Experience has proved that even animal oils are so far injurious to timber as to render it brittle, whilst they preserve it from rottenness; and that, on the other hand, a mineral salt more or less combined with fatty substances does not produce that effect. The staves of whale-oil casks become quite brittle, whilst those of beef, pork, and tallow barrels remain tough and sound. Ships constantly in the Greenland trade have their timbers and planks preserved so far as they have become impregnated with whale oil.
Experiments with fish oil prove that of itself, unless exposed to sun and air, it may be injurious; that it loosens the cohesion of timber; but that animal fat, combined with saline matter, is preservative.
Fish oil used alone is ineligible, because capable of running into the putrefactive process, unless as a thin outside varnish. In hard, sound timber, it will hardly enter at all; and if poured into bore-holes in the heads of timbers, it will insinuate itself into the smallest rents or cracks, and waste through them. Used alone, or with any admixture, it is absorbed and dried quickly on wood in a decomposing state or commencing to be dry rotten. Used with litharge, it dries after some days; but with lamp-black it has scarcely so much tendency to dry as when used alone. Paint of fish oil and charcoal dries very quickly where there is absorption, and the charcoal extends its oxidating or drying effect to the fish oil in its vicinity.
We give the following to prove what we have written, and also to serve as an example for those who wish to try experiments:—
EXPERIMENTS ON FISH OIL.
June 9.—Upon a piece of old oak scantling, with its alburnam on one side in a state of decay, fish oil was poured several times, viz. on this day, on June 25, and July 3, which it rapidly absorbed in the decayed part.
July 26.—It was payed (or mopped) with fish oil and charcoal powder, and the following day it was put under an inverted cask.
October 1.—The end of this piece was covered with a greenish mould. This proves that fish oil must be injurious, except where exposed to sun and air to dry it.
A compound of fixed oils and charcoal is liable to inflame, but as a thin covering or pigment it may not be so.