The following coating for piles and posts, to prevent them from rotting, has been recommended on account of its being economical, impermeable to water, and nearly as hard as stone: Take 50 parts of _resin_, 40 of _finely powdered chalk_, 300 parts of _fine white sharp sand_, 4 parts of _linseed oil_, 1 part of native _red oxide of copper_, and 1 part of _sulphuric acid_. First, heat the resin, chalk, sand, and oil, in an iron boiler; then add the oxide, and, with care, the acid; stir the composition carefully, and apply the coat while it is still hot. If it be not liquid enough, add a little more oil. This coating, when it is cold and dry, forms a varnish which is as hard as stone. Another method for fencing, gate-posts, garden stakes, and timber which is to be buried in the earth, may be mentioned. Take 11 lb. of _blue vitriol_ (sulphate of copper) and 20 quarts of water; dissolve the vitriol with boiling water, and then add the remainder of the water. The end of the wood is then to be put into the solution, and left to stand four or five days; for shingle, three days will answer, and for posts, 6 inches square, ten days, Care should be taken that the saturation takes place in a well-pitched tank or keyed box, for the reason that any barrel will be shrunk by the operation so as to leak. Instead of expanding an old cask, as other liquids do, this shrinks it. This solution has also been used in dry rot cases, when the wood is only slightly affected. It will sometimes be found that when oak fencing is put up new, and tarred or painted, a fungus will vegetate through the dressing, and the interior of the wood be rapidly destroyed; but when undressed it seems that the weather desiccates the gum or sap, and leaves only the woody fibre, and the fence lasts for many years. About fifteen years ago, Professor Crace Calvert, F.R.S., made an investigation for the Admiralty, of the qualities of different woods used in ship-building. He found the goodness of teak to consist in the fact that it is highly charged with _caoutchouc_; and he considered that if the tannin be soaked out of a block of oak, it may then be interpenetrated by a _solution of caoutchouc_, and thereby rendered as lasting as teak. We can only spare the space for a few words about this method. 1st. We have seen lead which has formed part of the gutter of a building previous to its being burnt down: lead melts at 612° F.; caoutchouc at 248° F.; therefore caoutchouc would not prevent wood from being destroyed by fire. At 248° caoutchouc is highly inflammable, burns with a white flame and much smoke. 2nd. We are informed by a surgical bandage-maker of high repute, that caoutchouc, when used in elastic kneecaps, &c., _will perish_, if the articles are left in a drawer for two or three years. When hard, caoutchouc is brittle.