46 HOW CROPS 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 (C 6 H 10 5 )n. The value of n in this form- 

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

 formula C 12 H 2 o0 10 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 crutlf <v//"/o.se are often met 

 with. These are applied to more or less impure cellulose, which is ol>- 

 ta'ned as a residue after removing other matters, as far as possible, by 

 alternate treatment with dilute acids and alkalies. The methods are 

 confessedly imperfect, because cellulose itself is dissolved to some ex- 

 tent, and a portion of other matters often remains imattacked. 



The method of Henneberg, usually adopted ( J",s. >Y.,VI. 4 ( ,7, 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 1J 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 \\ 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 witli water, then 

 with alcohol, and, lastly, with ether, as long as these solvents take 

 up anything. This crude cellulose contains ash and nitrogen, for wliich 

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

 albuminoid, 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 from the pea is 

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

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

 by this method. 



Grouven gives the following analyses of two samples of crude cellu- 

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

 (2ter Salzmiinder Bericht, p. 456.) 



Rye-*t i-d 11- fi >>rr. Flax fiber. 



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 



