For the renewal and the regular continuance of the operation, an adjusting weight i is placed on the handle of the pump, which is a small single stroke forcing pump with a weight w performing the office of an air-vessel. At the end of the pump handle is a chain m which is connected with a single crank move ment, and thus by a corresponding adjustment be tween the escape valve v, the throttle valve (which is not shewn in the figure) and the weight i, a certain quantity of water is forced into the generator at every stroke of the pump, and a corresponding quantity forced from beneath the loaded valve d to become steam.
From the difficulty, we presume, of constructing generators of sufficient strength, Mr. Perkins has more recently substituted a numerous series of very thick and strong cast iron tubes of small bore, and all con nected with each other, in place of his cylindrical generator.
Such is a brief account of Mr. Perkins's method of generating powerful steam. Among the practical difficulties which Mr. Perkins encountered was the difficulty of constructing generators of the requisite strength ; but it is probable that the real causes of his failure were the great force which was lost by the injection of the cold water into the generator, and the loss contained by the passage of heat up the chimney.
Secount of Mr. Scott's Engine without a Boiler.
In the year 1823, our ingenious countryman Mr. Alexander Scott of Ormiston, constructed a model of a steam-engine without a boiler, with which expe riments were made in presence of several persons in his neighbourhood. Owing to accidental causes, the engine itself was not completed till 1829. The fol lowing account of it transmitted to the editor of this work by Mr. Scott, and published in the Edinburgh Journal of Science, New Series, No. III, p. 21, will convey a clear idea of this important invention.
When water of a low temperature is forced by a pump into a small generator placed over a fire, every stroke of the pump tends to lower the temperature of the whole body of water. This led to devise a gene rator by which water of a low temperature can be forced into it without lowering the temperature of the hottest part of the water. in constructing a generator with that property, two truly flat circular patterns of wood were made, having each corresponding pro jecting parts. In one pattern a continued spiral
groove was cut from the centre to nearly its circum ference; the other pattern was left plain. Fig. 8, Plate DIX, .,;presents the one, and Fig. 9 the other. Both these patterns were made twenty-one inches in diameter, exclusive of the projecting parts. The spiral grooved pattern was one inch and three quarters in thickness, and the plain pattern one inch and a quarter thick, as also were the projecting parts or both patterns. The spiral groove was cut hall an inch in depth, half an inch wide at bottom, and seven eighths of an inch at top. The ridge between the grooves was left half an inch in depth, half an inch in breadth at top, and seven-eighths of an inch at bottom. From these two patterns iron casts were taken. The faces of both these cast-iron plates were made truly flat, and a very small chiseled groove was cut along the middle of the ridge between the grooves, and a corresponding chiseled groove was cut in the inch and quarter thick plate. These two plates were then cemented together by means of well prepared iron cement, part of it filling the chiseled grooves in both plates ; the projecting parts a, b, e, e, f, g, h, Figs. 8 and 9, were bolted together by screw bolts, five-eighths of an inch square, made of the best iron; in all fifteen bolts, as marked by the small square bolt holes in Figs. 8 and 9; the projecting parts of Fig. 8 being all, except that marked h, one and a quarter of an inch in thickness, which leaves a space of half an inch between the. projecting parts of the two plates, for the more effectually screwing the plates close to gether. These two plates when thus joined form only the one-half of the generator, as there is another half almost in every respect similar to be placed perpen dicularly over the one described ; having a strong cast-iron pillar with flanges, as represented by Fig. to, placed in the centre between the halves : These flanges are strongly secured by four screw bolts to each of the halves of the generator. The centre pillar is twelve inches in height and four and a half inches in diameter, with a bore up its centre of one inch and a quarter in diameter.
Fig. 4 represents a section of the generator an swering to the description already given, placed in a furnace, of which a section is also given.