Experiments in wood preservation have to do with the kind of preservatives it is best to use, the character of the wood to be treated, and the methods of injection. Experiments have developed the best methods for treating railroad ties, mine timbers, fence posts, wood paving blocks, telephone and telegraph poles, and wharf piling. Untreated mine timbers have been found to last only from 1 to 2 years, while treated ones are usually entirely sound at the end of 4 years. Untreated railroad ties last from 5 to 10 years, while treated ones will last over 15. Such experiments as these have shown the advisability of treating all kinds of timbers with creosote or zinc chloride, or some other preservative. Many new preservatives are being proposed or marketed each year by various companies or individuals. These are all tested to determine their value to prevent the growth of fungi in the wood. Their efficiency varies greatly and many of them have been shown to have very small value. Studies in wood distillation seek to find new woods which can be used for this industry, new and more efficient methods which can be employed, and new uses for wood waste and stumps. Charcoal, wood alcohol, acetate of lime, and tar are derived from the distillation of such woods as beech, birch, and maple, to which tar oils and turpentine are added for the pines and other resinous woods. These by-products of wood distillation have many uses, as well as the many products which are, in turn, made from these by-products. Charcoal is used in the manufacture of black powder, acetic acid is used in the manufacture of explosives, and wood alcohol is converted into formaldehyde for disinfection against contagious diseases. By means of temperature control methods developed at the Laboratory in the destructive distillation of hardwoods, the net gain per annum of one company's plant was over $17,000. About one-half of the plants of the country have adopted the new method developed by the Forest Products Laboratory. Experiments have been conducted by the Laboratory in the distillation of the needles of coniferous trees and the distillation of the crude gum of some of the important timber trees of the South and West. The oils distilled from many trees in this way have found great use for various purposes. Shoeblacking owes its peculiar aromatic odor, faintly suggestive of the deep spruce and hemlock woods, to an oil which is distilled from these same kind of needles. Evergreen tree leaf oils are used for the perfume of soap, and in the manufacture of liniments, insecticides, and medicinal preparations.