Oil Lamps.—The general character of oil lamps is described under ARGAND LAMP. We shall advert here to a few special matters.
One of the difficulties which have lessened the usefulness of common oil-lamps is the tendency of the oil to thicken in cold weather; while another lies in the imperfection of the means for keeping the wick well moistened with oil up to the verge of the flame. Both of these matters have engaged attention within the, last few years. The mechanical or Cared lamp, so generally used by the opulent families in Paris, has an apparatus by which the oil is raised through tubes by clock work, so as continually to overflow at the bottom of the burning wick ; thus keeping it thoroughly soaked, while the excess of the oil drops back into the cistern below. Less mechanical and more effective is the Moderator lamp, a later invention than the Carrel. The Meteor lamp, having some of the properties of the Camel, is intended to burn rape oil. The internal arrangements of this lamp are curious and com plicated. The lower part of the pedestal consists of a reservoir for containing the oil ; and in this reservoir is a kind of piston or plunger, worked up and down by a nut and screw from the outside ; the rising of this piston occasions the pressure or tightening of a coiled spring, and this pressure causes the oil to be forced up a central tube towards the flame.
Oue of the modes adopted for maintaining the oil in a liquid state, is by the use of a lamp constructed by Mr. Parker, in which the oil is used in a hot state. At a small distance around the tube which con tains the wick is another tube ; and the space between the two tubes, of capacity sufficient to hold a pint, constitutes the reservoir for the oil. The oil is thus so near the flame, that it speedily becomes warm, by which its facility of burning is much increased. A slide valve is opened to allow the oil to descend from the reservoir to the wick. The intensity of the flame is modified by raising or loivering a bell mouthed glass chimney by means of rackwork mechanism. In a series of experiments on the illuminating powers of different kinds of lamps and candles, Dr. Ure found that the hot-oil lamp, with a given quantity
of oil, gave a brighter light than any other form of lamp ; or, the light being equal in intensity, the hot-oil lamp was the most economical.
Argand'a privoiple of the mode of admitting air to act on the wick has been the one most generally followed since his time; and many of the eutesequest inveutions have bad relation merely to some modifies catsen of arrangement. The Solar letup, 0110 of the modern kinds, has a prorision for sending up air through the interior of the wick, sa iu the Argand ; but the action of the air on the exterior of the wick is mule more decided. The wick 'Waal through a hole in the centre 01 • cap or cone; and the air Is admitted ao as to act ou the flame close to this hole, and in a horizontal direction, while the flame is yet small ; DJ that the exposure of the gaseous products to the air Is much more intimate than in the ordinary lamps, and the combustiou more com plete. Nibb's oxyclite condensing lamp has A fiat wick, with a condensing cap fixed to the upper part of the ghee-holder, circular at the base, but tepering upwards to an oblong slot or opening, to allow the flame to emerge from the fiat wick. Archer'. pressure lamp has the oil placed in a flexible leg, with a wick holder, • moveable disk, and a wiled spring. Clark's prefers lamp has • strainer or percolator on the lower pert of the supply pipe, to prevent impurities from peeling into the lamp. Bright's double-wick lamp has hollow cylindrical wicks made in a stiffened state reedy for use ; the wicks am of two different height., so that one or both parts may be used, according as • weak or a strong light is ueede. Among numerous modern arrangements of oii.lampa, some are especially intended for the use of cole,a or rapeseed oil.
.Spirit-Lamps.—In chemical exporimenta the spirit-lamp has long been a valuable piece of apparatus ; but the use of spirit instead of oil, as a food for lamps intended for domestic purposes, is a modern inno vation, and has led to much mechanical ingenuity in the construction of the apparatus.