In another and similar scheme a chemically treated paper is put on the
cylinder, and upon this, as it rotates, a metallic point is gently
pressed.
When the incoming electric current from the sending station passes
through the paper under the contact point an electrolysis occurs which
appears as a discoloration of the paper.
And as these discolored dots-and-dashes appear, as before, in an order
controlled by the distant station, a picture is again built up on the
paper, a copy of the picture at the sending station.
One of the best solutions for the purpose is made up of Iodide of
Potassium one-half pound; Bromide of Potassium two pounds; Dextrine or
Starch one ounce; and Distilled Water one gallon. (Use an iron contact
needle). There are other solutions made of Ferricyanide, but are not so
satisfactory.
Still another scheme, the simplest of mechanisms, consists of a metal
disc upon which electrolytic paper is clipped. This plate is then put on
the rotating table of a talking machine. A rubbing electrical contact is
made with the disc, and the other wire attached to the tone arm to
complete the circuit through the steel needle of the sound box.
As no groove is available to carry the arm toward the centre of the
disc, a spurred-wheel is attached thereto, so as to engage the paper on
the disc. The wheel can be adjusted diagonally of the tone arm to give
any separation required in the convolutions of the spiral line.
One of the schemes employed, and with considerable success for its time,
consisted of an engraving tool, moved up and down radially of a coated
cylinder, cutting a groove of varying width in the soft coating of the
cylinder.
When this coating was stripped off the cylinder, laid out flat and
hardened, it was mounted on a printing block, inked, and impressions
taken therefrom on a suitable printing press.