VEGETABLE FIBEE AND CELLULOSE 357 



tissues of the plant, the soft parts, as of leaf, flower, and fruit, 

 being composed of more or less rounded cells, while the wood 

 and veins of the leaves and other parts consist of fibres. The 

 cells and fibres contain sap, which is water holding in solution 

 gum, sugar, albuminous and saline matters, together with solid 

 deposits of starch, green colouring matter (chlorophyll), crystalline 

 solids, and resinous incrustations. Now when a mass of vegetable 

 tissue, say sawdust, has been boiled with water, with caustic 

 soda, with alcohol, and other solvents a mass of colourless, 

 odourless, and tasteless material remains, composed of the 

 membrane which forms the wall of the cell and consists of 

 cellulose. This is the universal basis of vegetable tissue as already 

 explained. Cellulose is found naturally in a nearly pure form as 

 cotton, the hair from the seed of several species of gossypium, 

 which grows in tropical and sub-tropical climates. Examined 

 under the microscope cotton is seen to consist of long translucent 

 fibres more or less flattened and twisted. 



In the form of cotton wool, and woven in the various cotton 

 and linen fabrics, as well as in paper, cellulose is familiar. But 

 regarded from the chemical point of view the question is more 

 difficult. Its composition is expressed by the formula (C 6 H 10 5 )n, 

 but it seems not improbable that the substance called cellulose 

 may consist of a mixture of two or perhaps more substances of 

 the same ultimate composition, with some difference of con- 

 stitution. Cotton wool duly washed and purified may be re- 

 garded as normal cellulose, of which, however, the value of n 

 in the above formula is unknown, that is the molecular weight of 

 the compound is unknown. Though insoluble in all ordinary 

 neutral solvents cellulose behaves towards acids as a kind of 

 alcohol, yielding sulphates, nitrates (gun-cotton), acetates, and 

 benzoates when acted on by the respective acids. 



There are, however, several liquids which possess the property 

 of dissolving cellulose' without obvious change of composition, so 

 that by appropriate treatment of the solution a substance having 

 the same composition as cellulose may be recovered in the form 

 of a gelatinous mass. Very important practical applications of 

 these facts have been made within comparatively recent times. 

 Thus it has long been known that a solution of copper oxide or 

 hydroxide in solution of ammonia will dissolve cellulose, and 

 that when the liquid is neutralised by an acid or mixed with 

 various other liquids the cellulose is thrown down again as a 



