TALC. Syn. Foliated talc; Ubruc. A transparent, foliated, siliceous magnesian mineral, flexible, but not elastic, found in Scotland, the Tyrol, and elsewhere. It is used as a cosmetic, to impart a silky whiteness to the skin; also in the composition of rouge végétal, and to give a flesh-like polish to alabaster figures. A second and harder species of this mineral (French chalk, SOAPSTONE, STEATITE; creta Gallica) is employed as a crayon by carpenters, glaziers, and tailors, and forms the boot-powder of the boot-makers. Writing executed with it on glass, even after being apparently removed by friction, becomes again visible when breathed upon.
TAL′LOW and other fats are commonly purified by melting them along with water, passing the mixed fluids through a sieve, and letting the whole cool slowly, when a cake of cleansed fat is obtained.—Another plan is to keep the tallow melted for some time, along with about 2% of oil of vitriol, largely diluted with water, employing constant agitation, and allowing the whole to cool slowly; then to remelt the cake with a large quantity of hot water, and to wash it well.—Another method is to blow steam for some time through the melted fat. By either this or the preceding process a white hard tallow may be obtained.—Some persons add a little nitre to the melted fat, and, afterwards, a little dilute nitric or sulphuric acid, or a solution of bisulphate of potash. Others boil the fat along with water and a little dilute nitric or chromic acid, or a mixture of bichromate of potash and sulphuric acid; and afterwards wash it thoroughly with water. These methods answer well for the
tallow or mixed fats of which ordinary candles are made.
Tallow converted into stearic acid by saponification is readily hardened and bleached, if moderately pure. A mixture composed of 1 part of oxalic acid and 2000 parts of water is sufficient to bleach 1000 parts of stearic acid. The mode of operating is as follows:—Throw the stearic acid, cut into small pieces, into a vessel of cold water, and turn on steam; as soon as it has melted and assumed a turbid appearance, add the solution of oxalic acid, and boil the mixture. After boiling for 3⁄4 hour, long threads appear in the liquid; the liquid itself, which previously was of a greyish colour, becomes black, and the threads unite together. The boiling must now be discontinued, and the contents of the vessel, having been allowed to settle for three or four hours, must be drawn off into the coolers.
As commercial stearic acid frequently contains undecomposed tallow, as well as various foreign matters, this process is occasionally unsuccessful. To obviate the inconveniences connected with the use of this impure material, the candle may be run at two operations, as follows:—“The stearic acid, treated as above, is exposed for a month to the sun, by which means the foreign matters are oxidised, and the bleached stearic acid acquires a dirty yellow colour; the oxidised blocks are then melted in water containing a little sulphuric acid, at about 150° Fahr.; an addition of about 10 per cent. of good white wax (or spermaceti) is next made, and the whole boiled for half an hour; the white of an egg, previously beaten up in a quart of water, is then added to each 1 cwt. of stearic acid, the temperature of the mass having been reduced to 100°, or at most 120° Fahr., after which the mixture is again well stirred and boiled, when the liquid soon becomes clear, which is seen by the dark colour it assumes.
“This mixture of stearic acid and wax or spermaceti is very suitable for forming the exterior coating of the candle; it is transparent, and of perfect whiteness, and, as it is devoid of oxalic acid, it does not injure the moulds; whilst at the same time, as it is less fusible than pure stearic acid, candles made with it do not run. The first coating may be run hot without crystallising; the interior of the candle, being protected from without against too sudden a cooling, may also be run somewhat hot; by this means the candle acquires a whiteness and a transparency which cannot be realised by other processes.” (‘Le Moniteur Industriel.’)
The sulphuric acid saponification of inferior tallow and other solid or semi-solid fatty bodies is now carried out on a very large scale for producing the cheaper varieties of ‘stearine candles.’ For this purpose, the tallow or fat is mixed with 5 or 6% of concentrated sulphuric acid, and exposed to a steam heat of 350° to 360° Fahr. After cooling, the black mass thus
obtained crystallises to a tolerably solid fat, which is well washed once or twice with water, or high-pressure steam, and is then submitted to distillation by the aid of steam heated to about 560° Fahr. The product of the distillation is beautifully white, and may be at once used for making candles. It is better, however, to first submit it to the processes of cold and hot pressing, whereby a much more solid fat is obtained.
According to M. Pohl, palm oil or palm tallow is most easily purified by simple exposure to a high temperature, provided it has been first well defecated. When quickly heated to about 465° Fahr., and kept at that temperature for from 5 to 15 minutes, it is completely decoloured. The product has a slight empyreumatic odour, but this disappears by age, exposure, or saponification, and the natural violet odour of the oil returns. Cast-iron pans should be employed in the process, and should be only 2-3rds filled, and well covered during the operation.
By the distillation of sulphurated palm oil in closed vessels, at a heat ranging from 570° to 600° Fahr., from 68% to 75% of a mixture of palmitic and palm-oleic acid passes over, of which 25% to 30% is colourless, hard, and crystalline, and the rest darker and softer. (Pohl.) The residuum in the still is a fine hard pitch. See Candles, Fat, Glycerin, Oils (Fixed), Stearic acid, &c.