Mr. Faraday has proved that the specific electricity of different substances is also in proportion to their atomic weights, that is to say, a given quantity of electricity will separate combined substances into parts represented by their atomic weights. For example, 32·5 parts of zinc will generate voltaic electricity enough to separate nine parts of water into eight parts of oxygen and one part of hydrogen gas. The weights thus derived from decomposition are exactly the same with those determined by composition, and thus the atomic weights derived from electro-decomposition accord exactly with those obtained from chemical composition. Moreover, Mr. Faraday, as already mentioned, proved that the very same quantity of electricity necessary to decompose a body into its elementary atoms, is requisite to unite them again. The analysis and synthesis of compound matter, solid or fluid, show a constant and definite proportion of the component elements expressed by number, and by an equivalent or multiple ratio of parts in every chemical change. The atomic theory unites, by a common bond, specific gravity, chemical affinity, heat, and electricity. Taking atmospheric air at the temperature of 60° Fahr. and a barometric pressure at 30 inches as the standard unit of specific gravity; the quantity of heat required to raise a volume of water 1° Fahr. as the unit of specific heat; hydrogen gas as the unit of atomic weight; and atomic electro-chemical electricity as the unit of specific electricity, the following numbers have been established: +----------+----------+------------+----------+-------------+ | | Specific | Equivalent | Specific | Specific | | | gravity | atomic | heat | electricity | | | | weight | | | +----------+----------+------------+----------+-------------+ | Hydrogen | 0·0693 | 1 | 0·2936 | 1000 | | Oxygen | 1·111 | 8 | 0·2361 | 125 | | Carbon | 13·2 | 6 | 0·2631 | | | Nitrogen | 0·978 | 14 | 0·2750 | | +----------+----------+------------+----------+-------------+ The distances between the atoms of the gases are equal, hence the atomic weights of simple gases are proportional to their densities; and for the same reason, equal volumes of the same fluid contain an equal number of atoms, and the number of atoms in the same volume of different fluids is in the simple ratio of one to one, one to two, one to three, &c.