The Bet hell Process of impregnation has always been associated with the use of creosote. The original patent taken out in England in 1838 did not include the word "creosote," hut, in stead, referred to a method by which any one of eighteen sub stances or mixtures might be introduced into wood. Creosote was an ingredient in one of the mixtures mentioned, and is yet the preservative associated with this process. A distinct feature of the Bethell Process as first practised in Europe was that the woods to be treated were not steamed and this detail is yet prac tised where the process is; exactly follows.
More or less completely seasoned wood is placed in cylinders, a vacuum is drawn by air pumps after which warm creosote is directed into the cylinder and held a pressure of from one hundred to one hundred and eighty- pounds until the required absorption has taken place. It is amusing to note than an early objection to this process was founded upon the fact that it forced "too much creosote" into the wood.
The Bethell Process was not at first accepted in the United States because it was costly, and because it was not designed to treat unseasoned woods. Andrews, writing in 1878, stated that this "defect" of the Bethell system had always been recognized in Europe, where ties and timbers intended for creosoting were stacked up for nine to ten months to season.
The Bethell was the original creosote process and it is yet the standard. The best results have been obtained through its instrumentality. But the fact that the process as first detailed abroad is suitable only for the treatment of seasoned woods, and the further fact that large amounts of oil are required, have led to some modifications.
In the United States the principal demand is for the treatment of green or imperfectly seasoned woods and with this in mind, in 1872, Hayford suggested that woods be prepared by steam instead of by drying. With the difference noted the Bethell and Hayford processes are alike. The latter title is now seldom used, while the title "Bethell Process" has been extended in the United States to include the preliminary steaming of green woods, as well as the preliminary drying of seasoned woods.' The London, Brighton & South Coast Railway Company apply creosote under a specification as "The sleepers, when sufficiently dry, are to be placed in a wrought iron cylinder, and, when closed, a vacuum is to be created by air pumps. The creosote, at a temperature of not less than 120 degrees Fahr., and not more than 150 degrees, is to be allowed to enter the exhausted cylin der, and afterwards is maintained there by pumping at a pressure of not less than 120 pounds to the square inch. The sleepers are to be kept under this pressure until each sleeper has absorbed at least three gallons of creosote on the average, the quantity to be ascertained by weighing. Any charge of sleepers not giving the average impregnation of at least three gallons is to be returned to the cylinder for further treatment." The Eppinger & Russell Company employ details as follows: Wood is steamed at about twenty-five pounds pressure. The steam is succeeded by vacuum of about twenty-eight inches; the oil is then admitted and held under a pressure of from fifty to two hundred pounds, as the quality of the wood may indicate. Such minor changes are made from time to time as appear to be sug gested from experience.
A specification prepared by the Southern Creosoting Company of Slidell, Louisiana, is as follows: "Steaming Process. The seasoning of the timber shall be accom plished by the direct application of live steam admitted into the treating cylinders. The steam gauge pressure in the cylinders shall be regulated according to the dimensions of the timber. During the process of steam ing the cylinder must be frequently drained by a valve located at the lowest possible point. The steaming must continue from three to fif teen hours, according to the size of the lumber and the quantity of oil to be injected into it. At the end of the steaming period a vacuum shall be created in the cylinder, the temperature being at all times maintained above the boiling point. The vacuum must continue until the gauge shows a reading of from twenty-two to twenty-six inches, and to be kept at that reading until no moisture comes from the bottom of the cylinder.
"After the material has been thoroughly seasoned and it has been ascertained that no sap or moisture remains in the cylinder, the oil shall be admitted at a temperature of not less than 120 degrees Fahr., which temperature shall be raised to not less than 185 degrees Fahr. under a pressure of not less than 125 pounds per square inch. The force pump producing this pressure shall be kept in operation until the established system of measurement shows the wood to have absorbed the desired quantity of oil.
"The pressure shall then be released and the timber completely treated shall be immediately removed from the cylinders." The American Telephone and Telegraph Company applies creosote to timber other than Douglas fir under the very complete specification that follows.' The specifications do not cover the treatment of crossarms: "General. These specifications describe the processes to be used in impregnating timber, except crossarms, with dead oil of coal-tar and are intended to include all instructions necessary for the proper performance of the work.
" Testing Facilities. The manufacturer shall provide and install such apparatus as is necessary to enable the inspector to determine that the requirements of these specifications are fulfilled. It is suggested that recording temperature and pressure instruments be provided.
" Workmanship. All material shall be of the best quality unless other wise specified herein and all workmanship shall be sound and reliable in character and of the best grade.
"Timber. The timber subjected to the creosoting treatment shall conform to the requirements of the specifications and drawings furnished by the telephone company. All timber shall be framed, shaped, and bored before treatment.
"The material in each charge shall be in approximately the same con dition so far as air-seasoning is concerned, and under no circumstances shall green, partially seasoned, or seasoned timber be treated together in the same charge.
"Two kinds of timber, for example yellow pine and black gum, shall not be treated together. When the southern yellow pines are treated, longleaf and Cuban pine shall not be included in charges with shortleaf and loblolly pines.
"Only one class of material shall be treated in any one charge, for example, poles and ducts shall not be treated together.
Dead Oil of Coal-tar. The dead oil of coal-tar used in impregnating the timber shall conform to the requirement of the American Telephone and Telegraph Company's Specifications for Dead Oil of Coal-tar or Coal-tar Creosote. The telephone company shall have the right to take samples of the oil whenever its inspector shall elect. The sample of oil so collected shall he tested wherever the telephone company shall elect.
"Quantity of Oil. All timber shall be so impregnated with dead oil of coal-tar that the average impregnation of the material in each cylinder load shall not be less than the quantity of oil called for in the specifica tions for the material or in the contract. The .volume of timber and the quantity of oil absorbed shall be determined by the inspector. The inspector shall have access to all records of treatment.
"Excess of oil in one charge shall not be offset against a shortage of oil in another charge.
"The treating plant shall be equipped, to the satisfaction of the tele phone company, so as to allow a close determination of the amount of oil injected into the timber.
"The quantity of oil injected into the timber, as determined by the volume of oil withdrawn from the measuring tanks, shall be based on the standard temperature of 100°F., and the quantity increased by an amount equal to 0.00044 of the required volume at 100°F. for each degree Fahrenheit of oil temperature above the standard temperature of 100°F.
"General. The treating cylinder shall not be opened during the proc ess of treatment.
"Classification. For the treating process timber shall be classified as heavy or small.
"Heavy timber shall be understood to include poles and stubs; small timber shall, unless otherwise specified, include all other timber, except crossarms, ordered by the telephone company.
"Steaming and Heating Process. Steam when used shall be main tained at a uniform pressure and temperature in the treating cylinder as indicated in the following table: "The temperature readings shall be taken by means of standard ther mometers placed in the treating cylinder so that the bulbs thereof are within the shell.
"At the beginning of the steaming process the exhaust valve shall be open and shall not be closed until a steady flow of steam escapes through the valve. The duration of the steaming process shall be timed from the closing of the exhaust valve. The exhaust valve shall be opened and the condensation blown off at intervals during the steaming process.
"The duration of the steaming process shall be as directed by the inspector and shall depend upon the condition and character of the tim ber, but shall in no case be carried to such an extent as to injure the timber. The timber shall not be steamed in excess of the interval given in the following table: "Exhaustion Process. Green and Partially Seasoned Timber. When the steaming process shall have been completed the steam shall be blown off and the treating cylinder exhausted to a vacuum of at least twenty four (24) inches at or near sea level, or proportionately less at higher altitudes. The vacuum shall be maintained at the above minimum for a period: for heavy timber, of not less than 2 hours; for small timber, of not less than 1 hour; and if necessary thereafter until the condenser discharge is clear. During the exhaustion process the temperature within the treating cylinder shall be maintained, by means of saturated steam in the closed heating coils, above that at which water would boil at that degree of vacuum.
"Exhaustion Process. Seasoned Timber. With seasoned timber it is not required that a vacuum shall be drawn after the heating process and before the filling process, provided that the specified amount of dead oil of coal-tar is in the timber on its removal from the treating cylinder.
"Filling Process. After the exhaustion process, the cylinder shall be completely filled, as rapidly as possible, with dead oil of coal-tar and in no case shall the flow of oil into the treating cylinder be stopped before the overflow of the cylinder. Pressure shall then be applied until the specified amount of oil has been forced into the timber.
"The total amount of oil forced into the timber shall be determined from the initial reading on the measuring tanks and the readings on the measuring tanks after the oil in the cylinder at the conclusion of the pressure process, including all drip from the timber, has been returned to the measuring tanks.
"The oil at introduction into the cylinder shall have a temperature of not less than 140°F. and not more than 175°F. The oil in the meas uring tanks shall be maintained at a uniform temperature during the filling process.
"Subsidiary Specifications. The following specifications of the American Telephone and Telegraph Company form a part of these specifications: "Specifications for Dead Oil of Coal-tar, or Coal-tar Creosote.
" Specifications for Analysis of Dead Oil of Coal-tar, or Coal-tar Creosote." The specification adopted by the American Railway Engineering Association is given on page 448 of the 1911 Manual published by that organization.
The Burnett Process.
This process, which was patented by Burnett in 1838, depends upon the use of zinc chloride. The immediate value of this salt as an enemy of wood-destroying fungi is about equal to that of creosote, but because the salt dissolves readily in water, the results are not as lasting. Neither is it known that zinc chloride repels the attacks of teredos and other shipworms.
The method of impregnation is similar to that employed in the Creosote Process. The wood is steamed, partly dried in a vacuum of from twenty to twenty-five inches, and then treated with warm zinc chloride solution which is held under pressure until the required absorption has taken place. Here as elsewhere, results are influenced by attention paid to details. The object is to transfer the required quantity of antiseptic to the interior of the wood, and to secure the greatest practicable uniformity of distribution without injuring the wood.
The Burnett Process is essentially a tie-preserving process and is not suitable for timbers that are to be exposed in marine positions. It is cheaper than creosoting, and particularly useful with ties which are to be exposed in climates and surroundings that are not too wet. Under such conditions the life of the ties is frequently doubled. A field of usefulness is with inferior woods that must now, with the scarcity of better kinds, he employed. It is needless to urge that prevention of decay should be adjusted as far as possible to the natural mechanical life of the tie and that expensive treatments are not warranted with ties that wear out before they rot. The Burnett and Full-cell Creosote Processes were compared by Chanute as follows:' "An average life of ten to twelve years is being obtained by the use of zinc chloride in this country. It would be possible to obtain a life of fifteen to thirty years by the use of creosote, but it will be seen from the figures that this would cost three to four times as much as zinc chloride.
" We must be content, therefore, either to allow our cheap ties to decay in the good old way, or to adopt for the present some of the cheaper and inferior methods which will produce shorter lives than obtained in Europe." The Burnett method is much used in the United States and Europe.