108 
PRESERVATIVE TREATMENT. 
insects burrow both while immature and when adult, as the white ants whose 
paramount object appears to be the formation of passages and galleries in which 
the species may breed and multiply. White ants attack living trees as wed as dead 
timber, (b) Aquatic bo?'ers. These live only in salt or fresh water. They are 
molluscs kindred to the animals popularly but erroneously called shellfish. There 
are many of them, of which Teredo navalis may be cited as the most widely known 
representative. For ages these soft-bodied innocent-looking creatures have levied 
heavy toll upon all seafaring peoples. The building of our ships with steel and 
of our wharves with concrete has greatly restricted their ravages. But steel ships 
must not touch concrete wharves. Everywhere there must come between them a 
shield or fender of wooden piling. To this extent the aquatic borer still has his 
opportunity to hasten destruction and decay. Apparently the only remedy 
generally available is periodical renewal of the woodwork; and this means that 
suitable trees must be grown somewhere to keep up the supply. 
The preservative treatment of wood is directed almost exclusively against the 
vegetable and animal enemies that attack our wooden structures on land — bacteria, 
fungi, and boring insects. These require for their most active development 
moisture, warmth, and exclusion of strong sunlight. Bacteria and fungi can 
flourish at temperatures below 60° F. Insects become most active above 60° F. 
Generally sapwood offers the enemy easy penetration and abundant albumen. 
Heartwood is more resistant and less palatable. But certain micro-organisms when 
present and favoured by moisture can make cellulose available as food for the 
animal borers. Even heartwood, therefore, is never safe unless perfectly dry or in 
some other way protected. 
A perfect preservative against these enemies would kill all spores, germs, and 
organisms in or upon the wood at the time of application and thereafter render 
the tissues permanently immune from attack. Many preservative agents have 
proved partially successful; but the verdict of long experience gives preference to 
the tars and oils extracted from wood and coal as coming nearest to the ideal. Tar 
and pitch have long been used for preserving the standing rigging of ships and 
for treating the joints and seams in their decking. Creosote is a distillate from 
tar. It contains the oils that are most adapted for both penetrating wood and 
permanently combining with its tissues. Whether tar alone or creosote alone or 
both combined shall be used in any given case is a question to be decided by 
circumstances. Preparations derived from creosote and claiming to have advantages 
over the cruder material must be judged on their merits as tested by experiment. 
When we have selected our preservative we have still to consider how it can 
be applied economically as well as effectively. Any treatment will add to the 
cost of the wood; and if the addition of cost is very great, it may become prohibitive. 
Here, as everywhere else in industry, we must take full advantage of natural law. 
Wood lasts longest when it is thoroughly and continuously dry, and perishes 
most quickly when it is damp or alternately wet and dry. The reason is that 
its enemies require moisture for their destructive activity, and must either remain 
dormant or perish when moisture is not available. Wood is considered quite dry 
when it contains less than 10 per cent, of water. The difficulty in keeping it in 
such condition is that it absorbs moisture from the air, which contains water in 
varying amounts. In buildings and in furniture the problem to be solved is to 
