In this saponification by means of lime, the melted fat is stirred some hours with a mixture of lime (about 14 per cent, of the weight of the fat) and water. The lime combines with the acids to form a soap, and the glycerine, dissolved in the water, is then run off. Next, the lime soap is decomposed, under heat, by means of sulphuric acid, which unites with the lime, the fatty acids being set free. 100 parts of the fatty acids, at this stage, give on an average 45 , 9 parts of a mixture of stearic and palmitic acids. The acids are washed with water, and allowed to cool and solidify. They are then pressed in press bags, both in the cold state and with application of heat, to expel oleic acid, which is liquid. After further purification, they are ready to be made into “stearine candles.”
Various other methods of saponification have come into practice. Thus it was found that the amount of lime in the foregoing process might be greatly reduced if the mixture were heated to a higher temperature with superheated steam. In another method, sulphuric acid is added to the fat, and the mixture is heated. The black mass produced is washed with boiling water till all the fatty acids are completely freed from sulphuric acid. Then they are distilled with the aid of superheated steam, cooled and pressed. This process offers advantages in treatment of impure and refuse fats, but it involves some waste of fat. Distillation has been dispensed with in the simpler process of De Milly (who found that fat could be saponified with sulphuric acid without formation of tarry matter), and more recently in that of Bock. According to the latter, most neutral fats consist of small fat spherules, with thin albuminous skins. A little strong sulphuric acid introduced, under given conditions, has the effect of partly carbonizing the skins and liberating the neutral fat, which is then ready for decomposition by boiling with water in open vessels. The fatty acids obtained after decomposition (they are about 94 per cent, of the original fat) are of a dark colour, from the presence of portions of the carbonized skins. By suitable oxidation with acid, the colouring matters are rendered precipitable. The fatty acids are afterwards pressed. A method of saponification specially suitable for palm oil is that of heating the substance in a still to a temperature of 290° to 315° C., and passing a current of superheated steam through it. Saponification by water under high pressure seems to have been first observed by Faraday in 1823; a∏d the process has been developed industrially by Tilghmann, Meisens, and others.
The wicks of candles are generally of cotton-yarn, and, to secure good steady combustion, they should be of uniform thickness, and free from knots or loose threads. The parallel threads of the wick are commonly twisted into a loose spiral. Plaited wicks were introduced by Cambacérès, his object being to do away with the necessity of snuffing. Through twisting of the plaited wick as it burns, the protruding end is kept just outside the flame, and consumed to ash by the surrounding air. In stearine candles, the combustibility is often aided by impregnating the wicks with a solution of boracic acid; a glass bead is formed at the top of the burning wick through the action of the acid on the constituents of the ash, and this by its weight turns the wick out of the flame. Another form of wick for stearine candles is prepared by first winding cotton-yarn round a wire. The covered rod is inserted in the mould, and after moulding is withdrawn from its covering, which remains as the wick. Machinery is now used in making various kinds of wick.
In the production of candles by dipping, the wicks are first arranged in pendant position on sticks on a frame corresponding in size to the dipping-trough, and each frame is suspended from one of a number of cross arms projecting from and jointed with an upright beam which turns on pivots. The workman turns these arms round, and as each frame comes over the dipping-trough, he presses the frame down, so that all the wicks are immersed in the tallow. This coats the wicks with one thin layer; the arms are then turned round, and each frame, as it successively arrives over the cistern, is treated the same way. The layer of tallow added in the dipping becomes consolidated before the turn comes for that set of candles to receive a second dip; and the arms are turned round and the candles dipped again and again, until all have acquired the requisite thickness and weight, which is known by a counterpoise fixed to the arm.
In the process of moulding, on the other hand, a number of slightly conical pewter moulds (ten to eighteen), finely-polished inside, are fixed by the larger extremity to a kind of trough, their taper ends projecting downwards. The wick is then fixed in the centre of the mould by being drawn through an aperture at the point of the mould which forms the upper end of the candle, and is retained in its place at the open extremity within the trough by means of a wire or other arrangement. The liquid material, being υoured into the trough, fills all the moulds, and as soon as it is solidified, any redundance is removed and the candie drawn out of the mould by the end of the wick which has been held by the wire. Moulding-machines are in common use, in which as one set of candles is discharged from the moulds, the latter are, by the same movement, rewicked for the next process of filling. A reel of wick is connected with each mould. The discharged candles are held in a horizontal position, while a knife severs the wicks. Before receiving the fat, the moulds are slid on a railway into a hot closet to be heated. Each machine holds about 200 frames of moulds, and each frame contains 18 bobbins, each of which at first has 60 yards of cotton wick.
The stearine candles are made by moulding. A difficulty arose from the tendency of stearic acid to crystallize in large foliated crystals, the candles produced being thus irregular in structure and brittle. The remedy at first adopted was the addition of a little arsenious acid, but this proved detrimental to health. The method now employed is to mix 2 to 6 per cent, of white wax with the stearic acid when molten, or to add about 20 per cent, of paraffin.
Wax is a material not very suitable for moulding on account of its contraction in cooling and adhesion to the moulds. Several varieties of wax, besides that of bees, are used in candle-making. The wax is first submitted to a bleaching process; and the candles are generally made by ladling molten wax upon the wicks from a large basin over which they are suspended from an iron ring. When the proper thickness has been acquired, the candles are taken down and rolled on a marble slab, or wooden table, and arc then cut and trimmed. Where wax candles are made by the hand, the wax, being kept soft in hot water, is applied bit by bit to the suspended wick. Presses have been contrived for making wax candles; they are of similar arrangement to those for making continuous lengths of lead and block-tin pipes. The wick is so directed that it is concentrically surrounded with soft wax when ejected from the spout of the cylinder of the press, thus forming a continuous candle, which is afterwards cut up into lengths. Wax tapers of various thickness are produced by drawing the uncut wick through molten wax in a pan, then through a draw iron provided with somewhat conical apertures, arranged like those for wire-drawing, in the side of the vessel. The waxed wick is wound very slowly on a drum, the wax having time to solidify in its passage. The process may be repeated several times with drawing irons of increasing aperture.
Paraffin, now largely made into candles, is obtained from native petroleum (Rangoon oil), or from the products of dry distillation of peat, brown coal, Boghead mineral, lignite, bituminous schist, or ozokerit. The paraffin of candles is generally a mixture of several paraffins having different melting points. A little stearic acid (5 to 15 per cent.) is usually added, in order to make the candles more rigid, and in some instances to raise the temperature of fusion; it also facilitates colouring. The candles are moulded much in the same way as stearine candles. The molten paraffin, however, is solidified suddenly by immersion of the warm moulds in cold water, the paraffin being thus prevented from becoming crystalline and opaque. For black paraffin candles the paraffin is heated with anacardium shells, the resin of which is dissolved by it.
The mineral wax dr paraffin known as ozokerιt is found in the Carpathian Mountains, Galicia, Bohemia, and elsewhere. At the low temperature of 66° C. it becomes fluid, and other less fusible substances can then be added. Dr Letheby has observed that the light of 754 ozokerit candles equals that of 891 paraffin, or 1150 wax candles. Sperma- ceti is the solid matter obtained from the oil of the sperm whale by filtration. In further preparation for candles it is hardened and whitened by pressure, and refined by a weak alkaline ley. A little wax or paraffin is added to prevent crystallization. Sperm candles have a high illuminating power, and notwithstanding their costliness, a considerable trade is done in them. The well-known composite candles are made of a mixture of palm-acid and the stearine of cocoa-nut oil in various proportions. Belmont sperm is made of hot-pressed distilled palm-acid; Belmont wax of the same mineral tinged with gamboge. Night lights are short thick cylinders of fat, with a very thin wick, calculated usually to burn from six to ten hours. In making them, the melted fat is poured into shallow moulds having movable bottoms, with a projecting wire which moulds a narrow tube for the wick. By pressing up the bottom the cylinders of fat are ejected; a wax-covered wick supported on a small piece of tin is afterwards inserted, and is cemented at the bottom part by pressing the night light on a warm porcelain slab. Child’s night lights are made in paper cases of the nature of pill boxes, having a hole in the bottom through which the tin-supported and waxed wick has been inserted.
A candle is a simple but ingenious contrivance for supplying a flame with as much melted material as it can consume without smoking. If the thickness of the candle be properly adapted to that of the wick, the fatty matter immediately below the flame is melted, so that a cup-like reservoir is produced, always properly filled for feeding the flame. The fibres of the wick act as a congeries of capillary tubes which convey the fluid fat into the flame, where, being exposed to a high temperature and sheltered from the air by the outer shell of flame, it becomes subjected to a dry distillation. The inflammable vapour thus produced rises, and by constant combustion diminishes in quantity and consequently in diameter, until at length it entirely disappears in a point. A current of air from below is produced by the heat of the flame; the oxygen of the air, aided by the high temperature, decomposes the inflammable vapour of the føt into hydrogen and carbon, and unites with these to form water and carbonic acid.
The interior dark part of a candle or other flame contains unignited inflammable vapour which will not of itself support combustion; it may be drawn off with a glass tube and ignited at a distance. According to Frankland, the luminosity of an ordinary candle, lamp, or gas flame is due, not, as commonly supposed, to the separation of solid particles of carbon, but to that of very dense hydrocarbons, which produce the same effect as the vapours of arsenic and phosphorus in their respective flames.
The excise duty of ½d. per lb. on tallow candles, and 3½d. per lb. on wax and spermaceti candles, was repealed in 1832. (a. b. μ.)
