The telegraph manual: a complete history and description of the semaphoric, electric and magnetic telegraphs of Europe, Asia, Africa, and America, ancient and modern.

692 TELEGRAPH POLES ON FRENCH LINES.
it is best to first prepare in a special cask a concentration of
the liquid, having about two and a quarter pounds of the sulphate for about twelve gallons of water. It is sufficient to take
from the cask ten parts for one hundred parts of water, which
is put into the reservoir situated at the foot of the scaffold.
In proportion as the liquid in the lead caps passes off, it must
be replaced. The workmen charged with this labor must
visit them several times during the night, in order that they
may not be left empty. The caps, however, may be made
large enough to hold a sufficient quantity of the solution to run
all night. When once the injection commences, it ought not
to be stopped.
After several hours the sap is seen to flow in the little gutter
or trough at the little or top end of the pole. When this is seen.
the injection is not yet completed, and it is only when the sulphate of copper is seen flowing out of the pole, that the injection has been perfected. For a pole twenty feet long, the injection requires thirty-six to forty-eight hours. For a pole
thirty-two feet long, at least five to six days. It frequently
happens, at the commencement, that the operation of absorption does not take place, on account of the collection of the
rosin of the pine at the butt end of the pole. This is easily
remedied by sawing off a slice at the end, and the replacement
of the lead cap. This difficulty may be avoided by allowing
the end of the pole to soak several hours in a vat or pool of the
sulphate solution, when the poles are brought to the shanty or
shed. A slice should always be sawed off the end of the pole,
before capped for injection. The liquid that runs from the
gutter or trough, will answer to soak the end of the pole, as
preparatory before injection.
When the post is properly injected, it is known by striking
at the small end with a hatchet, and the greenish hue of the
sulphate is seen. The fact can be ascertained also by employing the cyanuret of potassium. By rubbing this substance on
an unbarked part of the pole, the wood will become red.
This mode is carried on to a very great extent in the provinces of France, but a new mode in the application of the sulphate has been adopted, where many poles are to be injected.
This new mode requires less labor, and the injection is more
rapid, the solution of copper being pressed by a considerable
force, so that it will penetrate rapidly into all parts of the wood,
and completely drives out the sap.
In figure 2, it will be seen that the reservoir R is placed
upon a scaffold of about twenty-five feet high. It is fed by the
casks g g' g, in which the solution of the sulphate of copper is