An engine in which the motive force is derived from the alternate expansion and condensation of the liquefiable gases. For the discovery that certain gases may be reduced to the liquid form, and for the suggestion of such gases as prime movers of machinery, we are indebted, (as we have already noticed under the word Gas,) to Sir Humphrey Davy and Mr. Faraday. The important advantages which seemed likely to be realized by this discovery, naturally attracted the attention of engineers and scientific mechanists, and many of the most eminent occupied themselves in endeavouring to devise such arrangements as would render it applicable in practice. The person who pursued the subject with the greatest perseverance was Mr. Brunei, who obtained a patent for an apparatus, in which the liquefiable gases are employed to furnish the moving power, and more especially the carbonic acid gas. This gas may be obtained by decomposing any of the carbonates by the action of the common acids. The mode of obtaining the liquid from the gas is by forming the gas under a gasometer, and condensing it afterwards in another vessel by means of a condensing pump, and continuing the operation until it passes to the liquid state.
The engraving on the next page represents Mr. Brunei's apparatus. This apparatus, as shown at Fig. 2, consists of five distinct cylindrical vessels; the two exterior vessels a and b contain the carbonic acid, reduced to the liquid form, and are called the receivers; from these, it passes into the two adjoining vessels c and d, termed expansion vessels; these last having tubes of communication with the working cylinder e, the piston therein (shown by dots) is operated upon by the alternate expansion and condensation of the gas giving motion to the rod f, and consequently to whatever machinery may be attached thereto. As the working cylinder e is of the usual construction, no further description of that part of the apparatus is necessary; and as the two vessels on ore side of the cylinder are precisely similar to those on the other, a description of the receiver a and the expansion vessel c will apply to their counterparts b and d; the two former (a and c) are therefore given in a separate Fig. 1 on a larger scale, in section, that their construction may be seen, and their operation better understood.
The same letters of reference designate the like parts in both figures.
The communication of the condensing pump (before mentioned) with the receiver a, is through the orifice g, which can be stopped at pleasure by the plug or stop-cock h. When the receiver has been charged with the Fig.1 liquid and closed, a pipe i is applied to, and connected with the expansion vessel c at k; 11 is a lining of wood (mahogany) or other non-conductor of heat, to prevent the absorption which would otherwise be occasioned by the thick substance of the metal. The expansion vessel is connected through a pipe m to the working cylinder e; these vessels contain oil, or any other suitable fluid shown at n, as a medium between the gas and the piston. The receiver is a strong gun metal vessel, of considerable thickness, in the interior of which are placed several copper tubes, as represented at o o o; the joints of these tubes through the top and bottom of the receiver are made perfectly tight by packing. The use of these tubes is to apply alternately heat and cold to the liquid contained in the receiver, without altering very sensibly the temperature of the cylinder. The operation of heating and cooling through the thin tubes o o o may be effected with warm water, steam, or any other heating medium; and cold water, or any other cooling medium.
For this purpose, the tubes o o o are united by a chamber and cock p p, by the opening of which, with the pipes o o, hot and cold water may be alternately let in and forced through by means of pumps, the cocks being worked in a similar manner to those in steam engines. Now if hot water, say at 120°, be let in through the tubes of the receiver a, and cold water at the same time through the receiver b, the liquid in the first receiver will operate with a force of about 90 atmospheres, while the liquid in the receiver b will only exert a force of 40 or 50 atmospheres. The difference between these two pressures will therefore be the acting power, which through the medium of the oil will operate upon the piston in the working cylinder. It is easy to comprehend that by letting hot water through the receiver b, and cold water through the opposite one a, a re-action will take place, which will produce in the working cylinder e an alternate movement of the piston, applicable by the rod f to various mechanical purposes, as may be required. It is to be observed, that the use of the gasometer, and of the forcing pumps, is simply for obtaining the gas, and for charging the receivers with the liquid.
When the receiver is once charged, and has been closed with the stop-cock h, the gasometer and forcing pumps are to be disconnected from the receiver by unscrewing the pipe i at the joint. The same pipe may however be used as the means of connecting the receiver with the expansion vessel; the adoption of two distinct pipes for these purposes is intentionally avoided, as it would become necessary in consequence to have two orifices as well as two stop-cocks. It is obvious that no difficulty exists in connecting the forcing pump with both receivers, as the small pipes used for that purpose may be made to reach either.
Several years have elapsed since the engine just described was patented, but hitherto no machine upon the same principle has been brought into operation; and as the mechanical talents of Mr. Brunei are unquestionable, and as he is known to have devoted much time to bring the invention to perfection, it is probable that the cause of the want of success lies in the principle itself, and that owing to one or both of the causes noticed in Mr. Tredgold's remarks upon the subject, which we have quoted under the word Gas, the liquefiable gases are not so applicable as mechanical agents as the vapour of water or steam. Another difficulty attending such application arises from the very imperfect means we are at present acquainted with of producing the degree of cold necessary for the purpose of condensing the gases; for the present, therefore, there seems little hope of advantageously substituting these gases for steam as a prime mover of machinery.