Creosote oil has the following good points: (1) It fills the cells with oil, thus keeping water out. (2) It does not leach or lose strength in water or soil. (3) It is a fungicide, and is also poisonous to boring insects and crustaceans, like the white ants, the ship worm, and the Limnoria, creatures that honeycomb furniture, ship bottoms and wharves, giving no visible warning until the structure is a wreck. Creosote prevents the rusting of spikes and nails driven into timbers treated. They remain tight whatever happens. Creosote can be thoroughly applied with moderate cheapness. It can be had in large quantities from gas works. The average tie of white oak costs sixty cents and thirty cents to lay it. Creosoting costs but twenty cents additional. Treated ties are still sound after untreated ones have been replaced several times.
A very fortunate coincidence was discovered in the course of the investigations on wood preservation. Hard woods, like white oak and longleaf pine, do not absorb preservatives as rapidly nor as thoroughly as cheaper, more porous woods, with thicker sap wood, like red oak and Cuban pine. Therefore, the cheap woods, well saturated, outlive the dear ones. White oak, for which railroads offer fifty cents a tie, will bring double that sum at the furniture factory. Railroads cannot longer afford to use white oak. Beech, properly impregnated, will outlast white oak. Its normal life of five years can be extended to twenty-five years.
The Bureau of Forestry, with the co-operation of railroad corporations in different sections of the country, has elaborate experiments in progress bearing upon the preservation of wood. The work is disinterested and scientific, and creosoting is the method that has proved best. The important railroad systems of England and the Continent have reached the same conclusion. Creosoting ties is there as much a matter of course as laying them. The higher prices and greater scarcity of timber in Europe ex plain why they are so far in advance of us in the practice of wood preservation.
The importance of thoroughly seasoning wood before im pregnating it with chemicals cannot be over-estimated. Green wood, full of sap, resists the entrance of any substance, especially oils. Even if this difficulty could be surmounted, the seasoning of wood produces cracks through which decay gets in, and im pregnation counts for naught. Before treating, railroad ties are bored with holes for the entrance of the spikes, so that even these small apertures offer no untreated surfaces for water containing disease spores to enter.
Creosoting paving blocks, piles for bridges, wharves and cribs and the exposed hulls of wooden vessels is successfully and extensively done nowadays. The ship worm does not like the taste of treated wood, though this attenuated crustacean bores his way through the hardest of wood (except green heart) that is not medicated to discourage him.
Trees that fall in bogs and lakes lie too far down for destruc tion by fungous organisms. The water-soaked fibres have their protoplasmic contents dissolved out, and mineral substances held in the water are deposited by slow degrees. Bog oak of Ireland is black as ebony from bark to pith. It is also heavy by the weight of the mineral substance that impregnates its cells. Wood impregnation by natural processes reaches its highest perfection in the petrifactions that occur. The petrified forest of Arizona contains trees which preserve their form and structure, even to wood rings, but silica has been infiltrated to the utmost cell, turning the whole tree into agate, chalcedony or other forms of quartz. Montana has an extensive forest of trees turned to stone of a translucent, opaline character. The colours are blue, white and smoky black. Doctor Merrill of the National Museum found this forest in igo3, and his report wisely withholds its location. It is scarcely desirable that this remark able opalised wood should be nabbed by a syndicate and cut up into paper weights—a fate that has overtaken the fossil forest of Arizona.
Paint gives effectual protection to wood exposed to the weather, with its alternation of heat and cold, sun and rain. It needs renewing every few years. The basis of paint is oil— pure linseed oil being the best. Ground pigments mixed into the oil until it has the consistency of rich cream supply colour and filling. The paint applied, the oil soaks in and fills the wood cells, while the pigments form a protective layer, or film, over the surface. When this layer cracks and scales off, a fresh painting is needed Oil alone is a protective covering. Or oil may be left out, and pigments dissolved in other liquids may be applied. Whitewash is a familiar example of this treatment. All such applications last but a short time. In the chapter that follows some account is given of the processes that preserve wood and at the same time beautify it.