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The annexed engraving is a perspective view with one side in section, of a steam boiler patented by a Mr. Wright, in England and illustrated in the " London Expositor and Mining Journal," who say that " in experiments conducted with care before several engineers and ecientific men, it has shown an evaporative power of upwards of 12 lbs, of water for one of coal." This is about 4e lbs. or water more than is evaporated by a pound of coal by our best marine boilers. The improvement consists in applying to the boilers of engines, or other vessels for evaporating or heating fluids, a cellular apparatus, such as may be easily understood by the engraving. " They are constructed of malleable cast-iron, and are hollow throughout ; one such set of tubes being placed underneath the boiler, over the fire, and two other sets within the boiler ; they are connected together by bent tubes, as shown, so that all the tubes have a free communication with each other, but the water contained in them is insulated, and is, therefore, distinct from that in the boiler, by which means it can be raised to a temperature of 400 or 500 Fah., without being converted into steam. The general size of the boiler, which is of the wagon form, without a flue, is 6 feet 9 inches long, 3 feet 6 inches wide, and 2 feet 6 inches high ; the area of the bottom if about 21 superficial feet. It is set with brick flues, so as to circulate the heat round the concave sides and the ends, being in this respect like an ordinary boiler. The Sue surface is about 23 feet area. The area of the cellular plates exposed to the direct action of the fire is about 25 feet, and that of the plates within the boiler about 23 feet. The fire-bar surface is equal to 4 square feet The quantity of water in the boiler is about 1,500 lbs, and that contained in the cellular vessels about seven galllons. The quantity of water evaporated by this boiler is about 12 cubic feet per hour, making it capable of raising steam sufficient for a 12 horse- power engine, although its dimensions are| only equal to that of an ordinary 4 horsepower boiler. By this arrangement the fame can only impinge on the boiler through the perforations in the cellular vessels, and all remaining saloric passes over the bridge, and among the remaining portions of the tubes, causing the insulated water therein, to take up a large portion of the heat, which heated water circulates through the tubes within the boiler, when the excess of ealoric is instantly given off to the water contained in the boiler, and the insulated water having thus parted with its heat, descends, being replaced by the ascending current of heated water, and which in turn gives off its excess, and again descends. Thus a constant circulation of the insulated water is kept up through the cells and tubes, which water is the receiver and transmitter of heat, instead of the caloric or the fire acting directly on the boiler." [This description from our cotemporary the "Expositor" presents the idea clearly, that the isolated water in the cellular apparatus and tubes, is made to heat the water in the boiler, by absorption through the tubes. We cannot see what advantage is thus obtained over the common direct exposure to the fire of the water to be converted into steam, in the main boiler.
