sing coal tar creosote and zinc chloride have proved
most efficient. The purpose is to force the preservative into the
pores of the wood, either by painting, soaking, or putting under
pressure. Such impregnation methods double or treble the life of
railway ties. It is now being used with great success to preserve
electric wire poles, mine-props, piling, fence-posts, etc.

Wood preservation has three great advantages, it prolongs the life
of timbers in use, reduces their cost, and makes possible the use of
species that once were considered worthless. For example, the cheap
and abundant loblolly pine can be made, by preservative methods, to
take the place of high priced long-leaf pine for many purposes.

PRACTICAL SUGGESTIONS FOR STORING LUMBER.

Under the hasty methods prevalent in the mill, very little wood comes
to the shop well seasoned, and it should therefore be carefully stored
before using, so as to have the fullest possible air circulation
around it. Where the boards are large enough, "sticking" is the best
method of storage, i. e., narrow strips of wood are placed at short
intervals between the pieces which are piled flat. The weight of the
boards themselves helps to prevent warping. Boards set upright or
on edge are likely to be distorted soon. It is often wise to press
together with weights or to clamp together with handscrews boards that
show a tendency to warp, putting the two concave sides together. Then
the convex side is exposed and the board may straighten thus: Fig. 58.
By wrapping up small boards in paper or cloth in the intervals between
work on them, they may be kept straight until they are assembled.

[Illustration: Fig. 58. Clamping up Boards to Prevent Warping.]

Another precaution to take is to be sure to plane both sides of a
board if either is planed, especially if the board has been exposed to
air-drying for some time.

WOOD MEASUREMENTS.

Lumber is a general term for all kinds of sawn wood. Logs may be sawn
into timber, that is, beams and joists, into planks, which are 2" to
4" thick, or into boards which are from 1/4" to 1-3/4" thick. These
may be resawn into special sizes.

Lumber is measured by the superficial foot, which is a board 1" thick,
12" wide, and 12" long, so that a board 1" thick, (or 7/8" dressed) 6"
wide and 12' 0" long, measures 6' B. M. (board measure). Boards 1"
or more thick are sold by the "board foot" which is equivalent to 12"
square and 1" thick. Boards le