For additional remarks on iron, see chap. IX.
156. Nature and Strength of American Woods.
| Name of the wood. | Weight per cubic foot. | Resistance to Extension. | Resistance to Compression. | Value of S. | Elasticity. |
|---|---|---|---|---|---|
| White Pine | 26 | 12,000 | 6,000 | 1,229 | |
| Yellow Pine | 31 | 12,000 | 6,000 | 1,185 | |
| Pitch Pine | 46 | 12,000 | 6,000 | 1,727 | 4,900 |
| Red Pine | 35 | 12,000 | 6,000 | 1,527 | 7,359 |
| Virginia Pine | 37 | 12,000 | 6,000 | 1,456 | |
| Spruce | 48 | 12,000 | 6,000 | 1,036 | |
| Larch | 33 | 12,000 | 6,000 | 907 | 2,465 |
| Tamarack | 26 | 12,000 | 6,000 | 907 | |
| White Cedar | 22 | 8,000 | 4,000 | 766 | |
| Canada Balsam | 34 | 12,000 | 6,000 | 1,123 | |
| White Oak | 48 | 15,000 | 7,500 | 1,743 | 8,595 |
| Red Oak | 41 | 15,000 | 7,600 | 1,687 | |
| Live Oak | 72 | 15,000 | 7,200 | 1,862 | |
| White Beech | 44 | 18,000 | 9,100 | 1,380 | 5,417 |
| Red Beech | 48 | 18,000 | 9,000 | 1,739 | |
| Birch | 44 | 15,000 | 7,000 | 1,928 | |
| Black Birch | 41 | 15,000 | 7,200 | 2,061 | |
| Yellow Birch | 36 | 15,000 | 7,200 | 1,335 | |
| Ash | 38 | 16,000 | 8,100 | 1,795 | 6,581 |
| Black Ash | 35 | 16,000 | 8,000 | 861 | |
| Swamp Ash | 57 | 16,000 | 8,000 | 1,165 | |
| Hickory | 51 | 15,000 | 7,200 | 2,129 | |
| Butternut | 54 | 15,000 | 7,600 | 1,465 | |
| Ironwood | 54 | 16,000 | 8,100 | 1,800 | |
| Rock Elm | 45 | 16,000 | 8,011 | 1,970 | 2,799 |
| The mean tensile strength of wood is | 14,080 | lbs. |
| Reducing by 4 for safety | 3,520 | lbs. |
| Reducing for want of seasoning | 2,000 | lbs. |
| The reduced mean compressive strength | 1,000 | lbs. |
| Reduced resistance to detrusion | 150 | lbs. |
| Ratio of tensile to compressive strength | 2 to 1. | |
| Mean value of S in formula (WL = 4Sbd2) for the woods most used in practice | 1,250. | |
157. The lateral adhesion of fir was found, by Barlow, to be six hundred pounds per square inch. (Lateral adhesion is the resistance which the fibres offer to sliding past each other in the direction of the grain; as, in pulling off the top of a post where it is halved on to the chord.)
158. As regards the nature of timber, seasoning, time of cutting, etc., although these are important items, still, generally, commercial considerations outbalance all else. The most complete treatise on the nature of woods, is “Du Hamel, L′exploitation des bois;” from which it appears that the best oaks, elms, and other large trees, are the product of good lands, rather dry than moist. They have a fine, clear bark, the sap is thinner in proportion to the diameter of the trunk, the layers are less thick, but more adherent the one to another; and more uniform than those of trees growing on moist places. The grain of the latter may look very fine and compact, but microscopic examination shows the pores to be full of gluten.
The density of the same species of timber, in the same climate, but on different soils, will vary as 7 to 5; and the strength, both before and after seasoning, as 5 to 4.
In trees not beyond their prime, the density of the butt is to that of the top, as 4 to 3; and of centre to circumference, as 7 to 5. After maturity, the reverse occurs in both cases.
Oak, in seasoning, loses from ¼ to ⅓ of its weight; but its strength is increased from 30 to 40 per cent.