ed into vapour: or I put into the said case or cases mer. cury or mixtures* of metals, as of tin, bismuth, and lead, capable of being kept in a state of fusion in a lower tem perature than that intended to be employed in working the steam-engine; and I so form the surrounding case or cases as to make it or them admit the aforesaid oil, or other substance employed, to come into contact not only with the sides of the steam vessel or vessels, or working cylin der or cylinders, but also with the bottom and top of the same, so that the whole may be as much as possible maintained at one uniform temperature; and this temperature I keep up by a fire immediately under or round the case or cases that contains the aforesaid oil or other substance, or by connecting the said case or cases with a separate vessel or vessels kept at a proper temperature, filled with the oil or other substance made use of as aforesaid. In some circumstances, or whenever the same may be convenient or desirable, I employ the fluid metals, or mixtures of metals, and oil or other of the substances before enumerated, at one and the same time in the same engine: that is to say, in the part of the case or vessel exposed to the greatest action of the fire, I sometimes have the aforesaid metals or mixtures of metals, and in the parts less exposed to the action of the fire, I put oil, or other substances capable of bearing the requisite heat without being converted into vapour. By this arrangement, and method of applying the surrounding heat, I not only obviate the necessity of employing steam of a great expansive force round the steam vessel or vessels, or the working cylinder or cylinders, as already mentioned, to maintain them at the temperature required, but I am enabled to obtain from steam of a comparatively low temperature, or even from water itself ad * Chancellor Livingston suggested this idea many years ago to Dr. Priestley. T. C. mitted into the steam vessel or vessels, all the effects that can be obtained from steam of a high temperature, without any of the risk with which the production of the latter is accompanied, not only to the boiler and other parts of the machinery, but even to the lives of the workmen ; for such low steam, or even water, (but in every case steam is preferable,) being admitted into a steam vessel or vessels, or working cylinder or cylinders, kept at the requisite higher temperature by the forementioned means, will there be expanded in any ratio required, and produce an effect in the working of the engine which cannot otherwise be obtained but at a greater expense of fuel, or with the risk of an explosion. By this means I can make use of steam expanded in any required ratio, or of any given temperature, without the necessity of ever having the steam of any greater elasticity than equal to the pressure of the common atmosphere. "Another improvement which I make use of in steam engines consists in a method of preventing, as much as possible, the passage of any of the steam from that side of the piston which is acted upon by the said steam to the other side which is open to the condenser; and this I effect, in those steam engines known by the name of double engines, by employing upon or above the piston mercury or fluid metal, or metals in an altitude equal to the pressure of the steam. of the steam. The efficacy of this arrangement will appear obvious, from attending to what must take place in working such a piston. When the piston is ascending, that is, when the steam is admitted below the piston, the space on its other side being open to the condenser, the steam endeavouring to pass up by the side of the piston is met and effectually prevented by the column of metal equal or superior to it in pressure, and during the down stroke no steam can possibly pass without first forcing all the metal through In working what Vol. II. BB is called a single engine, a less considerable altitude of metal is required, because the steam always acts on the upper side of the piston. For single engines, oil, or wax, or fat of animals, or similar substances, in sufficient quañtity, will answer the purpose, if another improvement, which constitutes part of my said invention, be applied to the engine, namely, to take care that either in the double or single engine so to be worked, the outlet that conveys the steam to the condenser shall be so posited, and of such a size, that the steam may pass without forcing before it or carrying with it any of the metal or other substance employed, that may have passed by the piston; taking care at the same time to provide another exit for the metal or other substance collected at the bottom of the steam vessel or working cylinder to convey the same into a reservoir kept at a proper heat, whence it is to be conveyed to the upper side of the piston by a small pump worked by the engine or by any other contrivance. In order that the fluid metal or metals used with the piston may not be oxidated, I always keep some oil or other fluid substance on its surface, to prevent its coming in contact with the atmosphere and to prevent the necessity of employing a large quantity of fluid metal, I generally make my piston of the depth of the column required, but of a diameter a little less than the steam vessel or working cylinder, excepting where the packing or other fitting is necessary to be applied; so that, in fact, the column of fluid metal forms only a thin body round the piston. In some cases I make a hollow metallic piston, and apply an altitude fluid of metal in the inside of the same, to press its outside into contact with the steam vessel or working cylinder. "It may be necessary, however, to state, that in applying my improved method of keeping the steam vessels of steam engines at any required temperature to the engine known by the n of Savary's, in any of its improved forms, in which a separate condenser has been introduced, I sometimes employ oil (or any other substance lighter than water, and capable of being kept fluid in the temperature employed, without being converted into vapour,) in the upper part of the tube or pipe attached to the steam vessel by which means steam of any temperature may be used without being exposed to the risk of partial condensation by the admission of any colder body into the steam vessel; for the oil, or other substance employed for this purpose, soon acquires the requisite temperature; and to prevent unnecessary escape of heat, I construct of, or line with, an imperfect conductor of heat, that part of the tube or pipe attached to the steam vessel which may not be heated exteriorly. And further, (as is already the practice in some engines, and therefore not exclusively claimed by me,) I cause the water raised by the engine to pass off through another ascending tube than the one attached to the steam vessel, but connected with it at some part lower than the oil or other substance employed in it is ever suffered to descend to in the working of the engine. The improvement which I have just men. tioned, of introducing oil into the pipe attached to the steam vessel of such engines, may also be introduced without applying heat externally to the steam vessel; but in this case part of the effect which would otherwise be gained is lost." Description of a Portable Steam Engine. By Mr. MATHEW MURRAY. SIR, To Mr. NICHOLSON. I take the liberty of handing you the description of a portable steam engine of my construction, which you will have the goodness to insert in your Philosophical Journal. I will just observe it is reduced to the fewest parts that practical utility will admit, which must necessarily render it of great advantage; as the simplicity of its parts make it nearly impossible to be out of order with a very moderate degree of management. The following description and reference to the plate will explain the nature of this engine. I am, Sir, Your much obliged humble servant, Leeds, May 7th, 1805. Description of a Portable Steam Engine.-Plate I. AA. Represents the ground or floor on which the engine stands. B. Section of a recess made in the ground for the beam O to work in. C. Iron cistern resting upon the ground or floor covering the recess for the beam. D. An opening in the floor to admit a boy to oil the centres of the beam. E. A double steam cylinder, having an upright pipe in the intermediate space, which effects a communication between the top and bottom, and the valve box G. F. A steam pipe that communicates with the boiler through which all the steam passes and surrounds the inner cylinder in its way to the valve box, prior to its application against the piston. G. The valve box fixed upon a projection from the cylinder bottom, having an opening or connection with the interval between the two cylinders. In this opening is a regulating valve for adjusting the quantity of steam (that acts against the piston) in its passage through the valve box. There are also three other openings in the bottom of this valve box, one of which connects with the top of the cylinder by the pipe in the intermediate space, the second with the bottom, and the third with the educ |