The use of alum, to prevent substances from taking fire, is not a new invention; notwithstanding we find it recommended in modern works, not only for wood, but also for paper, and linen and cotton dresses, &c. Aulus Gellius relates, that Archelaus, one of the generals of Mithridates, washed over a wooden tower with a solution of alum, and thereby rendered it so much proof against fire, that all Sylla's attempts to set it in flames proved abortive. A writer in the _Anthologia Hibernica_, vol. iii, for 1794, observes, that the use of alum to prevent the action of fire, on wood, or other combustible bodies, is not new, and those, who lay claim, are not entitled to originality on that head. Another mode to prevent wood from taking fire may also be adopted. It consists in mixing together, one ounce of sulphur, one ounce of red ochre, and six ounces of green vitriol. The wood work is covered with joiners' glue, and the mixture is then put over it. This process is to be repeated three or four times, allowing the glue to dry before a new coat is applied. There are several other preparations for the same purpose, not only for the covering of wood, but also paper. But M. Ruggeri is of opinion, that they cannot be depended upon, when used on paper; for the paper will, in part, be consumed. The formula for one of these compositions, is thus given by that gentleman: To a pound of flour, mix a handful of powdered alum, and add to it strong glue-water, and bring it to a proper consistence with clay. Flour and glue-water, mixed together, with the addition of a small quantity of muriate of soda, (common salt), is also recommended for the same purpose. Wood, steeped in a solution of common salt, so as to be thoroughly impregnated with it, is very difficult of combustion. In Persia, salt is used to prevent timber from the attack of worms. The practice of _salting_ ship timber is highly recommended. Wood, in fact, may be rendered incombustible by several processes, some of which we have given. Earl Stanhope, among others, made some interesting experiments on this subject.[23]