mineral waters. It is not, however, to be obtained in a simple state by any process, and the purest is in that of carbonic acid gas, which was formerly known by the names of fixed and fixable air, from its uniting with chalk, lime, magnesia, &c. in a solid form. It was also called mephitic (or poisonous) air, from its destroying life when inspired into the lungs; and was long known to miners under the name of choak-damp.

Carbonic acid, united with the alkalies, lime, magnesia, and some other of the earths, reduces them to the state of carbonats, neutralises them, and deprives them of their caustic (or burning) properties. I shall have to add more upon this subject under the class of Acids.

With the other simple combustibles, and some other bodies, carbon unites, forming carburets.

VIII. Of the MURIATIC radical little is to be said, because it never has been found in an uncombined state. It has not been yet obtained even in the gaseous state uncombined with oxygen, so strong is its attraction for that substance. In that form, however, the muriatic acid is to be procured, and is termed muriatic acid gas.

Muriatic acid and black oxide of manganese being heated, a gas is evolved, in which combustible bodies burn with splendour, as in oxygen, and with which they also form binary compounds:

some of these possessing acid properties. This gas is named CHLORINE, and used to be termed Dephlogisticated Muriatic or Oxymuriatic Acid, being supposed to be a combination of oxygen with muriatic acid. This gas being mixed with an equal quantity of hydrogen gas a sour compound is formed, commonly called muriatic acid gas, but which is really a hydrochloric acid gas.

The muriatic or chloric acid is the basis of common salt, hence called muriat of soda. It also combines with potass, ammonia, and many of the earths and metals, forming muriats or chlorats.

IODINE is another of the acidifying principles. It is obtained by adding sulphuric acid to a solution of Kelp, and exposing it to heat, when the iodine rises in purple fumes which condense in opaque crystals, with a metallic lustre. By the action of chlorine on iodine the chloriodic acid is formed.

IX. The ALKALIES are properly only two, but are generally treated as being three in number. Two of them, potass and soda, are termed the fixed alkalies; because they do not rise or become volatile by heat: the third, ammonia, is called the volatile alkali, for the opposite

reason.

Potass, the hydrate of Potassa, was formerly called the vegetable alkali, because it was obtained from the ashes of land vegetables, and was never found in a mineral state. Soda was

called the mineral alkali, because it was found in some mines, especially in Egypt. That which is used in commerce is obtained from the ashes of certain marine plants, and is known in commerce under the name of barilla.

These two have been very lately decomposed by Professor Davy, and are found to be the hydrated oxides of peculiar metals, the nature of which is, however, as yet but very little known; and they may (as to the metallic bases at least) be still classed among simple substances. The third, ammonia, has been long ascertained to be a compound of nitrogen and hydrogen; an account of it will therefore come properly under the class of Alkaline Salts, when some further observations will be introduced on the fixed alkalies.

X. XI. The earths and metals will require distinct lectures; and being substances of a peculiar character, and not entering so copiously into the composition of those bodies which are found on the surface of the earth as those I have been describing, any observations on their nature or combinations would be foreign to the object of this lecture.

I have thus endeavoured to lay before you a general outline of the doctrines of modern chemistry. I fear this lecture will appear uninteresting to many of you.-It is, however, of so much importance that, if it is well understood, it will greatly facilitate the study of all

the remaining branches of this science. What follows will be rather a comment upon or an elucidation of the contents of this lecture, and an application of its principles to practical purposes. I must therefore recommend your particular attention to it.

LECTURE XXVI.

CHEMISTRY.

THE CHEMICAL EFFECTS OF CALORIC; EXPANSION, FUSION, FLUIDITY, VAPOUR, AND COMBUSTION.

It was necessary in the last lecture to give a general view of the properties of caloric. I fear I shall be thought in the present to be guilty of something like repetition; but it is necessary to the understanding of the effects of caloric as an agent in chemistry, to call your attention at present to the subject rather more in detail.

1st. The presence of caloric EXPANDS all-bodies.

There are three forms under which matter can appear.

The first comprehends solid bodies, as iron, &c. ; the second, unelastic or incompressible fluid bodies, as water, oil, spirit of wine, &c.; the third, elastic compressible fluids, as air. I shall now show the effects of caloric in expanding all these. If an iron or brass wire of about a quarter of an inch in thickness is cut so as when cold to fall just withinside, or short of two rings made to receive it, by rubbing it very hard with your hands or a piece of cloth it will be made warm; it will consequently be expanded, and lengthened