CANDLE, a thing so universally known as to need
no particular description. Its use, however, is so great, that every information tending to its improvement must, we should think, be acceptable to our readers. Of the common method of making candles, whether of wax or of tallow, a sufficient account has been given in the Encyclopædia; but candles of every kind are far from being yet brought to that degree of perfection of which they seem susceptible. Thus, for example, 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. Hence 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. It may likewise be worthy of inquiry, since the cost and duration of candles are easily ascertainable, 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 of greater thickness.
To determine this last point, a method must be found of measuring the comparative intensities of light, for which see PHOTOMETER in this Supplement. With respect to the desideratum first mentioned, we have some very ingenious observations and well-contrived experiments by Mr Nicholson, in the second number of his valuable Journal, which we shall here insert nearly in the words of their author.
In every process of combustion the free access of air is of the utmost consequence. When a candle has a very slender wick, the flame is small and of a brilliant white colour; if the wick be large, the combustion is less perfect, and the flame brown; and a wick still larger, not only exhibits a brown flame, but the lower internal part appears dark, and is occupied by a portion of volatilized matter, which does not become ignited till it has ascended towards the point. When the wick is either very large or very long, part of this matter escapes combustion, and shews itself in the form of coal or smoke. The same things take place in the burning of a lamp; but when the wick of a lamp is once adjusted as to its length, the flame continues nearly in the same state for a much longer time than the flame of a candle.
"Upon comparing a candle with a lamp (says Mr Nicholson), two very remarkable particulars are immediately seen. In the first place, the tallow itself, which remains in the unfused state, affords a cup or cavity to hold that portion of melted tallow which is ready to flow into the lighted part of the wick. In the second place, the combustion, instead of being confined, as in the lamp, to a certain determinate portion of the fibrous matter, is carried, by a slow succession, through the whole length. Hence arises the greater necessity for frequent snuffing the candle; and hence also the station of the freezing point of the fat oil becomes of great consequence. For it has been shewn, that the brilliancy of the flame depends very much on the diameter of the wick being as small as possible; and this requisite will be most attainable in candles formed of a material that requires a higher degree of heat to fuse it. The wick of a tallow candle must be made thicker in proportion to the greater fusibility of the material, which would otherwise melt the sides of the cup, and run over in streams. The flame will therefore be yellow,
low, smoky, and obscure, excepting for a short time immediately after snuffing. Tallow melts at the 92d degree of Fahrenheit's thermometer; spermaceti at the 133d degree; the fatty matter formed of flesh, after long immersion in water, melts at 127 degrees; the pela of the Chinese at 145 degrees; bees-wax at 142 degrees; and bleached wax at 155 degrees. Two of these materials are well known in the fabrication of candles. Wax in particular does not afford so brilliant a flame as tallow; but, on account of its less fusibility, the wick can be made smaller, which not only affords the advantage of a clear perfect flame, but from its flexibility it is disposed to turn on one side, and come in contact with the external air, which completely burns the extremity of the wick to white ashes, and thus performs the office of snuffing. We see therefore 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, 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, lastly, the tallow itself must be rendered less fusible by some chemical process. I have no great reason to boast of success in the endeavour to effect these; but my hope is, that the facts and observations here presented may considerably abridge the labour of others in the same pursuit.
"The makers of thermometers and other small articles with the blow-pipe and lamp, give the preference to tallow instead of oil, because its combustion is more complete, and does not blacken the glass. In this operation the heat of the lamp melts the tallow which is occasionally brought into its vicinity by the workman. But for the usual purposes of illumination, it cannot be supposed that a person can attend to supply the combustible matter. Considerable difficulties arise in the project for affording this gradual supply as it may be wanted. A cylindrical piece of tallow was inserted into a metallic tube, the upper aperture of which was partly closed by a ring, and the central part occupied by a metallic piece nearly resembling that part of the common lamp which carries the wick. In this apparatus the piece last described was intended to answer the same purpose, and was provided with a short wick. The cylinder of tallow was supported beneath in such a manner that the metallic tube and other part of this lamp were left to rest with their whole weight upon the tallow at the ring or contraction of the upper aperture. In this situation the lamp was lighted. It burned for some time with a very bright clear flame, which, when compared with that of a candle, possessed the advantage of uniform intensity, and was much superior to the ordinary flame of a lamp in its colour, and the perfect absence of smell. After some minutes it began to decay, and very soon afterwards went out. Upon examination, it was found that the metallic piece which carried the wick had fused a sufficient quantity of tallow for the supply during the combustion; that part of this tallow had flowed beneath the ring, and to other remote parts of the apparatus, beyond the influence of
the flame; in consequence of which, the tube and the cylinder of tallow were fastened together, and the expected progression of supply prevented. It seems probable, that in every lamp for burning consistent oils, the material ought to be so disposed that it may descend to the flame upon the principle of the fountain reservoir. I shall not here state the obstacles which present themselves in the prospect of this construction, but shall dismiss the subject by remarking, that a contrivance of this nature would be of the greatest public utility.
"The wick of a candle being surrounded by the flame, is nearly in the situation of a body exposed to destructive distillation in a close vessel. After losing its volatile products, the carbonaceous residue retains its figure, until, by the descent of the flame, the external air can have access to its upper extremity. But, in this case, the requisite combustion, which might snuff it, is not effected: for the portion of oil 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 efflux 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 does not then give more than one-tenth of the light emitted in its best state. Hence it is that a candle of tallow cannot spontaneously snuff itself. It was not probable that the addition of a substance containing vital air or oxygene would supply that principle at the precise period of time required; but as experiment is the test of every probability of this nature, I soaked a wick of cotton in a solution of nitre, then dried it, and made a candle. When this came to be lighted, nothing remarkable happened for a short time; at the expiration of which a decrepitation followed at the lower extremity of the flame, which completely divided the wick where the blackened part commences. The whole of the matter in combustion therefore fell off, and the candle was of course instantly extinguished. Whether this would have happened in all proportions of the salt or constructions of the candle I did not try, because the smell of azote was sufficiently strong and unpleasant to forbid the use of nitre in the pursuit. From various considerations I am disposed to think 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.
"The most promising speculation respecting this most useful article, seems to direct itself to the cup which contains the melted tallow. The imperfection of this part has already been noticed, namely, that it breaks down by fusion, and suffers its fluid contents to escape. The Chinese have a kind of candle about half an inch in diameter, which, in the harbour of Canton, is called a lobbock; but whether the name be Chinese, or the corruption of some European word, I am ignorant. The wick is of cotton, wrapped round a small stick or match of the bamboo cane. The body of the candle is white tallow; but the external part, to the thickness of perhaps one thirtieth of an inch, consists of a waxy matter coloured red. This covering gives a considerable degree of solidity to the candle, and prevents its
guttering, because less fusible than the tallow itself. I did not observe that the stick in the middle was either advantageous or the contrary; and as I now write from the recollection of this object at so remote a period as 25 years ago, I can only conjecture that it might be of advantage in throwing up a less quantity of oil into the flame than would have been conveyed by a wick of cotton sufficiently stout to have occupied its place unsupported in the axis of the candle.
"Many years ago I made a candle in imitation of the lobstock. The expedient to which I had recourse consisted in adapting the wick in the usual pewter mould: wax was then poured in, and immediately afterwards poured out: the film of wax which adhered to the inner surface of the mould soon became cool, and the candle was completed by filling the mould with tallow. When it was drawn out, it was found to be cracked longitudinally on its surface, which I attributed to the contraction of the wax, by cooling, being greater than that of the tallow. At present I think it equally probable that the cracking might have been occasioned by too sudden cooling of the wax before the tallow was poured in; but other avocations prevented the experiments from being varied and repeated. It is probable that the Chinese external coating may not be formed of pure hard bleached wax.
"But the most decisive remedy for the imperfection of this cheapest, and in other respects best material, for candles, would undoubtedly be to diminish its fusibility. Various substances may be combined with tallow, either in the direct or indirect method. In the latter way, by the decomposition of soap, a number of experiments were made by Berthollet, of which an account is inserted in the Memoirs of the Academy at Paris for the year 1780, and copied into the 26th volume of the Journal de Physique. None of these point directly to the present object; besides which, it is probable that the soap made use of by that eminent chemist was formed not of tallow, but oil. I am not aware of any regular series of experiments concerning the mutual action of fat oils and other chemical agents, more especially such as may be directed to this important object of diminishing its solubility; for which reason I shall mention a few experiments made with this view.
1. Tallow was melted in a small silver vessel. Solid tallow sinks in the fluid, and dissolves without any remarkable appearance. 2. Gum sandarach in tears was not dissolved, but emitted bubbles, swelled up, became brown, emitted fumes, and became crisp or friable. No solution nor improvement of the tallow. 3. Shell-lac swelled up with bubbles, and was more perfectly fused than the gum sandarach in the former experiment. When the tallow was poured off, it was thought to congeal rather more speedily. The lac did not appear to be altered. 4. Benzoin bubbled without much swelling, was fused, and emitted fumes of an agreeable smell, though not resembling the fumes of benzoin. A slight or partial solution seemed to take place. The benzoin was softer and of a darker colour than before, and the tallow less consistent. 5. Common resin unites very readily with melted tallow, and forms a more fusible compound than the tallow itself. 6. Camphor melts easily in tallow, without altering its appearance. When the tallow is near boiling, camphoric fumes fly off.
The compound appeared more fusible than tallow. 7. The acid or flowers of benzoin dissolves in great quantities without any ebullition or commotion. Much smoke arises from the compound, which does not smell like the acid of benzoin. Tallow alone does not smoke at a low heat, though it emits a smell something like that of oil olive. When the proportion of the acid was considerable, small needled crystals appeared as the temperature diminished. The appearances of separation are different according to the quantity of acid. The compound has the hardness and consistency of firm soap, and is partially transparent. 8. Vitriolated tartar, nitre, white sugar, cream of tartar, crystallized borax, and the salt sold in the markets under the name of salt of lemons, but which is supposed to be the essential salt of sorrel, or vegetable alkali super-saturated with acid of sugar, were respectively tried without any obvious mutual action or change of properties in the tallow. 9. Calcined magnesia rendered tallow opaque and turbid, but did not seem to dissolve. Its effect resembled that of lime.
"It is proposed to try the oxygenated acetic acid, or radical vinegar; the acid of ants, of sugar, of borax, of galls, the tanning principle, the serous and gelatinous animal matter, the fecula of vegetables, vegetable gluten, bird-lime, and other principles, either by direct or indirect application. The object, in a commercial point of view, is entitled to an extensive and assiduous investigation. Chemists in general suppose the hardness or less fusibility of wax to arise from oxygen; and to this object it may perhaps be advantageous to direct a certain portion of the inquiry. The metallic salts and calcines are the combinations from which this principle is most commonly obtained; but the combinations of these with fat oils have hitherto afforded little promise of the improvement here sought. The subject is, however, so little known, that experiments of the loosest and most conjectural kind are by no means to be despised."
Thus far Mr Nicholson: but it is probable that many of the advantages which he proposes by these mixtures might be obtained merely by purifying the tallow, and keeping it in that state for a long time exposed to the air before it be formed into candles. It is certain that tallow is rendered more difficult of fusion by age; and this is the sole reason that old candles are less apt to run, and therefore more valuable than such as have been lately made.