(33) Melsens impregnated blocks of wood with tar by alternate heatings and coolings; they were then kept 2 years in a corner of a garden in earth saturated with the products of a urinal, and were unaltered: on breaking across, it was found that lines were noticeable where the tar had not penetrated completely; the one set of split halves were kept some years in ordinary earth, the others carefully preserved; they were then steamed at 212° F. (100° C.) for 12 hours, quickly cooled in water, frozen, and left out in the open air all winter, at the end of which time they were unaltered. They were then placed in a wet situation in a garden, then on an isolated building, and then in sandy soil under a rain-water tub. Finally, after 20 years' exposure to varied deteriorating agencies, no change whatever was produced in them. By utilizing the mechanical force of condensing steam, or of the atmosphere, wood may be wholly or partially injected with tar (or other preservative agents); when not preserved, the natural course of decay is along the direction of growth, and not across it; the direction in which the preservative body is forced into the wood is the same.
(34) The value of creosote as a wood preserver is generally recognised, but the direct injection requires great quantities of heavy oil, and a desiccation of the injected pores. The high boiling-point of creosote does not permit its employment in vapour. Blythe formed the idea of saturating a jet of steam with creosote in minute division, forming, so to speak, a gaseous emulsion. The apparatus comprises a high-pressure steam-boiler; another boiler containing creosote, in which the steam is saturated; a vat, filled with creosote, to be pumped into the boiler; sheet-iron cylinders, for the pieces which are to be injected; and a system of tubing connecting the several parts. In this way Blythe completely fills the heart of oak, pine, or red beech; he uses 4 to 6 lb. of creosote for a cross-tie, and 4 lb. of brown phenic acid per cub. yd. of saturated wood or cross-ties. The apparatus can prepare 500 ties per day. The wood comes out softened, so that it can readily be bent or shaped, but it rapidly hardens. At first it shrinks, but after a few weeks it becomes seasoned, and resists the influences of moisture.
Finally, the fibres are greatly strengthened.
(35) Krug employs the following simple preparation for preserving wood used in mines by a combination of creosote and soda: - An iron basin, 1/8 in. thick, about 6 1/2 ft. deep, and 4 ft. in diameter, is sunk in the ground rather more than half its depth. By the side, and with its rim below the bottom of the first basin, is a second, not quite half its size. A third basin, about midway between the other two in size, stands with its lower edge rather higher than the upper rim of the first basin. This first one is provided with a cover, half of which is screwed on, the other half may be opened or shut close. Above the bottom it has a sieve-bottom of wire-gauze, and at the bottom a discharge-cock. Moreover, a pipe goes to the bottom, through which steam can be directly conveyed. From beneath the upper edge a pipe passes over the edge into the second basin. In the second basin is a hand forcing-pump, for pumping the impregnating fluid into the third basin, which is furnished with a discharge-cock. The operation is as follows: - The pieces of wood to be impregnated are cut to the suitable lengths required for door-posts, lintels, piles,* etc, and placed perpendicularly, as closely as possible, together in the first basin, the cover of which is then closed.
It is not necessary that the cover should be air-tight. Meanwhile, the third basin has been filled with creosote soda-lye, either directly or out of the second basin, by means of the hand-pump. The lye is then admitted into the first basin till it is about 3/4 full, and then steam is conveyed directly through the pipe mentioned before to the lye. The fluid gradually begins to boil, while it is increased by the condensation water of the steam, which pours in, and at last begins to flow away through the pipe which passes over the edge of the second basin. The steam is then turned off, and the wood may be left to boil for some time in the lye. When at last the lye has been discharged, and the wood been acted upon by direct steam, the cover of the basin is opened, and the impregnated wood removed. Although wood treated in this way is penetrated with the impregnating fluid only to the depth of 1/2 to 3/4 in., it has been found perfectly unimpaired after 5 years in districts where wood not so treated rots and becomes unfit for use after 9 or 12 months. Above ground, and in places where there is no danger of fire, it is sufficient to pour creosote-oil over the wood.
In a few days the wood will be sufficiently penetrated to withstand the action of the weather. (Stummer's Ingenieur.)
(36) The following method of preserving garden labels is recommended in a German paper: - Thoroughly soak them in a strong solution of copperas (sulphate of iron), then, after being dried, lay them in lime-water. This causes the formation in the wood of sulphate of lime, a very insoluble salt. The rapid destruction of labels by exposure to the weather is thus, it is said, prevented. Bast, mats, twine, and other substances used in tying up or covering trees and plants, when treated in the same manner, are similarly preserved. At a recent meeting of a horticultural society in Berlin, wooden labels treated thus were exhibited, and although they had been continually exposed for 2 years, they were apparently m no way affected.
(37) Paulet compares the relative advantages of copper sulphate and creosote. As regards the former preservative, this salt is poisonous to the vegetable and animal parasites which appear at the beginning of all organic decomposition. The quantity of salts of copper should be excessive when the wood is intended to be immersed in water or buried in a moist soil, because the water dissolves this salt slowly; and since sea-water enters into combination with it still more rapidly, it should be excluded from use for wood used in the sea. There is, in wood impregnated with the salts of copper, a portion of the sulphate closely united with the ligneous tissue, and another portion in excess remaining free. The latter portion dissolves first, and, carried off by the exterior fluids, only retards the loss of the metallic salt combined with the wood; but this combination itself, although more stable, does not escape removal, being accelerated or retarded according to the rapidity and ease with which the dissolving liquid is renewed. On the contrary, the quantity of metallic salts should be diminished in wood intended for constructions in the open air, in order to prevent the mechanical effect of intra-vascular crystallizations.