Page:The American Cyclopædia (1879) Volume XII.djvu/491

NOMENCLATURE 477 combining with acids, the distinguishing prefix of each is retained in the name of its salts ; as sulphate of protoxide of iron, and sulphate of sesquioxide of iron. These salts are also often called respectively protosulphate and persulphate of iron, the prefixes being under- stood to refer to the degrees of oxidation of the metal. As the number of salifiable oxides of any element is rarely if ever greater than two, it was proposed by Berzelius to distin- guish them in some cases, like the acids, by the terminations OKS and ic. The two oxides of iron he called ferrous oxide and ferric oxide respectively, and the salts just mentioned fer- rous and ferric sulphate ; and so with the ox- ides of various other metals. These changes are very convenient in certain cases, and for these they have been extensively adopted. It often happens that an acid can combine with the same base in several different propor- tions. Of the salts thus formed, one is called neutral, or more properly normal, since the definition now depends upon some one constant relation in which the oxygen of the acid stands to that of the base for the salts of each indi- vidual acid ; those containing more base than this are termed basic, and those containing less, acid salts. The term neutral or normal is not usually expressed, being understood to belong to any salt which is characterized neither as basic nor as acid. When several acid salts of any one base occur, they are distinguished from each other by the Latin prefixes bi, ter, &c., which are attached to the name of the acid ; thus, monochromate (or simply chromate), bi- chromate, and terchromate of potassa. When several basic or sub-salts occur, they are usual- ly distinguished by prefixing the terms bibasic, sesquibasic, terbasic, &c., to the name of the salt. Thus, five acetates of lead are known : mono- basic (or normal) acetate of lead, symbol PbO A ; bibasic do., (PbO) 2 A~; sesquibasic do., (PbO) 3 Aa; terbasic do., (PbO) 3 A; sexbasic do., (PbO) 6 A. It has also been proposed to denote the amount of base in a sub-salt by prefixing to its name the Greek numerals dis (twice), trie (thrice), tetraMs (four times), &c., in contra- distinction to the Latin ones used for acid salts. Thus, instead of bibasic acetate of lead, the term diacetate of lead would be used ; in- stead of terbasic acetate of lead, trisacetate of lead, and so on. Many oxides act as bases under certain circumstances, and as acids un- der others ; they may have therefore two dif- ferent names. Thus, the oxide of aluminum when acting as a base is called sesquioxide of aluminum (or alumina) ; but when playing the part of an acid, it is termed aluminic acid. Water (protoxide of hydrogen) is an- other oxide which is either acid or basic ac- cording to circumstances ; when it plays the part of an acid its salts are termed hydrates, as hydrate of potassa, &c. The principles of the nomenclature have not been carried out, how- ever, in regard to the compounds in which it acts as a base. Several of our most common acids are such compounds ; but instead of say- ing sulphate of water, nitrate of water, &c., they are termed hydrated sulphuric acid, hy- drated nitric acid, &c. ; or, oftener, simply sul- phuric or nitric acid, terms which ought, strict- ly speaking, to be applied only to the anhy- drous compounds. In like manner certain salts, which contain two equivalents of acid united with one equivalent of a metallic base and one equivalent of water, which ought to be regarded as double salts, are named as if they were bisalts, containing two equivalents of acid to only one of base, the water being left out of account. Thus the compound of one equivalent of water, one equivalent of po- tassa, and two equivalents of sulphuric acid, is commonly called bisulphate of potassa. The names of some of the ternary sulphur com- pounds (sulphur salts) are formed in a similar manner to those of the corresponding com- pounds of oxygen ; thus the compound of sul- phide of sodium and sulphantimonic acid is called sulphantimoniate of the sulphide of sodi- um. Like the names of the oxygen salts, these are usually abbreviated. In the instance cited, the salt is commonly termed sulphantimoniate of sodium, it being understood that the latter element is united with sulphur. But this system is limited to only a few of the sulphur acids ; the terms sulpharseniate, sulphantimoniate, and sulphomolybdate are well understood ; but the sulphophosphates, for example, of Berzelius (MS, PS&) have never been generally so called. So long as the attention of chemists was principally directed to the consideration of inorganic compounds, the system of nomen- clature just described, in spite of its numer- ous faults and inconsistencies, was found to be sufficiently expansive to meet all require- ments. It has, however, failed to furnish suitable names for many new classes of com- pounds which have recently been discovered. This is especially true of the great variety of organic substances, with the study of which chemists of the present day are chiefly occu- pied. But the radical fault of the system is its intimate connection with the so-called du- alistic theory as just developed, which sup- poses all compounds to be capable of division into two prime factors, as salts into acids and bases, and these into still simpler antagonistic components ; a view which is at present gen- erally discarded. The system of nomenclature in question has moreover been found to be incapable of expressing innumerable decompo- sitions and changes which occur among com- plex substances. But this difficulty has been in a measure obviated by the introduction of certain written abbreviations (see SYMBOLS, CHEMICAL) and formulas, which exhibit at once to the eye the composition of bodies and the alterations to which they are subject. In- deed, since the adoption of these symbols the name of a substance is of comparatively little scientific importance. The introduction of many names synonymous with those now used