The mode of filling the lamp is as follows: close the hole f in No. 2 and open 1, 2, and 3, and through 5 pour quicksilver till a is filled to the level of the top of the bent leg g, then close 5 by its stopper k. In the top of 3 insert a bent tube, (shown by the dotted lines,) and suck the air out of the column, when the mercury will rise in 3, pass through the holes in its upper end, and occupy the space shown by the dotted lines. Remove the bent tube, and insert the stopper l, and through 4 pour water into a, up to the line b b, and oil up to the cock c, and close No. 4, and the operation is complete. When the lamp is wanted foruse, take the stopper out of No. 5, and raise 5 till the hole f becomes open, when the mercury will descend and pass over g into the bottom of a, forcing the oil up No. 1 to the burner e, to which a light being applied, it will continue burning steadily till the oil in a and the mercury in i are exhausted, when the lamp is to be refilled by exhausting the air in i, and pouring oil through No. 4. The flame may be regulated or extinguished by means of the stop-cock. The height of e above g may be equal to, but must not exceed, that of a column of oil, whose pressure shall be equivalent to the pressure of the column of mercury.
From the foregoing description, it will be seen that the columns of oil and of mercury always maintain their respective heights, and the supply of oil to the burner is consequently always uniform. The inventor states, that the lamp (which was merely got up for an experiment) afforded a steady light upon trial.
In the lamp which is represented in section in the annexed engraving, and which is the invention of R. F. Jenour, the air is compressed in a closed reservoir, by means of a condensing syringe, and a communication being formed between the air chamber and the oil chamber, the air by its expansion forces the oil up the supply pipe to the burner. The body of the lamp is divided into three compartments by two discs, a and b; c is the oil vessel, d a space to receive the overflowings from the burner, and e the air vessel; f is a condensing syringe, the piston rod of which g is hollow; the lower end of the syringe is closed by a valve h, pressed against it by springs; a rod from this valve passes through g, and can be screwed up by the nut k; l is a tube connecting the oil vessel c with the air vessel e, which has arother aperture to the atmosphere, closed by the nut m; n is the tube for supplying the burner, having a capillary tube o, cemented into its lower end, which descends to the bottom of the oil vessel; p is a stop-cock for cutting off the communication with the burner, which being of the common description is not shown.
The middle compartment d opens to the atmosphere by a short tube q, surrounding n; r is a tube opening into c; it is pierced with numerous holes at the lower end, and is closed by a valve which is secured by a nut s screwing on to the top of a rod attached to the valve; t an air pipe descending from the top of e to the bottom of c; the air, therefore, ascends through the oil in c, and collects above its surface and in the air vessel d. To charge the lamp with oil unscrew the nut in. and slacken the nut s, then pour in oil by the tube q, and it will descend into c through the holes in r; the nuts m and s must then be screwed down again. The nut k must now be unscrewed from the rod of the valve h, and the air injected by the syringe, taking care to close the orifice of the piston rod, by applying the finger to it at each stroke; when the resistance against the valve increases, till the syringe can no longer be worked, the nut k must be again screwed on, and the lamp is ready for use, by merely opening the stop-cock p.
There have been many lamps upon the principle of the one just described, but from the difficulty of regulating them, they have not come into general use; this difficulty arises in part from the continually varying pressure of the condensed air, occasioned by its increase of volume as the oil consumes, and also from the difficulty or regulating the supply of oil to the burner, so as neither to overflow nor fall short of what is required. In a lamp invented by Mr. Machell, a piece of cotton is introduced through the bore of a cock, when, by turning the plug, the passage may be regulated with considerable accuracy. In the present lamp, the patentee effects this by a capillary tube, which retards the flow of oil in proportion as it is lengthened, and this is the principal improvement claimed in the patent. The objection to this seems to be that the flow cannot be regulated at pleasure. Upon the whole, although many of the lamps with the oil reservoir contained in the base, exhibit considerable ingenuity in various parts of their details, yet very few have been found to answer in practice, being mostly either troublesome to manage, or unequal in their action; and the only lamp of this description which we have yet seen which seems to be of decided practical utility is one of French invention.
In this lamp there are two small pumps worked by a train of clock-work situated beneath the reservoir of oil in the pedestal of the lamp. These pumps, which in their construction resemble a pair of bellows, work with very little friction, and impel the oil in a copious stream to the burner, and no inconvenience can result from an excess in the supply as the overflow merely returns into the reservoir.
We shall now proceed to notice one or two lamps adapted to the burning of concrete oils and solid unctuous substances, as fat, tallow, butter of cacao. For the purpose of illumination these substances are on a par with oil, affording an equally brilliant light and at a much less cost; but in order to burn them in a lamp it is requisite previously to render them fluid, and to maintain them in that state so long as the lamp is in use. Various arrangements are employed for this purpose, but the principle is the same in all; viz. to convey a portion of the heat arising from the flame of the lamp to the combustible matter, by means of some good conductor, as an iron or copper tube or wire inserted in the combustible mass, and coming in contact or nearly so with the flame. A very simple lamp of this description is exhibited in the annexed cut; a is the fat rendered fluid, lying in the body of the lamp; (the cover of the lamp being removed to show the interior;) c is a small tube to convey air into the middle of the flame (to perfect the combustion, on the principle of the Argand burner); this tube opens at the lower end into the large tube b, as shown by dots; a small perforation is also made at d, to allow the air to flow freely into the tube c, when the lamp is fixed in the socket of a candlestick.