Editing Wood (section)

===Water content===
Water occurs in living wood in three locations, namely:
* in the [[cell wall]]s
* in the [[protoplasm]]ic contents of the [[cell (biology)|cells]]
* as free water in the cell cavities and spaces, especially of the xylem
[[File:Hailwood-Horrobin EMC graph.svg|thumb|Equilibrium moisture content in wood.]]
In heartwood it occurs only in the first and last forms. Wood that is thoroughly air-dried (in [[Equilibrium moisture content#Equilibrium moisture content of wood|equilibrium]] with the moisture content of the air) retains 8–16% of the water in the cell walls, and none, or practically none, in the other forms. Even oven-dried wood retains a small percentage of moisture, but for all except chemical purposes, may be considered absolutely dry.

The general effect of the [[Water content#Wood moisture measurement|water content]] upon the wood substance is to render it softer and more pliable. A similar effect occurs in the softening action of water on rawhide, paper, or cloth. Within certain limits, the greater the water content, the greater its softening effect. The moisture in wood can be measured by several different [[moisture meter]]s.

[[Wood drying|Drying]] produces a decided increase in the strength of wood, particularly in small specimens. An extreme example is the case of a completely dry [[spruce]] block 5&nbsp;cm in section, which will sustain a permanent load four times as great as a green (undried) block of the same size will.

The greatest strength increase due to drying is in the ultimate crushing strength, and strength at [[yield (engineering)|elastic limit]] in endwise compression; these are followed by the modulus of rupture, and stress at elastic limit in cross-bending, while the [[elastic modulus|modulus of elasticity]] is least affected.<ref name="Record-1914"/>