Wood as a combustible, is divisible into two classes: 1st, the hard,
compact and comparatively heavy, such as oak, ash, beech, elm. 2d,
the light colored soft, and comparatively light woods as pine, birch,
poplar.
Wood when cut down contains nearly half moisture and when kept in a dry
place, for several years even, retains from 15 to 20 per cent. of it.
The steam producing power of wood by tests has been found to be but
little over half that of coal _and the more water in it the less its
heating power_. In order to obtain the most heating power from wood it
is the practice in some works in Europe where fuel is costly, to dry
the wood fuel thoroughly, even using stoves for the purpose, before
using it. This “hint” may serve a good purpose on occasion.
The composition of wood reduced to its elementary condition will be
found in the table with coal.