LAMP is a well known apparatus for producing artificial light.
A lamp, in the most simple form, has a wick, composed of several cotton threads, partially immersed in oil, con tained in a flat dish, furnished with some small suppol t, to hold the upper end of the wick in a perpendicular direc tion, a small height above the surface of the oil ; this oil holder, or dish, when suspended in a globular glass-case, is the common street lamp. When the wick is lighted, by the application of a burning torch, the heat of its flame causes the oil, which is contained in the wick, to boil, or rise in vapour ; and the combustion of this vapour is the flame w inch produces the light. As fast as the oil in the wick is carried off, by this vaporization, a fresh supply is drawn up, by the capillary attraction of the wick, from the oil contained in the oil-holder.
Hence it appears, that lamps and candles, are both of the same nature as gas-lights. The difference consists in the materials from which the Bass is to be extracted, and the manner in which the extracting of it is performed; but in all cases, flame is nothing more than the combustion of gas. In gas lights, an apparatus is previously employ ed, to make and preserve the gas, and to conduct it to the place where artificial light is to be obtained from its com bustion ; but in lamps and candles, the heat of the same flame, which produces the light, is employed to vaporize the combustible matter, and form gas for its own main tenance. The difference between lamps and candles is, that lamps are supplied with the combustible matter in a fluid state, but candles are supplied with a solid material ; and the heat of the flame must first be employed, to re duce the tallow or wax to a fluid state ; and this fluid, which forms itself round the base of this wick, sustains the flame just in the same manner as the oil in lamps. The process of burning in candles has been explained in our article CANDLE ; but, as the combustion is more per fect in well constructed lamps than in candles, it is now ne cessary to explain these circumstances rather more fully.
The flame which we employ for artificial light, is pro duced by the combustion of some gas which contains car bonaceous matter ; and it is most probable, that the matter, while it burns in these gases, is chiefly composed of parti cles of carbon, in a very minute state of division. Combus
tion takes place when the carbon combines with the oxygen of the atmospheric air, in the requisite proportion to pro duce the carbonic acid gas : and if the oxygen is supplied in a less proportion, the oxide of carbon will be produced in the form of smoke or soot.
The chief circumstance influencing the combustion of the different carbonaceous matters which are used for producing light, is the degree of temperature which they require, in order to make them ,combine with the oxy gen of the atmosphere, in sufficient proportion to produce flame.
The relative affinities of oxygen and carbon increase or diminish according to the degree of heat which they pos sess at the time of union ; and, for this reason, the same carbonaceous matter, which, when properly heated, will combine with oxygen in such a proportion as to produce flame, will only produce smoke, when heated to a less de gree ; and that degree of heat, which is sufficient co vola tilize the carbonaceous matter, is not sufficient to create that affinity for oxygen, which will inflame it ; but a higher degree of heat must he applied, or we shall have smoke instead of flame. This we see, whenever a lamp burns with the wick up too high, or when a candle burns with too long a snuff. The wick then exposes a greater quantity of oil to volatilization than the flame can perfect ly consume ; for the heat of the flame is carried off so ra pidly by this volatilization, that it is not sufficient to heat all the gas to that temperature which is necessary for its inflammation. In this state of things, such a portion of the gas as is sufficiently heated, combines fully with the oxy gen, and produces flame ; another portion is heated suffi ciently to combine with the oxygen in that proportion which produces soot ; and some small portion will be so little heated, as to escape in the state of vapour of oil, or tallow, part of which will condense by cold into an empy reumatic grease.