Chemistry : general, medical, and pharmaceutical including the chemistry of the ; a manual on the general principles of the science, and their applications in medicine and pharmacy . w,they must be considered to stand for a compound of the elements,that is to say, hydrochloric acid gas (HC1). The collection of sym-bols representing a molecule is termed & formula. H2, Cl2, and HC1are the formulas of hydrogen, chlorine, and hydrochloric acid gas. H2 + Cl2 == 2HC1. Such a set of letters, figures, and marks as that on the above lineis collectively termed an equation, because it in
Chemistry : general, medical, and pharmaceutical including the chemistry of the ; a manual on the general principles of the science, and their applications in medicine and pharmacy . w,they must be considered to stand for a compound of the elements,that is to say, hydrochloric acid gas (HC1). The collection of sym-bols representing a molecule is termed & formula. H2, Cl2, and HC1are the formulas of hydrogen, chlorine, and hydrochloric acid gas. H2 + Cl2 == 2HC1. Such a set of letters, figures, and marks as that on the above lineis collectively termed an equation, because it indicates the equalityof the number and nature of the atoms before and after chemicalaction. On the left hand of the sign of equality are shown twomolecules, and on the right hand two molecules; but, of the mole-cules on the left, one contains two atoms of hydrogen and the other 4* 42 GENERAL PRINCIPLES OF two atoms of chlorine, while of the molecules on the right each con-tains one atom of hydrogen and one of chlorine. The equation formsa short and convenient plan of recording the facts of experiment. Instead of an equation, a diagram maybe employed to exhibit thesame facts. Thus :— ~HC1. n (C1 ^2 J CI- Z^^HCl PHYSICAL AND CHEMICAL CONSTITUTION OF MATTER. Kelatioxs of Gases. Liquids, and Solids. The molecules of a gas are not close together, for a quantity ofgas may be compressed with very little force to half or one-fourthits bulk—in short, to such an extent that in many cases the moleculessufficiently approximate to form a liquid. In a liquid the moleculesare still free to glide about with ease amongst each other ; and thoughin solids they exhibit less mobility, still even solids may be compressedby powerful pressure, so that probably in no instance are moleculesin absolute contact. (Moreover, from the researches of Caignard dela Tour and, recently, of Andrews, there would seem to be no sharplines of demarcation between the gaseous, liquid, and solid conditionsof substance
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