The second invention we have to notice is that of Dr. Ernst Alban, a physician of Rostock, in Germany, a patent for which was obtained in this country in 1825. The heating medium is, in this case, such a mixture of tin and lead as will remain in a fused state at the temperature required for the steam, which is generated in small vertical tubes suspended in the bath of liquid metal. The subjoined diagrams exhibit two baths of this kind connected together, in each of which are deposited eight generating tubes. Fig. 1 %bows a longitudinal section of one of the vessels, and Fig. 2 a transverse section of both ; they are made of cast iron, in the form represented at a a a, b b indi cating the metallic mixture. Supported upon the cover of the metal vessel, is a strong top c c of the generator, containing a cylindrical chamber of 2 inches in diameter; d d d, are the wrought-iron generating tubes, suspended in the metallic mixture ; they are of 1* inch bore, and are screwed into the top c c, so that they may be taken out whenever they require cleaning; e is the injection pipe, through which the water is conducted into the generating tubes, through a small pertbration made over each. The double vessel, as best seen in Fig. 2, is suspended in the furnace, so as to expose all its four sides and ends to the action of the fire; so that although it is but 4 feet long, 3 feet 6 inches high, and 9 inches wide, it exposes a surface of 64 feet to the fire. The two injection tubes are connected externally, and communicate in one pipe with the forcing pump. This pump is of the usual construction, furnished with a lever and weight, which are raised by the engine. If the production of steam in the generators be too great for the wants of the engine, the pressure in the steam chamber will act against the injection, and the weight will be insufficient to force down the piston of the pump, which will thus remain inactive, until the pressure is diminished by the ceasing of production and the expenditure of the engine. To prevent the metallic fusion from being overheated, in cases where a smaller supply of steam is required, or where a suspension of steam genera tion takes place, by the stoppage of the engine or otherwise, the inventor has arranged a heat regulator, which governs the intensity of the fire. The apparatus indicates the temperature of the fused metal, upon which solely its action depends, and the generation of steam in the generators has no influence what ever upon it, the regulator continuing to act when the generation of steam has ceased, on which account it appears to be essentially different from any heat regulator previously used. Its application to this apparatus is indispensable, to prevent such a heating of the generating tubes as might occasion a decompo sition of the water injected therein. It consists of two pipes filled with atmo spheric air, one of each being inserted into each vessel, (Fig. 1, g) and surrounded by the metallic medium. To both pipes, very narrow tubes are fixed, shown at h, Fig. 1, and i, 3 ; these are joined externally into one tube, which opens inside the mercurial cistern a, Fig. 3. Within the mercury therein contained is immersed a vertical tube b, with a float c swimming on the to of the mercury. This float is connected, by means of the rod d, with the rod e, and acts by the rod f, upon the damper g, which regulates the draught of the fire in the ash-hole. When the air in the pipes, Fig. 1, g g, becomes heated by the fusion, it expands progressively as this becomes hotter, presses on the mercury in a, Fig. 3, and causes it to ascend in the tube b. By the rising of the mercury, the float c is made to ascend likewise, and acts by the rod d on the lever e, and thereby on the damper g, so that should the temperature of the fusion be greater than is required, it gradually closes the air-hole h, by which the supply of air to the fire is prevented, and the heat consequently diminished. Although the intelligent inventor of this apparatus was, as we are informed, unsuccessful in the introduction of it, yet it has strong claims upon the attention of engineers for the originality and ingenuity of many of its arrangements. The employment of a fluid metal, possessing a high conducting power, for the heating medium, instead of an inflammable substance like oil, possessing but feeble conducting power, promised much better results, while it rendered the nse of the apparatus perfectly safe.
Mr. Porter, a scientific gentleman, who was connected with Dr. Alban in the last described project, subsequently invented, in conjunction with Mr. Beale, an engineer, the third plan we have alluded to. In this apparatus, the arrange ment is such as to render it impossible to impart a higher degree of heat to the generator than the boiling point of the fluid employed as the medium, as the vapour from the latter is allowed to escape as it is formed. The annexed figure affords a longitudinal section of the apparatus; a a is the vapour chest, formed of thin plate iron ; b the generator, which this drawing may be considered as representing by an edge view of a system or coil of wrought iron tubes; the dotted line c mark. the height of the fluid medium ; d the " breathing-pipe," which in the event of injudicious firing, serves as an outlet and condenser, for such portion of the vapour as may not otherwise be condensed by the lower temperature of the boiler; e an ordinary furnace and flue; f, the ash-pit ; g the chimney; h the supply pipe to the generator, through which water is injected by means of a forcing pump, worked by the engine ; i is the steam pipe communicating with the engine. The water injected through the supply pipe h being expose during its progress through the generator, to the heat of the vapour furnished by the boiling fluid under neath, is thereby converted into steam, with a temperature and elastic force answering to the temperature of the vapour, which, losing a portion of its heat, resumes the liquid form, and falls to the bottom of the chest a, while the partial vacuum formed by its condensation causes a fresh portion of vapour to supply the void, and thus keep up a constant action. It is manifest that the temperature of the steam must be uniform, and that no greater degree can be communicated than the boiling point of the fluid medium chosen, and all injury to the machinery is therefore avoided, while, from the same cause, all those sudden accessions of elastic force, which have frequently proved so disastrous, are rendered impossible. This mode of heating has, we are informed, been very successfully employed in the preparation of vegetable extracts, and in other chemical operations where regulated degrees of heat are essential. As respects its application to the generation of steam for engines, we are not aware of Its having been so used by any other persons besides the patentees. Objections have probably been raised to the combustible media employed in the vapour chest, and the expense attending the supplying the loss of it occasioned by evaporation. These media were chiefly the spirit of turpentine, naphtha, naphthaline, and other products of coal tar, forming a variety of mixtures, whose boiling points vary from 2000 to 700° Fahrenheit.
In the former part of this article, we have had occasion to notice the incon venience arising from the deposit in boilers, and to mention some of the modes adopted for cleansing them. Occasionally these deposits are several inches in thickness, and as hard as the artificial stone pottery, caused by the baking they receive while in contact with the metal of the boiler, which receives the direct action of the fire. To remove these incrustations is a work of considerable labour; it being a general practice for workmen to get inside the boilers, and break up the stony matter, by means of heavy hammers and cold chisels. These deposits are also the cause of other serious inconveniences; they form a non-conducting shield between the fire and the water, rendering the boiler liable to become red-hot, by which its destruction orpremature wearing out is effected, and a considerable waste of fuel is made. To obviate these injurious tendencies, a variety of plans have been proposed. Some engineers throw into the boiler a quantity of some fibrous and mucilaginous vegetable matter, such as bran or husks, to which the earthy matter in the water adheres, and is thereby prevented from becoming concrete and hard, and consequently more easy to be removed.