LION IN ; This substance may be considered as a compound of carbon and water. It is of great importance in photography, first because pyroxyline is made from it, and secondly because paper is a nearly pure form of it.
Lignin forms the solid framework of plants. It is obtained in a pure form by removing from saw dust, or any other kind of finely divided woody fibre, all soluble matter, by steeping it in hot and cold water, boiling it in alcohol, water, solution of potass, weak hydrochloric acid, and lastly in distilled water, and then drying the residue at 212°. Or in addition to the above treatment, it may be bleached by chlorine, and rinsed in acetic acid. The cleansed and bleached fibres of linen or cotton, are tolerably pure lignin.
Pure lignin is white, tasteless, and insoluble in water, alcohol, ether, and the oils, or hydro-carbons. Its S. G. is 1.6. When acted on by a cold concentrated solution of sulphuric acid, it is converted into dextrine and grape sugar ; cold concentrated nitric acid converts it into xyloidin, having nearly the same properties as that obtained from starch ; the continued action of hot nitric acid on it produces oxalic acid; hydrochloric acid blackens, but does not dissolve it, and the acid becomes red or brown ; a hot and strong aqueous solution of produces oxalate and acetate of potass. It is evident, therefore, that in the process of making pyroxyline by acting on lignin with nitro-sulphuric acid, other com pounds may be formed which would in general be injurious in collodion.
Lignin combines' energetically with various salts and metallic oxides, and this property is very important in the arts of dyeing and calico printing, in which colouring matters are made to combine with textile fabrics ; and also in the preservation of timber from dry rot, and of canvas from mildew, he. This-property lies also at the founda
tion of the photographic processes on collodion and paper, for had lignin, in its natural form as paper, or in its altered form as pyroxy line, no power of combining chemically with metallic oxides, the photograph would merely lie upon the surface of the film, and could be blown by a breath or removed by a touch from it. It may how ever be the presence of the organic matter that is necessarily asso ciated with the material of photographs which either causes or assists them to fade.
ct,ty be preserved from dry rot by Kyan's patented proc,ess „ iu a solution of bichloride of mercury ; or in one of ot iron, sulphate of copper, or chloride of zinc. The latter cvecially useful in protecting sail cloth from mildew.
,vcobines energetically with calico and linen, and is much used 4, a mordant in dyeing.
ookly fibre appears to be permanent in dry air, or completely water %titer, but not when exposed alternately to the action of air akhl damp ; the ultimate effect of the gradual process of decay being Ow removal of all the elements but a portion of the carbon from the hoin. Hence it is that some forms of coal, as anthracite, are nearly pure carbon. One of the products of the decomposition of lignin is fire damp ;" another, carbonic acid. The beds of coal in different parts of the world are supposed to have been formed by the decom position of the forests of monster fems which at one time covered a large portion of the earth's surface, in all latitudes, before it cooled down to its present temperatum, and when its atmosphere was too much impregnated with carbonic acid to be fit for the support of animal life.