Page 474

The WMconsin Lwmberman.
PRESERVATION OF WOOD.     o
The Thimanyu roons to inpr lte Wood 0
With Silpt of copper and Chloride of tA
Barium. 6
The great and constantly increas- o
ing extent of our wood pavements de- t
mands that every person interested s
in its permnanence should give atten- c
tion to the best and most economical a
mode of preparing the same.      c
It is well known that the se-alled d
"Nicholson Pavement," where the
blocks are only dippedin coal tar, c
has proved a failure in all our cities.
In some, where the " Nicholson" has c
been laid in the ordinary manner, it I
shows, at the expiration of three or E
four years, alarming signs of decay.
In fact, no wood can be made to last 4
any great length of time, unless the I
preserving substance is made to per- X
meate thoroughly the pores of the
wood, and as the coal tar cannot pen-
etrate the wood, but merely covers
the surface, it will be seen that, as
soon as this coat is worn off the wood
has no protection whatever, and will
quickly decay. From dipping the
blocks into coal tar results another
great disadvantage.  Generally we
have to use blocks for paving, which
are not thoroughly seasoned. By
dipping such blocks into coal tar, the
external pores are closed, the water
or sap cannot evaporate, and decay
will shortly take place. Matters
grow worse as soon as the external
coal tar coating on the surface of the
street is worn off. Then the water
can freely, enter the pores at the top,
of the blockbut cannot be discharged
at the bottom of the same because
there the pores are still closed.
The really preserving substance of
oal tar is creosote, a light, ethereal
il, which evaporates at a very low
tmperature. The remaining con-
tituents of the coal tar, consisting
f greasy substances and minute par-
icles of coat cannot enter into the
mail cellular tissue of the wood, be-
ause of their tough, syrupy nature
and form, as stated above, a surface
coating, which can only accelerate
Lecay.
Let us examine the wood and its
constituents.
Wood, in its chemical combination,
consists of a fibrous substance and a
iquid filling up the interstices, called
sap. The clear wood fibre, as dem-
onstrated by chemistry, is composed
Af 52. 4 parts carbon, 41.9 parts of
Oxygen, and 5.7 parts of hydrogen,
and is the same in all the different
varieties, but the sap of each kind of
wood contains a great many different
substances; in pine the resin pre-
dominates, and the oak is well known
for the superiority of its tanning
qualities. Some varieties contain
glutinous and saccharine matter,
while from others we extract coloring
pigments, salts and mineral sub-
stances, all soluble in water. Chem-
istry shows that it is almost impossi-
ble to destroy the clear wood fibre,
and that it can be done only by the
strongest acids or alkalies.
Wood, free from sap, will not de-
cay for a very long time, even when
put in the ground or exposed to rain
or dampness. The cause of its de-
cay, when so exposed, will be simply
found in the different substances of
which the sap is composed; its'albu-
men parts act as yeast for all the oth-
ers, and excite fermentation, which
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