In its natural state, fat of animals is always associated with cellular tissue and other foreign matters, which must be separated before it can be used as candle stock. In dry melting, the rough suet is cut into coarse pieces and exposed to the action of a moderate heat. By more recent processes the fat is not exposed to heat till it has been subjected to mechanical and chemical appliances, for the purpose of destroying the tissues. The first method possesses the decided advantage that the residue can be profitably used as food for hogs and fowls. There is also an economy in fuel, and the simplicity of the process commends itself to inexperienced manufacturers. The disadvantages are an obnoxious smell, from the heating of rough tallow which has been collected and suffered to remain till it has become rancid, and the cellular tissues, blood, or other portions advanced towards putrefaction, and the small amount of fat obtained, as portions always remain with the residue when heated in this manner. The fat for tallow ought to be freed from the membranous and muscular parts, then cut into thin slices and hung up in a cool place, not heaped up while yet warm.
By operating thus, the disagreeable odour can be delayed for several days.
First, the fat is chopped; cutting machines are often used similar to the straw-cutting table; sometimes a thin, sharp-edged, mince-hatchet is employed, about 2 1/2 ft. in length. This is held with both hands, and the fat, spread out on a beech block, is chopped into small pieces in all directions. A third instrument is a kind of stamp trough with muller, having a sharp blade in the form of an S, a contrivance frequently adopted for cutting beets. A more desirable instrument, however, is the ordinary rotary sausage-cutter. The fat is then placed in melting caldrons, hemispherical in form, and made of cast iron, which are heated by open fire. These caldrons are covered with movable tin-plate hoods, so adjusted that, by means of pulleys, ropes, and counter-weights, they can be easily raised or lowered, whilst, at the same time, they serve to carry off the offensive vapours arising from the heated fat. Water is sometimes mixed with the fat in the caldrons, and this addition is specially beneficial when the fat has been long kept during the summer months, and has thereby lost its natural moisture by evaporation. By. gradually raising the temperature in the pan, the fat runs from the cells, and the whole is kept boiling from 1 to 1 1/2 hour.
During the whole operation of melting and boiling, the ingredients must be constantly stirred in order to keep the fat and cracklings in incessant agitation, otherwise pieces of unmelted suet, coming in contact with the sides or bottom, would become scorched and acquire a brownish tint, of which the whole melting would necessarily partake. Scorched tallow is not readily whitened. For separating the melted fat from the cracklings, it is ladled off from the caldron into a fine willow basket, or a copper box perforated at the bottom with innumerable small holes, set over large copper coolers, and allowed to remain undisturbed till all foreign matters have settled down. Before it congeals, it should be transferred into small wooden pails. This operation is continued so long as the cracklings yield any fat; and during the process the heat must be maintained at a moderate degree, to avoid scorching the materials. When the cracklings begin to harden they acquire a darkish tint, and hence are said to be browning.
They are then pressed, and the fat thus obtained possesses somewhat of the brown colour of the cracklings,-but not so much as to render it unfit for use as soap stock; it may, consequently, be mixed with that which has spontaneously separated while heating.
By mere melting and straining we do not obtain a fat entirely free from admixture of fine, undissolved substances. For separating these substances, it must be clarified, by remelting it in water, either on free fire or by steam. Generally, no more water than 5 per cent. is taken, and stirred well with the fat till the mixture becomes emulsive. The whole is then allowed to rest, without further heating, till the water has separated, when the fat may be drawn off, or dipped off. Sometimes, to conceal the yellowish tint, a very little blue colour is added, consisting of indigo rubbed finely with some oil, of which a few drops are sufficient for large quantities of tallow. The process of clarifying is occasionally repeated. At the line of demarcation between the water and fat, a grey slimy substance is often perceptible, and the liquid itself is turbid. Instead of pure water, some tallow-melters take brine or solutions of alum, saltpetre, chloride of ammonium, or other salts. These agents hare no chemical action upon the fats, but simply induce a more rapid settling of the impurities and water, principally when strong agitation is used.
This mineral is used in the production of illuminating oils of a high firing point, and of solid hydro-carbons, more particularly adapted to the manufacture of candles of a high melting point; the raw material is . distilled by heat, thereby producing an oily distillate, the solid and liquid constituent parts of which are then separated by pressure. The pressed solid material is purified by mixing and stirring with sulphuric acid when melted. After standing for some time, in order to effect the complete separation . from the acid, the supernatant melted material is carefully decanted off, and thoroughly washed with hot water. The water having been removed, the material is repeatedly filtered through animal charcoal until the requisite degree of whiteness is attained.
Wicks are twisted or plaited; the former, loosely twisted, present the appearance of a spiral similar to the separate strands of a rope; the latter, now generally adopted for most kinds of candles, is made by interlacing and crossing the strands of the wicks in the same manner as plaiting straw of bonnets. Common wicks are simply an aggregation of several loosely-twisted threads forming one general cord of many fibres. The yarn employed is No. 16. For tallow candles, 8 to the lb., the wick contains 42 threads; 7 to the lb., 45 threads; 6 to the lb., 50 threads; 5 to the lb., 55 threads, 4 to the lb., 60 threads. These wicks, composed of 10, 12, or even 16 cords, are very loosely twisted, and form a kind of hollow tube. For stearine candles, three - corded plaited wicks are generally used, smaller in size and of finer yarn. Stearine candles, 4 to the lb., the wicks consist of 108 threads; 5 to the lb., 96 threads; 6 to the lb., 87 threads; 8 to the lb., 63 threads.