Potassa consists of 39.2 parts potassium in union with 8 oxygen, it constitutes about 12 per cent. of the granites and basalts (primitive rocks) in union with silica and alumina, it is also found in the fluids of many vegetables in union with carbonic, oxalic, and other acids.
Soda consists of twenty-three parts sodium with eight oxygen, it however does not exist in this form in nature, but in union with chlorine instead of oxygen, constituting chloride of sodium or common salt, this substance forms strata of considerable extent in some localities and being soluble has no doubt been washed out by the rains from many other places and has thus communicated saltness to the waters of the ocean. The other metallic elements exist chiefly in those forms of earth called "ores" being metals in union with oxygen, sulphur, &c., or are found in the metallic state, as gold, platinum, &c., it is from these ores that most of our useful metals are procured by the process called smelting, as in the case of iron, copper, lead, tin, &c. All the substances known result from the combinations of the elements, but these elements do not chemically combine in all proportions, but in certain definite quantities only; these quantities or proportions are signified by the numbers attached to each element in the list given,[1] and the union of these substances must be in the proportion of these numbers (or multiples of them) only, all superfluity of the substances combined remaining in a state of mere mechanical mixture. For example, if six parts of carbon (charcoal) made red-hot be plunged into a jar containing twenty parts of oxygen, it will unite with sixteen parts only of the oxygen (a multiple of eight), and form twenty-two parts of carbonic acid, the extra four parts of oxygen still remaining as oxygen mixed with the carbonic acid; and if into this carbonic acid twenty parts of lime be put, it will unite with the twenty-two of carbonic acid, forming forty-two of carbonate of lime, still leaving the four parts of oxygen untouched. Had forty parts of lime been put into the mixture, instead of twenty, still only forty-two of carbonate of lime would have been formed, and the other twenty parts (like the four of oxygen) being superfluous, would still have remained as lime, mixed with the carbonate of lime. These combining quantities are called the "equivalents" of the substances.
[1] See the list of the elements at [page 45]; those which are distinguished by an asterisk, are elements of which the "equivalents" are not known.
Upon examining various portions of the earth's surface, they will be found to differ in character from each other; in one place perhaps sandy soil will be found, in another, hard rock, in a third, clay, in a fourth, chalk, and so on. Now, if this examination were carried no further, it might well be presumed that each of these kinds of soil were continued downwards into the earth for an indefinite distance, but upon digging (as in sinking a shaft or well) it is found that the stratum of soil upon the surface is soon passed through, that others in succession present themselves and that this succession of strata is not a matter of chance, but (with certain restrictions) follows in invariable order. It is true some strata are occasionally not present, and that others replace them; but yet (taken altogether) there is the same order of succession everywhere found. The following diagram (fig. 1) gives the section of these strata from the earth's surface to the granite which is the lowest of all formations and through which no one has ever penetrated. The figures give an approximation to their average thickness in feet. These strata do not all run in a direction parallel to the surface of the earth, or else it would result that the surface would everywhere be made up of the highest, but they have been contorted and heaved up into mounds or depressed; and the granite has often been pushed upwards, carrying with it all the upper strata to a certain extent, at last thrusting quite through them all and presenting itself above the surface, forming in this way the tops of many very high mountains, Mont Blanc for instance. Such a mountain if cleft from the summit to the base would present a section similar to that shown in fig. 2, and thus it occurs (contrary to what would at first thought be supposed) that the highest ground is generally formed of the lowest strata, while the valleys are nearly always covered with the latest formations, which is partly owing to the elevating process before alluded to, and partly to the winds, rains, &c., tending to carry away and wash down every kind of soil from the upper ground and deposit it in the lower.
FIG. 1.—DIAGRAM SHOWING THE POSITIONS AND RELATIVE THICKNESSES OF THE STRATA.
FIG. 2.