The practice of chemistry requires, in most cases of solid bodies, previous to the application of heat, or of one body to another, for the exercise of the attrac tions, that some mechanical means should be taken to divide their parts from each other. These are, 1, chopping or cut ting; 2, rasping, filing, or shaving ; 3, pulverizing or grinding ; 4, granulation, as when shot is formed by pouring lead into water, or a powder of the metal is ob tained by shaking it in a box, in the fus ed state, till it congeals ; 5, elutriation, or washing, to separate the finer or light er parts of bodies from the coarser or larger, as when earthy matters are wash ed from the heavier metallic ones, or when a fine powder, such as that of pounded emery, is suspended by agita tion in water, which is decanted off; and then set to subside, while the coarser par ticles, which settle, immediately, are left behind ; 6, hammering, or forging, as in the making of tin foil, or leaf gold, or in the extension of other metals, whether hot or cold ; 7, laminating, as when the metals are passed between steel rollers, or when wax is poured upon a wooden cy linder, turned round in cold water; and, 8, wire drawing, as when the metals are drawn through a hole in a plate to make wire, or forced through an engine, such as that employed for glazier's lead, &c.
Bodies are distinguished, with regard to heat, into fixed, volatile, and refrac tory. The first can scarcely, if at all, be evaporated ; the second are easily raised or driven off; and the third undergo no change.
The simple application of heat is dis tinguished by various terms, according to the nature of the operation, or of the ef fects produced. These are, 1, roasting, which consists in exposing minerals to an open fire, to drive off their volatile con tents ; 2, calcination is the exposure of a body to strong heat, in an open vessel, till it undergoes no farther change. This word, which was formerly used in a ge neral way, is now confined to earths and some of the salts, and is indeed seldom used; 3, oxyclation is the like process with metallic bodies : 4, fusion, or melt ing, is the production of the state of dense fluidity ; 5, cementation is a pro cess, wherein solid bodies of different kinds, one or more of them being in pow der, are exposed to heat in a vessel near ly closed, with the intention that the more volatile parts of the one may unite with the other, or its fixed parts ; 6, eliqua tion is the exposure of a compound body, usually metallic, to heat, sufficient to fuse one of its ingredients, which runs out, and leaves the other solid an po rous ; 7, digestion consists in keeping bo dies for a considerable time immersed in a fluid more or less heated, in order to effect some combination between them ; 8, evaporation is the dissipation of a fluid by heat ; 9, concentration consists in di minishing the proportion of water in any solution of saline matter, either by heat ing it, or by freezing the surplus water and taking out the ice ; 10, when evapo ration is performed in any apparatus of vessels, partly or quite closed, and the vapours, after being raised by heat in one part or vessel, are received in another sufficiently cold to condense them into the fluid state, this process is called dis tillation; 11, when a fluid obtained by distillation is again distilled, in order to obtain the most volatile part of the first product, this last part is said to be recti fied, and the process is called rectifica tion. This term has become nearly ob.
solete in scientific description, but is still retained in the arts; 12, there are many products of evaporation, which congeal, or become solid, at a temperature much higher than that of the atmosphere, and are not, therefore, obtained in the fluid, but the solid state. These usually ad here in the form of crystals to the upper part of the apparatus, and on this account, as well as because the operation does not in general require the same kind of ves sel, it is distinguished by the name of su blimation, and the products themselves are called sublimates, and in some in stances flowers ; but these two last terms are more particularly confined to the arts. Other terms are also used, such as fusible, evaporable, &c. but their sense is manifest.
For the apparatus used in these and the other operations of chemistry, see