CANDLE (Lat. candela, from candere, to glow), a cylindrical rod of solid fatty or waxy matter, enclosing a central fibrous wick, and designed to be burnt for giving light. The oldest materials employed for making candles are beeswax and tallow, while among those of more recent introduction are spermaceti, stearine and paraffin wax. Waxlights (cereus, sc. funis) were known to the Romans. In the midlde ages wax candles were little used, owing to their expense, except for the ceremonies of the church and other religious purposes (see Lights, Ceremonial Use of), but in the 15th century, with the cheapening of wax, they began to find wider employment. The tallow candle, mentioned by Apuleius as sebaceus, was long an article of domestic manufacture. The tallow was melted and strained, and then lengths of cotton or flax fibre, or rushes from which most of the external skin had been stripped, only sufficient being left to support the pith ("rushlights"), were dipped into it, the operation being repeated until the desired thickness had been attained. In Paris, in the 13th century, there was a gild of candlemakers who went from house to house to make tallow candles, the manufacture of wax candles being in the hands of another gild. This separation of the two branches of the trade is also exemplified by the existence of two distinct livery companies in the city of London - the Waxchandlers and the Tallowchandlers; the French chandelle properly means tallow candle, candles made of materials less fusible than tallow being called bougies, a term said to be derived from the town of Bougie in Algeria, either because wax was produced there or because the Venetians imported wax candles thence into Europe. The old tallow "dips" gave a poor light, and tallow itself is now used only to a limited extent, except as a source of "stearine." This is the trade name for a mixture of solid fatty acids - mainly stearic and palmitic - manufactured not only from tallow and other animal fats, but also from such vegetable fats as palm-oil. Paraffin wax, a mixture of solid hydrocarbons obtained from crude North American and Rangoon petroleum, and also yielded in large quantities by the Scotch shale oil industry, is, at least in Great Britain, a still more important material of candle-manufacture, which came into use about 1854. Spermaceti, a crystalline fatty substance obtained from the sperm whale (Physeter macrocephalus), was introduced as a material for candles about a century earlier. In practice the candlemaker mostly uses mixtures of these materials. For instance, 5-10% of stearine, which is used alone for candles that have to be burnt in hot climates, is mixed with paraffin wax, to counteract the tendency to bend with heat exhibited by the latter substance. Again, the brittleness of spermaceti is corrected by the addition of beeswax, stearine, paraffin wax or ceresin (obtained from the mineral wax ozocerite). In some "composite" candles stearine is mixed with the hard fat ("cocoa-nut stearine") expressed from cocoa-nut oil by hydraulic pressure; and this cocoa-nut stearine is also used for night-lights, which are short thick candles with a thin wick, calculated to burn from six to ten hours.
The stearine or stearic acid industry originated in the discovery made by M.E. Chevreul about 1815, that fats are glycerides or compounds of glycerin with fatty acids, mostly palmitic, stearic and oleic. The object of the candlemaker is to remove this glycerin, not only because it is a valuable product in itself, but also because it is an objectionable constituent of a candle; the vapours of acrolein formed by its decomposition in the flame are the cause of the unpleasant odours produced by tallow "dips." He also removes the oleic acid, which is liquid at ordinary temperatures, from the palmitic and stearic acids, mixtures of which solidify at temperatures varying from about 130° to 155° F., according to the percentage of each present. Several methods are in use for the decomposition of the fats. In the autoclave process the fat, whether tallow, palm-oil or a mixture of the two, mixed with 25 or 30% of water and about 3% of lime, is subjected in an autoclave to steam at a pressure of about 120 lb per square inch for eight or ten hours, when nearly all of it is saponified. On standing the product separates into two layers - "sweet water" containing glycerin below, and the fatty acids with a certain amount of lime soap above. The upper layer is then boiled and treated with enough sulphuric acid to decompose the lime soap, the calcium sulphate formed is allowed to subside, and the fatty acids are run off into shallow boxes to be crystallized or "seeded" prior to the separation of the oleic acid, which is effected by pressing the solid blocks from the boxes, first cold and then hot, by hydraulic machinery. In another process saponification is effected by means of concentrated sulphuric acid. The fat is mixed with 4-6% of the acid and treated with steam in boiling water till the hydrolysis is complete, when on standing the glycerin and sulphuric acid sink to the bottom and the fatty acids rise to the top. Owing to the darkness of their colour, when this process is employed, the latter usually have to be distilled before being crystallized. The autoclave process yields about 45% of stearine, one-third of which is recovered from the expressed oleic acid, but with sulphuric acid saponification the amount of stearine is higher - over 60% - and that of oleic acid less, part of it being converted into solid material by the action of the acid. The yield of glycerin is also less. In a combination of the two processes the fat may first be treated by the autoclave process, so as to obtain a full yield (about 10%) of glycerin, and the resulting fatty acids then subjected to acid saponification, so as to get the higher amount of stearine. At the best, however, some 30% of oleic acid remains, and though often sought, no satisfactory method of converting this residue into solid has been discovered. It constitutes "red oil," and is used in soap-making and in woollen manufacture. In the process patented by Ernst Twitchell in 1898, decomposition is effected by boiling the fat with half its bulk of water in presence of a reagent obtained by the action of sulphuric acid on oleic acid and an aromatic hydrocarbon such as benzene.
The wick is a most important part of a candle, and unless it is of proper size and texture either too much or too little fuel will be supplied to the flame, and the candle will gutter or be otherwise unsatisfactory. The material generally employed is cotton yarn, plaited or "braided" by machinery, and treated or "pickled" with a solution of boracic acid, ammonium or potassium nitrate, or other salt. The tightness of the plaiting varies with the material used for the candle, wicks for stearine being looser than for paraffin, but tighter than for wax or spermaceti. The plaited wick is flat and curls over as the candle burns, and thus the end is kept projecting into the outer part of the flame where it is consumed, complete combustion being aided by the pickling process it has undergone. In the old tallow dips the strands of cotton were merely twisted together, instead of being plaited; wicks made in this way had no determinate bias towards the outside of the flame, and thus were not wholly consumed, the result being that there was apt to be an accumulation of charred matter, which choked the flame unless removed by periodical "snuffing."
Four ways of making candles may be distinguished - dipping, pouring, drawing and moulding, the last being that most commonly employed. Dipping is essentially the same as the domestic process already described, but the rate of production is increased by mounting a number of wicks in a series of frames, each of which in turn is brought over the tallow bath so that its wicks can be dipped. Pouring, used in the case of wax, which cannot well be moulded because it contracts in cooling and also has a tendency to stick to the moulds, consists in ladling molten wax upon the wicks suspended from an iron ring. When of the desired thickness the candles are rolled under a plate on a marble slab. In drawing, used for small tapers, the wick, rolled on a drum, is passed through the molten wax or paraffin, drawn through a circular hole and slowly wound on a second drum; it is then passed again through the molten material and through a somewhat larger hole, and reeled back on the first drum, this process being repeated with larger and larger holes until the coating is of the required thickness. In moulding, a number of slightly conical moulds are fixed by the larger extremity to a kind of trough, with their tapered ends projecting downwards and with wicks arranged down their centres. The molten material is poured into the trough and fills the moulds, from which the candles are withdrawn when solidified. Modern candle-moulding machines are continuous in their operation; long lengths of wick are coiled on bobbins, one for each mould, and the act of removing one set of candles from their moulds draws in a fresh set of wicks. "Self-fitting ends," which were invented by J.L. Field in 1864, and being shaped like a truncated cone enable the candles to be fixed in candlesticks of any diameter, are formed by means of an attachment to the tops of the moulds; spirally twisted candles are, as it were, unscrewed from their moulds. It is necessary to be able to regulate the temperature of the moulds accurately, else the candles will not come out freely and will not be of good appearance. For stearine candles the moulds are immersed in tepid water and the cooling must be slow, else the material will crystallize, though if it be too slow cracking will occur. For paraffin, on the other hand, the moulds must be rather hotter than the molten material (about 200° F.), and must be quickly cooled to prevent the candles from sticking.
A candle-power, as a unit of light in photometry, was defined by the (London) Metropolis Gas Act of 1860 as the light given by a sperm candle, of which six weighed 1 lb and each burned 120 grains an hour.
See W. Lant Carpenter, Soaps and Candles (London, 1895); C.E. Groves and W. Thorp, Chemical Technology, vol. ii. "Lighting" (London, 1895); L.L. Lamborn, Soaps, Candles and Glycerine (New York, 1906); J. Lewkowitsch, Oils, Fats, and Waxes (London, 1909).
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)