PART III. OF SECONDARY COMPOUNDS. By secondary compounds, is meant the compounds formed by the union of the primary compounds with each other. Now as the neutral primary compounds enter into but few combinations, it is obvious that the secondary compounds must consist chiefly of combinations of the acids with the bases. Such compounds are called salts. They constitute a very numerous and important set of bodies, which it is of great consequence to understand well. Part III. The word salt was originally confined to common salt; a Salt, what. substance which has been known and in common use from the remotest ages. It was afterwards generalized by chemists, and employed by them in a very extensive and not very definite sense. Every body which is sapid, easily melted, soluble in water, and not combustible, has been called a salt. Salts were considered by the older chemists as a class of bodies intermediate between earths and water. Many disputes arose about what bodies ought to be comprehended under this class, and what ought to be excluded from it. Acids and alkalies were allowed by all to be salts; but the difficulty was to determine concerning earths and metals; for several of the earths possess all the properties which have been ascribed to salts, and the metals are capable of entering into combinations which possess saline properties. In process of time, however, the term salt was restricted to three classes of bodies; namely, acids, alkalies, and the compounds which acids form with alkalies, earths, and metallic oxides. The first two of these classes were called simple salts; the salts belonging to the third class were called compound or neutral. This last appellation originated from an opinion long entertained by chemists, that acids and alkalies, of which they are composed, were of a contrary nature, and that they counteracted one another; so that the résulting compounds possessed neither the properties of acids nor of alkalies, but properties intermediate between the two. Chemists have lately restricted the term salt still more, by tacitly excluding acids and alkalies from the class of salts alto Chap. III. I determined the constituents of these different species by heating them in contact with peroxide of copper. The following tables exhibit the result of these experiments.* PART III. OF SECONDARY COMPOUNDS. By secondary compounds, is meant the compounds formed by the union of the primary compounds with each other. Now as the neutral primary compounds enter into but few combinations, it is obvious that the secondary compounds must consist chiefly of combinations of the acids with the bases. Such compounds are called salts. They constitute a very numerous and important set of bodies, which it is of great consequence to understand well. Part III. The word salt was originally confined to common salt; a Salt, what. substance which has been known and in common use from the remotest ages. It was afterwards generalized by chemists, and employed by them in a very extensive and not very definite sense. Every body which is sapid, easily melted, soluble in water, and not combustible, has been called a salt. Salts were considered by the older chemists as a class of bodies intermediate between earths and water. Many disputes arose about what bodies ought to be comprehended under this class, and what ought to be excluded from it. Acids and alkalies were allowed by all to be salts; but the difficulty was to determine concerning earths and metals; for several of the earths possess all the properties which have been ascribed to salts, and the metals are capable of entering into combinations which possess saline properties. process of time, however, the term salt was restricted to three classes of bodies; namely, acids, alkalies, and the compounds which acids form with alkalies, earths, and metallic oxides. The first two of these classes were called simple salts ; the salts belonging to the third class were called compound or neutral. This last appellation originated from an opinion long entertained by chemists, that acids and alkalies, of which they are composed, were of a contrary nature, and that they counteracted one another; so that the resulting compounds possessed neither the properties of acids nor of alkalies, but properties intermediate between the two. Chemists have lately restricted the term salt still more, by tacitly excluding acids and alkalies from the class of salts alto Part III. gether. At present, then, it denotes only the compounds. formed by the combination of acids with alkalies, earths, and metallic oxides.* As there are nine classes of acids, it is obvious that there must be as many classes of salts. I shall give an account of these different classes in succession. Nomencla ture. CLASS I. OXYGEN ACID SALTS. This class of salts has been longest known and most completely investigated. Of course the salts belonging to it are by far the most numerous. According to the nomenclature introduced by Morveau, which is still followed in chemistry, the genera of these salts are named from their acid. Thus if the acid be sulphuric the salt is called a sulphate, if the acid be the nitric the salt is called a nitrate, and so on. The species are distinguished from each other by adding the name of the base. Thus sulphate of soda is a salt composed of sulphuric acid and soda; oxalate of lime is a salt composed of oralic acid and lime. When the salt is a compound of one atom of acid with one atom of base, it is distinguished simply by the name. If the salt contains two atoms of acid united to one atom of base, the Latin numeral adverb bis or bi is prefixed. Thus bisulphate of potash is a salt composed of two atoms sulphuric acid and one atom potash. Were there 3, 4, &c. atoms acid, the numeral adverbs ter, quater, &c. would be prefixed. Thus quateroxalate of potash means a compound of 4 atoms oxalic acid and 1 atom potash. When there exists an atom and a half of acid united to one atom of base, the Latin term sesqui (one and a half) is prefixed. Thus sesquicarbonate of soda is a compound of 1 atom carbonic acid with 1 atom soda. When two atoms of base are combined with one atom of acid this is denoted by prefixing the Greek numeral adverb dis. Thus diphosphate of potash means a compound of two atoms potash with one atom phosphoric acid. The prefixes tris, tetrakis, &c. indicate three, four, &c. atoms of base with one atom of acid. After considering the subject with considerable attention, I *The terms salt and neutral salt are often confounded. In this work the epithet neutral is confined to salts having no excess of acid or base. think the mode of arranging the salts according to the bases is attended with such advantages as to induce me to adopt it in this work. We should therefore divide this class into 42 sections, allowing a section for the salts formed by the combination of each salifiable base with the different acids. But there are several of the acid bases which combine with acids and form salts. This, together with the double salts, will oblige us to divide the class into no fewer than 52 sections. SECTION 1.-SALTS OF AMMONIA. 1. The salts of ammonia, with a very few exceptions, are all soluble in water. Class I. 2. When potash or quicklime is mixed with an ammoniacal Characters, salt, a smell of ammonia is emitted. 3. If to an ammoniacal salt dissolved in water a little salt containing magnesia be added, and afterwards some phosphate of soda dropped in, a copious white precipitate falls. 4. When an ammoniacal salt is exposed to heat it is completely dissipated in vapours; except when the acid has a fixed metal, or phosphorus, or boron for its base, in which last case the acid alone remains behind. 5. The ammoniacal salts are not precipitated by infusion of nut-galls or prussiate of potash. 6. When a solution of platinum is dropped into a salt of ammonia, a yellow coloured precipitate falls in very small crystals. This genus of salts has been very fully investigated. The following are the different species: ammonia, Sp. 1. Sulphate of ammonia. This salt was discovered by Sulphate of Glauber, and called by him secret sal ammoniac. It was also called vitriolated ammoniac. It may be prepared by saturating ammonia with sulphuric acid, or by decomposing sal ammoniac by means of sulphuric acid. It exists native, and is then distinguished by the name of muscagnin. There are two subspecies of this salt, differing from each other in the water of crystallization. (1.) Proto-hydrated sulphate. I obtained it crystallized in regular rectangular plates, and consider the form of the crystal to be a four-sided prism with square bases. It is transparent and colourless. Its specific gravity is 2. It has a sharp bitter taste. It is soluble in twice its own weight of water at the temperature of 60°, and in its own weight of boiling water. Water of the temperature of 144° dissolves 0.78 of its weight |