CONDITION OF THE DEAD TIMBER.

The principal defect of fire-killed timber is check. This appears soon after the death of the tree, and apparently does not greatly increase later. Timber above 9,000 feet elevation is not affected by decay for many years. Such timber has been used after more than fifty years have elapsed since burning, and vast quantities of timber killed by fire twenty or thirty years ago are entirely free from decay. Fire-killed timber should be barked soon after it is killed, in order to prevent decay of the surface. If the bark has been left on, the sapwood is somewhat decayed. Lodgepole pine and Engelmann spruce have about the same durability; after twenty-five years about 50 per cent is usually standing, and the fallen timber, if not flat on the ground, lasts five or six years. Balsam lasts about one-third as long. Standing Douglas fir lasts almost indefinitely, and even when flat on the ground decays but slowly. Yellow pine decays more rapidly, since it occurs mainly below an elevation of 9,000 feet. On the other hand, on account of the openness of its stand, it is rarely killed by fire.

STRENGTH OF FIRE-KILLED TIMBER.

In many places it is the popular opinion that dead timber is very much weaker than seasoned green timber. It is even held that timber which has been dead a number of years is weaker than green timber, and that the longer it stands the weaker it becomes. These views are quite wrong. By actual test it has been shown that sound timber, as a matter of fact, is almost as strong as seasoned green timber and much stronger than green timber before seasoning. The following table gives the strength of white fir (Abies concolor) killed by fire twelve years ago and that of green timber of the same species and from the same locality:

Seasoning greatly adds to the strength of timber, so that in order to make the comparison a fair one the green and the dead timber must be brought to the same condition of seasoning. When this is done, the tests indicate that dead white fir is about nine-tenths as strong as green white fir which has been seasoned and about twice as strong as green timber freshly cut.

USES OF DEAD TIMBER.

Since the principal defect of dead timber is check, it has been used largely in the round for mine timbers, coal props, telephone poles, railroad ties, and fence posts. The better grades are also used for dimension stock, which is not seriously affected by the shallow checks found in these grades. It is not much used for inch stuff, however, except as cut-up stock, because of frequent cross checks. The chief use to which dead timber is now put is for mine timbers. For this purpose it is even better suited than green timber, because it is perfectly seasoned and is light.

It is estimated that the mines of Leadville, Colo., use each month 350,000 feet B. M. of dead timber. There are also many other large mining camps that use it in wholesale quantities. In these camps it is decidedly preferred to green timber.

For fifteen years dead timber has been used for railroad ties in the Pikes Peak National Forest, where it has proved entirely satisfactory. Wherever dead timber is located sufficiently near the track, it is readily sold for ties. Douglas fir, limber pine, yellow pine, range pine, and, occasionally, Engelmann spruce, are the species used.

In Denver, Colo., dead timber has been used for a number of years for boxes, with excellent results. The species used were mainly Engelmann spruce and lodgepole pine. Limber pine and Douglas fir were also used in small quantities. The first two did very well, especially the spruce, which was used for such exacting packages as cracker and biscuit boxes. Dead timber is eminently suited for making boxes and crates, because it is odorless and is perfectly seasoned. A package made from it does not shrink or warp, but remains as tight as when first made. Since dead timber, when sawed, is largely cut-up stock, it should find a wide use for such purposes.

In smaller quantities dead timber has been used for telephone and telegraph poles, dimension stuff, and fence posts. In fact, it has been used for everything for which green timber is used, except thin sawed lumber, and there is no reason why it should not be used for this to a considerable extent also. Narrow widths of the best material, not damaged by checking, could be worked up into flooring and ceiling, and it could be used for second-grade lumber, which would not be seriously affected by a certain amount of checking.

The use of dead timber results in a double economy-the prevention of waste and a saving of more valuable timber for better uses.

CONCLUSION.

It is past question that sound dead timber, particularly when firekilled, has decided value and keeps this value for a considerable length of time. Decay does not readily affect it. The strength is

not impaired by standing in the dead condition. Some of it is checked, to be sure, but even the best sound green timber is sometimes checked very seriously in seasoning.

Sound dead timber has this especially in its favor: It is perfectly seasoned, and is therefore easily handled and cheap to ship.

Dead timber, moreover, is in an excellent condition for preservative treatment, as the moisture has evaporated from the wood so there is no watery sap to act as a mechanical barrier to the entrance of the preservative. Green or seasoned timber must be piled for several weeks before it is in a proper condition for treatment, or else it has to be subjected to various processes to season it artificially. This artificial seasoning is expensive and is liable to reduce the strength of the timber; therefore sound dead timber is really more valuable for preservative purposes than green is. It also happens that most dead timber in the West has an open, porous structure and can be treated by a simple and inexpensive process without the use of complicated apparatus required by other kinds of wood.

Property of the United States Ecvernment

Issued November 5, 1907.

United States Department of Agriculture,

FOREST SERVICE CIRCULAR 114.

[NOTE.-The Forest Service has received many inquiries about the commercial distillation of hardwoods and softwoods and the quantity of the products obtained. It has been impossible to answer these inquiries by letter as fully as desired, and the growing need of a popular publication which would briefly state a few facts on wood distillation has been strongly felt. For this reason this circular has been compiled. It is not intended to be technical in nature or to contain the results of original investigations, but rather to furnish a few facts concerning the wood distillation industry as it now stands in this country. Circulars of a more technical character and dealing with concrete problems in wood distillation will follow.]

INTRODUCTION.

There are two distinct processes for obtaining valuable products from wood by distillation-destructive distillation and steam distillation. In the destructive process the wood fiber is broken down and new compounds are formed, but in the steam process this is not properly the case. In both processes the volatile compounds of the wood are vaporized.

In destructive distillation heat is applied below the wood-containing vessel, which has a comparatively small pipe as its only outlet. The heat vaporizes the volatile compounds, such as water and turpentine, and breaks down the nonvolatile compounds, such as cellulose and the wood gums; it forms a number of new compounds, usually of a simpler chemical nature, and these in turn are vaporized with the water and turpentine, leaving a residue of charcoal. The decomposition of the wood in this process is exceedingly complicated and is not yet fully understood.

In steam distillation, which is much simpler, the wood is chipped and placed in a closed receptacle into which steam is blown from a boiler, and the volatile compounds which are not chemically united with the rest are vaporized and carried out of the retort with the steam. Though in practice the wood is often so much overheated that the wood fiber is slightly decomposed, and though it is quite possible to carry the overheating so far that the process becomes one

of destructive distillation, it is nevertheless true that "steam distillation," as the term is technically used, signifies the separation of volatile products from wood with, at most, but little decomposition of the wood fiber.

With both these processes the vaporized compounds after leaving the retort pass through water-cooled tubes, where they are condensed into the crude liquors which after refining yield marketable products. Different woods give different marketable products after distillation. Thus, the hardwoods-beech, birch, and maple-yield acetate of lime, wood alcohol, and charcoal, and longleaf pine yields turpentine, tar, pine oils, and charcoal. This difference in the products is due to the fact that pine woods are resinous, while hardwoods are nonresinous. From the point of view of products, therefore, it is necessary to distinguish between the kinds of wood used, as well as between the distillation processes.

DESTRUCTIVE DISTILLATION OF HARDWOOD.

Hardwood distillation has been an established industry in the United States for a number of years. The products already mentioned are wood alcohol, charcoal, and acetate of lime, each of which has important uses. The plants are located in the northern part of the United States, where, except for the Appalachian hardwood belt, the hardwoods are most common.

The woods used are largely beech, birch, and maple, with the last preferred. The wood is cut into cordwood lengths and allowed to season for a year. According to the best information, the amount of the products obtained from green wood and from ordinary dry wood is not different, cord for cord, but the higher water content of green wood dilutes the distillate and necessitates more fuel for the carbonization. Excessive seasoning will doubtless reduce the yield of valuable constituents. Body wood is better than slab wood. Very small wood, such as thin edgings, carbonizes so rapidly that it must be mixed with larger pieces. The problem of the destructive distillation of sawdust has not yet been satisfactorily solved.

APPARATUS.

Wood is heated or carbonized in three forms of apparatus: (a) In brick kilns, (b) in retorts, (c) in ovens.

The charring of wood is a process as old as civilization. In the early days the wood was charred under sod in the old charcoal kiln, which has been a familiar sight over a good part of the world. The modern charcoal kiln is so made that valuable vapors are condensed from the smoke, which in the old-fashioned kiln escaped into the air and were wasted. Kilns are now mainly used to produce charcoal for blast furnaces for pig iron. They are made of brick, with a circular base, and divided approximately into two semicircular sections. They hold each about 50 cords, and are charged and discharged by hand. The vapors are carried off into condensers, where the condensable ones are liquefied.

The name "retort" is given to a small form of cylindrical vessel holding about three-fourths of a cord. The retorts are set horizontally in brickwork, in pairs, each pair forming a "battery," and heated from beneath. They are filled and discharged from a single