Page:Willich, A. F. M. - The Domestic Encyclopædia (Vol. 1, 1802).djvu/453

421&#93; C AL mkal solution, become a part of another vegetable, or animal ; such is the general transmigration of matter. Unburnt calcareous earth is said to forward the putrefaction of ani- mal and vegetable substances ; while pure lime, though it appa- rently prevents putrefaction, de- stroys, or dissolves, the texture of the flesh. If lime be mixed with oak-bark, after the tanner has ex- tracted its solubleparts in water, the bark will, in two or three months, be reduced to a fine black earth ; but, if it were only laid in heaps, as many years would be required to effect its spontaneous fermen- tation, or putrefaction. See Lime. Von Crell, a celebrated Ger- man chemist, a short time since made experiments, in order to as- certain the comparative effects of alum, magnesia, and calcareous earth, in the dying of cloths with madder ; by which it appeared that no advantage was derived from the two last mentioned sub- stances, as alum, and its solu- tions, produce finer colours, and may always be employed in prefe- rence to the others. CALCINATION is the redac- tion of solid bodies by fire, to a state of powder, or ashes : a pro- cess which is attended with a change of their quality, and is es- sentially different from comminu- tion, or mechanical trituration. Having, under the article Ashes, treated of the burning of vegetable and animal matters, we shall con- fine our account, in this place, to metals. To calcine such metals as melt before ignition, they must be kept in fusion for some time; nor will this operation succeed, without a free admission of air : the surface CAL [421 of the metal must therefore be kept clear of the calx. Should any part be excluded from die air, no such change of quality will take place : and if any coal, or unctu- ous, inflammable matter, be suf- fered to fall into the vessel, it would reduce even the quantity, already calcined, to its former metallic state. The continuance of fusion causes the increase of the particles of fire ; which, as they penetrate every pore, decompose the whole so completely, that the fluidity can no longer subsist. The body is thus left porous, ex- tremely brittle, and easily redu- cible to the finest powder. This accounts for the parts of the body calcined being much broken and rarefied, and specifically lighter than in their original state. The calcination of metals, gold, silv' r, and mercury excepted, is much promoted by nitre : the pro- cess of which is usually termed de- flagration, or detm&tion. Fusion with any vegetable, or animal inflammable matter, will restore all calces and scoria? to their natural metallic state. They are, however, more difficult of fusion than the metals themselves, and scarcely any btit those of an- timony, lead, or bismuth, can be melted, without some additional flux, consisting chiefly of alkaline salt, in the strongest fire that can be furnished by the common fur- naces. The reducing fluT, which is a mixture of alkaline salt with inflammable matter, brings the calx into fusion, and revives it into metal. The common preparation of such a mixture, consists of two parts of water, and one part of nitre, well ground together, then set on fire, and covering the de- flagrating powder, with some ves.- £ e 3 »4