_Chlorine._—Dry chlorine gas has no action upon jute even when the temperature is raised to 140° C. (284° F.), but the presence of moisture determines rapid combination, at ordinary temperature, accompanied by evolution of heat. The colour of the jute changes to a bright yellow, which, on treatment of the fibre with a solution of sodium sulphite, gives place to a pure magenta. This reaction is characteristic of all lignified tissues, and is a valuable aid in the micro-chemical examination of plant structures. For this purpose, the reagent may be employed in the form of chlorine water; the sections or small fragments to be examined are allowed to remain in this solution a short time, and then mounted for observation in a dilute solution of sodium sulphite. By combination with chlorine the fibre substance or _ligno-cellulose_ is partially resolved. Alcohol dissolves away from the chlorinated fibre, a bright yellow substance, which is precipitated in yellow flocks on pouring the solution into water. This chlorinated derivative has the composition C_{19}H{18}Cl_{4}O_{9}. By this formula, as well as by its colour reactions, and by its yielding protocatechuic acid on fusion with potash, it is {19} shown to be related to the trihydric phenols, and to the tannins which are derivatives of these. After dissolving away this compound by exhaustive treatment with alcohol, the fibre still gives a brilliant reaction with sodium sulphite, showing that a portion is still held back in combination with the cellulose, or cellulose residue. On treating the residual fibre with boiling nitric acid, a considerable quantity of chloropicrin CCl_{3}NO_{2} is formed, and it is probable that the union of the molecule C_{19}H_{18}Cl_{4}O_{9} with the cellulose may be effected by the aldehyde[5] molecule CCl_{3}COH; each group being contained in the original lignocellulose, the action of the chlorine tending to disturb the atomic equilibrium and to rearrange the atoms into groups, which in their modified form have less mutual coherence. If the chlorinated fibre be directly boiled with the sodium sulphite solution, its resolution into cellulose and soluble non-cellulose derivatives is complete: and this treatment constitutes the most simple and rapid method of estimating the cellulose in lignified tissues. It is only necessary finally to wash the cellulose with hot water containing a little acetic acid (when placed in a funnel it acts as its own filter), and then with, alcohol, when it may be dried and weighed. In order to ensure the resolution of the fibre by a single chlorination (in the case of jute, and the like), it must, previously to exposure to the gas, be boiled in a dilute (1 per cent.) solution of potassic hydrate. In the case of wood and other more resistant structures, it will be necessary to repeat the chlorination. [Footnote 5: Furfural may also be isolated from the chlorinated jute; the survival of this aldehyde is noteworthy.]