It is not permissible, however, to compare such widely different woods as oak and pine on a basis of their weights.[27] [Footnote 27: The oaks for some unknown reason fall below the normal strength for weight, whereas the hickories rise above.
Certain other woods also are somewhat exceptional to the normal relation of strength and density.] The weight of wood substance, that is, the material which composes the walls of the fibres and other cells, is practically the same in all species, whether pine, hickory, or cottonwood, being a little greater than half again as heavy as water.

It varies slightly from beech sapwood, 1.50, to Douglas fir heartwood, 1.57, averaging about 1.55 at 30 deg.

to 35 deg.

C., in terms of water at its greatest density 4 deg.

C.The reason any wood floats is that the air imprisoned in its cavities buoys it up.
When this is displaced by water the wood becomes water-logged and sinks.