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Wood Preservatives
in the
19th and Early 20th Centuries
Written and Edited by
Lewis Brown Jr.
AE 681
Fall 1976
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Since wood construction began it has been threatened by several
destructive things. Rot and fire are the two most dangerous and troublesome
maladies that wood construction faced. A third problem was that of animal
attack such as termites or marine borers. In pre nineteenth century America
wood was plentiful and was easily replaced, but as more and more trees were
felled and fewer and fewer became available it became necessary to shift
efforts toward preservation of wood before construction. Several methods
were discovered or invented during the nineteenth and early twentieth centuries.
Some of the methods were organic or natural and required no foreign agents or
machinery while others did.
The durability of wood---i.e., its power of resisting the destructive
influences of wind and weather---varies greatly, and depends as much upon
the particular kind of wood and the influences to which it is exposed as upon
the origin of the wood (timber) its age at the time of felling, and other
conditions. Beech wood and oak placed permanently under water may last
for centuries. Alder wood is very lasting and substantial under water, as
also is fir, though in a dry situation alder quickly perishes.
Pure woody fibre by itself is only very slightly affected by the destructive
influences of wind and weather. Wood may in some instances last for several
centuries and remain thououghly sound; thus, the roof of Westminster Hall
was built about a.d. 1090. Since resinous woods resist the action of damp
and moisture for a long time, they generally last a considerable time; next
in respect of durability follow such kinds of wood as are very hard and compact,
and contain at the same time some substance which---like tannic acid---to
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some extent counteracts decay. The behaviour of the several woods under
water differs greatly. Some woods are after a time converted into a pulpy
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mass.
Before studying the various preservatives that help prevent wood
decay it is necessary to understand what decay really is.
S9LIP6 [( The decay of a plant body, such as wood, is not an inorganic process
like the rusting of iron or the crumbling of stone, but is due to the activities
of low forms of plant life called bacteria and fungi. Bacteria are among the
simplest of all forms of life, often consisting of but a single cell, microscopic
in size. Sometimes several such cells may be attached to each other, and so
form a thread or filament. Usually they are colorless, and multiply by the
division of the parent cell into other cells, which, in turn, divide again.
Fungi, although much more complicated than bacteria, are also low
in the scale of creation when compared with familiar flowering plants and
shrubs. They consist merely of tinythreads or hyphae, which are
collectively known as the mycelium. In many of the higher forms of fungi
the threads grow together to form compact masses of tissue. Familiar
examples of these forms are the toadstools which grow on damp, rotting
logs, and the "punks," or "brackets," on the trunks of trees in the forest.
The causes of decay in wood, however, are not these fruiting bodies
themselves. Spores, very primitive substitutes for seed, which are borne
in the countless compartments into which the under surfaces of the fruiting
bodies are sometimes divided, are produced in infinite number, and are so
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fine that they can be distinguished only by the microscope. When seen in
bulk they appear as the finest dust. Like dust, they are carried by the
wind and strike all portions of the surrounding objects. Few species of
fungi successfully attack healthy living trees, and only a comparatively
small number can attack and destroy wood. Yet the spores of some find a
lodging in dead portions of a tree or in cut timber, and, if the wood is
moist and in the right condition for the spore to grow, it germinates and
sends out a thin, filmlike white thread, which, by repeated branching,
penetrates the entire structure of the wood. These are the real agents
of decay.
This is not the only way that a fungus can enter a sound stick of
timber; for if a good stick is lying close to a rotting one, the mycelium
may grow over or through the moist ground and so reach the sound stick,
which it immediately attacks. Sometimes, too, when a tree is cut it
already has a fungus growing in its wood. If the fungus happens to be a
true parasite---that is, if it can grow only in living tissues---it will die
when the tree is felled; but if it has been accustomed to growing in the
heartwood of the tree, which is practically dead, it may continue to live
and develop even after the tree has been sawed into timber.
Wood is composed of minute cells. The chief material of the cell-
walls is a substance called cellulose, and around this there are incrusted
many different organic substances known collectively as lignin. Most
of the wood-destroying fungi attack only the lignin; others attack the
cellulose alone, while a third class destroy all parts of the wood structure.
The lignin and the cellulose are dissolved by certain substances secreted
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in the fungi, and thus serve as food for the fungus growth. In this way
the fungi can develop until they extend throughout every portion of the
timber. After a time the amount of fiber changed into food and assimilated
by the fungus causes the wood to become discolored. Discoloration may
also be produced by pigments in the fungus or secreted by it. Finally so
much of the wood fiber is eaten away or changed in composition that its
strength is greatly diminished, the texture becomes brittle and
disconnected, and the wood is said to be "rotten".
But food is not the only thing that a fungus requires for its growth
and development. It must also have heat, air, and moisture. If any one
of these is lacking the fungus cannot develop. The necessary heat is
supplied by almost every climate, and it is only in rare cases, as under
water or deep under the surface of the ground, that air can be excluded
from the timber. Of the four requirements, therefore, two are beyond
control. It is only by depriving the fungi of food or moisture that the
destruction they cause can be prevented.2
The belief prevailed, that the interfibrous and cellular system of
wood contained elements denominated sap, which according to recognized
authority was vicious, and generative of destructive fungus. 3
Since the constituents of the sap are the chief cause of the
decomposition of wood, and they should consequently be removed; many
plans were adopted. The constituents of the sap could be eliminated from
the felled tree by three methods:---
(1) By treatment with cold water, with which the wood must be
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thoroughly saturated to dissolve the constituents of the sap, which were
removed when the wood was exposed to a stream of water. It is evident
that with large timber a long time was necessary to ensure perfect
saturation.
(2) By employing boiling water the sap was removed much more
quickly and efficiently. The pieces of wood were placed in an iron vessel
with water, and boiled. Large pieces of timber cound not be treated in
this manner, but were immersed in a cistern in which the fluid was
heated by means of steam. According to the thickness of the wood, the
boiling occupied some six to twelve hours.
(3) By treatment with steam ( steaming of wood) ---the most
effectual method of removing the constituents of the sap, the hygroscopicity
of the wood thus treated being rendered much less, while the wood is far
more fitted to resist the effects of weather. The apparatus employed in
carrying out the method consisted of a boiler for the generation of steam,
and a cistern or steam chamber for the reception of the wood, this
chamber being constructed of masonry and cement, of boiler-plate,
or being simply a large and vary wide iron pipe. In most cases a jet of
steam was conveyed from the boiler to the steam chamber, where it penetrated
the wood, and dissolved out the constituents of the sap, which, on being
condensed, was allowed to run off. The steam was sometimes worked at
a temperature of above 100 but generally the contents of the steam chamber
were maintained at from 600 to 700. Towards the end of the operation
some oil of coal-tar is introduced into the boiler, and is consequently
carried over with the steam, impregnating the wood.
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One of the most usual and most effective means of preventing
the decomposition of wood was by producing a chemical change in the
constituents of the sap, so that fermentation could no longer be set up.
To this class belonged the well-known plan of protecting wood work that
was to be exposed to the action of the moisture of the earth by charring the
wood, either by fire or by treatment with concentrated sulphuric acid, so
that the wood was coated to a certain depth with a layer of charcoal, the
charcoal acting as an antiseptic. The charring or carbonisation of the
wood could be effected either with the help of a gas flame or the flame
from a coal fire. The apparatus of De Lapparent, invented for this
purpose, became very generally employed in 1866 at the dockyards of
Cherbourg, Pola, and Dantzic. According to another method, the wood
was impregnated throughout its whole mass with some substance that
either entered into combination with the constituents of the sap, or so
alters their properties as to prevent the setting up of decomposition.
To this class belonged the following methods, these being the only ones
that have met with more extensive use .
Kyan's preserving fluid, patented 1832, was a solution of mercuric
chloride of various degrees of concentration. The specific solution was
one pound of chloride of mercury to four gallons of water. Long
immersion of wood in the liquid in open vats or great pressure upon
both solution and wood, in large wrought iron tanks was necessary for
the complete injection of the liquid. The duribility of well kyanized
timber was proved, but the expensiviness of its operation forbade its
extensive adoption. A great objection to this method was the danger
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to which the carpenter or joiner who would later shape the wood was
exposed, the free chemicals acting upon his system through his hands,
nostrils andmouth. In the United States convicts were used to handle
wood treated by kyanization.
Burnett's fluid, patented 1840, consisted of a solution of chloride
of zinc---one pound of salt to 10 gallons of water.---Was forced into
the wood under a pressure of 150 pounds per square inch. Wood
treated with Burnett's fluid was buried in the earth for five years
without undergoing any change, while untreated wood buried in the ground
for the same amount of time was completely destroyed. Besides this
salt, copper sulphate and zinc acetate have been employed. The action
of the copper and zinc salts may be explained by considering that the
metallic oxides of the basic salt formed during seasoning separated, and
combined with the coloring matter, tannic acid and resin of the wood to
form an insoluble compound.
Bethell's method, patented 1838, consisted in treatment under strong
pressure with a mixture of creosote and carbolic acid, this mixture being
known commercially as "Gallotin". Bethell inclosed the timber and dead
oil in huge iron tanks, and subjected them to a pressure varying between
100 and 200 pounds per square inch, at a temperature of 1200 F. about
twelve hours. From eight to twelve pounds of oil were injected into
each cubic foot of wood. Lumber thus prepared was not affected by
exposure to air and water, and required no painting.
Cresote is a by product of coal tar, which was produced at most
plants for the manufacture of illuminating gas and at by product
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coke-oven plants. This tar was distilled, and during the process the
condensed vapors were run into three separate vessels and thus separated
into the light oils of coal tar or nephthas, the dead oil of coal tar or
creosote, and pitch.
In and near London wood treated by Bethell's process remained
eleven years in the earth without undergoing change; other pieces of timber
so treated were subjected to the action of the sea for four years, and were
still in good condition.
One writer said that if creosote ever failed to prevent decay, it
was because of an improper treatment, or because the oil was deficient
in carbolic acid.
Sir Robert Smirke was one of the first architects to use this process,
and when examined before a Committee on Timber, stated that this process
does not diminish the strength of the material which is operated upon. He
afterwards said, "I cannot rot creosoted timber, and I have put it to the
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severest test I could apply."
Payne's method which included two patents, the first having been
taken out in 1841. Both were based on the impregnation of the wood---
first with one salt, and then with another salt, which was capable of producing
with the former a precipitate insoluble in water and in the sap of the tree.
The first solution was usually one of iron sulphate or of alum; then
followed a solution of calcium chloride or of soda. The wood to be
impregnated was placed in a vessel from which the air was exhausted,
the first solution being then admitted, and pressure subsequently applied.
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The first solution being removed, the second was admitted, and pressure
again applied. It was necessary to dry the wood partially between the two
impregnations. Payne's method, possessed, the advantage of rendering
the wood somewhat uninflammable. 8
Boucherie's Method consisted in the impregnation of the wood with
the necessary substance, in a manner similar to the natural filling of the
pores with sap; that is to say, the solution was introduced into the tree from
its roots, and was thus made to take the place of the sap in all parts of the
timber. When the tree was felled, the root end was placed in a solution
of the salt and allowed to remain for some days; at the end of the required
time the wood became completely impregnated with the salt. Occasionally
this method was employed in colouring woods, colouring matter being used
instead of, or as well as, the salt. The linden, beech, willow, elm, alder,
and pear tree could be treated in this manner. The fir, oak, ash, poplar,
and cherry tree did not, however, absorb the impregnating fluid
sufficiently.
In a later development Boucherie used the same chemicals
( sulphate of copper, one pound of the sulphate to 12- gallons of water
or one gallon pyrolignite of iron to six gallons of water) but he enclosed
one end of the green stick in a close-fitting collar, to which was attached
an impervious bag communicating through a flexible tube with an
elevated reservoir containing the salt liquid. Hydrostatic pressure
soon expelled the sap at the opposite end of the log; and when the solution
also made its appearance the process was completed.
He found that the fluid would pass along the grain, a distance of
12 feet, under a lower pressure than is required to force it across the
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grain, three-fourths of an inch. The operation was performed upon
green timber with the greatest facility.10
Along with any study of wood preservation processes should
be a study of application-methods. For the processes previously mentioned
three main application methods were used. In the United States the pressure
process was the most common. With creosote it was known as the Bethell
process, and with zinc chlorid the name of Burnettizing was applied.
The timber to be treated was placed on iron trucks or "cylinder buggies"
and drawn by steel cables into huge horizontal cylinders, some of which
were 8 or even 9 feet in diameter and more than 150 feet long. These
were capable of withstanding high pressure, and their doors were so
arranged that, after the timber was drawn in, they could be closed and
hermetically sealed. It was the common practice in this country---a
practice which long experience in Europe, as well as in America, was
proved to be unwise---to treat the timber before it had time to dry out
in the open air. The following was the usual method. After the doors
were closed live steam was admitted into the cylinder, and a pressure of
about 20 pounds per square inch was maintained for several hours, the
exact time depending upon the individual opinion of the operator, as well
as upon the moisture content and size of the timber under treatment. In
some cases the steam pressure was allowed to go considerably above
20 pounds, but there was constant risk of injuring the strength of the
timber. When the steam was at last blown out of the cylinder, the vacuum
pumps were started and as much of the air as possible was exhausted from
the cylinder and from the wood structure. This process also continued
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for several hours. Finally, after the completion of the vacuum
period, the preservative was run into the cylinder and the pressure pumps
were started and continued until the desired amount of preservative fluid
was forced into the wood. The surplus preservative was then blown back
into the storage tanks, the timber was allowed to drip for a few minutes,
and finally the cylinder doors were opened and the treated timber was
withdrawn.
C-LIPE f- The injection of the preservative by the open-tank process depended
upon a different principle. The wood was first thoroughly seasoned, and
much of the moisture in the cells and intercellular spaces was replaced
by air. If the timber was peeled soon after cutting, and stacked in open
piles, the time required for seasoning could be greatly lessened. The
seasoned timber, or that portion of it which was to be preserved, was
immersed in a hot bath of the preservative contained in an open iron tank.
This hot bath was continued for from one to five or six hours, depending
*e t!3 upon the timber. During this portion of the treatment the air and
moisture in the wood expand and a portion of them pass out, appearing
as little bubbles on the surface of the fluid. At the end of the hot bath,
as quick a change as possible was made from the hot to a cold preservative.
This causes a contraction of the air and moisture remaining in the wood,
and, since a portion of it had been expelled, a partial vacuum was
created which could be destroyed only by the entrance of the preservative.
Thus atmospheric pressure accomplishes that for which artificial press-
* 4 ure was needed in most of the commercial plants. Whether the open-
tank or pressure-cylinder method was the more desirable depends upon
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'5LIP eF r
the particular conditions of each case. Both methods have their
particular uses and neither could always be wholly substituted for
the other.
The Brush Method.---A less efficient but cheaper treatment
could be secured by painting the surface of the timber with at least
two coats of hot creosote or some similar preservative. The liquid may be
applied with an ordinary brush, but care should be taken to fill thoroughly
with the preservative all checks, knot holes, and similar defects. The liquid
could penetrate only a very short distance into the wood, but as long as
there remains an unbroken antiseptic zone around the surface, the spores
of the wood-destroying fungi cannot enter. It was especially important
in this method that the timber should be thoroughly air-dry before
treatment. Otherwise the evaporation of water from the interior of the
stick would cause checks to open up and so expose the unprotected wood
to fungous attack.
This process finds its principal use where the amount of timber
to be treated was too small to justify the erection of even a small treating
plant; where the land was so rugged, as in the building of mountain telephone
lines, that it was impracticable to transport the timber for even short
distances, or where it was necessary to restrict the cost of the
treatment to the lowest possible figure. 11
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The preservative methods aforementioned were invented and
developed during the nineteenth century. At the beginning of the
twentieth century. A new method was patented in Germany which
utilized a fixed body which became solid upon being instilled into the
pores of the wood. This substance was sulphur, the physical properties
of which offered interesting advantages, being fusible at about 115 degrees,
a temperature which the wood could support without any perceptible
change. The sulphur was applied in liquid form, and in hardening
completely filled up all the interstices of the fibrous tissue.
To protect wood by means of sulphur the following must be
observed, viz.: Sulphur was fused in a befitting receptacle, making
use of steam to avoid an excess of heat, which deteriorates the sulphur.
Into this liquid, and at a temperature of about 140 deg., were steeped the
boards which were to receive the treatment, care being taken to immerse
them completely. The foam which gathers at first, called forth by the
separation from the wood of the air and humidity it contained, disappeared
at the moment the wood thoroughly assimilates the temperature of the
bath, which was then lowered to 110 deg. At that point the sulphur
became hard and, while the air contracted itself, the sulphur penetrated
into the fibrous tissues, propelled by atmospheric pressure. The boards
were then slowly withdrawn from the bath, allowing a thin and even coat
of sulphur to form and cover the wood, as any superfluous surcharge
could be removed only with the greatest difficulties afterward. This coat
of sulphur had a vitreous appearance and formed a very tenacious crust,
excluding all tendencies to chip or break.
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The degree to which the wood was impregnated varied according
to the nature of the wood, the temperature, and the duration of the bath.
It could be gaged by the increase in weight of the boards, which amounted
to from 30 to 35 per cent where the process was conducted in an open
receptacle, and to 100 per cent if in a vacuum pan. Theoretically it
could be said that a complete fullness of the pores of the wood would
increase its weight by 200 per cent.
In numerous experiments poplar was the best wood to take the
sulphur treatment. Oak and pine wood do not admit of the process quite
so favorable, because their dry distillation began at 140 deg., which
could be proved simply by observing that while the wood was immersed
in the bath bubbles were continually rising, marking the escape of volatile
substances. Moreover, the resin blackened the sulphur. The process
in question was up to date been applied only to thin boards, but in view of
the satisfactory results the hope was entertained of its soon becoming
popular for timbers. 12
The various methods of preserving wood have been mainly
dependent upon submitting the wood to a prolonged steaming at a high
temperature, the application of pressure, or the extraction of the sap
under vacuum. But such methods were far from satisfactory, as
numerous tests and investigations carried out by the United States
government had conclusively proven. Instead of acting as a preservative,
such methods accelerated the deterioration of the wood; for although the
albuminous matter contained in the sap was coagulated, the fibers and
tissues were seriously affected, and cosequently the strength of the wood
uDPg #7
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was greatly impaired. For this reason the government had emphatically
condemned all processes dependent upon the utilization of high
pressures or vacuum.
The Powell preserving process differed entirely from any
previously exploited system, both in the material employed for
displacing the sap and in its method of application.
By this means any kind of wood could be preserved quickly,
whether it be newly-felled green timber or wood that was partly
seasoned naturally, though the best results were obtained with timber
in the green state. This peculiarity arises not from any curious affinity
for the green wood on the part of the solution, but was due to the fact
that very often partly seasoned wood had developed cracks and shakes.
The wood upon arrival at the works was immersed in a tank contained cold
water to which was added a certain percentage of sugar. This solution
was then gradually brought to the boiling point, and was maintained at
this temperature for a certain period, varying with the size and
description of wood under treatment. The latter was then withdrawn
from the tanks and was ready for drying. At the London works of the
Powell Wood Process Syndicate, which was using the patents, the
boiling was carried out in a long cylinder about eight feet in diameter.
In this chamber any sized piece of wood, ranging from small blocks to
long heavy balks, could be packed. When fully charged, the end of the
cylinder was closed and secured by hold-down bolts. The chamber was
then filled with the cold solution and slowly heated. Precisely how long the
timber should be immersed was a matter of judgment on the part of
the operator, but it had to be sufficiently long to permit the solution to
permeate to the innermost cells of the wood, and to allow them to become
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fully saturated with the sugar. The action that took place in the bath
was that as the temperature of the solution slowly increased the air in the
wood expanded a large proportion forcing itself out of the wood into the
solution, whence it escaped to the surface. Owing to the fact that the
sugar boils at a point exceeding that of water, the moisture contained in
the wood was converted into steam, and escaped in the same manner as
the released air. The moisture and air having been completely driven
out, the solution was permitted to cool, during which stage it was being
constantly absorbed by the wood. In this way every cell and interstice
became filled with sugar, and when the wood was dried, the sugar was found
to be thoroughly assimilated by its tissues. Some of the sugar was so
absorbed by the tissues that it could not be readily parted from them,
and the whole piece of timber was converted into a solid, homogeneous
mass. When a piece of Powellized wood was examined under the micro-
scope, no traces of the sugar were visible, either in the form of crystals
or drops of syrup; the sugar was evidently in some loose molecular
combination with the walls of the histological elements of the wood, as water
is in the walls of living cells.
When the wood was withdrawn from the chamber, it was transported
in wire caged trolleys to the drying room. The temperature of the air
within this apartment was at first approximately equal to that of the wood,
but it was afterward increased by the circulation of a current of hot air.
When sufficient desiccation had taken place, the temperature of the
chamber was slowly brought to equal that of the outer atmosphere.
The wood was then ready for use. During the whole process no
mechanical force of any description, either pressure or vacuum, was
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applied; this feature being one of the vital factors of the efficiency of the
system, since there was no tendency in any way to disturb the natural
fiber and tissue construction of the timber. The length of time
occupied in the treatment naturally varied according to the description
of wood and the dimensions of the pieces under treatment, hard-grained
wood of close texture, such as Jarrah or oak, occupying longer time
for complete impregnation than the common and softer woods. It
generally occupied a few days, but in special cases three to four
weeks would be required in the process. Although at the Powell
works in London a cylindrical inclosed chamber was utilized for the
boiling and saturating phases of the process, it was found that open tanks
and vats were equally serviceable and possess the additional advantage
that the method could be watched much more easily and the different
woods in the bath withdrawn with more facility at the moment when the
impregnation was complete. Little attention was required during the
boiling it being only necessary to maintain the density of the solution
at the given point; since the boiling point of the sugar solution was higher
than that of water, considerable evaporation took place, and this loss
had to be compensated by the addition of more water. It was
imperative that the wood should be kept entirely submerged to insure
a complete treatment.
Sugar as a preserving medium has the decided advantage of
being free from grit, so that it offers no more resistance to the finest
and most delicate toolwork than the unpreserved timber. Futhermore,
unlike creosote, it does not present a surface unsuseptible to paint or
polish. Indeed, in this respect it is distinctly beneficial, as the pores of
the wood are so filled up that no further stopping or priming is necessary
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for working. In the case of timber having "shakes" and cracks,
such as develop in the natural dry seasoning of wood, the sugar
acted upon these as a cement, binding the opened walls together.
Owing to the great penetrating power of the sugar solution, it
constituted an excellent vehicle for the conveyance of other substances
into the wood, such as antiseptics, and mediums for preserving the timber
against the ravages of termites, or for rendering it non-inflammable.
In such cases chemicals for fulfilling these objects were mixed with
the sugar solution before the wood was immersed, and in this manner
these preserving agents were carried with the sugar into the interior
of the wood. Powellized wood treated with chemicals for preserving
it against the white ant was employed in several countries where this
pest was encountered. 13
The problem of wood protection, of converting it from a highly
inflammable into an absolutely non-inflammable product, has floated
before the minds of generations of men rather as a vague, dreamy
proposition than as subject-matter upon which to concentrate intense
intellectual attention. Sporadic efforts void of practical utility are
historically recorded at irregular epochs, from Roman days to the
present time. The elimination of the inflammable characteristic from
wood was therefore a matter of vital consequence. And such treatment,
as shall cause it to resist disintegration from fierce heat the greatest
length of time was the most desirable.
The sum of values arrived at, as a resultant of all recorded study,
inventions and scientific deduction, up to the beginning of that time, as
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to protective treatment of wood, may be stated as:---
(1) That wood was susceptible of absorbing varied percentages
of liquids.
(2) That certain chemical solutions, when injected into the
cellular structure of wood and afterward dried, leave a residual
deposit of dry chemical therein, from which, with water, the
solution was originally formed.
(3) That such impregnation may be effected by pressure
mechanically applied and by incidental processes.
(4) That such deposit of chemical substance in the wood-cells
has in one case a preservative and in another a fire-resistant effect.
The saturation of wood to make it fire-resistant differed in many
respects from preservative treatment. Wood treated to make it
fire-resistant was subjected to many stringent requirements not
essential in the case of preservative. For instance, the saturation
must be complete to the heart. The color of the original wood must
not be impaired. The strength of fibre must be preserved. There
must be no lingering of flame on withdrawal of attacking flame. To
effect this, the strength of solution must be as high as possible. This,
of course, added to the cost and the density of solution required greater
pressure to infiltrate.
The effectiveness of ammonia salts to repel flame from a wood
surface depends upon the rapid volatilization of the ammoniacal gas.
The greater the applied heat, the more rapid the exhaustion of the
protective gas, and, when exhausted, no residual inert substance
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remains to bar the advance of flame or progress of disintegration.
The gaseous emission chemicals were the only known materials
used, up to five years ago, in any commercial fireproofing plant.
It became necessary to seek for practical materials, operating on
a reverse principle from the gaseous emission, and after years of
laborious effort sulphate of aluminum was discovered to be the
substance endowed with the property of fire-resistance inconceivably
beyond any previous conception. For instance, the best results from
the gaseous emission substances was an added life over untreated wood
of thirty-one minutes. The average of 2,800 pieces of 1-inch white
pine treated with sulphate of aluminum had an added life of seven
hours and thirty-eight minutes, or over fourteen times that of wood
treated with the gaseous emission chemicals.
This most satisfactory result came from the simple fact that
sulphate of aluminum under flame loses its water of crystallization,
its sulphuric acid of combination, and remains then residual pure
aluminum which has the admirable property of expansion in the
vacant cells of wood, to two and one-half or three times its original
volume of dry sulphate; and in doing so it interposes between flame
and wood fiber a compact mass of pure alumina, infusible by the flame
of any conflagration, and an admirable non-conductor of heat.
A casual remark was made by a prominent insurance man, to
the effect that the saturation of wood by sulphate of aluminum was
assuredly a great gain to it in fire-resistant quality, but that he was
quite as much, if not more, interested in the preservation of
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existent structures, from attack by fire, than he was in preparation
for protection of non-existent structures, or those only in
contemplation; and he counselled the serious study of this phase of
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wood treatment.
Of the many enemies of wood exposed to sea water the
teredo worm is by far the worst. Any of the aforementioned
chemical solutions were useless against this animal because they
tended to wash out after a short while leaving any wooden structure
defenseless against attack by this worm.
At an early stage of growth the teredo is free swimming,
traveling about in the water and attacking any woodwork which may
have been left exposed, entering it by a hole not larger than a pin
head. After they have started their boring the teredoes grow not
only in length but also in diameter, and sometimes have been known
to have reached diameters as great as three-fourths of an inch. The teredo
is whitish in color, and has two small flexible tubes or siphons
continuously extending into the water from the small entrance hole in
the wood. It is very important that these vital organs be constantly
submerged in comparatively pure salt water, as it is through these
organs and from the water that the teredo gets his nourishment. Thus it
is that any substance which will permanently cut off the surface of the
wood from contact with pure salt water, will not only kill the teredoes
that are already in a pile but will prevent the entrance of other teredoes.
It is extremely difficult to inspect a pile and discover the presence
of the teredo until a vast amount of damage has been done, for the reason
Page 22
that although the interior may be perfectly honey combed, the exterior
presents an almost perfect appearance.
, #10 -Engineer Charles M. Ripley once took occasion to weigh a 3-foot
section of a 12-inch pile which had been withdrawn from a bridge in a bay
within a radius of 50 miles of New York city, and was astonished to find
that the weight of the section mentioned was but 11 per cent of its original
weight as yellow pine, which was calculated on a basis of 0.9 specific
gravity. This fact was more astonishing since there were no openings
upon the exterior of the pile save the tiny holes at which the teredo
originally entered.
It was once attempted in Holland to preserve the piling of dikes
by means of driving thousands of round-headed iron tacks into the pile.
Small boys were employed for this purpose and more or less success
attended it, but the expense is obviously prohibitory and on existing
structures the work can only extend from low water upward unless the
services of a diver were employed.
The copper sheathing method is a good protection. However,
copper is liable to corrode in salt water, not only at the joints, but
around the nail heads. The expense, both for material and for labor,
in applying copper is to be considered, as is also the fact that the
exact depth to which a pile is to be driven is not always known in
advance, and hence the copper sheathing is likely to be made to extend
either too close to the bottom of the pile, where it is useless in the
mud, or too high toward the top of the pile, where it is unnecessary
above the high water line.
Page 23
Engineers attempted to protect piles by means of tarred
burlap wound spirally around the pile. Materials floating down stream
tended to tear the burlap; also barnacles and oysters clinging to the
material after the tar was more or less covered with weeds and slime
tended to pull away the protection and leave the pile exposed near the
top.
The lowering of the old mud line often occurs where the stream
is narrowed by the introduction of piling or other obstructions. The
tar burlap necessarily had difficulty penetrating the old mud line as
the pile was driven, and hence as the mud line later receded, the pile
was left exposed at the bottom, a point which couldn't be inspected
without a diver.
5LI1C 11 Concrete was used as a coating around piles, molds being placed
by divers and the concrete poured in; one difficulty incidental to this
method was that as the mixture was poured down through the water in
the mold it tended to weaken. Cases have been found where piles
protected by this method were really exposed at the bottom since nothing
but gravel descended through the water to that depth and the teredo
could enter the interstices between the grouting.
A later attempt was split vitrified pipes placed around the pile,
held in place by wires, and then filled with concrete.
Another method was ordinary sewer pipe strung over the top
of the pile and filled with sand. This method overcame the difficulty
mentioned in connection with a concrete covering or filling, as the
sand filling allowed the sewer pipe to descend as the mud line receded,
but in a new structure this method had to be installed before the deck
Page 24
was placed. In old structures caps of the piles must be removed
before the pipes could be placed. This obviously interfered with
the speed of construction of new work and also interfered with
traffic when applied to old structures. A serious objection is that
repairs to one section or one pile necessitated the removal of the cap
from that entire bent.
of time; and if one vulnerable spot shows, the teredo may enter in and work
destruction through the pile. All the methods mentioned-- -with the
exception of the sewer pipe---are liable to undermining. The coverings
are attached to the pile, and when the scour of the water removed the
wood or earth from the base, a line of attack was offered to the teredoes.
An improvement on the sewer pipe was the lockjoint pipe. This
consisted of sections of a concrete pipe, cast in halves so that could be
bolted round a pile when the latter is in position. The pipe was
larger than the pile, and the space between is filled up with fine sand.
Thus it was claimed that the pipe did not adhere to the pile but settled
gradually and followed the mud line, always keeping the pile protected
throughout the field of attacks of the marine wood borers. It may be
interesting in this connection to know that the teredo must have
continued access to the water in order to live. It is thus impossible
for the teredo to enter a pile above this protection and live so long as
this protection stands above the high water mark.15
Footnotes
1. Manual of Chemical Technology, Rudolph Von Wagner, D. Appleton
and Company, New York, 1897, page 944.
2. Scientific American Supplement,Vol. 68, page 78,
3. The American Architect, Vol. 81, page 12, "Protection and
preservation of wood".
4. Manual of Chemical Technology, Rudolph Von Wagner, D. Appleton
and Co. New York, 1897, page 946.
5. ibid, page 947.
6. A Treatise on the Resistance of Materials and Appendix on the
Preservation of Timber, De Volson Wood, John Wiley and Sons,
New York, 1883, page 285.
7. ibid
8. Manual of Chemical Technology, Rudolph Von Wagner, D. Appleton
and Company, New York, 1897, page 948.
9. ibid
10. A Treatise on the Resistance of Materials and Appendix on the
Preservation of Timber, De Volson Wood, John Wiley and Sons,
New York, 1883, page 284.
11. Scientific American Supplement, Vol. 66, page 78, Ag. 1, 08,
"Decay and how it may be checked", W.F. Sherfesee.
12. Scientific American, Vol. 95, page 79, Ag. 4, 06, "Sulpher
process for the preservation of wood."
13. Scientific American Supplement, Vol. 63, page 26216, My. 17, 07,
"Powell process of wood preservation with saccharine".
14. The American Architect, Vol. 81, page 12, "protection and
preservation of wood".
15. Scientific American Supplement, Vol. 67, page 12, "Destructive
marine wood borers." C.M. Ripley.
Bibliography
Manual of Chemical Technology, Rudolph Von Wagner, D. Appleton
and Company, New York, 1897.
A Treatise on the Resistance of Materials and Appendix on the
Preservation of Timber, De Volson Wood, John Wiley and Sons, New York,
1883.
Scientific American Suppliment
Vol. 59: 24281-2, Ja. 14, 05, "Creosote oil and timber
preservation"
Vol. 66: 78-80, Ag. 1, 08,"Decay and how it may be checked",
W.F. Sherfesee.
Vol. 67: 12, Ja. 2, 09,"Destructive marine borers"' C.M. Ripley.
Vol. 67: 162, Mr. 13, 09, "Impregnation of timber".
Vol. 68: 147, S. 4, 09, "Methods of wood preservation".
Vol. 63: 26216-7, My. 17, 07, "Powell process of wood
preservation with saccharine".
Vol. 66: 222-4, 0. 3, 08, Primer of wood preservation",
W.F. Sherfesee.
Vol. 59: 24456-7, Ap. 1, 05, "Strength of timber treated with
preservatives".
Vol. 64: 311, N. 16, 07, "Timber and its protection from marine
enemies".
Vol. 65: 356-8, Je. 6, 08, "Treatment of timber; open tank
method". C.G. Crawford.
Vol. 58: 24180-1, D. 3, 04, "Wood preservation".
Scientific American
Vol. 95: 79, Ag. 4, 06, "Sulpher process for the preservation
of wood".
Vol. 86: 91, Mr. 15, 02, Electrical process for preserving wood".
Vol. 83: 133, S. 1, 00, "Process for preserving wood".
American Architect
Vol. 60: 87, "Wood preserver".
Vol. 64: 78, "Timber preserving and fireproofing".
Vol. 81: 12, "Protection and preservation of wood".
Bibliography
Nature
Vol. 37: 182- 514, "Timber and some of its diseases".
Vol. 38: 108- 307, "Timber and some of its diseases".
Science
Vol. 16: 326, "Preservation of timber".
Slides
1. "Piece of wood magnified 100 times", Nature, Vol. 37, page 185.
2. "Tank for treating fence posts", Scientific American Supplement,
Vol. 65, Je. 6, 08, page 356.
3. "Tank used for treating telephone poles", ibid
4. "Tank used for treating mine timbers", ibid, page 357.
5. "Diagram of small treatment plant", ibid.
6. "Powell process cylinder before closing", Scientific
American Supplement, Vol. 63. My. 11, 07, page 26216.
7. "The cylinder and trolley(Powell process)", ibid.
8. "Ash fellies", ibid.
9. "A section of balk riddled by teredoes", Scientific American
Supplement, Vol. 67, Ja. 2, 09, page 12.
10. "Another example of teredo destruction", ibid.
11. "Where the teredo does his work", ibid.
12. "Various methods of protecting wood piles", ibid.
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