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

PREPARATION OF TELEGRAPH POLES. 689
with tar as far up the pole as forty inches above the surface
of the earth. In latter years, the poles are generally impregnated with a solution of sulphate of copper, for the particulars
of which I am indebted to Mr. Blavier.
The process of injecting the posts is simple, and easy of
execution on any route of the telegraph. To repeat, in
part, what I have stated in the preceding chapter, wood, exposed to air and moisture, very soon decays, first the white or
sap wood, and then follows, but in a less rapid degree, the
dark wood, or the heart. The alteration is the result of the
soluble substances contained in the wood, which, under the action of moisture and heat, ferment, decompose, and form acids.
Rottenness is, also, produced by worms and insects which feed
upon the soluble substances, and gnaw the woody fibres. Wood
containing the greater quantity of sap, the earlier decays;
while, on the contrary, wood with little sap, such as red-cedar,
black-locust, &c., remains solid for a very long time. It has been
found that by causing the wood to be penetrated, in every direction, by a solution of a metallic salt, the sap is forced out,
and the imperishable substances, precipitated into the cavities
of the wood, penetrating its fibres, so as to form in the interior
an unalterable compound, renders the wood more permanent.
The principal cause of destruction being thus removed, the
wood remains unchanged for an indefinite time, even under the
most unfavorable circumstances.
Mr. Blavier gives great credit to the success of Dr. Boucherie, who has given the subject much study and particular attention; and from the facts gathered on my repeated visits to
France, I am led to suppose the great desideratum has been
attained. He has made many experiments, and he has announced his preference for the material known as the sulphate
of copper. The best solution he found to consist of one pound
of copper to one hundred pounds of water. Among the materials which he tried were the pyrolignite of iron, sulphate of
zinc, and acetate of lead, but none of these equaled the sulphate of copper.
The mere soaking of the wood in the solution does not answer the purpose. The sulphate must penetrate into all the
pores, and take the place of the sap and other liquids in the
wood. In order to properly inject a cubic metre, or about three
and a half cubic feet of wood, about five and a half kilogrammes,
or about twelve pounds of sulphate of copper is required.
All parts of the wood are not susceptible of undergoing an
injection to the same and equal extent. A tree is formed of
two parts, the heart and the sap-wood. The sap-wood is trav44