Page:Willich, A. F. M. - The Domestic Encyclopædia (Vol. 4, 1802).djvu/472

436] means of Copying Machines:—we have, therefore been induced to subjoin the following directions.

First, the letter to be copied, must be written with good black ink, in which a little sugar has been dissolved. Damp, unsized paper, or such as has previously been rendered sufficiently porous by suspending it over steam, is then to be adapted to the size of such letter, and be laid on the writing, which ought to be in a dry state. Several clean sheets are now to be arranged on the copying paper; and a flat iron, moderately heated, should be passed uniformly over the whole, till it be thoroughly dried.—If the original be written on both sides, it must be placed between a double sheet of such unsized paper, and managed in the manner above directed; when an exact copy will be procured. In this instance, however, the iron must be applied with the greatest expedition, lest the unsized paper become too dry, or communicate its dampness to the ink; in which cases, either no impression would be taken, or the ink would sink: lastly, the iron ought to be pressed on the paper longer than is usual for single sheets; in order that the heat may be regularly diffused, and the full effect be ensured.  LIVERWORT.—All the indigenous species of the lichens contain a considerable portion of viscid matter; which has, by the Earl of, been successfully converted into a gum, possessing all the properties of the , 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 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 con-