Nomenclature of Binary Compounds.—These are often named by attaching the termination ide to the more important element of the two; as, the Oxide of Hydrogen, or Water; the Chloride of Silver; the Sulphide of Silver. Binary compounds of Sulphur however are sometimes termed Sulphurets, as the Sulphuret or the Sulphide of Silver indifferently.
When the same body combines with Oxygen, or the corresponding element, in more than one proportion, the prefix proto is applied to that containing the least Oxygen; sesqui to that with once and a half as much as the proto; bi or bin to that with twice as much; and per to the one containing the most Oxygen of all. As examples, take the following:—The Protoxide of Iron; the Sesquioxide of Iron: the Protochloride of Mercury; the Bichloride of Mercury. In these examples the Sesquioxide of Iron is also a Peroxide, because no higher simple oxide is known, and the Bichloride of Mercury is a Perchloride for a similar reason.
When an inferior compound is discovered, it is often termed sub; as the Suboxide of Silver, the Subchloride of Silver. These bodies contain the least known quantity of Oxygen and Chlorine respectively, and are hence entitled to the prefix proto; but being of minor importance, they are excepted from the general rule.
The combinations of metallic elements with each other are termed "alloys;" or if containing Mercury, "amalgams."
Nomenclature of binary Compounds possessing acid properties.—These are named on a different principle. The termination ic is applied to one element. Thus, taking as an illustration the liquid known as "Oil of Vitriol," it is truly an Oxide of Sulphur, but as it possesses strong acid properties it is termed Sulphuric Acid. So Nitric Acid is an Oxide of Nitrogen; Carbonic Acid is an Oxide of Carbon, etc. When there are two oxides of the same element, both possessing acid properties, the most important has the termination ic, and the other ous; as Sulphuric Acid, Sulphurous Acid; Nitric Acid, Nitrous Acid.
Nomenclature of the Hydracids.—The Hydrogen Acids are distinguished from Oxyacids by retaining the names of both constituents, the termination ic being annexed as usual. Thus, Hydrochloric Acid, or the Chloride of Hydrogen; Hydriodic Acid, or the Iodide of Hydrogen.
Further illustrations of the nomenclature of Binary Compounds.—The Oxides of Nitrogen, and also of Sulphur, afford an interesting illustration of the principles of nomenclature. The former are as follows:—
| Nitrogen. | Oxygen. | |||
| Protoxide of Nitrogen | 1 | atom. | 1 | atom. |
| Binoxide of Nitrogen | 1 | " | 2 | " |
| Nitrous Acid | 1 | " | 3 | " |
| Peroxide of Nitrogen | 1 | " | 4 | " |
| Nitric Acid | 1 | " | 5 | " |
Observe, that two only out of the five possess acid properties, the others being simple oxides. Nitric Acid is, strictly speaking, the "Peroxide," but as it belongs to the class of acids, that term naturally falls to the compound below.