it with camphor we get celluloid, a plastic solid
capable of innumerable applications. But that is another story and must
be reserved for the next chapter.

But before leaving the subject of cellulose proper I must refer back
again to its chief source, wood. We inherited from the Indians a
well-wooded continent. But the pioneer carried an ax on his shoulder and
began using it immediately. For three hundred years the trees have been
cut down faster than they could grow, first to clear the land, next for
fuel, then for lumber and lastly for paper. Consequently we are within
sight of a shortage of wood as we are of coal and oil. But the coal and
oil are irrecoverable while the wood may be regrown, though it would
require another three hundred years and more to grow some of the trees
we have cut down. For fuel a pound of coal is about equal to two pounds
of wood, and a pound of gasoline to three pounds of wood in heating
value, so there would be a great loss in efficiency and economy if the
world had to go back to a wood basis. But when that time shall come, as,
of course, it must come some time, the wood will doubtless not be burned
in its natural state but will be converted into hydrogen and carbon
monoxide in a gas producer or will be distilled in closed ovens giving
charcoal and gas and saving the by-products, the tar and acid liquors.
As it is now the lumberman wastes two-thirds of every tree he cuts down.
The rest is left in the forest as stump and tops or thrown out at the
mill as sawdust and slabs. The slabs and other scraps may be used as
fuel or worked up into small wood articles like laths and clothes-pins.
The sawdust is burned or left to rot. But it is possible, although it
may not be profitable, to save all this waste.

In a former chapter I showed the advantages of the introduction of
by-product coke-ovens. The same principle applies to wood as to coal. If
a cord of wood (128 cubic feet) is subjected to a process of destructive
distillation it yields about 50 bushels of charcoal, 11,500 cubic feet
of gas, 25 gallons of tar, 10 gallons of crude wood alcohol and 200
pounds of crude acetate of lime. Resinous woods such as pine and fir
distilled with steam give turpentine and rosin. The acetate of lime
gives acetic acid and acetone. The wood (methyl) alcohol is almost as
useful as grain (ethyl) alcohol in arts and industry and has the
advantage of killing off those who drink it promptly instead of slowly.

The