Reverting to natural materials, there remains to be mentioned that
great class, timber. In new countries the engineer is commonly glad to
avail himself of this material to an extent which among us is unknown.
For here, day by day, owing to the ready adaptability of metals to
the uses of the engineer, the employment of wood is decreasing. Far,
indeed, are we from the practice of not more than a hundred years ago,
when it was not thought improper to make the shell of a steam engine
boiler of wooden staves. The engineer of to-day, in a country like
England, refrains from using wood. He cannot cast it into form, he
cannot weld it. Glue (even if marine) would hardly be looked upon as
an efficient substitute for a sound weld; and the fact is, that it is
practically impossible to lay hold of timber when employed for tensile
purposes so as to obtain anything approaching to the full tensile
strength. If it be desired to utilize metals for such a purpose,
they can be swollen out into appropriate "eyes" to receive the needed
connection; but this cannot be done with wood, for the only way of
making an enlarged eye in wood is by taking a piece that is big enough
to form the eye, and then cutting away the superfluous portion of the
body. Moreover, when too much exposed to the weather, and when too
much covered up, wood has an evil habit of rotting, compared with
the rapidity of which mode of decay the oxidizing of metals is
unimportant. Further, one's daily experience of the way in which
a housemaid prepares a fire for lighting is suggestive of the
undesirability of the introduction of resinous sticks of timber, even
although they may be large sticks, into our buildings. Many attempts,
as we know, have been made to render timber proof against these two
great defects of rapid decay and of ready combustibility, and, as
it appears to me, it is in these directions alone one can look for
progress in connection with timber. With respect to the first, it was
only at the last meeting of the Institution we presented a Telford
medal and a Telford premium to Mr. S. B. Boulton for his paper "On the
Antiseptic Treatment of Timber," to which I desire to refer all those
who seek information on this point. With respect to the preservation
from fire of inflammable building materials, the processes, more or
less successful, that have been tried are so numerous that I cannot
even pretend to enumerate them. I will, however, just mention one, the
asbestos paint, because it is used to coat the wooden structures of
the Inventions Exhibition. To the employment of this, I think, it is
not too much to say those buildings owed their escape, in last year's
very dry summer, from being consumed by a fire that broke out in an
exhibitor's stand, destroying every object on that stand, but happily
not setting the painted woodwork on fire, although it was charred
below the surface. I do not pretend to say that a surface application
can enable wood to resist the effects of a continued exposure to fire,
but it does appear that it can prevent its ready ignition.
(_To be continued._)
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