ABSORPTION, in Chemistry, is the most bodies possess, of drawing into their substance and assimilating others of a different constitution. Thus stones, wood, and animal fibre, arc variously dis posed to imbibe and retain moisture ; and thus water has the faculty to incorporate with itself air and other elastic fluids. It is in this way, that gases become uni ted to liquids, and that both eases and liquids are swal lowed up and lost in the interior composition of solids.
In all such cases, a real chemical force is exerted, en trely distinct hmit the power employed in producing mere capillary ascent. Absorption is constantly at tended by change 01 temperatut e and alteration of s () lumen the circumstances which unequivocally mark a new combination. When a splinge draws up water into its tabulated structure, it acts only by the ap proximation of its numerous internal surfaces. The result is a mechanical compound, and both the spunge and the water, quite independent of each other, pre serve their peculiar character. If a solid body he re duced to minute contiguous fragments, it will like wise admit the penetration of a liquid, which insinu ates itself along the winding interstices. In this way, sand is capable of being wetted. But, when paper is soaked in water, a very different process obtains; the particles of the fluid, attracted into the substance oldie; paper, occasion a general distention, with a sensible cu:trication of heat ; the paper, in consequence, be comes denser, and partakes in some degree of the soft ness and transparency of the water, to is licit it is now so intimately united. The water must therefore, in its combination with paper, exist in a concentrated state. The same thing takes place in the union of the gases with liquid or solid substances. That portion of air, for instance, which is lodged in charcoal, appears to be highly condensed : it is only disengaged from its basis by the application of water, to which the charcoal shows a superior affinity. The singular properties of the by drophanous opal are owing to a similar cause.
To consider solution as essential to chemical union, is, therefore, to overlook the economy of nature. The
combination of bodies take a much wider range. 'When a liquid joins with a gaseous substance, or solid matter unites to liquid, the opposite ingredients may enter into the composition in every possible proportion. The re ciprocal action of copper and mercury will serve as an example : the copper first absorbs the globules of mer cury into its mass; and, retaining its solidity, it only becomes brighter and more brittle:. By degrees, it softens, and passes into the state of an amalgam. And as the proportion of the mercury farther increases, the resulting. compound begins to assnme the character of a liquid, and continually approaches to the fluidity of mercury itself. In this instance, we trace a continuous chain of character, extending from the one ingredient to the other. It often happens, howeeer, that the inter mediate links are less apparent. But, in every cas' , the extreme limits of combination, on either side, de serve to fix attention ; and we may state it as a principle, that, whenever a solid has a close attraction to a fluid substance, two opposite products will result from their union, the one presere ing the form and con sistence of the solid, and the other again retaining more obvious qualities of the fluid. In the olif! the character of solidity predominates ; in the other, that of fluidity maintains the ascendency. If a given steno be shown to absorb moisture, we may stifely draw tile inverse conclusion, that water. in its turn, is capable of dissolving the stony matter. The attraction of the water may yet be too feeble to overcome the mutual co hesion of the particles of the stone ; but when the dis integration is efft•cted by other means, the assimilating powers of the fluid will act with full effect. Such a process has the most extensive operation, and its diffuse energy may very often elude the ordinary and imperfect modes of chemical analysis. This view of the subject is evidently favourable to the Neptunian, or aqueous, hypothesis of the formation of rocks.