minated, as the brushes never come in contact with the printing
face of the mold; they merely polish the high built-up spots, thereby
insuring better electrical conductivity to the wax, and a more uniform
deposition of the copper shell.

Two of these especially designed machines are in constant operation in
the ad department, which means the highest grade of advertising
plates.

DEPOSITING THE SHELL

Those who are not technically familiar with electrochemistry are prone
to think that the length of time a mold is kept in the electrolytic
bath, i. e., the copper bath, determines the thickness of the shell
deposited thereon. As a matter of fact, one electrotyper may keep his
molds in the copper bath for three hours and get only as thick a shell
as another who keeps his in but two hours. The element of time does
not determine the thickness nor quality of the shell deposited.

The determining factors in this phase of electrotyping are the
composition of the electrolytic bath, its temperature, and the current
density applied. In addition, the purity of the materials, the
cleanliness of the batteries, the perfection of the electrical
connections as well as the distance between the anode and the cathode
are all matters of importance. These factors are all variables and
must be confined between narrow limits.

This important phase of manufacture in The Rapid Electrotype Company
is under the supervision of an electro-chemical engineer.

Plus this fact is the accuracy of mechanical operation in handling wax
molds from the time they are put into the batteries until they are
taken out with the shell deposited thereon and ready for tinning and
backing-up.

The molded cases are suspended at regular intervals of twenty inches
from an endless chain-conveyor operating directly over the batteries.
This conveyor carries the cases edge-wise through the electrolytic
bath between two rows of anodes which are four inches apart. At the
end of each battery the conveyor automatically lifts the cases out and
over into the next battery in the series, of which there are seven.
The eighth tub contains pure running water for washing the case after
the complete deposition of the shell.

The speed of this conveyor is regulated so that when the molded case
has reached the end of its journey through the series of seven
batteries, the other factors also being regulated, a shell of uniform
thickness and texture throughout is deposited thereon.