Page:The New Monthly Magazine - Volume 097.djvu/80

70 Several thousand "blocks," or double sleepers, lie piled about the ground. Each block is nine feet long and ten inches square, so as to make, when sawn down the middle, two sleepers of the usual English narrow-guage size of nine feet long, ten inches wide, and five inches thick. Semicircular sleepers, of the same proportions, are also sometimes used; but they are more common abroad than in England.

The cutting of the blocks is the first process which they undergo. The sleepers which they form are carried from the saw-mill to the drying-house, where they remain for twenty-four hours in an atmosphere of dense smoke, at a temperature of 180 degrees; the effect produced upon them is almost exactly similar to the "curing" of herrings or bacon. The whole of the inherent moisture of the wood being thus expelled, and the albumen in the sap-vessels being coagulated by the heat, the sleepers are placed on trucks, and are run along the tramway right into the cylinder. As many truck loads as it will hold are pushed into it one after the other, and when it is packed full, or, in creosoting language, "charged," the doors are closed and made air tight. A steam exhausting pump is then applied to the cylinder; all the atmospheric air in it is sucked out, and a vacuum is created in it, and in the wood which it contains. The creosote oil is then thrown, by an hydrostatic force-pump, from a neighbouring reservoir, into the cylinder, at a continuous pressure of 180lbs. to the inch, and it naturally and necessarily rushes into the pores of the wood to replace the air which has been withdrawn from them. The force-pump is kept at work Tor ten or twelve hours, by which time a sufficient quantity of oil (usually two-thirds of a gallon, or 7lbs. weight, to a cubic foot of pine timber) has been injected. The doors are then opened, the pickled wood is drawn out again in the trucks, and a fresh "charge" is introduced in its place. The finished wood is reloaded into barges, and is carried off to its thenceforth eternal duties.

In cases where it is not considered essential to so thoroughly imbue the wood with the preservative oil, it is simply thrown, after having been smoke-dried, into an open tank full of hot creosote, and is allowed to soak there for forty-eight hours. This less expensive process can, however, only be applied to short lengths of timber; long pieces must be submitted to pressure in the exhausting cylinder; for as the oil enters at the ends, and not at the sides, force is necessary to send it up to any distance beyond four or five feet.

As the men at the Greenwich establishment are paid by piece-work, they will sometimes dispense with the trucks and tramway, and will, in order to get a larger charge at once, pack the wood into the cylinder with their own hands; and as they must also, in that case, withdraw it themselves, they are obliged to go right into the oil-dripping cylinder to perform their duties, and have to breathe an atmosphere of tar which, though it almost blinds them, from its effect upon the eyes, yet gives them an amount of appetite which no other known stimulant can impart. Perhaps the chef of some illustrious gourmet will act upon this information, and will invent, as a substitute for hunger-inspiring oysters, a "vol-au-vent à l'huile de goudron."

The action of creosote upon wood is to completely fill up the pores, and to coat the fibres; so that it almost loses the character of wood, and acquires the consistency of pitch. It is, when thus prepared, utterly insensible to the action of air or water; its natural tendency to