The violent effervescence which takes place on treating a _Carbonate_ of any kind with an acid is due to the _gaseous_ nature of Carbonic Acid and its escape in that form, which greatly facilitates the decomposition. _Insolubility_ is also a cause which exercises a great influence on the result which will follow in mixing solutions. If the formation of an insoluble substance is possible by any interchange of elements, it will take place. A solution of Chloride of Sodium added to Nitrate of Silver invariably produces Chloride of Silver; the _insolubility_ of Chloride of Silver being the cause which determines its formation. So again, Sulphate of Lead and Protonitrate of Iron are produced by mixing Nitrate of Lead with Sulphate of Iron; but if Nitrate of _Potash_ be substituted for Nitrate of Lead, the result is uncertain, because there are no elements present which can, by interchanging, form an insoluble salt; Sulphate of Potash, although _sparingly_ soluble in water, not being _insoluble_, like the Sulphate of Lead or the Sulphate of Baryta. ON CHEMICAL NOMENCLATURE. The nomenclature of the chemical _elements_ is mostly independent of any rule; but an attempt has been made to obviate this in the case of those of later discovery. Thus the names of the newly-found _metals_ usually end in _um_, as Potassium, Sodium, Barium, Calcium, etc.; and those elements which possess analogous characters have corresponding terminations assigned to them, as Chlorine, Bromine, Iodine, Fluorine, etc. _Nomenclature of Binary Compounds._--These are often named by attaching the termination _ide_ to the more important element of the two; as, the Ox_ide_ of Hydrogen, or Water; the Chlor_ide_ of Silver; the Sulph_ide_ 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 _Per_oxide, because no higher simple oxide is known, and the Bichloride of Mercury is a _Per_chloride 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."