many sawmill plants, particularly in the West. It runs over a unit package, elevates it clear of the ground with an internal mechanism, conveys it where desired, and sets it down.

Figure 18 shows a car with elevated platform that facilitates high piling by hand. This photograph was taken in a Wisconsin mill yard by the Forest Products Laboratory.

A jack is often used in elevating lumber to the top of the pile, consisting of a bar which is inserted between the boards in a pile, with an iron spike in the end across which the board is placed, when by bearing down on the rear end the board can be raised to a vertical position and swung in reach of the man on the pile. The spike often marks the lumber, and Figure 19 shows an improved form of jack, the corrugated face of which holds the lumber securely without mak

Most of the lumber at this plant

is kiln-dried, but stock better suited for air-drying is piled here. Photograph courtesy of Forest Products Laboratory

ing holes in it. It will be noticed that the head has both horizontal and vertical swivels, so that it always swings flat to the face of the board.

Pile height is usually dictated by convenience, by the height to which the lumber can be elevated without labor costs mounting too heavily.

SIDE AND REAR SPACING OF LUMBER PILES

The drying rate of lumber in a yard is affected by the spacing between the piles, as well as the horizontal and vertical spacing within the piles, and the height of piling. Questionnaire replies show that a little over 41 per cent of them have a side spacing between piles of 32 feet or less, while the rest show spacing of 6 feet or more; and while 54 per cent use rear spacings of 8 feet or less, the others have rear spacings of 10 feet or more.

PILE STICKERS, AND CHIMNEY OR TUNNELS, AND SPACING BETWEEN BOARDS

Air seasoning of lumber is accomplished by the contact of air with the surface of the lumber and requires circulation of air throughout the pile. It is probable that the general movement of air outdoors, in light or heavier breezes, is the main motor power of air circula

FIGURE 15. Simple portable horse, one of a pair used in forming unit packages of lumber for mechanical handling. The horse indicates width and height of the pile and holds it off the ground so slings can be passed under

tion inside the pile. Another important factor is the tendency of air to become cooler by the evaporation of moisture from the lumber, which absorbs considerable quantities of latent heat, and this cooler air tends to sink downward and out of the pile at the bottom, drawing fresh air in its place. This movement tends to be most active where there is most evaporation from the lumber, and there

fore shows most activity in the greenest portion of the pile. This is a strong factor for even drying of the lumber throughout the pile, but it also introduces a factor of variability, in that the movement of air in the pile bottom is chiefly of air that has passed downward from the lumber above and whose drying power has been partially exhausted. It is air at a lower temperature and higher humidity than fresh air and consequently has a slower evaporative effect. If

FIGURE 16.-Sling used in handling unit packages by cable, as seen at Weyerhaueser cargo terminal at Baltimore, Md. The three cross arms are of steel and the two that pass under the arm are attached to the cable at one end, while the farther ends shown in the sketch are held by slip rings engaging in notches on the underside

in addition to the downward movement there is also a sidewise movement of air through the pile, this will bring fresh air in at the sides of the bottom of the pile, but the influence of the breeze is less potent near the ground.

In considering the influence of air circulation in the pile on drying rate it should be remembered that the lumber loses its moisture by surface evaporation, and chiefly, of course, from the largest sur

faces and nearest to the interior of the piece. Obviously, this evaporation is accomplished by air moving horizontally between the layers of lumber rather than by the streams that move downward through the air spaces between boards in the layer. The vertical movement of air is chiefly useful in promoting and assisting this lateral movement.

When dimension widths of lumber are being piled the spaces between boards in the layer will tend to line up vertically and thus produce continuous narrow chimneys. In piling random widths two or three such spaces may occasionally line up vertically, and downward circulation through the gap will impinge on the face of the board at the bottom and become diverted horizontally. This

FIGURE 17. Straddle lumber carrier seen in use in an eastern distributing yard and widely used around sawmills. It passes over a unit package, elevates it off the ground with its lifting mechanism, and carries it where wanted, letting it down on the ground again

may result in too rapid drying where the air current strikes the obstructing board, and random piled lumber usually surface checks more than where even widths are piled for this reason.

The Inland Empire air-seasoning study reports that four manufacturers are piling random-width western pine shop and selects with four or five vertical chimneys in the pile, spacing boards close together between these chimneys. This gives a positive vertical circulation and puts more lumber in the pile, reduces checking and also loss from blue stain, and produces a depreciation $2.75 per thousand feet less than that caused by the usual spacing in connection with a 12-inch center chimney. One manufacturer is also piling even-width stock in like manner, putting three close-spaced boards in each group when of 4 or 6 inch width and two boards together when of 8 or 10 inch width, using chimneys 5 inches wide between groups and 7 to 11 inch chimneys across the width. Such piling put 1,000 feet more

of lumber in the pile and produced an equivalent drying rate, with seasoning losses about the same; stain damage was reduced, and the stock dried to a lower average final moisture content. The " group method also facilitated piling.

A Louisiana hardwood millman used a similar expedient successfully in air-drying swamp oak which was very liable to surface checking. Numerous experiments showed that the most successful method was to make piles 6 feet wide with a center chimney, but with no

FIGURE 18.-Car with elevated platform, a very useful device in top-
piling of lumber. Photograph courtesy of Forest Products Laboratory

spaces between boards elsewhere. In the fastest-drying season the chimney was omitted.

The usual space left between boards in the course is about 3 to 4 inches. Experiments have shown that increasing this to 5 inches increases the drying rate but beyond that has little effect. Too open spacing may increase losses from surface checking. Undoubtedly good results would follow adjusting the spacing distance according to the season of year.

Questionnaire replies report that 20 manufacturers use spacing between boards of 3 to 4 inches, 15 use 5 inches up, and 14 use 2 inches