(1) By Payne's process, patented in 1841, the timber is enclosed in a close iron vessel in which a vacuum is formed. A solution of sulphate of iron is then admitted into the vessel, which instantly insinuates itself into all the pores of the wood, previously freed from air by the vacuum, and after about a minute's exposure, impregnates its entire substance. The sulphate of iron is then withdrawn, and another solution, of muriate of lime, thrown in. The two salts then react upon each other and form two new combinations within the substance of the wood - muriate of iron and sulphate of lime. Timber thus treated is preserved both from rot and from the attack of worms, and is perfectly incombustible.
(2) Dr. Burnett's process consists in treating the timber to a solution of chloride of zinc, 1 lb. chloride of zinc to 4 gal. water. It requires to be immersed for about 2 days for each inch in thickness, and afterwards left to dry for a period of 14 to 90 days. This renders the wood incombustible, but not so thoroughly so as the former process. It is likewise a preservative.
(3) There are many chemicals employed to render articles uninflammable, such as common salt, sulphate of ammonia, tungstate of soda, etc. The wood would require to be thoroughly dried, and then saturated with one of the above salts dissolved in water. The woods least inflammable are beech, oak, American elm, plane-tree, and other non-resinous woods.
(4) A trial at Devonport Dockyard, ordered by the Admiralty, of the method of rendering wood uninflammable by saturating it with tungstate of soda, showed that the prepared wood is under all circumstances much less readily inflammable than ordinary wood; that shavings and chips of the prepared wood, although they may be made to burn, cannot be made by themselves to set fire to substantial timbers of the prepared wood; that prepared timber steadfastly resists mere flame, although it may be made to burn when acted upon continuously by great heat. The cost of preparation and the largely increased weight of the prepared wood are disadvantages to be set against these advantages.
(5) Some years since, experiments were made by Prof. Pepper, with a view of rendering articles fireproof by the use of chemical solutions. The following were the results: - Treated with alum, the article soon yielded, and burst into flames; with borax, it lasted longer; with tungstate of soda, longer still; with phosphate of ammonium, it resisted best of all.
(6) Wood can be rendered practically fireproof by first drying it thoroughly and then coating it with common whitewash. If the wood is not thoroughly dry, the coat of whitewash shells off, but it is a very difficult matter to burn wood which has been plastered over with whiting or even limewash.
Paterno reviews several substances which are used; some of them, as sodium tungstate, answer very well, but are objectionable on account of cost. The author has made numerous experiments with various substances in their power of rendering fabrics non-inflammable. He recommends the following as being quite equal to sodium tung-state.
(7) A mixture of borax and sulphate of magnesia. To prepare this, for 20 lb. water take 3 lb. borax and 2 1/4 lb. sulphate of magnesia. The action of this mixture depends on the formation of a borate of magnesia, insoluble in water, hot or cold, which surrounds and impregnates the threads of the texture or the fibres of the wood, and thus renders the development of combustible gases and the spread of flame very difficult.
(8) A mixture of sulphate of ammonium and sulphate of lime, or gypsum, in various proportions according as it is to be applied to materials oi greater or less fineness. The sulphate of lime is transformed, with the salt of ammonium, into a double compound, which produces none of the disagreeable effects of the latter, or at least in a very slight degree. The action of this mixture of salts - which on account of its cheapness may be extensively employed - depends on an incrustation of the fibres, which prevents the spread of fire, and, on the other hand, extinguishes flame in consequence of the volatilisation of the salt of ammonium at a high temperature. Take 1 lb. liquid ammonia and 2 lb. sulphate of lime, and a single coating with a concentrated solution of this compound, which costs little, suffices to preserve wooden structures from burning. The wood is not rendered absolutely incombustible, but it is not easy to light, and ceases to burn when the action of foreign inflammable substances comes to an end. Roofing often washed with rain-water, and presenting every condition favourably for easily taking fire, was impregnated with this mixture. It had been covered with a layer of tar and drying oil, and thus rendered more liable to burn.
Nevertheless, all attempts to set it on fire failed. The experiments made have been so satisfactory that the Austrian Minister of Finance has recommended this method to be used in all the establishments of the empire. (Oest. Zeit. fur Berg-u.-Hut-W.