Page:Report from the Select Committee on Steam Carriages.pdf/90



John Farey, Esq. 10 August, 1831. by that expedient for ensuring safety, and the progress of the invention has been impeded between those two difficulties in a greater degree than from any other circumstance. It was a desideratum for a long time to contrive a boiler, which being made of such thin metal as would not render it too heavy, should have sufficient strength to retain high pressure steam without danger of bursting; also that it should expose a sufficient external surface of metal to the fire and flame and of internal surface to the contained water, to enable the required quantity of steam to be produced from such a small body of water as could be carried on account of the weight, both these conditions were fulfilled by subdividing the contained water into small tubes or into flat chambers, which expose a great surface in proportion to their internal capacity, and admit of being made strong with thin metal, but there is also another condition which is rather incompatible with the two former; viz, that there shall be such a very free communication between the interior capacities of all the tubes or narrow spaces, as will combine them all into one capacity, and permit the contained water to run from one to another, and also permit the steam, which is generated in innumerable small bubbles within the narrow spaces, to get freely away from them, to go to the engines without accumulating and collecting into such large bubbles as would occupy the spaces and displace or drive out the water before them; for if that effect takes place it produces three great evils; the water boils over into the engines along with the steam and is wasted, and the thin metal which remains exposed at the outside to the fire, becomes burning hot in an instant, after the water is so driven away from the internal surface, and the further production of steam is suspended, so long as the water continues absent. If such displacement of the water takes place frequently, and in many of the narrow spaces at once, the boiler will not produce its proper quantity of steam, and the thin metal will soon be destroyed by the fire and burned through.

Have you seen Mr. Hancock's boiler?—Yes; I