Page:Encyclopædia Britannica, Ninth Edition, v. 4.djvu/887

Rh 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. Accord ing 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; and the process has been developed industrially by Tilgh- niann, Melsens, and others. The wicks of candles are generally of cotton-yarn, and, to secure good steady combustion, they should be of uni form 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 Cainbace res, his object being to do away with the necessity of snuffing. Through twisting of the plaited wick as it burns, the pro truding 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 The covered rod is inserted in the mould, and after moulding is withdrawn from its covering, which remains as the wick.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 uoxired into the trough, fills all the moulds, and as soon as it is solidified, any redundance is removed and the caudie 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 em ployed 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 arc 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 are 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 j 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 caudle, 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 arc 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 pre vented from becoming crystalline and opaque. For black paraffin candles the paraffin is heated with anacardiuui shells, the resin of which is dissolved by it. The mineral wax or paraffin known as ozokcnt is found in the Carpathian Mountains, Galicia, Bohemia, and else where. 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 caudles. Sperma ceti is the solid matter obtained from the oil of the sperm whale by filtration. In further preparation for candles it ia hardened and whitened by pressure, and refined by a weak 