In 1815 it occurred to Mr. Wade that it would be a good practice to fill the pores of timber with _alumine_, or selenite; but two years after, Chapman observed, “Impregnation of ships’ timbers with a _solution of alum_ occurred to me about twenty years since, because on immersion in sea-water the alumine would be deposited in the pores of the timber; but I was soon informed of its worse than inutility, by learning that the _experiment had been tried_, and, in place of preserving, had _caused the wood to rot speedily_. Impregnation with _selenite_ has been tried in elm water-pipes. On precipitation from its solvent it partially filled the pores, and hardened the wood, but _occasioned speedy rottenness_.” If, by using a _solution of alum_ to render wood uninflammable, we at the same time cause it to _rot speedily_, it becomes a question _whether the remedy is not worse than the disease_. Captain E. M. Shaw, of the London Fire Brigade, in his work, ‘Fire Surveys’ (1872), recommends _alum and water_. Probably he only thought of fire, and not of rotting the wood. The alum question does not appear to be yet satisfactorily settled. While upon the subject of uninflammable wood, we may state that in 1848, upon Putney Heath (near London), by the roadside, stood an obelisk, to record the success of a discovery made in the last century of the means of building a house which no ordinary application of ignited combustibles could be made to consume: the obelisk was erected in 1786. The inventor was Mr. David Hartley, to whom the House of Commons voted 2500_l._, to defray the expenses of the experimental building, which stood about one hundred yards from the obelisk. The building was three stories high, and two rooms on a floor. In 1774, King George the Third and Queen Charlotte took their breakfast in one of the rooms, while in the apartment beneath fires were lighted on the floor, and various inflammable materials were ignited to attest that the rooms above were fire-proof. Hartley’s secret lay in the floors being double, and there being interposed between the two boards sheets of laminated iron and copper, not thicker than stout paper, which rendered the floor air-tight and thereby intercepted the ascent of the heated air; so that, although the inferior boards were actually charred, the metal prevented the combustion taking place in the upper flooring. Six experiments were made by Mr. Hartley in this house in 1776, but we cannot ascertain any particulars about them, or any advantages which accrued to the public from the invention, although the Court of Common Council awarded him the freedom of the City of London for his successful experiments.