Mr. Woolf (_Monthly Magazine_ vol. xxxii, p. 253) has taken out a patent for a steam apparatus for various purposes, among which that for the drying of gunpowder is specified. This patent is considered under three heads; _viz._ the construction of the boilers, which are cylindrical vessels properly connected together, and so disposed as to constitute a strong and fit receptacle for water, or any other fluid, intended to be converted into steam, and also to present an extensive portion of convex surface to the current of flame, or heated air or vapour from a fire. Secondly, of other cylindrical receptacles placed above these cylinders, and properly connected with them, for the purpose of containing water and steam, and for its reception, transmission, &c. Thirdly, of a furnace so adapted to the cylindrical parts just mentioned, as to communicate heat with facility and economy. By means of this invention, he states, that any desired temperature, necessary for the drying of gunpowder, may be produced where the powder is to be dried, without the necessity of having fire in, or so near the place as to endanger its safety; for by employing steam only, conveyed through pipes, and properly applied and directed, without allowing any of it to escape into the room or apartment where the powder is, any competent workman can produce a heat equal to that found necessary for drying gunpowder, or much higher if required. The heat may be regulated, to effect the purpose, without producing the sublimation of the sulphur, which has sometimes taken place. Among the numerous patents of the late D. Pettibone are some for ovens, both fixed and portable, for the drying of gunpowder. Speaking of the use of heated air (_Description of the Improvements of the Rarefying air-stove_, p. 19) he observes, that powder makers would derive a very great advantage by using rarefied air for drying their gunpowder. Mr. Ingenhouz (_Nouvelles experiences et observations sur divers objects de physique_) attributed the effect of gunpowder to the simultaneous disengagement of dephlogisticated air from the nitre, and inflammable air from the charcoal at the moment of ignition. He followed the calculation of Bernouilli with respect to the quantity of gas generated, _viz_: that one cubic inch of gunpowder at the moment of inflammation, calculating at the same time its expansion, occupies not less than 2276 cubic inches.