The names of the binary compounds of the other

elements are formed like those of the oxides.

Moreover, the specific names in the several classes of compounds also follow the analogy of the oxides, thus:

And here, before we pass on to the names of compounds of a higher order, let me ask you to carefully fix in your memory the fact that the termination ide always indicates a compound containing only two elements.

Of compounds of three or more elements the most prominent class is that of the acids, bodies originally so called on account of their sharp or acrid taste. Now, the greater part of the inorganic or mineral acids are

composed of the two elements hydrogen and oxygen, united to some third element, which is the characteristic constituent in each case; and, from this third element the acid takes its name, the terminations ic and ous being used as in the case of binaries to indicate a greater or less amount of oxygen in the compound. Thus we have

In every acid we can by various chemical processes replace the hydrogen it contains with different metallic elements, and we thus obtain a very large class of compounds called salts. The generic name of the salts of each acid is formed by changing the termination ic, of the name of the acid, into ate, or the termination ous into ite, thus:

and the different salts of the same acid are distinguished

by adjectives as before. For example :

The terminations ous and ic, used in the names of these salts, indicate the same difference in the condition of the metallic element which determines the union of the metal with more or less oxygen. Ferrous and ferric sulphates, for example, correspond to ferrous and ferric oxides. The nature of this difference will be discussed in the chapter on quantivalence.

There is an important class of compounds which bears to water a relation similar to that which salts sustain to their respective acids. This class of compounds is called the hydrates, and may be regarded as derived from water, by replacing one-half of its hydrogen. Thus we have

The very interesting theoretical relations of the hydrates will hereafter be discussed.

When the hydrogen of an acid is only in part replaced, or is replaced by more than one metallic element, the constitution of the resulting salt may still be indicated by the name, as in the following examples:

Hydro-disodic phosphate..
Potassio-aluminic sulphate...

H,Na2PO,
K2Al2(SO4)4

In like manner the relative proportions of the several ingredients of a salt may be indicated, as in—

Tetrahydro-calcic diphosphate....... H.Ca(PO4)2
Disodic tetraborate (borax).........

But, as is evident, names like the last two are practically useless, and, when we attempt to extend the nomenclature to organic compounds, we are led into still greater absurdities; so that, although by giving arbitrary names to various groups of atoms called compound radicals we have been able, to a limited extent, to adapt the nomenclature to this class of substances, yet we have been compelled in many cases to resort to trivial names like those used before the adoption of the nomenclature. The names oil of vitriol, corrosive sublimate, calomel, saltpetre, borax, cream-of-tartar, etc., of the last century, have their counterparts in aldehyde, glycol, phenol, urea, morphine, naphthaline, and many other familiar names of our modern science. Of course, such names are subject to no rules, and, although they have been usually selected with care, and indicate by their etymology important relations or qualities, they must be associated separately with the substances they designate.

LECTURE VIII.

CHEMICAL CHANGES CLASSIFIED.

AMONG chemical reactions we may distinguish three classes: 1. Those in which the molecules are broken up into atoms; 2. Those in which atoms are united to form molecules; and, 3. Those in which the atoms of one molecule change places with those of another. Reactions of the first kind are called analysis, those of the second synthesis, and those of the third metathesis -terms derived from the Greek, and signifying respectively to tear apart, to bind together, and to interchange.

This classification is one of great theoretical importance. But it must be further stated that a simple analytical or synthetical reaction, as here defined, is seldom if ever realized in Nature. Almost every chemical process is attended both with the breaking up of molecules into atoms and the regrouping of these atoms to form new molecules, that is, it involves both analysis and synthesis; and this is true even in the many cases where the products or factors of the chemical reaction are elementary substances; for, when the molecules of the elementary substances consist of two or more atoms, the breaking apart or coalescing of these atoms, although they are atoms of the same ele