From the discovery of these harmonious arrangements was deduced the beautiful atomic theory to which allusion has been already made. Indeed, there does not appear to be any other way of explaining these phenomena than by the hypothesis that the ultimate atoms of bodies have _relatively_ the weights which we arbitrarily assign to them, as their combining quantities. These views are further confirmed by the fact, that gaseous bodies unite together by volume in very simple definite proportions:--100 measures of hydrogen and 200 measures of oxygen form water; 100 measures of oxygen and 100 measures of vapour of sulphur form sulphurous acid gas. Ammoniacal gas consists of 300 volumes of hydrogen and 100 volumes of nitrogen, condensed by combination into 200 volumes; consequently, we are enabled most readily to calculate the specific gravity of ammoniacal gas. The specific gravity of nitrogen is 0·9722, that of hydrogen 0·0694. Now, three volumes of hydrogen are equal to 0·2082: this added to 0·9722 is equal to 1·1804, which is exactly the specific gravity obtained by experiment. There is no doubt, from the generality with which this law of volumes prevails, that it would be found to extend through all substances, provided they could be rendered gaseous; in other words, there is abundant proof to convince us that throughout nature the process of combination, in the most simple ratio of volumes, is in operation to produce all the forms of matter known to us. It has been shown, by the investigations of Dr. Dalton, in 1840, that salts, containing water of crystallization, dissolve in water without increasing the bulk of the fluid more than is due to the liquefaction of the water which these salts contain; while Joule and Playfair have shown that the anhydrous salts take up no space in solution. From this we are naturally led to conclude that the volume occupied by a salt in the solid state has a certain relation to the volume of the same salt when in solution, and has also a fixed relation to the volume occupied by any other salt. The law appears to be:--the atomic volume of any salt whatever (anhydrous or hydrated) is a multiple of 11, or of a number near 11, or a multiple of 9·8 (the atomic volume of ice), or the sum of a multiple of 11 or 9·8. Marignac, who has also paid much attention to the subject, does not think these numbers absolutely correct, but approximately so.[209] It would be a beautiful exemplification of the simplicity of Nature’s operations, if it should be clearly proved that the atomic volume of solid water (ice) regulated the combining proportions by volume of all other bodies,--that it was the standard by which chemical combination and ordinary solution were determined.