When coal or other solid matters are to be decomposed to obtain the gas, the pan f, the pipe g, and the reservoir h, are to be removed, and the operation conducted without them retaining however the use of a current of steam as before.

The subjoined engraving represents Mr. Gordon's portable gas lamp. The idea of employing gas as a substitute for lamps and candles, occurred to Mr. Murdoch, as we have seen, so early as the year 1792, when he made some experiments with that view, but seems to have subsequently abandoned the idea; but to Mr. Gordon is due the merit of realising it, and thus at length rendering inflammable gas applicable to every purpose of artificial illumination. These lamps consist of strong wrought-iron vessels of various dimensions and forms, in which the gas is compressed into one thirtieth of its bulk at the ordinary atmospheric pressure; the flow of the gas being regulated with the utmost exactness, according to the degree of light required, by a valve, which we shall subsequently describe.

A company having been formed to carry Mr. Gordon's invention into effect upon an extensive scale, works have been established in London, and at some of the principal country towns, at which the gas is manufactured; and the lamps being charged therewith, are furnished to the consumer as occasion requires. The gas with which the lamps are charged is usually procured from oil, on account of its greater purity, and of its occupying less space than coal gas, one foot of oil gas being equivalent in illuminating powers to nearly three feet of coal gas. The gas is generated by the usual processes, and the following engraving represents the apparatus employed at the London Portable Gas Works for charging the lamp. . a is the main horizontal shaft of a steam engine, upon which are fixed two spur wheels b b; the teeth of these take into the teeth of two similar wheels c c fixed on the axis of a three-throw crank, to which is thereby communicated a rotatory motion. The crank imparts (in the usual manner) an alternating motion to the rods e e e, which work three force pumps: for a description of the forcing pumps originally employed for this purpose, (which were of a singularly ingenious construction, although we believe they have since been replaced by others more nearly resembling the ordinary force pump,) we refer the reader to the article Air Pump.

As the plunger of each pump is successively raised, a quantity of gas equal to the space previously occupied by the plunger flows from the gasholder into the chamber at the opposite end, by means of a pipe of communication, part of which is brought into view at f. The valve by which the gas enters, opens inward, so that it cannot return the way it came; but there is another valve which opens outward, and this is kept closed by a spring of sufficient power to prevent the escape of the gas in the uncompressed state; upon the descent of the plunger the strength of this spring is overcome, the gas is forced out, and the valve closes again. From the pumps the gas proceeds along the tube g, and enters by the jointed valve h, into a strong wrought iron recipient i; in this vessel it is evident the gas might be collected and condensed to any required number of atmospheres; but the valve j being opened (by the cross-handled key shown), the gas is suffered to flow through the pipe k k, which is extended along the upper side of the "filling table" m, and from thence into the reservoirs ("portable lamps") l l l l, by which arrangement the pressure of the gas becomes equalized in all the vessels, however great their number.

The degree of condensation at which the gas has arrived by the continued action of the pumps, is shown throughout the process by a mercurial guage, applied in the following manner. The pipe n, which proceeds from the recipient i, conveys the gas under compression into the reservoir of mercury, at the bottom of the guage o o; the pressure of the gas upon the surface of the mercury causes the latter to rise in a long glass tube, hermetically sealed at top, and inclosing a portion of atmospheric air above the surface of the mercury; this air becomes compressed into a smaller space by the rise of the mercury, as the condensation of the gas advances, and the diminution of its volume indicates, upon a scale attached to the tube, the degree of condensation or pressure in the lamps; and when the mercury arrives at the line denoting thirty atmospheres, the valve j is shut by means of the cross handle. All the Tamps attached to the pipe in connexion with the closed valve being now filled, are taken away by unscrewing them from the sockets in the tube.

The external pressure being removed by turning off the gas, the lower valves of the lamps close by the pressure of the gas within them, and the contents are further secured from escaping by a workman screwing a cap over the lower valve as he successively removes each of them from the tube. To ascertain whether there is any leakage, the lamps are immersed one by one in a contiguous trough of water, where, if any leakage exists, it is immediately shown by the gas bubbling up. The perfect state of each lamp being thus ascertained, they are arranged in extensive racks or stands, ready to be taken out to the consumers by the Company's carts, which are regularly dispatched to all parts of the town.

To complete the subject, we shall proceed to describe the construction of these valves, of the uses of which we have only yet spoken: they are of three kinds, and were the subject of a patent granted to Mr. Gordon.

The annexed engraving gives a sectional view of an improved stop-valve (similar to those attached to the principal recipient i), especially adapted for transferring the compressed gas from one vessel to another, without occasioning loss during the process. It is composed of two pieces of metal, A and B, which are screwed together with a soft metal collar between them at a a; e e represents the openings through which the gas is allowed to pass. The piece A has the regulating steel screw c tapped through it, being formed at the lower part with a double cone, one part of which cone is adapted to fit correctly into the cavity in the under side of the piece A. Now when the lower cone of the regulating steel screw is screwed or forced tight down into the conical seat in the piece B, it prevents all escape of the gas; and when it is desired to transfer compressed gas from one lamp or reservoir to another, the regulating screw c is to be turned until its upper cone fits and applies correctly into the conical cavity of the piece A, and thereby prevents all escape of the gas up the threads of the regulating screw during the process of transferring, allowing, at the same time, free pas sage of the gas from one reservoir to another, through the openings e e.