Domestic Encyclopædia (1802)/Supplement/Liverwort
LIVERWORT.—All the indigenous species of the lichens contain a considerable portion of viscid matter; which has, by the Earl of Dundonald, been successfully converted into a gum, possessing all the properties of the Senega, at present used by calico-printers.—These vegetables abound chiefly on trees, growing in poor stiff soils: they attain to maturity in three or four years; so that a crop may be taken from the same tree, every fourth year.
The liverwort is furnished with an external skin, beneath which is found a green resinous substance: the remainder is composed partly of gum, and partly of an animal fibrous matter, that is insoluble both by heat and the action of alkalies. In order to extract the gum from such plants, they are first scalded two or three times in boiling water; in consequence of which, the rind or skin is separated, together with the greater part of the resinous ingredient. The vegetables, thus prepared, are next put into copper vessels and boiled, in the proportion of 1lb. to 2 gallons of water, for four or five hours; half or three quarters of an ounce of soda or pearl-ashes, or half a pint of volatile alkali, being added to every pound. The boiling is continued till the liquor acquires a gummy consistence; when it is strained through a hair sieve, and the residuum is expressed through hair-cloth bags, by means of presses similar to those used by tallow-melters.
The extract thus obtained, is then suffered to stand for 10 or 12 hours; after which it is strained, and evaporated in lead or tin vessels, placed over stoves moderately heated by fuel, or by the steam of hot water, till it be of a proper consistence for block-printing. If such gum, however, be intended for making ink, manufacturing paper, or staining and stiffening silks, crapes, gauze, &c. Lord Dundonald observes (in his Circular Letter addressed to the Calico Printers of Scotland), that no alkaline salts mast be employed for extracting the liverwort; and the boiling be continued for a longer time, and with a moderate degree of heat: thus, the gummy extract will become nearly colourless; but, if volatile alkali be used, it will be necessary to substitute iron vessels for those made of copper.
Lord D.'s gum has been found to answer every purpose for which it was designed: as its preparation is not only cheaper, and will produce a considerable saving of money annually sent to Senegal, but will also afford employment to numerous women, children, and others, in collecting, as well as in preparing, the lichens, it promises to be a national benefit.