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;
[Illustration]
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.
+-----------+--------+--------+----------+--------+---------+
| | | | Weight | | |
| | | | of the | |Distance |
| No. of | No. of |Time of | Candles |Strength| of the |
| the | the |burning.| consumed | of | Candles |
|Experiment.|Candles.| | in a | Light. |from the |
| | | | given | | Wall. |
| | | | time. | | |
+-----------+--------+--------+----------+--------+---------+
| | | h. | oz. dr. | | Feet. |
| {| 1 | 3 0 | 0 15 | 1 | 7 |
| 1 {| 3 | 3 0 | 1 1½ | 1 + | 7 |
| {| Mould | 3 0 | 0 15 | 1 | 7 |
+-----------+--------+--------+----------+--------+---------+
| {| 1 | 2 55 | 0 15 | 1 | 8 |
| 2 {| 3 | 2 55 | 1 0 | 1 + | 8 |
| {| Mould | 2 55 | 0 15 | 1 | 8 |
+-----------+--------+--------+----------+--------+---------+
| {| 1 | 3 0 | 0 15¾ | 1 | 8 |
| 3 {| 3 | 3 0 | 1 2 | 1⅛ | 8¾ |
| {| Mould | 3 0 | 0 0 | 1 | 9 |
+-----------+--------+--------+----------+--------+---------+
| 4 {| 5 | 3 0 | 1 5 | 1.18 | 8¾ |
| {| Mould | 3 0 | 1 1⅛ | 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 _a_² : Q ∷ _b_²
: (_b_² + Q)/_a_² = 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_ + Q)/_x_ = the quantity of light emitted by _m_ in that
time, by hypothesis.
Now, when (_b_² + Q)/_a_² (Theo. 1.) is = (Y + Q)/X (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. of candles| | No. of single |
| No. | to the pound |Length in|threads of fine|
| | avoirdupoise | inches. | cotton in the |
| | weight. | | 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| Weight of |Time one|The time |The expence in |
| | candles |one candle.| candle |that one |twelve hours when|
| | in one | | lasted.|pound will|candles are at |
| | pound. | | |last. |12s. per dozen, |
| | | | | |which also shews |
| | | | | |the proportion of|
| | | | | |expence at any |
| | | | | |price, per dozen.|
| +---------+-----------+--------+----------+-----------------+
| | | | | |Farthings and |
| | | Oz. Dr. |Hr. Min.| Hr. Min. |hundredth parts. |
|A small| 18¾ | 0 14 | 3 15 | 59 26 | 9.70 |
|wick. | 19 | 0 13½ | 2 40 | 50 34 | 11.40 |
|A large| 16½ | 0 15½ | 2 40 | 44 2 | 13.08 |
|wick. | 12 | 1 5¼ | 3 27 | 41 24 | 13.92 |
| | 10¾ | 1 8 | 3 36 | 38 24 | 15.00 |
| | 7¾ | 2 1 | 4 9 | 32 12 | 17.88 |
| | 8 | 2 0 | 4 15 | 34 0 | 16.94 |
| | 5¾ | 2 13 | 5 19 | 30 15 | 19.06 |
| |Mould | | | |Moulds at 14d. |
| |candles. | Each. | | | per dozen. |
|With | 3⅞ | 2 12 | 7 20 | 42 39 | 15.74 |
|wax’d | 4 | 4 0 | 9 3 | 36 20 | 18.56 |
|wick. | 3 | 5 2¾ |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.