LIGNIN. From the Latin lignum, wood. The structuro of wood is determined by the superposition of a number of little cells or vessels, more varied in shape but somewhat resembling those of the honeycomb. The material composing this structure is cellulose [CELLS; TISSUES, VEOETABLE, in NAT. HIST. Div.], but the chief substance which fills up the cell, which incrusts and even penetrates the walls, and which gives firmness and hardness to the whole, is lignin. The harder and tougher a piece of wood, the more lignin does it contain.
The purification of lignin, so as to obtain it in a state sufficiently free from other matter to admit of a determination of its composition being made, is exceedingly difficult. Like cellulose it is insoluble in water, alcohol, ether, or dilute acids, and may therefore be freed from many other matters by successively treating it with these agents. Its chief characteristic is, however, a greater solubility in alkaline liquids than is possessed by celluloee.
Lignin contains a greater per centagc of hydrogen than is necessary to form water with its oxygen, whereas cellulose contains these two elements in exactly the required proportions, cellulose being represented by the formula whilst lignin has been described as Submitted to destructive distillation lignin yields acetic acid, hence the source of that acid, when wood DI strongly heated in iron cylinders, as described in treating of pyroligneons acid [AcErio Am]. That it is
the lignin which chiefly furnishes the acid is proved by the fact that the hardest varieties of wood—those containing most incrusting matter, or lignin —yield the largest amount of acid, when equal weights of the wood are operated upon.
Lignin is slowly acted upon by chlorine, and is dissolved by an aqueous solution of that gas. Sulphuric acid abstracts water from it, and sets free carbon. Iodine does not colour it. It is tasteless and odourless, and is insoluble in water and alcohol.
Lignin is identical with the substance noticed by Payen as Mati&T inerustante.
In its isolated condition lignin has no practical value, but the appli cation of it as ligneous fibre in tho manufacture of linen, cotton, hemp, &c., &c., is obviously of the highest importance.
Sec also LIGNIN, in NAT. HIST. Dtv.