In 1820 when Mr. Woolf was appointed engineer of the consolidated mines, he was anxious to erect some double cylinder engines ; but this proposal met with opposition, and some very large engines of Watt's construction were made. Every attention was paid to proportion and workmanship, and from a performance of twenty and twenty-five millions of pounds lifted one foot by the combustion of a bushel of coal, they rose to forty and even forty-eight millions. The sufficiency of Mr. Watt's engines was now placed beyond a doubt, and only one of Mr. Woolf's has been since erected. Mr. Woolf, however, has great merit in having introduced that accuracy of workmanship and niceness of fitting by which Mr. Watt's engines ob tained their superiority.
Mr. Woolf made some improvements on the boilers of steam engines which merit notice. His boilers consisted of a horizontal cylinder or reservoir for con taining steam and water, having a series of horizontal tubes below it crossing it at right angles, and con nected by short necks with the reservoir. Between these tubes, and over and above them alternately, the flame and heated air traversed in its passage to the chimney. Ile proposed another ingenious plan of having an upper and a lower boiler connected by short tubes ; but though this exposes much surface, it is troublesome to execute ; but, as Mr. Henwood t re marks, being usually made of cast iron,and continually exposed to the intense action of the fire, the water was frequently driven out of them, and their temperature became considerably elevated ; by the readmission of water at a comparatively low temperature, they were rapidly cooled, and the consequent contraction occa sioned frequent fracture, not only of the joints, but also of the tubes themselves. Frequent trials demon strated their inferiority to those of Trevithick, in fa vour of which they were soon relinquished.
account of Mr. Grose's Improvements on the Steam Engine.
About the end of the year 1826, Mr. Grose was called upon to superintend the manufacture of some steam engines at Huel Towan, and the average duty (performance) of the one which was first worked was nearly 50 millions of pounds. Mr. Grose now applied a coating of saw dust about ten inches thick to the steam-pipes, nozle, cylinder, Ste., and a stratum of ashes of nearly the same depth to the top of the boiler. By this means the duty was raised to about 65 millions. As there was still, however, a consider able loss of heat, another coating of the same material of the same thickness was applied on the outside of the first coating, and the result of this was an increase of the duty to eighty-seven millions, which was the average of a trial made in the presence of Mr. Hen wood and several engineers and scientific individuals. Pursuing Mr. Grose's idea, Mr. Woolf has brought one of his engines to a duty of nearly 70 millions, as already mentioned.
The gradual improvement which has taken place in the steam-engines in Cornwall, may be seen from the following table drawn up by Mr. Hcnwood.
The details respecting these engines are given by Nr. Ilenwood in Dr. Brewster's Journal, No. XIX, p. 45 ; and the same gentleman publishes regularly in the same Journal quarterly reports of the per formance of the steam-engines in Cornwall.
Mr. Perkins' Steam, Engine.
Although the high expectations which were enter tained from Mr. Perkins' labours on the steam engine have not been realized, our readers will still look for sonic account of the method from which so much was anticipated.
The general construction of the apparatus is repre sented in Plate DIX, Fig. 6, where a a a represents the section of the Generator or boiler. It is a strong cylindrical vessel made of metal, about three inches thick in every part. This vessel is filled with water and heated in a cupola furnace fed by a blast, which almost entirely surrounds it. On the top of the gene rator there is an escape valve b pressed down by the loaded lever e, the pressure being capable of adjust ment by placing the weight at different distances from the fulcrum. This valve admits the steam to the steam-pipe d which leads to the working cylinder. A lateral ripe e, intended merely for safety, is connected with the generator, and has an apparatus f attached to it for indicating the pressure. A forcing pump h, wrought by the engine, feeds the generator with water by the pipe g, which terminates near the bottom of the generator.
In order to generate steam, the generator is filled with water by the forcing pump h. When the heat of the surrounding furnace has raised the water to a temperature of 400 or 500 of Fahrenheit, an additional quantity of water is pumped into the generator, suffi cient to force a portion of that which is already heated from under the loaded valve b at the steam-pipe d, where it instantly flashes into strong steam, which proceeds to the piston of the cylinder. The valve b is shown on an enlarged scale in Fig. 7. It is a spherical bulb falling into a concave scat in the lower part of the square chamber. The upper part of the valve is a cylindrical rod, on the top of which the weight of the pressing lever c is exerted. The lower part of the valve is a triangular stem sliding up and down in the cylindrical passage. When the additional quantity of water is injected into the generator as above de scribed, the bulb of the valve rises from its seat, and a corresponding quantity of heated water passes up between the cylindrical passage, and the sides of the triangular stem into the square chamber, where, from the pressure no longer operating on that portion of the water, it becomes steam, as already mentioned.