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At one time it was thought that the strong antiseptic powers possessed by the phenols and creysols were responsible for the immunity from attack by the vegetable fungi, but this theory has long since been exploded by the experiments made by the Belgian engineer, Mr. Goisne, who took shavings impregnated with the various portions of creosote and exposed them to a most favorable attack. His deductions were that the lighter phenols and creysols prevented decay, but did not long remain in the timber and that the greatest protection was afforded by those portions of high distillation, because they were just as efficient and remained present for the longest period of time.
In the open cell process, on account of the small quantity of oil left in the timber, impregnation should be made with an oil which is least volatile. For the full cell process the evaporation of small quantities is not so detrimental and a more volatile oil is permissible. The protection of marine work is another proposition, in that the portion exposed to the air-and therefore decay-has a great excess of creosote which, of course, can be more volatile, while the portion exposed to the water is less subject to evaporation. and more subject to leaching out. It is very probable in this case that the solidifying quality, rather than volativility, is the criterion.
The measure of value is service, which can only be proven by actual experience. The accelerated tests made to ascertain the value of creosotes are probably subject to the same criticisms as the accelerated tests on cement. For marine work, in view of the lack of experience with the oils lacking in naphthalene, it would seem best to at least take a middle course and use an oil containing a moderate quantity.
Many specifications show a positive lack of knowledge of the fundamental principles of creosote. The specifications of an "anhydrous oil" of an absolutely pure dead oil coal tar having a higher specific gravity than is possible to get as we frequently find in paving block specifications are ridiculous. The specifications of a minimum quantity of low boiling oils is wrong in the face of experience. These specifications are in most cases uneconomical. Creosote, as a commercial product, is the oily residue after the extraction of the portions which are more valuable for other purposes and which, if required to be in the creosote must add to the expense thereof. One should ascertain the quality which may be had for the work in hand, and if more than one quality suit
able for the particular work is to be had, then, the better the quality the less the quantity.
It is neither practical nor desirable to have adopted a uniform specification for creosote oil. Such a specification would increase the cost by excluding many of the oils now on the market and might tend to place the whole business in the hands of a few producers or their agents. The knowledge of efficiency of the oil has not advanced to a stage of certainty and even though it were known what is best, it probably would be found that the composition would vary according to the geographical location and the use to which the material was to be put. More irrational yet is the suggestion that in the present state of ignorance on the subject, no specification as to the constituents of the oil be made.
The standard specification of the American Maintenance of Way Association is open to criticism in that it practically excludes the great quantity of creosote produced in the United States and England, which even though it were not so efficient for their use, might be just as valuable in increased quantities and at a lower price. The writer will venture the opinion that where any effort is made to supply oils such as required in standard paving block specifications, the result is either failure or detrimental to the material through the trickery involved.
Many specifications will not allow light oils in excess of some stated per cent and yet allow the presence of a percentage of water without compensation, or a larger percentage with compensation. Why, then, is it not allowable to compensate for the presence of light oils in the same manner as for the water?
This paper is based primarily on the Bethell or full cell process, which is ordinarily used and unless otherwise stated, is the one meant whenever the creosoting process is mentioned. The treatment is made in large cylindrical retorts into which the timber is conveyed on small iron trucks or cars, called cages. The ends of the cylinder are closed tight by means of close-fitting doors capable of withstanding considerable pressure. If the timber has not previously been seasoned, it is usual to admit live steam into the cylinder for such time as the experience of the engineer in charge directs. On the exhaustion of the steam a vacuum is drawn, the heat in the cylinder being maintained by means of steam coils beneath the trucks. After the vacuum has been held a sufficient time,
creosote from a gauged tank is admitted and pressure held by means of a pump until the requisite quantity is absorbed by the timber. The excess oil is then returned to the tank from which it was originally taken, the gauge indicating the quantity absorbed by the timber. Variations of this process, known by various names, are used where peculiar conditions or theories warrant.
On the Pacific Coast the steaming process is replaced to a great extent by heating in hot oil, as the structure of the wood there treated is such that damage is done by the ordinary steaming process, probably due to the lack of cross ducts to relieve the internal pressure of volatilized moisture.
The preparation of the material for treatment is largely dependent on the extent of the treatment proposed and the nature of the timber to be treated. Care must be taken to keep the pieces separated in the cylinder so that the treatment may have the similar effect on all pieces to insure somewhat uniform penetration of the creosote. Dry timbers or timbers not to be steamed do not have to be spaced so carefully or so far apart as in the case of steaming. It must be remembered that during this process the timber becomes soft and will easily bend and that the more rigorous the steaming the softer the wood will become, and therefore greater precaution must be taken to prevent it from becoming misshapen or bearing down on the pieces underneath, thus preventing the full effects of the process or the penetration of the creosote.
Crooked piling can often be drawn back into shape by proper "building" in the cages and, on the other hand, many otherwise good sticks are rendered practically unfit for use by improper "building." Some timber is, of course, more apt to go together and prevent the penetration of the oil, and for that reason should be carefully separated. The pieces used as separators will press into the timber and allowance must be made for that.
Piling intended for the lighter treatment-15 pounds or under— should be free from the "skin" found next to the live wood unless considerable steaming is done, as this skin will prevent the penetration of the creosote. Many failures-especially of telephone poles -can be attributed to the failure to observe this precaution, the decay in the spots unpenetrated passing in to the unpenetrated center of the pole and causing a general disintegration. In this connection it must be remembered that the creosote penetrates more rapidly the tangential section than the radial, owing to the arrangement of the resin ducts and medullary rays. Where the
treatment is heavy the creosote will gradually penetrate underneath the skin, provided the patches are not excessively large, though the treatment is delayed thereby. If rigorous steaming is given, the skin will usually curl up or peel off sufficiently to allow the penetration throughout. Many specifications limit the size of the skin to be left on to 1 inch in width, it being assumed generally that the creosote will penetrate 1⁄2 inch tangentially before the extreme depth of penetration is reached.
For the reasons heretofore given there should be a uniformity of texture and seasoning of the timber, especially in the case of light treatment, or else great variation in penetration must be expected. When, as for heavy treatment, the oil pressure is continued for a long time and the cells must all be filled to take up the required amount of creosote it will appear that this precaution is not so necessary, but the necessity of steaming the more porous wood longer, in order to properly treat the harder pieces and the possible consequent weakening, is an argument for separation.
It is most important that the timber of a charge be of approximately the same cross-section. The effect of steaming, vacuum, and injection are largely dependent on the area of surface exposed per square inch of cross-section. The same depth of penetration can not be expected in large timbers as in small-much less the same amount of oil per cubic foot of wood. Examination of the relative depth of penetration in the butt and point of a pile will show much greater penetration at the point. It is to be remembered that the effect of the heat is retarded by the mass of cold material within the large pieces.
The writer has before him a record of a charge of timber treated under the supervision of an inspector, which was composed of small cross-arms, ties, piles, and large square timbers. This charge was unseasoned material, steamed for ten hours with an injection of 18 pounds per cubic foot. Can anyone expect proper treatment under these conditions? In another instance ties of pine, oak, and gum, together with piling and large square timbers, some green and some air-seasoned, were treated together with a supposed uniform treatment of 12 pounds.
It is well for the purchaser to remember such instances as these quoted and endeavor to place orders in such a manner that no great difficulty will be found in segregating the material for treatment. If the order is small, it is well to ascertain the manner in which the material will be handled at the works and, in any event,
to specify some treatment not conflicting with the general working of the plant.
Steaming. The question of whether to steam or treat material which has been air-seasoned must be settled from the conditions peculiar to the case at hand. The stock of timber carried by the various dealers is comparatively small, so that time for seasoning must usually be given if the air-seasoning method is adopted. The second consideration is whether or not the air-seasoning will be sufficient for the injection of the creosote, and, lastly, probably the most important of all, will the material air-season without decay?
Seasoning of timber in the open air will, under proper conditions, leave it free from a large portion of the moisture, but that solid portion of the sap and the resin will still be retained and will prevent the ingress of the creosote to some extent, though not enough to affect the lighter treatments. The heavy treatment for marine construction requires more than seasoning the extraction of a large part of the resins and the opening of the cells for the injection of the creosote. This can not be accomplished by air-seasoning, though the time of steaming necessary may be considerably reduced. For lighter treatment air-seasoning is sufficient, though the subsequent oil penetration is never so uniform as when steamed.
In longleaf timber the outer inch may contain as much as 50 per cent of the moisture. The heartwood contains only about 20 per cent, practically all of which is contained in the cell walls. Ordinarily, about 35 per cent of the moisture may be found in the cell walls, though this percentage varies greatly, as it is influenced to a large extent by the quantity in the cells. From this it would appear that the problem of injection is largely a problem of extraction of the contained liquids. To open the cells and allow the liquid contained to pass off without tearing down the cell structure and to replace those liquids with the creosote is the problem.
It is with some hesitation that the writer expresses his opinions on the effect of steaming timber in the seasoning process, as there has been so much evidence put forth to prove that steaming is not necessary and is exceedingly detrimental to the timber. The subjeet of the effect of steaming on the strength of the timber was elaborately experimented on and discussed from a physical standpoint, in Forest Service Circular No. 39, by Dr. Kendrick Hatt, and much valuable information may be had therefrom. The writer has never been able to find a discussion of the effects on the struc