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.[2]
[2] See Chemical Amusement, comprising minute instructions for performing a series of striking and interesting chemical experiments, p. 8, &c.
Before we consider the general nature of Gas-Light, it will be necessary to give a short sketch of the theory and action of the instruments of illumination employed for supplying light, together with some other facts connected with the artificial production and distribution of light; such a proceeding will enable us to understand the general nature of the new system of illumination which it is the object of this Essay to explain.
To procure light for the ordinary purposes of life, we are acquainted with no other ready means than the process of combustion.
The rude method of illumination consists, as is sufficiently known, in successively burning certain masses of fuel in the solid state: common fires answer this purpose in the apartments of houses, and in some light-houses. Small fires of resinous wood, and the bituminous fossil, called canel-coal, are in some countries applied to the same end, but the most general and useful contrivance is that in which fat, or oil, of an animal or vegetable kind is burned by means of a wick, and these contrivances comprehend candles and lamps.
In the lamp the combustible substance must be one of those which retain their fluidity at the ordinary temperature of the atmosphere. The candle is formed of a material which is not fusible but at a temperature considerably elevated.
All these substances must be rendered volatile before they can produce a flame, but for this purpose it is sufficient to volatilize a small quantity of any of them, successively; for this small quantity will suffice to give a useful light, and hence we must admire the simple, yet wonderful contrivance of a common candle or lamp. These bodies contain a considerable quantity of the combustible substance, sufficient to last several hours; they have likewise, in a particular place, a slender piece of spongy vegetable substance, called the wick, which in fact is the fire-place, or laboratory where the whole operation is conducted.
There are three articles which demand our attention in the lamp—the oil, the wick, and the supply of air. It is required that the oil should be readily inflammable; the office of the wick appears to be chiefly, if not solely, to convey the oil by capillary attraction to the place of combustion; as the oil is decomposed into carburetted hydrogen gas and other products, other oil succeeds, and in this way a continual current and maintenance of flame is effected.
When a candle is for the first time lighted, a degree of heat is given to the wick, sufficient first to melt, and next to decompose the tallow surrounding its lower surface; and just in this part the newly generated gas and vapour is, by admixture with the air, converted into a blue flame; which, almost instantaneously encompassing the whole body of the vapour, communicates so much heat to it, as to make it emit a yellowish white light. The tallow now liquefied, as fast as it boils away at the top of the wick, is, by the capillary attraction of the same wick, drawn up to supply the place of what is consumed by the cotton. The congeries of capillary tubes, which form the wick, is black, because it is converted into coal; a circumstance common to it with all other vegetable and animal substances, when part of the carbon and hydrogen which enter into their composition having been acted on by combustion, the remainder and other fixed parts are by any means whatever covered and defended from the action of the air. In this case, the burning substance owes its protection to the surrounding flame. For when the wick, by the continual wasting of the tallow, becomes too long to support itself in a perpendicular situation, the top of it projects out of the cone formed by the flame, and thus being exposed to the action of the air, is ignited, loses its blackness, and is converted into ashes; but that part of the combustible which is successively rendered volatile by the heat of the flame is not all burnt, but part of it escapes in the form of smoke through the middle of the flame, because that part cannot come in contact with the oxygen of the surrounding atmosphere; hence it follows, that with a large wick and a large flame, this waste of combustible matter is proportionately much greater than with a small wick and a small flame. In fact, when the wick is not greater than a single thread of cotton, the flame, though very small, is, however, peculiarly bright, and free from smoke; whereas in lamps, with very large wicks, such as are often suspended before butchers’ shops, or with those of the lamp-lighters, the smoke is very offensive, and in great measure eclipses the light of the flame.
A candle differs from a lamp in one very essential circumstance; viz. that the oil or tallow is liquefied, only as it comes into the vicinity of the combustion; and this fluid is retained in the hollow of the part, which is still concrete, and forms a kind of cup. The wick, therefore, should not, on this account, be too thin, because if this were the case, it would not carry off the material as fast as it becomes fused; and the consequence would be, that it would gutter or run down the sides of the candle: and as this inconvenience arises from the fusibility of the tallow it is plain that a more fusible candle will require a larger wick; or that the wick of a wax candle may be made thinner than that of one of tallow. The flame of a tallow candle will of course be yellow, smoky, and obscure, except for a short time after snuffing. When a candle with a thick wick is first lighted, and the wick snuffed short, the flame is perfect and luminous, unless its diameter be very great; in which last case, there is an opake part in the middle, where the combustion is impeded for want of air. As the wick becomes longer, the interval between its upper extremity and the apex of the flame is diminished; and consequently the tallow which issues from that extremity, having a less space of ignition to pass through, is less completely burned, and passes off partly in smoke. This evil increases, until at length the upper extremity of the wick projects beyond the flame and forms a support for an accumulation of soot which is afforded by the imperfect combustion, and which retains its figure, until, by the descent of the flame, the external air can have access to the upper extremity; but in this case, the requisite combustion which might snuff it, is not effected; for the portion of tallow emitted by the long wick is not only too large to be perfectly burned, but also carries off much of the heat of the flame, while it assumes the elastic state. By this diminished combustion, and increased afflux of half decomposed oil, a portion of coal or soot is deposited on the upper part of the wick, which gradually accumulates, and at length assumes the appearance of a fungus. The candle then does not give more than one-tenth of the light which the due combustion of its materials would produce; and, on this account, tallow candles require continual snuffing. But if we direct our attention to a wax candle, we find that as its wick lengthens, the light indeed becomes less. The wick, however, being thin and flexible, does not long occupy its place in the centre of the flame; neither does it, even in that situation, enlarge the diameter of the flame, so as to prevent the access of air to its internal part. When its length is too great for the vertical position, it bends on one side; and its extremity, coming in contact with air, is burned to ashes; excepting such a portion as is defended by the continual afflux of melted wax, which is volatilized, and completely burned, by the surrounding flame. Hence it appears, that the difficult fusibility of wax renders it practicable to burn a large quantity of fluid by means of a small wick, and that this small wick, by turning on one side in consequence of its flexibility, performs the operation of snuffing itself, in a much more accurate manner than can ever be performed mechanically. From the above statement it appears, that the important object to society of rendering tallow candles equal to those of wax, does not at all depend on the combustibility of the respective materials, but upon a mechanical advantage in the cup, which is afforded by the inferior degree of fusibility in the wax: and that, in order to obtain this valuable object, one of the following effects must be produced: either the tallow must be burned in a lamp, to avoid the gradual progression of the flame along the wick; or some means must be devised to enable the candle to snuff itself, as the wax-candle does; or the tallow itself must be rendered less fusible by some chemical process. The object is, in a commercial point of view, entitled to assiduous and extensive investigation. Chemists in general suppose the hardness or less fusibility of wax to arise from oxygen. Mr. Nicholson[3] is led by various considerations to imagine, that the spontaneous snuffing of candles made of tallow or other fusible materials, will scarcely be effected but by the discovery of some material for the wick, which shall be voluminous enough to absorb the tallow, and at the same time sufficiently flexible to bend on one side.
[3] Philosophical Journal, 4to Series, Vol. I. p. 70.
METHOD
OF
ASCERTAINING THE ILLUMINATING POWER
OF
CANDLES, LAMPS, GAS-LIGHTS,
AND
OTHER LUMINOUS BODIES.
Though the eye is not fitted to judge of the proportional force of different lights, it can distinguish, in many cases with great precision, when two similar surfaces, presented together, are equally illuminated. But as the lucid particles are darted in right lines, they must spread uniformly, and hence their density will diminish in the duplicate ratio of their distance. From the respective situations, therefore, of the centres of divergency, when the contrasted surfaces become equally bright, we may easily compute their relative degrees of intensity.
For this purpose it is assumed as a principle, that the same quantity of light, diverging in all directions from a luminous body, remains undiminished in all distances from the centre of divergency. Thus we must suppose, that the quantity of light falling on every body, is the same as would have fallen on the places occupied by the shadow; and if there were any doubt of the truth of the supposition, it might be confirmed by some simple experiment. Therefore, it follows, that, since the shadow of a square inch of any surface occupies at twice the distance of the surface from the luminous point the space of four square inches, the intensity of the light diminishes as the square of the distance increases. If, consequently, we remove two sources of light to such distances from an object that they may illuminate it in equal degrees, we may conclude that their original intensities are inversely as the squares of the distances.
Hence, if two lights of unequal illuminating powers shine upon the same surface at equal obliquities, and an opake body be interposed between them and the illuminated surface, the two shadows produced, must differ in blackness or intensity in the same degree. For the shadow formed by intercepting the greater light, will be illuminated by the smaller light only, and reversely the other shadow will be illuminated by the greater light: that is to say, the stronger light will be attended with the deeper shadow. Now it is easy, by removing the stronger light to a greater distance, to render the shadow which it produces at the common surface equal to that afforded by the less. Experiments of this kind may be conveniently made by fastening a sheet of white paper against the wall of a room; the two lights, of whatever nature they are, intended to be compared, must then be placed so that the ray of light from each shall fall with nearly the same angle of incidence upon the middle of the paper. In this situation, if a book or other object be held to intercept part of the light which would have fallen on the paper, the two shadows may be made to appear as in this figure;
where A represents the surface illuminated by one of the lights only; B, the surface illuminated by the other light; C, the perfect shadow from which both lights are excluded. It will easily be understood that the lights about D and E, near the angle F, will fall with equal incidences when the double shadow is made to occupy the middle of the paper; and consequently, if one or both of the lights be removed directly towards or from the paper, as the appearances may require, until the two shadows at E and D have the same intensity, the quantities of light emitted by each will be as the squares of the distances from the paper. By some experiments made in this way, the degree of illumination of different lights may readily be ascertained to the tenth part of the whole. And, by experiments of this kind, many useful particulars may be shewn. For, since the cost and duration of candles, and the consumption of oil in lamps, are easily ascertainable, it may be shewn whether more or less light is obtained at the same expence during a given time, by burning a number of small candles instead of one or more of greater thickness. It will therefore be easy to compare the power of different kinds of lamps or candles, or gas lights, so as to determine the relative cost of each particular kind of the combustible substance employed for furnishing light:—for example, if a candle and a gas-burner supplying coal-gas, adjusted by a stop-cock, produce the same darkness of shadow, at the same distance from the wall, the strength or intensity of light is the same. An uniform degree of intensity of the gas-light may readily be produced, by opening or shutting the stop-cock, if more or less be required, and the candle is carefully snuffed to produce the most regular and greatest quantity of light. The size of the flame in experiments of this kind of course becomes unnecessary, and will vary very much with the quality of the coal gas. The bulk of the gas consumed, and the quantity of tallow used, by weighing the candle before and after the experiment, furnish the data for ascertaining the relative costs of tallow and gas-light, when compared with each other.
From experiments made by Count Rumford, concerning the quantity of materials requisite for producing a light of a certain intensity for a given time: it was found that we must burn of wax 100, of tallow 101, of oil, in an Argand’s lamp, 129, of an ill-snuffed tallow candle 229 parts, by weight. And with regard to the quantity of carburetted hydrogen, or coal-gas, I have found that from 18 to 20 cubic feet (according to the purity of the gas) are required to give a light equal in duration and in illuminating powers to 1lb. of tallow candles, six to the pound, provided they were set up and burnt out one after another.[4]
[4] 112lbs. of Newcastle coal, called Tanfield Moor, produce, upon an average, from 250 to 300 cubic feet of gas, fit for illumination.
FURTHER ILLUSTRATIONS
OF THE
MODE OF COMPUTING THE RELATIVE COST OR VALUE
OF
LIGHT,
EMITTED BY MEANS OF
CANDLES, LAMPS, & OTHER BODIES.
It is sufficiently known that the light of a candle, which is so exceedingly brilliant when first snuffed, is very speedily diminished to one-half and is usually not more than one-fifth or one-sixth before the uneasiness of the eye induces us to snuff it.[5] Whence it follows, that if candles could be made so as not to require snuffing, the average quantity of light afforded by the same quantity of combustible matter would be more than doubled.
[5] Ezekiel Walker.—Nicholson’s Journal, Vol. IV. 8vo. Series.
When a lighted candle is so placed as neither to require snuffing or produce smoke, it is reasonable to conclude that the whole of the combustible matter which is consumed is converted to the purpose of generating light; and that the intensities of light afforded in a given time, by candles of different dimensions, are in proportion to the quantity of matter consumed. That is to say; when candles are made of the same materials, if one candle produce twice as much light as another, the former will in the same time lose twice as much weight as the latter.
To prove the truth of this position, Mr. Walker made the experiments contained in the following
TABLE.
| No. of the Experi- ment. | No. of the Candles. | Time of burning. | Weight of the Candles consumed in a given time. | Strength of Light. | Distance of the Candles from the Wall. | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| h. | oz. | dr. | Feet. | ||||||||||
| 1 | - | 1 | 3 | 0 | 0 | 15 | 1 | 7 | |||||
| 3 | 3 | 0 | 1 | 1 | 1⁄2 | 1 | + | 7 | |||||
| Mould | 3 | 0 | 0 | 15 | 1 | 7 | |||||||
| 2 | - | 1 | 2 | 55 | 0 | 15 | 1 | 8 | |||||
| 3 | 2 | 55 | 1 | 0 | 1 | + | 8 | ||||||
| Mould | 2 | 55 | 0 | 15 | 1 | 8 | |||||||
| 3 | - | 1 | 3 | 0 | 0 | 15 | 3⁄4 | 1 | 8 | ||||
| 3 | 3 | 0 | 1 | 2 | 1 | 1⁄8 | 8 | 3⁄4 | |||||
| Mould | 3 | 0 | 0 | 0 | 1 | 9 | |||||||
| 4 | - | 5 | 3 | 0 | 1 | 5 | 1 | .18 | 8 | 3⁄4 | |||
| Mould | 3 | 0 | 1 | 1 | 1⁄8 | 1 | . | 8 | |||||
These experiments, Mr. Walker informs us, were made in the following manner:—
Three candles, the dimensions of which are given in the table, against 1, 3, and mould. These were first weighed, and then lighted at the same instant. At the end of the time inserted in the third column of the above table, they were extinguished and weighed again, and the loss of weight of each candle is contained in the fourth column.
The three first experiments were made under such favourable circumstance, that there was little doubt of their results being more accurate than what practical utility requires, but the fourth experiment cannot be depended on so much, in consequence of the variable light of No. 5. This candle was moved so often to keep the two shadows equal, that it was found necessary to set down its mean distance from the wall by estimation; but as this was done before the candles were weighed, the experimenter’s mind could not be under the influence of partiality for a system.
The method which Mr. Walker employed in comparing one light with another in each experiment, was that which has been described [page 24].
1. The experiments were made at different times, and the light of the mould candle was made the standard, with which the lights of the others were compared; but it must not be understood, that this candle gave the same strength of light in every experiment.
2. The sign + in the 5th column, signifies that the candle against which it is placed, gave a stronger light than the others.
From the experiments contained in the table, it appears to be an established law, where combustion is complete, that the quantities of light produced by tallow candles, are in the complicate ratio of their times of burning and weights of matter consumed.
For if their quantities of matter be equal, and times of burning the same, they will give equal quantities of light, by the experiments.
And if the times of burning be equal, the quantities of light will be directly as their weights of matter expended.
Therefore the light is universally in the compound ratio of the time of burning and weight of matter consumed.
If the law which Mr. Walker has endeavoured to prove, both by reason and experiment, be admitted, we have a standard with which we may compare the strength of any other light.
Let a small mould candle, when lighted, be so placed as neither to produce smoke nor require snuffing, and it will lose an ounce of its weight in three hours. Let this quantity of light produced under these circumstances, be represented by 1.00.
Then should this candle at any other time, lose more or less of its weight in three hours than an ounce, the quantity of light will be still known, because the quantity of light in a given time is directly as the weight of the candle consumed.[6]
[6] To investigate rules for this purpose, 1. Let M represent the mould candle, a its distance from the wall, on which the shadows were compared, x its quantity of matter consumed in a given time, (t) and Q the quantity of light emitted by M in the same time: 2. Let m represent any other candle, b its distance from the same wall, and y its quantity of matter consumed, in the time t.
Then as the intensities of light are directly as the squares of the distances of the two candles from the wall, we have as a2 : Q ∷:: b2 : b2 + Qa2 = the quantity of light, emitted by m in the time.
Then let us suppose that the quantities of light are directly as the quantities of matter consumed in the time t, and we have, As x : Q ∷:: y : y + Qx = the quantity of light emitted by m in that time, by hypothesis.
Now, when b2 + Qa2 (Theo. 1.) is = Y + QX (Theo. 2.) the quantities of light of M and m are directly as their quantities of matter consumed in any given time.
METHOD
OF INCREASING
THE LIGHT OF TALLOW CANDLES,
AND TO OBVIATE THE
NECESSITY OF SNUFFING THEM.
Mr. Ezekiel Walker has shewn that, if a trifling alteration be made in the method of using common tallow candles, they will become excellent substitutes for those of wax.
A common candle, weighing one-tenth of a pound, containing fourteen single threads of fine cotton, placed so as to form an angle of 30 degrees[7] with the perpendicular, and lighted, requires no snuffing; and what is much more valuable for some purposes, it gives a light that is nearly uniform in strength without the least smoke. These effects are thus produced:
[7] Candlesticks may be made to hold the candle at this angle, or they may be so contrived as to hold the candle at any angle at pleasure.
When a candle burns in an inclined position, most part of the flame rises perpendicularly from the upper side of the wick, and when viewed in a certain direction, it appears in the form of an obtuse angled triangle. And as the end of the wick projects beyond the flame at the obtuse angle, it meets with the air, and is completely burnt to ashes: hence it is rendered incapable of acting as a conductor to carry off part of the combustible matter in the form of smoke. By this spontaneous mode of snuffing, that part of the wick which is acted upon by the flame continues of the same length, and the flame itself very nearly of the same strength and magnitude[8].
[8] The wick’s not being uniformly twisted throughout, may occasion a little variation in the dimensions of the flame.
The advantages which may be derived from candles that require no snuffing and afford no smoke, may be readily understood; but these candles have another property which ought not to be passed over in silence. A candle snuffed by an instrument gives a very fluctuating light, which, in viewing near objects is highly injurious to the eye; and this is an inconvenience which no shade can remove. But when a candle is snuffed spontaneously, it gives a light so perfectly steady and so uniformly bright, that the adjustments of the eye remain at rest, and distinct vision is performed without pain, and without uneasiness.
Candles, on which Mr. Walker has made experiments, are described in the following
TABLE.
| No. | No. of candles to the pound avoir- dupoise weight. | Length in inches. | No. of single threads of fine cotton in the wick. | |
|---|---|---|---|---|
| 1 | 14 | 8. | 5 | 10 |
| 2 | 13 | 9. | 12 | |
| 3 | 10 | 9. | 74 | 14 |
| 4 | 8 | 10. | 20 | |
| 5 | 6 | 10. | 25 | 24 |
| Mould | 6 | 13. | ||
Number 1, 2, and 3. These candles, when lighted and placed to form an angle of 30° with the perpendicular, require no snuffing: they give lights which are nearly equal, and combustion proceeds so regularly, that no part of the melted tallow escapes unconsumed, except from accidental causes.
No. 4, placed at the angle mentioned above, and lighted, requires no snuffing: it gives a light very little stronger than No. 1, but its colour is not quite so white, nor its flame so steady.
No. 5. This candle, placed at an angle of 30°, and lighted, requires no snuffing; its flame is rather fluctuating, and not so white as No. 4, nor is its strength of light much greater than No. 1. The melted tallow sometimes overflows when the air in the room is put in motion; yet the light of this candle is much improved by being placed in an inclined position.
The mould candle, treated in the same manner, affords a very pure steady flame, without smoke and without snuffing, and its strength of light is about equal to that of No. 1.
The experiments have not been sufficiently numerous to determine with precision which of these candles affords the most light at a given expence, but the few experiments which have been made seem to indicate, that the quantity of light is nearly as the quantity of combustible matter consumed, and thus a candle which is used in the manner pointed out gives more light than a candle of the same dimension set perpendicularly and snuffed, because one part of a candle that is snuffed, is thrown away, and another part flies off in the form of smoke. And this is not the only inconvenience that attends the using candles in this manner, and which the other method is free from, for the light which it gives is of a bad quality, on account of its being variable and undulating.
From the time that a candle is snuffed till it wants snuffing again, its strength of light scarcely continues the same for a single minute. And that variation which frequently takes place in the height of the flame, is a matter of still more serious consequence.
The flame of a long candle placed vertically when it is snuffed burns steadily, is about two inches high, but it very frequently rises to the height of four inches or upwards; drops down again in a moment, till it is less than three inches, and then rises again. In this manner the flame continues in motion for some time before it returns to its original dimensions. But it does not continue long in a quiescent state before it begins a new series of undulations. In this manner the candle burns till the top of the wick is seen near the apex of the flame, carrying off clouds of smoke. In this state of things the eye becomes uneasy for want of light, and the snuffers are applied to remove the inconvenience.
Mr. Walker further observes, that it is these sudden changes, and not the nature of candle-light itself, that do so much injury to the eye of the student and artist; and that that injury may be easily prevented, by laying aside the snuffers, and in the place of one large candle, let two small ones be used in the manner stated.
The following observations on this subject are copied from the Monthly Magazine, 1805, p. 206.
“It is scarcely necessary to observe, that the combustion of candles proceeds the quicker in proportion as the inclination is greater. From the experiments which I have made, I should consider an angle of forty degrees with the perpendicular as the maximum of inclination, beyond which several considerable inconveniencies would occur; and I should take 25 degrees as the minimum of inclination, less than which does not sufficiently expose the point of the wick to the action of the air.
“By those who are much in the habit of reading or writing by candle-light, it will also be esteemed no inconsiderable addition to the advantages already mentioned, that the trouble of seeking and applying the snuffers is superseded. A candle of common size in a vertical position, requires the application of the snuffers forty-five times during its complete consumption.
“But I found an obstacle to the adoption of Mr. Walker’s plan, which, from the inclined position of the candle, it did not immediately occur to me by what means to counteract. Any agitation of the air of the room, occasioned either by the opening or shutting of a door, or by the quick passage of a person near the candle, caused the melted tallow to run over, or, in more familiar language, caused the candle to gutter; which, with the candle in this position, became an insuperable bar to the use of it.
“For the prevention of this inconvenience, I have had a wire skeleton-shade adapted to a rod bearing the same inclination as the candle, and which at bottom joins the candlestick in an horizontal line of about two inches, terminating in a nozzle fitting that of the candlestick.—The distance of this rod from the candlestick, or, which is the same thing, the length of the foot or horizontal line, is of course to be determined by the distance between the two circles which form the upper and lower apertures of the shade.—It may serve, perhaps, more familiarly to describe this part of the apparatus, to state, that it bears a perfect resemblance to the two first strokes of the written figure 4; and the third stroke, if carried up as high as the first, and made sloping instead of upright, will very well represent the situation of the candle.
“When a strong light, for the purposes of reading or writing, be required, a white silk or paper may be used, as is common, over the skeleton; but when it be required that the light should be dispersed over the room, a glass of a similar shape may be adopted, for the purpose of preventing the flame from being influenced by any agitation of the air of the room. If the upper circle of the shade be four inches in diameter, the apex of the flame will be within it during more than half the time of the complete consumption of the candle; the shade will not, therefore, require adjusting for the purpose of preventing injury to the silk, or whatever else may be used over the skeleton, more than once during that time.
“Being myself much averse to the interruptions which a candle used in a vertical position occasions, and which, though short, may, under some circumstances, be highly vexatious, I wish to extend to others a benefit which I prize rather highly.”
Lord Stanhope[9] has published a simple method of manufacturing candles, which, according to his Lordship’s statement, is superior to the method usually employed. The principles upon which the process depends are the following:—First, the wick of the candle is to have only three-fourths of the usual number of cotton threads, if the candle be of wax or spermaceti; and only two-thirds of the usual number, if the candle be of tallow. Secondly, it is required that the wick in all cases be perfectly free from moisture, a circumstance seldom attended to in the manufacturing of candles; and thirdly, to deprive the wick of wax candles, of all the air which is entangled in its fibres, and this may conveniently be done, by boiling it in melted wax, till no more air bubbles, or froth appear on the surface of the fluid.
[9] Repository of Arts, Vol. I, p. 86.
If these circumstances be attended to, three candles of any size thus prepared, last as long as four of the same size manufactured in the common way. The light which they afford is superior and more steady than the light of common candles; and lastly, candles made in this manner, whether of wax, spermaceti, or tallow, do not require to be snuffed as often. Besides all this, they flame much less, and are consequently better for writing, reading, working and drawing, than candles made by the common method.
The following observations will enable any person who is willing to try the candles manufactured according to Lord Stanhope’s plan, to ascertain the real value of the improvements suggested by his Lordship. It shews also the result of some experiments, made to ascertain the expence of burning oil in lamps with wicks of various sizes.
A taper lamp, with eight threads of cotton, will consume in one hour 225⁄1000 oz. of spermaceti oil: at six shillings per gallon, the expence of burning twelve hours is 13.71 farthings.
At seven shillings, it is 15.995 farthings.
At eight shillings, it is 18.280 farthings.
N. B. This gives as good a light as tallow candles of eight and ten in the pound. This lamp seldom wants snuffing, and casts a steady and strong light.
A taper, chamber, or watch lamp, with four ordinary threads of cotton in the wick, consumes 1.664 oz. of spermaceti oil in one hour: the oil at seven shillings per gallon, the expence of burning twelve hours, 7.02 farthings.
At eight shillings, it is 8.022 farthings.
At nine shillings, it is 9.024 farthings.
TABLE,
Exhibiting a series of experiments, made with a view to determine the real and comparative expence of burning candles of different sorts and sizes.
| Number of candles in one pound. | Weight of one candle. | Time one candle lasted. | The time that one pound will last. | The expence in twelve hours when candles are at 12s. per dozen, which also shews the proportion of expence at any price, per dozen. | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Oz. | Dr. | Hr. | Min. | Hr. | Min. | Farthings and hundredth parts. | |||||
| A small wick. A large wick. | 18 | 3⁄4 | 0 | 14 | 3 | 15 | 59 | 26 | 9 | .70 | |
| 19 | 0 | 13 | 1⁄2 | 2 | 40 | 50 | 34 | 11 | .40 | ||
| 16 | 1⁄2 | 0 | 15 | 1⁄2 | 2 | 40 | 44 | 2 | 13 | .08 | |
| 12 | 1 | 5 | 1⁄4 | 3 | 27 | 41 | 24 | 13 | .92 | ||
| 10 | 3⁄4 | 1 | 8 | 3 | 36 | 38 | 24 | 15 | .00 | ||
| 7 | 3⁄4 | 2 | 1 | 4 | 9 | 32 | 12 | 17 | .88 | ||
| 8 | 2 | 0 | 4 | 15 | 34 | 0 | 16 | .94 | |||
| 5 | 3⁄4 | 2 | 13 | 5 | 19 | 30 | 15 | 19 | .06 | ||
| Mould candles. | Moulds at 14d. per dozen. | ||||||||||
| Each. | |||||||||||
| With wax’d wick. | 3 | 7⁄8 | 2 | 12 | 7 | 20 | 42 | 39 | 15 | .74 | |
| 4 | 4 | 0 | 9 | 3 | 36 | 20 | 18 | .56 | |||
| 3 | 5 | 2 | 3⁄4 | 17 | 30 | 52 | 30 | 16 | .825 | ||
The time each candle lasted, was taken from an average of several trials on each size.
It has been suggested by Dr. Franklin, that the flame of two candles joined, gives a much stronger light than both of them separately. The same, has been observed by Mr. Warren, to be the case with flames of gas-lights, which, when combined, give a much stronger light than they would afford, when in a separate state.
Indeed, in all cases, where flames for producing light are placed near to each other, it is always beneficial to preserve the heat of the flame as much as possible. One of the most simple methods of doing this, is no doubt, the placing of the several flames together, and as near as possible to each other without touching, in order that they may mutually cover and defend each other against the powerful cooling influence of the surrounding cold bodies. This principle is now employed in the Liverpool lamp, which acts by several flat or ribband wicks placed in the form of a cylinder. The power of illumination of this lamp is superior in effect and more economical than any other lamp in use—and as flame is perfectly transparent to the light of another flame which passes through it, there is no danger of loss of light on account of the flames covering each other.