hinted at, which cannot fail to show its magnitude and importance. The methods of procuring and distributing light, during the absence of the sun, have not hitherto attained the extent of their possible perfection: there is yet a wide field for improvement in the construction of the instruments of illumination, and the subject is highly deserving the attention of every individual.

The scheme of lighting houses, streets, and manufactories, by means of the inflammable gas, obtainable by distillation from common pit-coal, professes to increase the wealth of the nation, by adding to the number of its internal resources, and on this ground it is entitled, at least, to a candid examination.

The apparent slight that has been thrown upon this new breach of civil economy by some individuals, who appear to be incapable of judging of its nature, has contributed to deter sensible and well disposed persons from wishing it success. It is the more necessary to state this fact, because, when a mistaken notion once becomes diffused, concerning the nature of a new project, persons of the best intention are liable to become affected with wrong impressions on their mind. I am neither a share holder, nor a governor, nor am I directly or indirectly concerned in any gas-light association.

The object of the succeeding pages, simply is to rescue the art of illumination with coal-gas from misconception and misrepresentation, and by a fair, and not overcharged statement of its merits and its disadvantages, to appeal from prejudice and ignorance, to the good sense of the community.

PART I.

PRODUCTION
OF
ARTIFICIAL LIGHT;
AND
THEORY
OF THE
ACTION OF CANDLES AND LAMPS.

The flame of burning bodies consists of such inflammable matter in the act of combustion as is capable of existing in a gazeous state. When all circumstances are favorable to the complete combustion of the products, the flame is perfect; if this is not the case, part of the combustible body, capable of being converted into the gazeous state, passes through the luminous flame unburnt, and exhibits the appearance of smoke. Soot therefore always indicates an imperfect combustion. Hence flame is produced from those inflammable substances only, which are either totally volatile when heat is applied to them, so as not to alter their chemical habitudes—or which contain a quantity of combustible matter that is readily volatilized into vapour by heat, or the elements necessary for producing such vapour or gazeous products, when the chemical constitution of the body is altered by an increase of temperature. And hence the flame of bodies is nothing else than the inflammable product, either in a vaporous or in a permanently elastic gazeous state. Thus originates the flame of wood and coal, when they are burned in their crude state. They contain the elements of a quantity of inflammable matter, which is capable of assuming the gazeous state by the application of heat, and subsequent new chemical arrangements of their constituent parts.

As the artificial light of lamps and candles is afforded by the flame they exhibit, it seems a matter of considerable importance to society, to ascertain how the most luminous flame may be produced with the least consumption of combustible matter. There does not appear to be any danger of error in concluding, that the light emitted will be greatest when the matter is completely consumed in the shortest time. It is therefore necessary, that the stream of volatilized combustible gazeous matter should pass into the atmosphere with a certain determinate velocity. If the quantity of this stream should not be duly proportioned; that is to say, if it be too large, its internal parts will not be completely burned for want of contact with the air. If its temperature be below that of ignition, it will not, in many cases, burn when it comes into the open air. And there is a certain velocity at which the quantity of atmospherical air which comes in contact with the vapour will be neither too great nor too small; for too much air will diminish the temperature of the stream of combustible matter so much as very considerably to impede the desired effect, and too little will render the combustion languid.

We have an example of a flame too large in the mouths of the chimneys of furnaces, where the luminous part is merely superficial, or of the thickness of about an inch or two, according to circumstances, and the internal part, though hot, will not set fire to paper passed into it through an iron tube; the same defect of air preventing the combustion of the paper, as prevented the interior fluid itself from burning. And in the lamp of Argand we see the advantage of an internal current of air, which renders the combustion perfect by the application of air on both sides of a thin flame. So likewise a small flame is always whiter and more luminous than a larger; and a short snuff of a candle giving out less combustible matter in proportion to the circumambient air; the quantity of light becomes increased to eight or ten times what a long snuff would have afforded.

The light of bodies burning with flame, exists previously either combined with the combustible body, or with the substance which supports the combustion. We know that light exists in some bodies as a constituent part, since it is disengaged from them when they enter into new combinations, but we are unable to obtain in a separate state the basis with which it was combined.

That in many cases the light evolved by artificial means is derived from the combustible body, is obvious, if we recollect that the colour of the light emitted during the process of combustion varies, and that this variation usually depends not upon the medium which supports the process of combustion, but upon the combustible body itself. Hence the colour of the flame of certain combustibles, even of the purest kind may be tinged by the admixture of various substances.

The flame of a common candle is far from being of an uniform colour. The lowest part is always blue; and when the flame is sufficiently elongated, so as to be just ready to smoke, the tip is red or brown.

As for the colours of flames that arise from coals, wood, and other usual combustibles, their variety, which hardly amounts to a few shades of red or purple, intermixed with the bright yellow light, seems principally to arise from the greater or less admixture of aqueous vapour, dense smoke, or, in short, of other incombustible products which pass through the luminous flame unburnt.

Spirit of wine burns with a blueish flame. The flame of sulphur has nearly the same tinge. The flame of zinc is of a bright greenish white. The flame of most of the preparations of copper, or of the substances with which they are mixed, is vivid green. Spirit of wine, mixed with common salt, when set on fire, burns with a very unpleasant effect, as may be experienced by looking at the spectators who are illuminated by such light. If a spoonful of spirit of wine and a little boracic acid, or nitrate of copper be stirred together in a cup, and then be set on fire, the flame will be beautifully green. If spirit of wine be mixed with nitrate of strontia, it will, afterwards, on being inflamed, burn with a carmine red colour. Muriate of lime tinges the flame of burning spirit of wine of an orange colour.