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any further filling causes a pressure. What is the profit to extract the air (and gases) from the lower timbers to allow the infiltration of the oil if this air, etc., is to be gradually compressed into the timber in the upper tiers of the cages?
In those cases when the best results were desired, especially with treatment of 12 or 14 pounds, it has been the practice of the writer to maintain the even vacuum during the filling process, even though the oil had to be admitted slowly or stopped for a while to regain the maximum vacuum. This practice has eliminated the poor penetration generally evident in the upper tiers of timbers.
The practice of alternating steaming and vacuum several times before the application of oil has never appealed to the writer as an economical one. The time required for alternating a steam pressure and the time for exhausting the cylinder, after the pressure has been held a sufficient time, seems to more than overcome any advantage which might be gained by the process.
The final process of treatment is the simplest of the processes of creosoting timber and yet is the process in which the interests of the purchaser are, in a majority of cases, most concerned. The condition of the timber as to strength can usually be seen sufficiently for practical purposes after treatment, but the quantity and quality of creosote contained can only be approximated, even by the most scientific analysis of the timber. The variation of the quantity of creosote contained in the different sticks of the same charge and the variation of the quantity, even in the two ends of the same piece, make any test as to quantity averaging in the entire charge a rather wide guess. The quantity of creosote contained in a single piece of timber may, of course, be ascertained very closely by extracting the oil contained in a section or several sections, but this method is rather expensive and laborious for any large quantity. The depth of penetration may be deceiving. The condition of seasoning and the condition of treating influence penetration to a great extent. If the timber is seasoned thoroughly the percentage of oil contained may be 50 per cent or more greater than in a partially seasoned specimen. As heretofore mentioned, the creosote, ordinarily at least, enters the cell spaces only and it is held by many that the creosote never does penetrate the cell walls.
If this really is the case it is rather peculiar, inasmuch as the cell walls will give up and take in water any number of times and
yet have such an aversion to substance like creosote. Without doubt, the cells walls do not contain creosote to any great extent immediately after the injection, especially in the instance of steamed timber, but it is the opinion of the writer, borne out to a limited extent by experiment and examination, that creosote is present in the cell walls after the escape of the moisture from that portion. Immediately after treatment there occurs a seasoning of the treated wood, during which it loses weight to a marked degree, even at low temperatures. The surface becomes dry and, in time, the interior does not show nearly so much "bleeding" when cut or pressed with a knife blade. Evidently some oil has been volatilized, but the loss is principally water. The loss during the first three days exposure after treatment from a piece of 1 inch plank exposed in the shade to a maximum temperature of 75 degrees, amounted to nearly 15 per cent of the entire weight of the injected creosote. Evidently this loss was nearly all water, as the creosote was rather heavy and would not volatilize so rapidly.
If after such a loss of moisture, which must necessarily come principally from the cell walls, the creosote is liquid, as will be the case when exposed out-doors to temperatures above 100° F., it is the opinion of the writer that the creosote will penetrate the material of the cell walls just as water has penetrated in waterlogged timber.
Creosote, being an oil, has no affinity for water, and if mixed there will be a separation with well marked strata of creosote and water. While this is a fact in experiment, it is not so in actual practice where other elements than water and creosote are present to emulsify the mixture and prevent a separation by sedimentation. Water, saps, and resins are present in the cells of steamed timber, and physically or otherwise mix with the creosote during the injection process, adding to the volume and causing a deeper penetration than in the case of timber seasoned by a process lacking in moisture, provided, of course, that the cells of both specimens are opened for this reception of the creosote.
For very light treatments-say those of 10 pounds or underthe absorption often becomes so rapid that the cylinder is barely filled before the required amount is absorbed. In fact, it has often been noticed that the timbers on top of the cage never were covered, the absorption being so rapid that the cylinder is never filled and no pressure applied. Where this is the case it would seem that the cheaper, open tank process would serve the same purpose, if a full
cell process is desired, or, better yet, the empty cell process— namely, Rueping or Lowery.
The use of less than 10 pounds of creosote per cubic foot of timber in the full cell process does not seem to the writer to be worthy of consideration for any timber coming into contact with the earth or exposed to any other chance for rapid decay. The lack of penetration on the heart side of sawn timber and the lack of penetration of entire sticks exposes them, as compared with the general average, to premature decay. If the vacuum is dispensed with entirely in these cases, it will be found that a deeper penetration is to be had approaching, in a much smaller degree, the Rueping process, in which the vacuum is not only dispensed with, but replaced by the injection of compressed air into the cells which, on the release of pressure after injection of the creosote, expands and forces out a large portion of the creosote.
The arrangement of pipes, valves, tanks, and cylinders at most creosoting works is a veritable labyrinth. Some of the arrangements are so cumbersome and unnecessarily complicated that it would seem that the management had determined on such complication to baffle inspectors and put oil into other places than the supposed one. This is probably not the case, but suffering from a reputation of crookedness given the entire business by a few individuals, it would seem to the interest of the reputable company to go to considerable trouble and expense to arrange the piping and valves so that an inspector could see what was actually going on, as well as to protect themselves from loss by leaking valves and pipes underneath the ground.
It is simple enough to figure the quantity of creosote taken from a tank, but to figure where that creosote has gone is another problem. Inspectors are paid to see what goes on and not to be the recipients of such information as the plant management sees fit to give them. Regardless of the honesty of the operators, it is the duty of the inspectors to see and check every movement of the oil and personally ascertain, if possible, any other fact bearing on the case. Unfortunately, inspectors are sometimes looked on as intruders and all information is grudgingly given.
The quality, as well as quantity, of creosote should receive attention during the injection or immediately prior thereto. A minimum specification having been decided on, it is the duty of the inspector to see that that quality is actually being used. The practice in paving block business of submitting a scientifically pre
pared and costly sample for analysis and then treating with a commercial product should be eliminated, first, by the adoption of a reasonable specification and, finally, by the employment of an inspector who knows the business and attends to it in a proper
Without a special reason the filling of the cylinder should not be made faster than the vacuum pump will extract the air and gases, for the reasons before given. The quantity absorbed will vary greatly and can in no case be more than approximated. With the proper arrangement of gauges, thermometers, etc., it is possible to compute, fairly closely, the amount absorbed after the cylinder has been filled. It may amount to as much as 8 pounds per cubic foot of timber in some cases, and for two charges of the same class of timber handled in very much the same manner, may vary 50 per cent-consequently, any figure on the total amount absorbed based on an assumed absorption is the veriest guess.
The rapidity of absorption with or without pressure depends to a marked degree on the temperature of the creosote; as a rule, the higher the temperature of the creosote the more rapid the absorption. Incidentally, there is another reason for high temperature in the oil, as the loss of water incident to the heating of the oil in preparation for the treatment usually will guarantee a small percentage of water in the oil at the time of treatment. It is hardly probable that the timber can be damaged by excessive pressure during the injection, as the absorption is too rapid to attain much pressure on the empty cells. The pressure used depends on the state of seasoning of the timber and the quantity of oil to be injected. Often it will not reach over 25 pounds, while in the heavier treatments it is the limit the cylinder is capable of withstanding, and that held for many hours.
The absorption at first is very rapid and may continue rapid until the sapwood is completely filled, after which it abruptly drops and continues very slowly. The time necessary to inject a certain quantity of creosote can not be foretold with any degree of precision and may vary 100 per cent with timber seemingly identical in structure and seasoning.
If the time of injection is to be prolonged the oil should be heated by means of the steam coils, for the double purpose of keeping the oil liquid and retaining as much heat in the timber as possible, so that the cell openings and cells may be kept open.
A few years ago it was commonly supposed that the heartwood
of the closer grained timber could not be penetrated, but it has been demonstrated that it is capable of absorbing, when properly handled, almost as much oil as the coarse grained or sapwood. It is merely a question of proper preparation during the seasoning process. In sawn timber, however, the penetration of the heart faces is so much less than the sap faces that in the lighter treatments it frequently causes weak places in the protection. The greater natural resistance to decay of the heartwood in a great measure remedies this fault.
After the injection is completed, it is not possible to withdraw any quantity of oil by means of a vacuum unless the vacuum process was omitted and air is contained in the timber. It is well, however, to withdraw the charge as soon as possible, or else chill the timber by means of air so that the oil may partially coagulate and prevent dripping.
Seasoning of treated timber by exposure to air is beneficial in may cases, as it allows the vaporization of the lighter oils and consequent crystallization of the oil remaining. Otherwise, if the timber is placed in contact with the ground, those light oils may keep the creosote liquid enough to flow out in considerable quantities. This is especially true in the case of ties.