COPYING-MACHINES. The various contrivances for procuring duplicates of writings without the labor of transcribing them, may be reduced to two classes. In the one, the writing is first made, and then copied; in the other, the copy and the original are pro duced at the same time. The essence of the first method is this- In writing the orig inal, an ink is used that is made for the purpose, or common ink thickened by the addi tion of a little sugar. When the writing is dry, a damped sheet of thin unsized paper is laid upon it, and over this a piece of oiled paper. The whole is then sub jected to pressure, and the damped paper is found to have taken off an impression of the writing. It is of course the reverse of the original, but the nature of the paper allows it to be read right on the other side. The machines for communicating the pressure are of various kinds. Some pass the sheets between rollers like the copper plate press; others act on the principle of the common printing-press. A simple plan
is to wrap the sheets round a wooden roller of about an inch diameter, lay this upon a table, and roll it under a flat board, pressing all the while. Another very common method of copying, is by means of prepared blackened paper laid between two sheets of thin writing-paper. The writing is traced firmly on the upper sheet, with a steel or agate point, or common black-lead pencil, and the lines are found transferred in black from the blackened sheet to the paper adjacent. By having several of these blackened leaves, a number of copies may be produced at once. The blackened paper is prepared by saturating it with a mixture of lard and lamp-black, and clean ing it so far that it will not soil paper unless pressed against it.