| Water | 9 |
| Nitrous oxide | 22 |
| Oxide of silver | 118 |
| Oxide of platinum | 104 |
| Potash | 48 |
| Oxide of chlorine | 44 |
| Oxide of mercury | 208 |
In these proportions, or in multiples of them, and in no others, will these bodies unite with the acids or other compounds. It will, of course, be understood that any other numbers may be adopted, provided they stand in the same relation to each other.[208]
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.
In addition to the laws already indicated, there appear to be some others of which, as yet, we have a less satisfactory knowledge, and, as a remarkable case, we may adduce the phenomena of substitution, or that power which an elementary body, under certain conditions, possesses, of turning out one of the elements of a compound, and of taking its place.[210] Thus, the hydrogen of a compound radical, as carburetted hydrogen, may be replaced by chlorine, equivalent for equivalent, and form a chloride of carbon, which being constructed on the same type as the original, will have the same general laws of combination.
Under the influence of these laws, all the combinations which we discover in nature take place. The metals, and oxygen, and sulphur, and phosphorus unite. The elements of the organic type, entering into the closest relations, give rise to every form of vegetable life. The acids, the gums, the resins, and the sugar which plants produce; and those yet more complicated animal substances, bone, muscle, blood, and bile; albumen, casein, milk, with those compounds which, under the influence of vital power, resolve themselves into substances which are essential to the existence, health, and beauty of the animal fabric, are all dependent on these laws. But these metamorphoses must be further considered in our examination of the more striking cases of chemical action. The changes which result from organic combination are so remarkable, and withal they show how completely the whole of the material world is in subjection to chemical force, and every variety of form the result of mysterious combination, that some particular reference to these metamorphoses is demanded.
In nearly all cases of decided chemical action, all trace of the characters of the combining bodies disappear. We say decided chemical action, because, although sulphuric acid and water combine, and salts dissolve in water, we may always recognize their presence, and therefore these and similar cases cannot be regarded as strict examples of the phenomena under consideration.
Hydrogen and oxygen, in combining, lose their gaseous forms, and are condensed into a liquid—water. Sulphuric acid is intensely sour and corrosive; potash is highly caustic; but united they form a salt which is neither: they appear to have destroyed the distinguishing characters of each other. Combined bodies frequently occupy less space than they did previously to combination, of which numerous particular instances might be adduced. Gases in many cases undergo a remarkable condensation when chemically combined. In slaking lime, the water becomes solid in the molecules of the hydrate of lime formed, and the intense heat produced arises from the liberation of that caloric which had been employed to keep the water liquid. When a solid passes into the liquid state, cold is produced by the abstraction from surrounding objects of the heat required to effect fluidity. An alteration of temperature occurs whenever chemical change takes place, as we have already shown, with a few trivial and uncertain exceptions. The disturbance caused by the exercise of the force of affinity frequently leads to the development of several physical powers.
Changes of colour commonly arise; indeed, there does not appear to be any relation between the colour of a compound and that of its elements. Iodine is of a deep iron-grey colour; its vapour is violet; yet it forms beautifully white salts with the alkalies, a splendid red salt with mercury, and a yellow one with lead. The salts of iron vary from white and yellow to green and dark brown. Those of copper, a red metal, are of a beautiful blue and green colour, and the anhydrous sulphate is white.