It has been already observed, that by throwing caloric into a solid body, or, in other words, heating it, the force of the attraction of cohesion, which preserved it in the solid state, is gradually weakened, and finally overcome. When the particles of a body which, at a low temperature, were immovable relatively to each other, are separated by interposed caloric, so as to move easily upon one another, but are yet within the limits of the sphere of the attraction of aggregation, the body is denominated a liquid, provided it remain in this state under the medium temperature of the atmosphere. Thus Ice, when brought into a place, the temperature of which exceeds 32°, loses its solidity and becomes a liquid, or water, which form it retains in every degree of temperature between 32° and 212° on the scale of Fahrenheit's thermometer. Let us now examine the constitution of liquids, their combinations with other liquids, and their combinations with solids.

1 Vauquelin. 2 Berzelius.

1. Of The Constitution Of Liquids

Liquids, as we have explained, are compounds of caloric with a solid base. Their parts move easily upon one another, and yield to the smallest impression; but they are not sensibly elastic The greater or smaller degree of liquidity of different substances depends upon a difference of the force of cohesion exerted between their particles, which may be regarded as placed in the limit between attraction and repulsion : thus the cohesion of mercury is greater than that of water. Liquids differ very much in specific gravity; and the degree of this bears a relation to their density. "The distances of the atoms are so regulated, that the attraction and repulsion by which they are at once actuated just balance one another; while their form, which is supposed to be spherical, is such, that they can move freely along each other without altering these distances. It is this which seems to constitute the real cause of liquidity."

All liquids may be arranged into two great classes. The following Table exhibits a list of almost the whole of them, arranged according to their composition:-

I. Simple

II. Compound. A. Simple Gases Combined

If mercury and bromine be excepted, all the known liquids are compounds, and the greater number of them contain water as an ingredient.

Water. The ordinary appearances and properties of this liquid are too well known to require description. Its maximum of density is at the temperature of 36°. A cubic foot of it, at 30 inches of the barometer, and 55° of the thermometer, weighs 998.74 avoirdupoise ounces of 437.5 grains troy each. Its specific gravity is supposedr =1.000, and it is made the standard of unity in the measurement of that of every other liquid. The gravity of ice is less than that of liquid water. It conducts heat slowly, conducts electricity imperfectly, and is a powerful refractor of light. In the form of steam, under a pressure of 28 inches of mercury, water occupies 1800 times the space which it does in the form of water. It is not decomposed by heat alone; nor altered by light: but it is decomposed by iron, zinc, antimony, and tin, when assisted by heat. It readily absorbs air and gases 1, and is a constituent of all gases. It is a compound of oxygen and hydrogen, 100 grains containing 88.9 of oxygen, and 11.1 of hydrogen2: or its constitution may be thus stated:-

It liquefies a great number of solid bodies, its solvent power being increased by diminishing the pressure of the atmosphere; and, as has been already stated, the greater number of liquids contain it as an ingredient. It is also present in some compounds, in fixed definite proportions, forming hydrates.

1 From Mr. Dalton's experiments, it appears that water absorbs its own bulk of carbonic acid gas, of sulphureted hydrogen gas, and of nitrous oxide; 1/27 of oxygen gas, nitrous gas, and carbureted hydrogen; and 1/8 of carbonic oxide, azotic gas, and hydrogen gas. 2 Biot and Arago.