SALT, (Encycl.) See also ACIDS and ALKALIES in this APPENDIX.—Acids and alkalies, and combinations of both, when in a concrete form, are salts, and of the purest sort. The bodies, therefore, to which the name of salts more properly belongs, are the concretions of those substances; which are accordingly called acid salts, alkaline salts, and neutral salts. These last are combinations of acid and alkaline salts, in such propor-
proportion as to render the compounds neither four nor alkaline to the taste. This proportionate combination is called saturation: thus the common kitchen-salt is a neutral salt, composed of marine acid and mineral alkali combined together to the point of saturation. The appellation of neutral salts is also extended to denote all those combinations of acids, and any other substance with which they can unite, so as to lose, wholly or in great measure, their acid properties.
Notwithstanding that the general definition of salts given above is commonly received, yet there are many writers, especially mineralogists, who confine the denomination of salts to those substances only which, besides the general properties of salts, have the power of crystallizing, that is, of arranging their particles so as to form regularly-shaped bodies, called crystals; when the water superfluous to their concrete existence has been evaporated.
Salts of various sorts are found already formed in nature, but a great many others are made by art, and even several of the natural ones may be imitated. We shall only consider those salts, either natural or artificial, which are mostly used.
The vitriolic acid, when combined with other substances, forms vitriolic salts, which vary both in specific names and properties, according to the various substances with which the acid is combined. Thus the vitriolic acid, combined with mineral alkali, forms the salt called Glauber's salt, or sal mirabile. When it is combined with calcareous earths, it forms vitriolic salts with bases of calcareous earth, which are commonly called salenites. When combined with argillaceous earths, it forms alum. When combined with metals, it forms vitriolic salts with metallic bases, to which the general name vitríols is given; and in commerce are commonly called copperas. The vitriols principally used are, 1. The martial vitriol; called also English vitriol, green vitriol, or green copperas, which is a combination of vitriolic acid with iron. 2. The vitriol of copper, called also blue vitriol, Cyprian vitriol, or blue copperas; which is a combination of vitriolic acid and copper. 3. The vitriol of zinc, called also white copperas, and Goslar vitriol; which is a combination of the same acid with a semi-metal called zinc. It is a property peculiar to the vitriolic acid, that all the combinations of it, with those substances with which it can form neutral salts, are susceptible of crystallization.
The nitrous acid, combined with all the substances with which it can mix, forms saline substances, in general called nitrous salts; specifying each particular salt by the name of the substance united to the acid. Thus nitrous acid, with fixed vegetable alkali, forms a saline substance called nitre, or saltpetre. With mineral alkali, forms cubic or quadrangular nitre. When mixed with metallic substances, forms metallic nitrés, which are specified nitre of gold; nitre of silver, or lunar nitre, lunar crystals, and crystals of silver, nitrous crystals of mercury; nitre of copper, &c.
The marine acid, combined with various matters, forms marine salts, or simply salts, specified by the names of their particular bases. The sea-salt, or kitchen salt, and sal gem, are combinations of marine acid and mineral alkali. When this acid is combined with
volatile alkali, it forms sal ammoniac (A). With metals it forms metallic salts, called salt of gold, salt of copper, &c. according to the various metals combined with the acid. The salt of silver is also called luna cornea; the salt of lead is often called plumbum corneum; and the salts of antimony, and of arsenic, are known by the names of butter of antimony, and butter of arsenic.
The acid of tartar (the purest part of which, or that saline substance which first crystallizes, by evaporation, in the vessels in which it is purified, is called cream of tartar), and also all other concrete vegetable acids analogous to it, when mixed with various other substances, form compounds, generally called tartareous salts, or soluble tartars, because they are dissolved by water more easily than the acid of tartar itself.
Acetous salts, that is, all salts containing the acid of vinegar, are also combined with various bases, and form saline substances of different names; the principal of which are, the acetous salt of copper, called crystals of Venus, or verdigris, by the chemists, and distilled or crystallized verdigris in commerce; the acetous salt of lead, commonly called salt or sugar of lead; and the acetous mercurial salts.
Sugar is an essential vegetable salt, of a pleasant sweet taste, containing a vegetable acid combined with earth and oil.
Potash is a fixed vegetable alkali, extracted from the ashes of wood. Concrete volatile alkalies are generally called volatile salts; although this name is sometimes also given to the volatile salt of amber, which is not an alkaline, but an acid salt.
Borax is a neutral saline matter, whose origin, whether animal or vegetable, is as yet unknown, its components being not sufficiently examined. It is soluble in water, and very nearly as crystallizable as alum. When borax is exposed to the fire, it first bubbles and foams very much, but afterwards it melts into a clear glass. When acids are combined with the alkaline part of borax, a substance of a singular nature is separated from it, commonly called sedative salt. Altho' this substance acts as an acid in borax, by saturating its alkali, yet it has no acid taste, nor doth it turn the tincture of heliotropium to a red, as other acids do. It is the property of borax to facilitate considerably the fusion of metals, of earths, and other minerals. Some species of stones and earths cannot be vitrified at all, except they are mixed with borax. For this property borax is commonly used as a flux (that is, a substance which facilitates the fusion of other bodies) in various manufactories; but especially in soldering metals, and in assaying ores.
Phosphoric salts are combinations of alkaline, earthy, and metallic substances with the acid obtained from the phosphorus of urine.
Besides the above-mentioned salts, there are several others to be met with in the writings of the chemical and medical authors; but, as they are of little consequence, we shall omit any account of them.