This section is from the book "The London Medical Dictionary", by Bartholomew Parr. Also available from Amazon: London Medical Dictionary.
(From calx, to burn to a calx or friable powder). Also, concrematio, deflagratio, com-bdstio, combustura, ambustio., The calcination of a body is, properly speaking, its exposure to the action of the fire which produces some change in it. This change is generally effected by separating the more volatile from the more fixed parts of any compound body; or the destruction of any principle capable of inflammation.
Bodies are deprived of their volatile parts by calcination, in the instances of burning calcareous stones to convert them into quick lime, which is effected by the separationof the carbonic acid and water; in the exposing gypsum, alum, borax, and several other salts, to the fire, which deprives them of the water that is necessary for their crystallization; and in the roasting of minerals, which carries off their sulphur, arsenic, and other volatile contents.
It was formerly supposed, that an inflammable principle gave to metals their distinguishing splendour, and other properties. As this was consumed in the fire, they were said to be reduced to the state of a calx. It is now, however, found, that the calx is the compound body containing air; but, as the change is produced hy fire, we still use the term calcined.
There is an evaporation of volatile parts, and a change to the state of a calx, without any sensible combustion, in exposing imperfect metals, combined with vitriolic and nitrous acids, to a due degree of heat; in this process the acid rises, and is at the same time decomposed, giving to the metal the oxygen necessary to reduce it to a calx. In the same way acids act by solution, calcining metals without the aid of fire, by being themselves decomposed.
Calcination is said to be actual, when effected immediately, and only by the action of fire; and potential, when a solvent is used to corrode the metal.
To this head belongs the burnings of vegetable and animal matters; otherwise called ustio, incineratio,
There are several species of calcination, by which different degrees of the same effect are produced, and thus calcination is perfect or imperfect: the first is where the utmost change, except vitrification, is brought about; the second is where the circumstances of the process are limited in proportion to the change intended.
The calcination of metallic bodies, gold and silver excepted, is promoted by nitre. This salt exposed to the fire in conjunction with an inflammable substance, extricates the inflammable matter, but bursts with it into flame, accompanied with a hissing noise: this process is called deflagratio, or detonatio. To understand the principle of this operation it must be observed, that the afflux of air is necessary to the support of fire; and that nitre, or any thing containing its acid, will supply the air.
The manner of operation varies according to the nature of the matter to be calcined, and may, according to the principle on which it is performed, be distinguished into threekinds, combustion, calefaction,and detonation.
Calcination by combustion is where the body kindled supports, with the assistance of the air, the fire which calcines it, as in the instance of coals in the culinary fire. Vegetables are thus calcined; and the operation is sometimes ailed incineration.
Calcination by calefaction is where the calcining heat is not generated in the body itself, but imparted to it from external fire. The methods are as various as the different kinds of matter thus treated; and in the management, regard must be had to the substance of the containing vessel, for some should be made of iron, others of glass or clay; and the heat must be differently regulated, or else vitrification, instead of calcination, may ensue. Calcinations of this kind are expedited by the increase of surface which is given to the calcined matter, and the copious admission of air through that part of the furnace where the matter is placed, by stirring it with a spatula, by previous pulverisation, and by raking off the calx from the surface of the metal, as fast as it appears. It should be further observed, that if any coal, or other inflammable matter, that docs not contain a mineral acid, be suffered to fall on the calcining matter, calcination will be prevented; and part of what is calcined will be revived or reduced, that is, it will return into its metallic form again.
Calcination by detonation -differs from combustion only in this: in the latter the assistance of air is necessary; in the former this want is supplied by the nitre that is added to the matter, which, producing a quicker and more intense fire, both shortens the operation, and, in some instances, renders it more perfect. Detonation is thus performed: a proper quantity of nitre is mixed with the matter to be calcined, a crucible is heated red-hot, then the matter thus mixed is gradually thrown in, an explosive effervescence soon follows. When it has ceased, another portion must be projected, till the whole is calcined. The crocus antimonii, and some other medicines, are thus prepared. A portion of the alkaline basis of the nitre sometimes joins with the calcined matter; but it may be separated by repeated washing with warm water: this is called edulcoration.
The metals which melt before ignition, are calcined by keeping them in fusion for some time. Those metals which require a strong fire to melt them, calcine with a much less heat than is sufficient to make them flow; hence the scorification, or burning, of such iron or copper vessels as are long exposed to a considerable fire without defence from the air.
In calcination the metals visibly emit fumes; yet the weight of the calx proves greater than that of the metal employed from the oxygen absorbed. Metallic calces are revived into their metallic state by fusion with any animal or vegetable inflammable matter.
Except those of lead and bismuth, all the metallic calces require an addition to make them melt in the strongest fire that can be made in common furnaces; and the additions, called fluxes, chiefly consist of a mixture of fixed alkaline salt with some inflammable matter. As these fluxes not only fuse the calx, but also revive it into metal, they are sometimes called reducing fluxes; of which the following is one of the chief, called the Black Flux.
Take of nitre one part, and salt of tartar two parts; grind them well together, then set the mixture on fire, by throwing in a bit of red hot coal; cover the vessel, and suffer them to burn until the whole is changed into a black alkaline coaly mass.
Metallic calces mixed with twice their weight of this black flux, and exposed to a proper fire in a close covered crucible, melt and resume their metallic form. But though the calx was heavier than the metal of which it was formed, on reviving to its original metallic state its weight is less than at the first.
See Newman's Chem. Works, Lewis's Materia Me-dica, the Dictionary of Chemistry.