Smoke-drying in an open chimney, or the burning of furze, fern, shavings, or straw under the wood, gives it hardness and durability ; and by rendering it better, destroys and prevents worms ; it also destroys the germ of any fungus which may have commenced. Scorching and charring are good for preventing and destroying infection, but have to be done slowly, and only to timber that is already thoroughly seasoned; otherwise, by encrusting the surface, the evapora tion of any internal moisture is intercepted, and decay in the heart soon ensues ; if done hastily, cracks are also caused on the surface, and which receiving from the wood a moisture for which there is not a sufficient means of evaporation, ren ders it soon liable to decay.
Various methods have been from time to time proposed for seasoning timber, and preventing its rapid decay ; but those which have most engrossed the public attention of late years, are those respectively distinguished as Ryan's, Payne's, Burnett's patents, &e. In the year 1S33 to 1S3t3, at the Arsenal, Woolwich, experiments were instituted, having for their object the establishing or otherwise the claims of that first mentioned, and the results of which were of a very satis factory nature ; the Kyanised specimens generally, which were submitted to the fungus-pit when taken out at the end of three years, being sound, while duplicate pieces unprepared were found in various stages of decay. Certain questions, however, presented themselves :-1st. Whether the impreg m.tion to which the timber had been subjected, might not be removable by some cause, and perhaps generate an atrno- 1 sphere noxious and injurious to health. 2nd. Whether the strength of the timber were impaired or otherwise. The first was satisfactorily determined by Dr. Faraday, who proved by experiment, that the combination was not simply mechani cal, but chemical ; and that a permanently compound mate , rial was formed ; the second was formed by experiments made by Captain Alderson, C.E., upon ash and Christiana deal, and which showed that the rigidity of the timber was enhanced, but its strength in some measure impaired, its specific gravity also being somewhat diminished. Another question yet remains open—how flt•, since the impregnation has not been traced to a depth greater than half an inch, does this process meet our requirements, and after the satis factory conclusion arrived at as above related, and the evi dence of the facts upon which it was so reasonably founded, how are we to meet the assertion of Mr. Pritchard, C.E. of
Shoreham, made in 1S42. The sleepers Kyanised five years ago, and in use at the W. I. Duck warehouses, have been discovered to decay rapidly, and the wooden tanks at the Anti-Dry-Rot Company's principal yard are decayed.
Mr. Ryan's infusion is corrosive sublimate, and the process consists in submersing the timber in tanks for about a week, then taking it out and drying. Sir Humphrey Davy had previously recommended a weak solution of the same thing, to be used as a wash where rot had made its appearance. Dr. Birkbeek made a favourable exposition of the process as pursued by Mr. liyan. Sir John Barrow and the Duke of Portland impugn it, and Lord Manners and Dr. Moore follow on the same side. The Payauising process, besides profess ing to preserve timber from dry-rot and the ravages of insects, is said to render it nnintlammable, or at least to deprive it in a great measure of combustibility.
Sir William Burnett's patent process seems to have met with great, and, as we think, deserved success. The various testimonials that we have seen in favour of it, and the time that it has maintained itself in the opinion of the public, induce us to think well of its efficacy in performing what it professes to do. Even if not quite realizing all its inventors claim for it, it certainly will effectually preserve timber for a great number of years. The effects ascribed to it arc, that it hardens and improves its texture. It enters into perma nent chemical combination with the ligneous fibre, and does not come to the surface of the wood by efflorescence, like other crystallizable salts, and no amount of washing or boil ing in water, will remove the chemical compound so formed. It preserves wood and other articles from the adherence of animal and vegetable parasites, and also from the attacks of insects, and from wet and dry rot. Further, it renders wood uninflammable, when used of a certain strength. The basis of his process is chloride of zinc, or, as it is more commonly called, the muriate of zinc, which seems to have a peculiar affinity to woody fibre, entering into intimate union with its component particles, and forming as it were a new min eralized substance. There is a chemical combination of the metallic base ; not merely by a mechanical alteratiod of the position of matter, which might again be disunited. There is no decomposition produced, but the fibre of the wood appears to be permanently pervaded by the zinc, and the atoms of which they are formed enter into a new and fixed arrangement.