The principal objection to this form of the engine arises from the great consumption of fuel, a considerable portion of the caloric employed in the generation of the steam being absorbed in heating the new surface of cold water last raised from the well; and where great heights are required, there appears no mode of completely obviating this objection. Should it, however, be required merely to raise water about thirty feet, there are few contrivances more economical or better adapted for general use.
While speaking of Savery's apparatus it may be adviseable to notice the very ingenious adaptation of the same principle to the construction of a gas engine, by Mr. Brown. In the latter case a vacuum is formed by the introduction of an inflamed jet of carburetted hydrogen gas, which consumes the oxygen, and rarefies the nitrogen, by the increase of temperature which ensues. The vacuum thus produced is much more perfect than would at first view have been supposed, from the nature of the process resorted to by the patentee; but the economy of employing carburetted hydrogen gas as a substitute for condensible vapour is still somewhat problematic.[10]
To more fully understand the nature of Mr. Brown's engine, it may be better to revert to a diagram, which will sufficiently explain its general principles.
In the above view, the cylinders c and d, are the vessels in which a vacuum is alternately effected; g i g and h j h are two pipes, leading into the lower cylinders x x, shewn in the next page, from which the water rises along those pipes to fill the vacuum cylinders alternately. The water thus supplied is discharged through the pipes B into the tank or trough z, where it falls upon the overshot water-wheel, and, by the rotatory motion thus produced, gives power to such machinery as may be connected to it. The water runs from the wheel along a case surrounding the lower half, into a reservoir v, from which the lower cylinders x x, are alternately supplied.
The gas is supplied to the cylinders by the pipes k k k, which must be, of course, attached to a gasometer, or some other reservoir of gas. The gas also passes along the small pipe l l (which communicates also with the gasometer), and being lighted at both ends of that pipe, is kept constantly burning in order to ignite the gas within the cylinders.
The gas being admitted along the pipe k, the flame from the pipe l is now freely communicated to the gas in the cylinder, through the orifice, by the opening of the sliding valve s, which is raised by the arm r, lifted by the rod o by means of the beam.
The water in the reservoir v passing down one of the pipes w, into one of the lower cylinders x, causes the float y in that cylinder to rise, and, pushing up the rod o, raises the end b of the beam, which, of course, draws up with it the cap f, and forces down the cap e of the other cylinder c.
