Dry Rot, an affection of timber which is often very rapidly destructive to ships, and to damp, ill ventilated houses. A general characteristic is the development of fungi, especially the polyporus hybridus, thelepora puteana, and merulius lachrymans, and also of lower forms. These growths are at the same time accompanied, although not necessarily in a corresponding degree, by a slow decay, akin to eremacausis. The only practical means of arresting dry rot is to expose the fibres of the timber to the action of certain metallic salts, or other substances which have the power of depriving the fungi of life and of so fixing the organic constituents of the wood as to prevent their oxidation. An ordinary process, long practised, is that of kyanizing (so called from being extensively employed by Mr. Kyan, at the suggestion of Sir Humphry Davy), which consists in steeping the wood in a solution of corrosive sublimate. The success of this process has been questioned, and the use of other salts has been introduced. Sir William Burnet has proposed chloride of zinc for preserving not only wood, but also canvas and cordage. Carbolic acid has been successfully employed, as also creosote, gas tar, and other coal products.
Sulphate of iron and calcium chloride, in Payne's process, are much used in Great Britain. This process is as follows: Into a large cylinder several pieces of timber are introduced; steam is forced in, by which most of the air is driven out; then a cold solution of sulphate of iron is let in, which, condensing the steam, produces a partial vacuum, which is completed by the air pump. The liquid flows into the pores, and is further forced into them by pressure. The iron solution is then allowed to flow off, when steam is again introduced and applied until all or nearly all moisture in the timber is vaporized. A cold solution of calcium chloride is then allowed to flow in; a vacuum is again produced, and the calcium salt enters the pores, and forms, by double decomposition with the iron salt, ferric chloride and sulphate of lime, or gypsum. A variation of the process has been used to stain and prepare common woods in imitation of rarer and more durable kinds.