« ZurückWeiter »
about Ith of its natural bulk, without previous exhaustion ; so that the difference between 5 lbs. and 30 lbs. forced into a sleeper, could not, he thought, be all due to exhaustion, but must depend upon other circumstances, not explained in this paper.
The President thought that the greater degree of absorption by the Scotch fir, might be accounted for by its open texture, whereas the foreign timber was more compact, and also contained more turpentine. It might also have been wetter than the Scotch fir, which he believed had been the case.
Mr. Taylor observed that hitherto the attention of the meeting had been entirely directed to mechanical action, but that the chemical combination of the corrosive sublimate with the albumen of the wood, was the point most insisted upon by Kyan; it was supposed to be similar to the operation of tanning hides, in which the tannin of the bark combined with and saturated the animal gelatine, which would not otherwise be permeable by the fluid in which it was placed. .
Lieut. Oldfield suggested that if the timber, when piled in the tank, was subjected to the action of heat, at 212°, the moisture contained in the capillary tubes would be expelled in the form of steam, and that on the admission of the solution, the tubes would instantly be filled with it, because of the partial vacuum formed in them. · Mr. Colthurst observed, with regard to the tests for ascertaining the amount of saturation of the timber, that he had tried all those described by Mr. Lynde, and had not been able to discover the presence of mercury in the heart of any of the timbers prepared for the Great Western Railway; their dimensions were 6 inches by 12 inches ; Dr. Faraday had, he believed, detected it, by the aid of the galvanic battery, in the heart of a piece of timber 2 feet square, after simple immersion in the solution for fourteen days. .
Mr. Moss had tried many experiments as to the most delicate tests for ascertaining the depth to which the mercury had penetrated ; the most satisfactory test was gold-leaf, as from its strong affinity for mercury, the presence of the latter was immediately detected. The mode of proceeding, was to put some fibres of the wood to be tested into a small test tube, mixed with a portion of dry carbonate of soda; then, to place over, but not in contact with it, a small piece of gold-leaf, and apply heat to the bottom of the tube. If any mercury was present, in however small a quantity, the fumes would rise and discolour the gold-leaf.
Mr. W. Cubitt said, that timber was at all times, more or less, charged with moisture: he had found deals, supposed to be dry, lose 10 per cent. of their weight from steam drying; it was evident, that the presence of moisture in the pores of the wood, must militate against the success of kyanizing by simple immersion, unless it was continued for a very long period. In close tanks, when exhaustion and pressure were resorted to, the moisture was perhaps of less importance, but still, if the sap was extracted, and the timber previously dried, the process of kyanizing would be more efficient.
Mr. S. Seaward adopted Mr. Palmer's position, as to the almost impossibility of forcing the solution through the capillary tubes of a long piece of timber, the pressure being applied equally all over the surface: he believed the present method of kyanizing to be very imperfect, and alluded to a number of sleepers so prepared for the West India Dock warehouses, having been recently discovered to be decayed.
Mr. Martin confirmed this account of the decay of the sleepers: fifty out of seventy were destroyed; they had been prepared by simple immersion, and had been down about five years. He had understood that some of the wooden tanks, in which the solution was kept at the Anti-Dry-Rot Company's yard, were decayed.
Mr. C. May believed, that the destruction of the tanks might have arisen from the constant corrosive action of the mercury, and not from decay. The capillary vessels of timber being filled with air and sap, under exhaustion, the air would expand and drive before it a considerable portion of the sap and moisture. In preparing the compressed trenails and wedges, he used steam, and found that the pores were opened by it ;-he suggested that steam should be blown through the tanks until all the timber in them was raised to a certain temperature, and then, by opening the communication wtth the reservoir, the solution would rush in and fill up the vacuum.
Mr. Cowper believed, that it was only necessary to bring the chlorine of the corrosive sublimate and the albumen of the timber into contact, when sufficiently dry, to insure the preservation of the wood. He had occasion to try experiments with paper pulp, and was constantly annoyed by its decaying—but the addition of a small quantity of chlorine had preserved it good for two years, and he believed that it would continue unchanged.
General Pasley confirmed the statement as to the increase of the specific gravity of timber from long immersion at considerable depths. He had found all the timber, except the mainmast, in the Royal George, at a depth of about 90 feet, water-logged. The oak timber had increased, on an average, more than 50 per cent. above its usual specific gravity.
Mr. F. Braithwaite remarked upon the doubt which appeared to exist among members as to the correctness of that part of Mr. Timperley's Paper, where a sleeper, containing 3 cubic feet of timber, was reported to have increased 30 lbs. in weight. Mr. Braithwaite had made some experiments, the results of which showed that a piece of Memel timber, containing 533 cubic inches, and weighing, when dry, 9 lbs., became double its weight when subjected to a pressure of about 320 lbs. per square inch, without previous exhaustion; the machine which he used, not being provided with an air-pump. A smaller piece of American pine, containing 76 cubic inches, and weighing 1 lb. 7 oz., increased in weight 3 lbs. under a similar pressure,—this he contended established the correctness of Mr. Timperley's Report.
There appeared also to be a misconception as to the amount of corrosive sublimate employed,—the Paper states that I lb. was the quantity used for each load of timber of 50 cubic feet.
He promised to make some further experiments, and report them to a future meeting.
Mr. Bull had prepared considerable quantities of boards for the Calder and Hebble Navigation, by immersing them in the solution for two or three days, which was about double the period allowed by the patentees. He had some specimens of the boards, and in almost all of them there was an appearance of decay in various stages. An oak board, 1 inch thick, kyanized in 1839, had lain ever since upon the damp ground, exposed to the air : the sap part was entirely decayed, but the heart remained sound; fungus was however growing upon it. Poplar boards, kyanized in 1838, 39, and 40, were all partially decayed—those which were not prepared, and had been exposed in the same situation for the same period, showed however more symptoms of decay. In preparing the timber, heh ad always followed the instructions of the patentees, and had tested the strength of the solution with the hydrometer, but had mixed up fresh solution even more frequently than was supposed to be required. On dismantling one of the tanks for holding the solution, he found the iron-work partially destroyed, and entirely covered with globules of mercury. : Mr. Thompson explained, that the hydrometer was not a correct testing instrument, if any vegetable matter was present in the solution : that the tanks, on the premises of the Anti-Dry-Rot Company were necessarily made of unprepared timber : that the bi-chloride of mercury in solution, would penetrate any length of timber, if the extremities of the sap vessels were exposed to its action, but that it would not penetrate laterally without pressure; it was not therefore surprising that a water-tight tank, of unprepared wood, should decay on the outside, even if filled with the solution. With regard to the strength of the solution, at first it was believed that i lb. of corrosive sublimate to 20 gallons of water, was sufficiently strong, and much timber had been so prepared, but experience had since proved, that the strength of the mixture should not be less than 1 lb. to 15 gallons, and he had never found any well-authenticated instance of timber decaying when it had been properly prepared at that strength: as much as 1 in 9 was not unfrequently used. In a cubic foot of wood, prepared under a pressure of 70 lbs. per square inch, mercury had been found by the galvanic battery to have penetrated to the heart.
: Mr. Horne mentioned, that a new process had been invented by Mr. Payne, for rendering timber proof against dry or wet rot, and the ravages of insects ; for increasing its durability, and rendering it incapable of combustion. The mode of proceeding, was to impregnate the wood with metallic oxides, alkalis, or earths, as might be required, and to decompose them in the interior of the wood, forming new and insoluble compounds. • Mr. Taylor drew the attention of the meeting to a Memoir on the Preservation of Woods, which had been read before the French Academy of Sciences, by Dr. Boucherie. It was argued, that all the changes in wood were attributable to the soluble parts they contain, which cause fermentation and subsequent decay, or serve as food for the worms, that so rapidly penetrate even the hardest woods. By analysis, it was found that sound timbers contained from three to seven per cent. of soluble matter, and the decayed and worm-eaten, rarely more than one or two per cent. ; since therefore the soluble matters of the wood were the causes of the changes it underwent, it became necessary, for its preservation, either to abstract these soluble parts, or to render them insoluble, by introducing substances which should prevent their fermenting. This might be done by many of the metallic salts or earthy chlorides. Pyrolignite of iron was particularly recommended as being a very effective substance, and cheaper than corrosive sublimate. The process was, to immerse the end of a tree, immediately after it was felled, in the solution of metallic salt, when, the vital energies not having ceased, the fluid was absorbed throughout all the pores of the tree, by a process which is termed “aspiration." The fluid had been applied in bags, to the base of the trees, when in a horizontal position, or to one of the branches, or by boring holes to the heart: a few branches and a tuft of leaves being always left at the top of the principal stem. It was necessary to apply the process speedily after felling the timber, as the vigour of the absorption was found to abate rapidly after the first day, and became scarcely perceptible about the tenth day,—whilst in dead wood, or where there was any accidental interruption of the flow of the sap during