NOMENCLATURE 475 ferent bodies. The last have but little chemi- cal activity. Acids and bases, however, pos- sess unlike properties, and, although they do not combine with the elements, still manifest a great disposition to unite one with the other. Ternary compounds, or salts, are thus formed. The resulting salt possesses new properties un- like those of its components, having usually but little affinity for other substances; but some salts can unite with others to form qua- ternary bodies (double salts). The distinctive properties of these several classes are by no means absolute. Indeed, there are many bodies which, according to circumstances, act either as acids or as bases: as acids when brought in contact with strong bases, and as bases toward strong acids. Those acids which are soluble in water are distinguished by their power of changing the blue color of a solu- tion of litmus to red. Bases, on the con- trary, reproduce the blue color of litmus which has been reddened by an acid. The most characteristic salts have but little or no action on red or blue litmus, the acid and basic quali- ties of their components having been entirely neutralized by combination. There are, how- ever, many exceptions to this, as will be seen further on. When a solution of a salt is sub- jected to a weak galvanic current, the acid and base of which it consists are separated from each other; the acid collects at the positive pole of the battery, the base at the negative pole. On the theory that like electricities repel, while unlike attract each other, it is evi- dent that the particles of matter which are attracted to the positive pole ought to possess negative electricity, while those attracted to the negative pole should be positively electri- fied. The base is therefore often called the electro-positive and the acid the electro-nega- tive constituent of the salt. The character of the respective constituents of a salt may hence be exhibited by submitting the latter to the action of galvanism. The same rule applies also to all binary compounds which can be electrolyzed. In view of the great prominence which oxygen had attained in consequence of the experiments of Lavoisier, and of the fact that most of the acids and bases known to the founders of the chemical nomenclature con- tained it, or were thought to contain it, as one of their constituents, it is not surprising that especial importance was attached to this ele- ment. Indeed, its compounds form the basis of the system. The binary compounds of oxy- gen are, with the exception of a few indifferent substances, either bases or acids. They are called oxides, the termination ide, which is indicative of combination, being added to the first syllable of oxygen. Although the term oxide is generic, and would, strictly speaking, apply with equal force to any compound of oxygen with an element, it is nevertheless usually restricted to those compounds which are destitute of acid properties, viz., to the bases and indifferent bodies. Its acids are often called oxy-acids. The name of any par- ticular oxide is formed by adding the name of its other element to this generic term.; thus, the base formed by the union of oxygen and lead is called oxide of lead, that containing oxygen and potassium, oxide of potassium, &c. Lead and potassium are in these instances electro-positive elements, oxygen being electro- negative in regard to them. As a general rule, the name of the electro-negative constituent of a compound determines its genus, while that of the electro-positive constituent defines the species. The names of the basic compounds which oxygen forms with metals whose names end in um are often made to terminate in a ; thus, instead of oxide of sodium and oxide of barium, the terms soda and baryta are used. Oxide of calcium furnishes the most striking exception to this rule, the common name lime being used instead of calcia. Oxygen usually combines with an element in more than one proportion, forming several bases. To distin- guish these, the prefix proto (Gr. Trpwro?, first) is applied to the oxide in which one equivalent of oxygen is united with one equivalent of the element. An oxide containing less than one equivalent of oxygen to one of the other ele- ment is called a sub-oxide (Lat. sub, under). The prefix sesqui (one and a half) denotes a compound in which the oxygen is to the other element in the ratio of 3 to 2 ; deuto (Gr. devrepos, second) or lin (Lat. lini, two), an oxide containing two equivalents of oxygen; and trito (TP'ITO?, third) or ter (terni, three), an oxide containing three equivalents of oxygen to one of the other element. The base con- taining the largest amount of oxygen is often called the peroxide (per, thorough). Thus, three compounds of the metal manganese and oxygen are distinguished as follows : Protoxide of manganese contains -J } e< ^' Sesquioxide of " Bin-, 1 it J 1 eq. of manganese, 1 2 eqs. of oxygen. t i j 2 eqs. of manganese, I 3 eqs. of oxygen. or per- j At the time when the nomenclature was framed, it was believed that only two acid compounds could be formed by the combina- tion of oxygen with another element. These were distinguished from each other by causing the name of the other element to terminate in ic for the combination containing the larger proportion of oxygen, and in ous for the com- pound containing less oxygen, the word acid being added in each case to the words thus formed. For example, two compounds of sul- phur and oxygen are respectively : Sulphurous .eld, composed of f ^ Su.ph^eacid, " Of the compounds which an element may form with oxygen, those containing the larger num-
