h] ^yEL E B A, B, C, D, E, F, represent six lengths of a metal pipe, each being eight feet long, and two inches in diameter: all these joints (except- ing that marked F, which is made of copper, for the better support of Jieat), are manufadured of tin- plate. G, is a tin-kettle, or vessel (con- taining about two gallons), that is fastened to the upper pi^ie F, and the sides^ of which are perforated weL for the admission of air, and con- sequently for supporting the fire. This vessel must be fixed in such a dire6tion as to have at least five feet of the pipe above its top. H, is a conical cap, designed to confine the heat to the sides of the tube. When the machine is applied to the well, a wire must be passed through the holes a, a, in the upper part of the length A, and in the lower extremity of B ; the joint ought to be luted with oil-putty, to render it air-tight ; the upper end of each joint should be covered with wire, to prevent it from bend- ing ; and to form a receptacle for the putty. The other lengths are then to be managed in a similar manner, till that marked A, reach nearly to the surface of the water. The vessel G, ought to be placed on two pieces of timber laid across the well. The apparatus, being now fixed, will speedily be filled with the foul air extracted from the well : and, as the gravity of the exter- nal and internal air is equal, they become stationary. Burning coal or wood must next be put huo the kettle G; by which the copper tube, F, is heated ; and, the inter- nal air being rarefied, while the ex- ternal air presses downward, the noxious vapours are gradually dis- sipated} and a purer element is introduced into the well, whence it issues during the continuance of the fire. Mr. Salmon remarks (in hi$ communication, inserted in the 9th volume of the "Repertory of Arts," &:c.), that however small the cur- rent of air passing out of the fun- nel or pipe, F, may appear, the vi' fed is considerable j because such discharge consists wholly of noxiouj vapour i
