of copper, 67 per cent of nickel, and 5 per cent of iron, manganese, and silicon), firmly inserted in the surface of the masonry, or between the foundation and the wood, with the projecting edge bent downward at an angle of 45° and extending horizontally at least 2 inches from the face of the foundation. In masonry buildings this shield can be inset in the masonry at a height at least 18 inches above the ground.

Floor sleepers or joists imbedded in masonry or concrete, or laid on concrete which is in contact with the earth, shall be impregnated with an approved preservative.

Expansion joists between concrete floor and wall shall be filled with liquid asphaltum and the right-angle joint covered with a sanitary cement mortar or Portland-cement concrete finish of an arc of at least 2 inches in length.

The ends of wooden beams or girders entering masonry or concrete shall not be sealed in but shall be provided with boxes affording an air space at the end of the piece of not less than 1 inch at side of member, unless the ends of such timbers are impregnated with coal-tar creosote or other approved preservative. Where there are spaces under floors near the earth they shall be excavated so that there will be no earth within 18 inches of the wood, and they shall be provided with cross ventilation. Such ventilating openings shall be proportioned on the basis of 2 square feet for each 25 linear feet of exterior wall, except that such openings need not be placed in front of such building. Each opening shall be provided with 20-mesh noncorroding-metal screening, including windows and attics.

Where timber is used in roofs of the flat type, the roof shall, unless protected on the weather side with a waterproof covering, have a slope and run-off sufficient to provide proper drainage.

All wooden forms on foundations shall be removed from masonry work within 15 days; grading stakes shall be removed before laying concrete floors.

HOW WOOD PRESERVATION PREVENTS WASTE

Some species of wood such as the cedars, chestnut, cypress, white oak, redwood, etc., are more resistant to decay than others. This resistance is due to natural oils or preservatives found in the wood, particularly in the heartwood, which is the most durable part of trees of every species. The quality and quantity of these natural preservatives vary, and a consequent variation occurs in the life of wood, even within the same species, and in different parts of a single tree. In the pines and in Douglas fir occasional pieces are very resinous or pitchy. Wood thus saturated is extremely resistant to decay and gives very long life in contact with the ground or in other places where conditions favor decay. The decay resistance or durability of heartwood in service is greatly influenced by the nature of the attacking fungi and by conditions of exposure, as well as by these differences in the character of the wood itself.

The sapwood of practically all species has low decay resistance and generally short life under decay-producing conditions, if used untreated. It is to be remembered, however, that the sapwood of most species, by reason of its peculiar structure, lends itself much more readily than the heartwood to preservative treatment. The heartwood is penetrated by the preservative either with greater difficulty or not at all.

General statements comparing the relative decay resistance of different species can not be exact and may be very misleading if understood as mathematically accurate and applicable to all cases. They may be very useful, however, if understood as approximate averages only, from which specific cases may vary considerably, and as having application only where the wood is used under conditions.

which favor decay. The following classification of common native species is subject to these limitations.

From such service records as are available, supplemented by general experience, the heartwood of the following species may be classed as durable, even when used under conditions which favor decay Black locust, black walnut, the catalpas, practically all of the cedars, chestnut, the junipers, osage orange, Pacific yew, red mulberry, redwood, and southern cypress.

Similarly, the heartwood of aspen, basswood, cottonwood, the true firs (not Douglas fir), and the willows, when used under conditions which favor decay, may be classed as low in decay resistance. The heartwood of chestnut, Douglas fir, oak, red gum, southern yellow pine, tamarack, and western larch may be classed as intermediate. The heartwood of dense Douglas fir, honey locust, white oak, and dense southern pine may also be classed as intermediate but almost as durable as some of the species named in the high-durability group. The heartwood of the ashes, beech, the birches, the hemlocks, the red oaks, sugar maple, and the spruces may be considered on the border line between the intermediate and nondurable groups and can not with assurance be placed wholly in either group.

A proper knowledge of the decay resistance of wood, together with the correct use of species will, in a great measure, reduce waste. The drain upon our resistant woods has been heavy, and in many instances the supply has been reduced to such an extent that values have increased to proportions precluding their use for certain purposes. Many nondurable species can be made even more serviceable than most of the decay-resisting species in their natural state by accepted standard preservative treatment. In so far as the attack of insects is concerned, however, there is not the great difference in resistance of the various species that is noted in the case of decay.

As stated previously, the fungi that cause decay feed upon the wood, and when this food supply is poisoned by injection of preservatives the fungi can not grow. The action of the preservatives on insects is similar in that the treated wood is distasteful or poisonous to them, and they will not enter it.

It is to be noted, therefore, that proper preservative treatment according to approved standards performs a triple service. It increases the life of the wood three or more times that of the natural life, thereby saving the consumer the cost of replacement several times during the life of the treated timber; it makes the sapwood longerlived than the more durable heartwood, thus removing the necessity to specify heartwood for durability and permitting closer utilization of the timber; and it permits the use for construction purposes of naturally nondurable woods which otherwise would have much more limited usefulness.

Having definitely established the fact that wood can be made immune to attack of decay and insects, two very important things must be kept in mind if the greatest success is to be attained in that direction: (1) The preservative itself must be an effective one; and (2) proper methods of injecting the preservative into the wood must be followed. The mere subjection of wood to the process of treatment with a preservative material will not produce desired results if these two points are not rigidly observed.

PRESERVATIVES

To be successful, wood preservatives must be toxic enough to kill fungi and insects; and they must penetrate the wood to a sufficient depth and remain there. These requirements must be met, if protec tion is to be afforded the wood. In addition, from the standpoint of operation, the preservative should be available in large quantities, of uniform composition, and reasonably priced.

There are many preservative materials on the market to-day. Some have great value, some have little or none, and some are so recent we have not yet sufficient knowledge regarding their performance under service conditions to judge of their merits.

Preservatives fall into two general classes. In the first class are those of an oily nature like coal-tar creosote, which are relatively insoluble in water. In the second class are the salts which are injected into wood in the form of water solutions. Because of this great difference in composition of preservatives, it naturally follows that wood treated with preservatives of one class possesses qualities which recommend it more specifically for certain uses than wood treated with preservatives of another class. The choice of type of preservative, therefore, is determined largely through knowledge of the purpose for which the treated wood is to be used.

The two preservatives most widely used in the United States are coal-tar creosote and zinc chloride. These are the oldest known preservatives which are used on a large scale, and service records extending over a long period of years are available to prove their effectiveness. These preservatives were used for more than 98 per cent of the wood treated in the United States in 1928.

Although coal-tar creosote and zinc chloride have about equal toxicity to wood-destroying fungi in laboratory tests, study has indicated that the two preservatives diverge in effectiveness in accordance with the use to which the treated wood is put. For certain purposes and under certain conditions the effectiveness of one would be greater than the other, and vice versa. Certain properties of the various preservatives therefore control their use. With the usual amounts of these preservatives used to impregnate wood, there is greater toxicity than is necessary to kill fungi; but, on the other hand, injection of the full amount recommended is advisable in order to obtain proper distribution of the preservative throughout the wood and to provide a factor of safety.

COAL-TAR CREOSOTE

Coal-tar creosote is an amber black or brownish oil made by distilling coal tar. The character of the various creosotes available may vary to a considerable extent. Small differences in the creosote, however, do not preclude it from giving good service, and satisfactory results in preventing decay may be expected from any reasonably good grade of coal-tar creosote properly applied.

Coal-tar creosote is the most effective and generally useful wood preservative, but because of its character it has certain limitations in its uses.

Its importance to the wood-preserving industry is evidenced by the fact that 220,000,000 gallons were used for treating wood in 1928.

The advantages of creosote are its high toxicity, which makes it very poisonous to wood-destroying fungi and to insects; its resistance to leaching and its low volatility, which cause it to remain in the wood for long periods; its ease of application; the readiness with

FIGURE 4.-Timbers impregnated with creosote were used in the construction of this coal dock. In such structures long service and durability are assured because of preservative treatment.-Courtesy Forest Service

which its depth of penetration can be determined, and its general availability.

For general service in structural timbers there is no better preservative than coal-tar creosote. (Fig. 4.) For certain purposes,

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however, it has properties which are a disadvantage. It has an odor which may be disagreeable to some, but this largely disappears in time. The color of creosote and the fact that it can not be painted over very satisfactorily make it unsuitable for finish lumber or other material where appearance and painting are of major importance. For these purposes water-borne preservatives which can be painted over will be more satisfactory.

Creosote is generally used for treatment of timber where its odor is of little consequence and where painting is not necessary, in railroad ties; posts; telegraph, telephone, and power poles; wood block for factory floors and pavements; railroad and highway bridge timbers; conduits; sills and subfloors; fencing; and many other structural purposes. For building construction 6 to 8 pounds of creosote per cubic foot of wood injected by one of the empty-cell processes (Lowry or Rueping) is usually recommended.

ZINC CHLORIDE

Zinc chloride is obtained by dissolving metallic zinc in hydrochloric acid. A water solution of 3 to 5 per cent is prepared from this salt for injection into the wood. About 23,500,000 pounds of the dry salt were used for treating wood in the United States in 1928. The principal advantages of this preservative are its high toxicity to decay and insects, its cleanliness and lack of odor, its availability in uniform quality, its ease of shipment, and its partially fireresistant nature. Since it is a water-soluble salt, timber treated with it should not be used in water or in extremely wet locations. Wood treated with ordinary quantities of zinc chloride will not contain appreciably more moisture than untreated wood, in the same location. The water injected into the wood with chemical salts temporarily adds considerably to the weight of the wood, which usually must be dried out before use. Timber so treated must be thoroughly dried before the application of paint.

Zinc chloride is extensively used for the treatment of railway ties. Approximately one-fifth of the railway ties treated in the United States in 1928 were treated wholly or chiefly with it. Since railway ties are continuously exposed to the weather, a certain amount of leaching undoubtedly takes place, but except in the wetter parts of the country the leaching is not rapid enough to prevent zinc chloridetreated ties from giving good service. The length of life obtained from zine chloride treated wood in partly protected locations is, of course, considerably greater than that obtained under the severe exposure to which railroad ties are subjected.

Zinc chloride has no odor and does not discolor the wood, which can after treatment be painted with any desired color. (Fig. 6.) These advantages are largely responsible for the increasing use of zinc chloride treated lumber in the roofing and subflooring of textile mills and paper mills, in mines, and in miscellaneous structures. A substantial market is being developed for zinc chloride treated wood for floors and other portions of residences which must be protected from decay and termites, but which are not in contact with the ground.

Zinc chloride treated wood does not ignite as readily as untreated wood, although this preservative, in the amounts commonly used