SALTS. The term salt, originally restricted in its application to common salt, which it still means when used merely by itself, is now applied to a vast number of substances which have in many cases few properties in common.
Common salt is the principal of a class composed of a metal and such bodies as chlorine, iodine, bromine, and fluorine, and the radicals of the hydracids, and which are included by Berzelius in his class of haloid-sulea (from lias, sea-salt, and Mos, form), because in constitution they are analogous to sea-salt. The whole series of the metallic chlorides, iodides, bromides, and fluorides, such as chloride of sodium, iodide of potassium, and fluor-spar, are, as well as the cyanides, sulpho cyanides, and ferrocyanides (though the three last are very differently coustituted from the former), included by Berzelius in his list of haloid-salts.
It wa.s for many years admitted as an unquestionable fact that com mon salt was a compound of muriatic acid and of soda ; and hence it was very commonly called muriate of soda. But it has been shown by Davy, that the acid and alkali during their action on each other suffer mutual decomposition ; and that while water is formed by the union of the hydrogen of the acid with the oxygen of the alkali, the chlorine of the former and the sodium of the latter unite to form chloride of sodium. At has since been proved that this occurs with all so called hydracids, when they act upon metallic oxides : thus hydro chloric acid and soda give chloride of sodium and water, hydriodic acid and soda yield iodide of sodium and water, and hydrocyanic acid, cyanide of sodium and water, &c.
While then the hydracids, by the decomposition which they suffer, do not yield hydro-salts with the metallic oxides, yet hydra-salts may be formed by saturating these acids with the vegetable alkaloids ; for example, hydrochloric and hydriodic acids yield respectively hydro chlorate and hydriodato of quinine, when made to act upon this base. With ammonia hydrochloric acid forms the salt called salsimmonirre; but these salts are analogous to the chlorides, chloride of ammonium being formed by the conversion of the ammonia into ammonium, by the transference of the hydrogen of the hydrochloric acid to the am monia, which is theoretically supposed to consist of one equivalent of nitrogen and four equivalents of hydrogen, instead of one equivalent of nitrogen and three equivalents of hydrogen, which exist in am monia.
The ary-salts form another numerous and important class of com pounds : these sre formed when an oxacid is made to combine with an oxidised base ; as, for example, when sulphuric acid unites with soda, the result being sulphate of soda. The sulphates of potash, lime, magnesia, &c., are similarly constituted; but a question has arisen whether these salts are not also analogous .to the chlorides, in containing a metal rather than an oxide ; thus, instead of supposing that sulphuric acid, composed of one equivalent of sulphur and three equivalents of oxygen, is combined with soda, formed of one equivalent each of sodium and oxygen, it has been, and with much plausibility, supposed that the oxygen is transferred to the sulphuric acid, forming a compound which has never yet been isolated, consisting of one equivalent of sulphur and four equivalents of oxygen, and that this is combined with sodium. Professor Daniell proposed the name of
orysulphion of sodium for such compound, while Professor Graham denominates it a sulphot-aricle composed of sulphat-oxygen and sodium.
Another class of bodies has been described by Berzelius as coming within the description of salts; namely, the sulphur-salts. Electro positive sulphides, termed sulphur-bases, are usually the protosulphidca of electro-positive metals, and therefore correspond to the alkaline bases of those metals; and the electro-negative sulphides, sulphur-acids, are the sulphides of the electro-negative metals, and are proportional in composition to the acids which the same metals form with oxygen. Thus aulpharsenious acid (AsS,) and sulpharsenic acid (ABS.) combine respectively with sulphide of potassium (KS) to form the sulphas senite and aulpharseniate of potassium. These salts obviously corre spond with the aracnite and arsenate of potassium. Hence, if the sulphur of a sulphur-salt were replaced by an equivalent quantity of oxygen, an oxy-aalt would result.
In general properties the various classes of salts, and indeed the individuals of the same class, differ as widely as possible; some are crystallisable, others uncrystallisable ; they are colourless, and of various colours; sapid and insipid; soluble and insoluble in water, alcohol, and other menstrua ; volatile and fixed in the fire; decom posable or undecomposable by the same reagent.
Salts have been conveniently, though not quite correctly, divided into alkaline, earthy, and metallic salts; for, strictly speaking, most of the two former belong to the latter, and to these classes must be added the aminoniacal salts and the salts of the vegetable alkaloids. Again, salts constituted of the same elements may contain one or other in excess; thus soda and various other bases combine with three different portions of carbonic acid. The first is the neutral carbonate, containing one equivalent each of acid and of base; the second contains one-half more carbonic acid, and is called the sesqui-carbonate ; and the third contains twice as much carbonic acid as the first, and is the bicarbonate.
Super-salts are such as contain an excess of chlorine or of acids, and sub-salts such as contain excess of base. Dr. Thomson has proposed— and it is very conveniently adopted in practice—to describe the degree of excess of acid In the auper-salt by Latin terms, and that of the excess of lase by Greek : thus while a compound of two equivalents of chlorine and one of a base, or of an acid and base, is called a hi-chloride or bl. sulphate, as the ease may be, a compound containing one equivalent of chlorine or acid to two of base, is termed a di-chloride, &e. [CHEMICAL NOMENCLATURE: .Vueieneiatitre of Salts.)