Red Or′piment. Syn. Red arsenic. Tersulphide of arsenic.
Red Vene′tian. Syn. Bolus Veneta, L. A species of ochre, brought from Italy.
Rose Pink. This is whiting coloured with a decoction of Brazil wood to which a little pearlash has been added. A very pretty colour, but it does not stand. It is always kept in a damp state. The colour may be varied by substituting alum for pearlash, or by the addition of a little spirits of tin.
Vermil′ion. (See under that word.)
REDUC′TION. Syn. Revivification. A term in its fullest sense applied to any operation by which a substance is restored to its neutral state; but now generally restricted, in chemistry, to the abstraction of oxygen, and hence frequently termed deoxidation or deoxidisement. This change is operated by either heating the substance in contact with carbon or hydrogen, or in exposing it to the action of some other body having a powerful affinity for oxygen. See Potassium, &c.
REFI′′NING. A term employed in commercial chemistry and metallurgy synonymously with purification. The separation of the precious metals from those of less value, as in the operation of parting, constitutes the business of the ‘refiner.’ See Gold, Silver, &c.
REFRAC′TION (of Light). The deviation of a ray of light from its original path on entering a medium of a different density or power. For the practical application of this property, see Gems.
REFRI′′GERANTS. Medicines or agents which tend to lessen the animal temperature without causing any marked diminution of sensibility or nervous energy. Among internal refrigerants cold water, weak acidulous drinks, and saline aperients, are those which are probably the best known and the most useful. Among external refrigerants are cold water, evaporating lotions, weak solutions of subacetate of lead, &c.
REFRIGERA′TION. The abatement of heat; the act or operation of cooling.
Among the purposes to which refrigeratory processes are applied in the arts, the principal are—the condensation of vapours—the cooling of liquids—the congelation of water, and—the production of extreme degrees of cold in chemical operations. The first of these is referred to under the heads Distillation, Still, &c., and the second under Wort. It is, therefore, only necessary to notice here the third and fourth applications of cold, artificially produced, above referred to.