producing H-Cl and H-Cl, but, as the number of mole-7 cules remains the same, the volumes remain unaltered. In the second case we have the dyad oxygen, the molecule of which is O=0. Each of its atoms links two of hydrogen, forming the triatomic molecule H2O. The total number of molecules is thus diminished a third, and the three volumes are consequently reduced to two. In the third example we have triadic nitrogen, the molecule of which is. N-N. Each nitrogen-atom takes three hydrogen-atoms, forming ammonia, H,N. All the molecules at first contain two atoms, and the resulting molecules contain four. There is, therefore, but half the number of molecules,. and the four volumes are reduced to two. Lastly, each atom of the tetrad carbon molecule, CC, unites with four atoms of monadic hydrogen, and the resulting molecule contains five atoms. The number of molecules formed equals the number of carbon-atoms, or twice the number: of the carbon-molecules, and hence the five volumes are condensed to two.

THE

CHAPTER X.

CHEMICAL

NOMENCLATURE.

280. The Science reflected in its Language.-The terms. used in chemistry bear the impress of the various theoreti cal stages of the science. Some of them, as gold, silver, iron, were applied to substances thousands of years ago, before the science had taken a separate form. The alchemists were the first chemists, and they worked under the mystical influence of astrology. Terms still survive that indicate the fancied relations of substances to celestial bodies. Quicksilver was associated with Mercury; silver with Luna or the moon (hence lunar caustic); and crocus

Martis, a compound of iron, is a vestige of the old association of this metal with Mars. The alchemists had a crude theory of the action of spirits in Nature, and named various products accordingly, as spirit of wine, spirit of salt, spirit of hartshorn, spirit of nitre, etc. The first general chemical theory, that of phlogiston, gave rise to a terminology which has disappeared with the system, and which renders many of the chemical books of the eighteenth century almost unintelligible to a modern student. The system of naming chemical substances called the Nomenclature, which originated with the French about a hundred years ago, has been of immense service, both in the advancement and the diffusion of the science. When the facts of chemistry were comparatively few, and its theory simple, the terminology, which conformed to the dual doctrine, was also simple and highly effective. But as facts of all orders rapidly multiplied, and assumed new relations, the old system of expression was disturbed; and now, with the changes of theory, the nomenclature has been unsettled at various points, and there is some want of uniformity among authorities in the use of chemical terms. The main principles, however, remain in full force.

281. Naming the Elements. The names of the elements generally given have been expressive of some leading quality, real or imaginary. Thus, oxygen, as has been stated, received a name signifying acid-former, while chlorine takes its name from its greenish color; iodine, from its purple vapor, and phosphorus from its being luminous in the dark. Analogy of properties is sometimes indicated by similarity of termination, as chlorine, bromine, iodine; while the metals discovered in modern times are marked by the termination um, as platinum, thallium, etc.

282. Naming of Compound Radicals. These substances, which, as we have seen, are analogous to elements, are generally named from one or more of their constituents, or from some compound into which they enter.

The

terminal syllable, generally, is yl. Thus, the radical composed of one atom of hydrogen and one of oxygen is called hydroxyl, and that composed of one atom of oxygen and one of carbon, carbonyl. Ethylene and benzylene are examples of compound radicals whose names terminate in ylene. Exceptions to the forms given are found in the case of cyanogen, and in the numerous compounds formed of carbon and hydrogen, or of carbon, oxygen, and hydrogen, whose names frequently bear reference to the number of their carbon-atoms, as, for example, trityl, tetryl, etc.

283. Naming of Binary Compounds. — Binary compounds, strictly speaking, result only from the union of two elementary substances, but the term is frequently extended to include combinations of two compound radicals. Thus, silicon and fluorine combine to form silicic-fluoride; while methyl and ethyl form methylic-ethide. All of these compounds are named by placing the positive element first, and the negative element, with its termination changed to ide, after it. Thus:

The termination of the name of the positive element is changed to ic, except in compounds, in which the positive element unites with the negative element in variable proportions, when the ending ic is confined to the compound containing the smaller proportion of it, while the termina

tion ous expresses the larger quantity of the positive element. Thus :

In some cases the terminations ous and ic are affixed to the names of the elements, as, for example, in the wellknown compounds sulphurous and sulphuric oxide. When the name of the positive element is not derived from the Latin or Greek language it is translated into the former before changing the termination; thus, the Latin for gold is aurum, and it forms two compounds with chlorine, one of which is termed aurous, and the other auric chloride. When the number of compounds formed of two elements exceeds two, hypo, under, and per, over, are employed to distinguish them; thus, a compound containing less oxygen than chlorous oxide is known as hypochlorous oxide, while one containing more oxygen than chloric oxide would be known as perchloric oxide.

284. Prefixes. A system of naming much used in the following pages consists in the use of numerical prefixes, expressing the number of atoms of the element. The compounds of nitrogen and oxygen, all containing two atoms of nitrogen, united with respectively one, two, three, four, and five atoms of oxygen, are distinguished as nitrous monoxide, dioxide, trioxide, tetroxide, and pentoxide; while a compound containing three atoms of iron and four atoms of oxygen is termed tri-ferrictetroxide. An exception to the previous rules is found in compounds consisting of carbon and hydrogen—these are so very numerous that the methods given cannot be rigidly applied. The termination adopted is generally ene.

285. Naming of Salts, Acids, and Bases.-The constitution of these compounds has been already explained (257).

and the method of naming them is a modification of the old system, which was derived from the dual view of their constitution. They are named, like binaries, from their constituent atoms. In the case of the negative element the termination is changed to indicate that the atoms are linked by oxygen. These negative terminations are ate and ite; the positive element follows the rule given (283). Thus, hydric nitride becomes, by the introduction of more oxygen, hydric nitrate; by less oxygen, hydric nitrite-both acids. In salts the element which replaces the hydrogen of the acid becomes the first term of the name. For example, when the element sodium replaces the hydrogen of hydric nitrate, we obtain sodic nitrate; when it replaces the hydrogen of hydric nitrite, we obtain sodic nitrite. Bases are named like the salts, water taking the place of the second term of the name. Thus, the base which consists of calcium and hydrogen, linked by oxygen, is termed calcic hydrate.

The common names of the acids are derived from those of binary compounds containing oxygen by merely substituting the word acid for the word oxide, thus ignoring, in the naming of the compound, the oxygen; but, when the linking element is not oxygen, but some of its analogues, a prefix is used. Arsenic acid is composed of arsenic and hydrogen, linked by oxygen; sulpho-arsenic acid of arsenic and hydrogen linked by sulphur.

286. Naming of Amides, Amines, and Alkalamides.— It will be remembered that these bodies are derived from ammonia (265) by replacing one or more of the hydrogenatoms by other elements or radicals. They are named by joining the names of the substituted elements, either with or without their terminal syllable, with the termination amide or amine. Thus, we have Cyanamide, Potassamine: and the replacing of more than one element or radical is indicated by numerical prefixes, thus: Di-iodamide, Di-sodamine; and, when these compounds are derived from more