw filber. Flaxfiiier. 



"Water 8.65 5:40 



Ash 2.05 1.14 



N 0.15 0.15 



C 42.47 38.36 



H 6.04 5.89 



40.64 48.95 



100.00 100.00 



On deducting water, and ash, and making proper correction for the 



