Utopian standard of perfection in a new system of notation; but in endeavouring to settle contested points on a firmer basis, they have incurred the risk of unsettling everything.""

When two elements unite together they form what is called a binary compound, such as oxide of zinc, or zincic oxide. This name gives at once the knowledge that the compound consists of two elements, zinc and oxygen, one equivalent of each being in the compound.

The non-metallic elements combined with each other, or with the metals, form the principal binary compounds.

In the following table* is shown the nomenclature of binary compounds: the symbols of the compounds are in the fifth column.

In employing symbols, the symbol of the basylous or electro-positive element is generally placed first.

When the same elements unite in various proportions, Latin or Greek numerals are used as prefixes to distinguish between the different compounds of the same elements. Thus the first oxide of ruthmium is called the protoxide, RuO; the second oxide is called the deutoxide, RuO,; the third is named the trioxide, RuO,.

The name binoxide is applied to the oxide that contains twice as much oxygen as the protoxide.

* From Miller's "Elements of Chemistry," Part II.

The prefix sesqui is given to compounds which contain two elements in the proportion of 3 to 2, or 1 to I, as sesquioxide of ruthmium, Ru,O,. The prefix per signifies the highest combinations, as perchloride of mercury.

Many oxides form, when united with the elements of water, acids.

Some bodies have two or more oxides, which form, with the elements of water, acids; and in order to distinguish between them a certain nomenclature is made use of. Thus the name of the acid containing the largest proportion of oxygen terminates in ic, as sulphuric acid, H2SO,, and that with the less amount ends in ous, as sulphurous acid, H2SO,.

An acid has sometimes been discovered containing a larger proportion of oxygen than the one to which the termination ic had been given.

Then the

prefix per has been used to denote this, as chloric acid HCIO,, and perchloric acid, HCIO

An acid containing less oxygen than the one ending in ous has the prefix hypo, as chlorous acid, HCIO,, hypochlorous acid, HCIO.

Besides these acids which contain oxygen, there are others which contain no oxygen; for instance, hydrogen and chlorine combine to form hydrochloric acid, HCl; also hydrogen and iodine form hydriodic acid, HI.

In the naming of the oxysalts-the union of an oxyacid with a base-the name of the salt containing the acid with the largest proportion of oxygen terminates in ate, as the compound of sulphuric acid and soda is called disodic sulphate, or sulphate of sodium, Na,SO,; whilst the salt of the acid containing less oxygen, and terminating in ous, ends in ite, as the compound of sulphurous acid and soda is named disodic sulphite, or sulphite of sodium, Na,SÒ,.

When a metal forms more than one basic oxide, i.e., more than one oxide capable of forming salts by the action of acids, the name of the metal in the oxide containing the smaller proportion of oxygen ends in ous; and in the oxide containing the larger amount of oxygen it terminates in ic, as in the case of iron.

The protoxide is called ferrous oxide, FeO, and the salts of this oxide ferrous salts, as ferrous sulphate, FeSO. (+7 H2O, water of crystallization).

The sesqui oxide is termed ferric oxide, Fe,O,, and its salts ferric salts, as ferric sulphate, Fe,3SO..

Most chemists of note now look upon acids as salts of hydrogen, the latter representing the metallic part. And when these hydrogen salts act upon other metals, they look upon the reaction as a replacement of hydrogen. There is no doubt that this system is quite consistent, and much more in accordance with observed facts, than the older ideas, which are daily losing ground.

When a molecule of an acid contains one atom of hydrogen capable of being replaced by one atom of a monad metal, it is called a monobasic acid, such as nitric acid, HNO,, the hydrogen of which can be replaced by one atom of the monad metal potassium. If it contain two atoms of replaceable hydrogen, it is called dibasic, such as sulphuric acid, H2SO, the two atoms of hydrogen which it contains being replaceable by two atoms of a monad metal like potassium, or one atom of a dyad metal such as copper. Those bodies which contain more than one atom of replaceable hydrogen are called polybasic.

The terms monad, dyad, triad, tetrad, pentad, and hexad are used to denote the equivalents of the different elementary bodies in compounds as compared with hydrogen.

If we compare the equivalents of the elements in compounds with hydrogen, we find that they differ very much in value. Thus:

The monad potassium is equivalent to 1 atom of hydrogen in a compound.

2 atoms of

TABLE OF THE SYMBOLS, AND NEW AND OLD COMBINING OR
ATOMIC WEIGHTS OF THE ELEMENTS.

The above is a list of the elements at present known to chemists, with

Usually triad, sometimes pentad.

their symbols, and their new and old combining or atomic weights. As it would be inconvenient, in expressing chemical reactions in writing, to write the whole name of an element, the first or first two letters of the name are used as symbols to denote any particular element; thus O stands for oxygen, H for hydrogen, Co for cobalt. In the case of some metals, the first and prominent letters of the Latin name are used as symbols, as Ag for silver (argentum), Pb for lead (plumbum). The first two letters of the name of an element are used as its symbols when there is another element beginning with the same letter. Thus C is used as the symbol of carbon, and Ĉl is used for chlorine, in order to distinguish between the two. The symbol of an element when used by itself not only stands for that element, but also for a certain proportion thereof by weight, called its atomic weight; such proportion being the smallest proportion by weight in which such element combines with, or is eliminated from, a chemical compound, hydrogen being taken as unity.

Thus C does not stand merely for carbon, but also for exactly 12 parts by weight of carbon, or O stands for 16 parts of oxygen.

The small figure placed to the right hand of the symbol of an element signifies the number of atoms of that element. Thus C, means 4 atoms, or 4X 12 parts of carbon; O, means 2 atoms, or 2 × 16 parts of oxygen,

The symbols of compounds are made by placing the symbols of the elements forming the compounds side by side, as

Water
Sulphuric acid
Ammonia

H2O

H2SO.

H&N

When more than one molecule of a compound has to be denoted, a large figure is placed to the left hand of the formula of the compound, and all the symbols in the formula are multiplied by the large figure which stands before it; thus 2H2O means two molecules of water.

Chemical reactions are expressed by equations. The symbols of the elements before the change are placed on one side of the equation, and the symbols representing the change effected on the other, thus:

It is necessary to distinguish clearly between the terms atom and molecule. An atom means something which cannot be further subdivided. And thus, in the table of elements (p. 542) O stands for one atom of oxygen, H fer one atom of hydrogen. A molecule may contain more than one atom, as, for instance, H2: this would be called a molecule containing two atoms of hydrogen; H2O would be a molecule of water; and H2O, a molecule of peroxide of hydrogen or hydric peroxide, or oxygenated water. These expressions are most important, and prevent the confusion of the term "atomic" with that of "equivalent," because they are quite different from each other. A molecule is very properly defined by Roscoe to be "the group of atoms forming the smallest portion of a chemical substance, either simple or compound, which can exist in the free state." And he gives a good illustration of the difference between atomic and molecular formulæ in the following: H+ClHCl is the atomic expression, whilst H2+Cl,=2HCl is the molecular expression for the same reaction.

ELEMENTS WHICH ARE NOT METALLIC.

OXYGEN.

Symbol, O. Atomic weight, 16.

In the month of August, 1774, Dr. Priestly discovered this important element, and Mr. George Rodwell has very properly insisted, in a learned paper in the "Chemical News," that it was not discovered by Swedenborg half a century before Priestley, and that there is not a particle of reliable evidence in support of this statement. "We are quite unable,” says Mr. Rodwell, to comprehend by what contortion of the meaning of the principal passage quoted, Swedenborg can be supposed to allude to oxygen. 'Air,' he writes, "consists superficially of fifth finites, and within it are enclosed the first and second elementaries. And again: The fifth finites have entered into the surface of the aërial particle, and the first and second elementaries into the internal space.' There is no possible reason for assuming that by the meaningless term 'fifth finites' oxygen gas is alluded to; and if there were any evidence at first sight, it would be speedily nullified by the fact that Swedenborg afterwards speaks of crystals of this matter. It is useless to pursue

the subject further: the only evidence in support of the supposition is so utterly shallow that it is not worthy of criticism, for it carries with it its own refutation."

Dr. Priestley obtained the first oxygen produced from "red precipitate," (the red oxide of mercury) by heating it at a temperature of 752° F.-expressed in symbols, HgO-yield Hg+0.

Lavoisier, in his "Elements of Chemistry," says this "species of air" was discovered about the same time by Dr. Priestley, Mr. Scheele, and "myself.”

In a pamphlet published in 1800 by Priestley, after his return to America, he says, "Having made the discovery some time before I was in Paris in the year 1774, I mentioned it at the table of M. Lavoisier, when most of the phiÍosophical people in the city were present, saying it was a kind of air in which a candle burned much better than in common air, but I had not then given it any name. At this all the company, and M. and Madame Lavoisier as much as any, expressed great surprise. I told them I had gotten it from precipitate per se, also from red lead. Speaking French very imperfectly, and being little acquainted with the terms of chemistry, I said plomb rouge, which was not understood until M. Macquer said I must mean minium. Mr. Scheele's discovery was certainly independent of mine, though, I believe, not made quite so early."

Scheele obtained oxygen from one of the minerals of his own country as he happened to be investigating the nature of the ores of manganese.

Lavoisier, with the quickness of wit belonging to his countrymen, does not appear to have been slow in verifying Priestley's experiment, which was analytical. Great credit is due to Lavoisier for reversing Priestley's experiment, and making it synthetical: by subjecting a given quantity of air to the action of boiling quicksilver, he made that which Priestley decomposed-viz., red precipitate.