154
THE SEAS
substance.
Scientic investigations into the most suitable
means
of aording this type of protection have been
.
conducted both in this country and in the United States
forsome years past, by the Sea Action Committee of the Institution of Civil Engineers in the former and by a Committee
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,
on Marine Filing Investigations in the latter.
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haustiVe. tests of a great variety of substances, various
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organic compounds containing arsenic,
of which
were used as poison gases during the war, have been found
the most efcacious, and important experiments are now
being carried out with these substances, by exposing in
the sea rafts containing timber treated in various ways,
;
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and nding the degrees of protection aorded by the various
poisons (Plate 57).
In all cases it is necessary to impregnate
them into the Wood in soluti0n'in créosote, otherwise they
wash out and the wood is “left fully exposed to infection.
The creosote alone, if the timber is well imprégnated with
it, often provides good protection {or-along period. The
wood has to be thoroughly dried before impregnation,’
the
process
Out_ either by the ”aid of a
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'
Vacuum which draws the cre‘os0te
else by
boiling,:With the impregnating'uid in an open tank.” Up :
to date these experiments are having‘good results so far
as the Shipworm is concerned but are not so’efcacious With
the Gribble, which appears_to be less susceptible to poisons.
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This is probably to be explained by the fact— that onlÿfùlly
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.
grown Gribbles attack new timber—" and these Will not be
so easily .poiSoned as the minute larval creatures Which are
.
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the ‘carriers of infection inthe case ”of the Shipworm,
The
problem of the protection of timber in the sea re— '
mains, though progress is Slow1y being made, still
:
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,
rock 'borers do not do a fraction of the damage
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of the wood borerS and are a‘minorï problem.. Mechanical
,
borefs, such as the Piddock, may do a good deal of damage
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