We are not ignorant of the recent attempts to e certain mechanical theories, concerning the mutual re lation of fluids. Water, it is alleged, imbibes alwa) s its own bulk of every kind of gas ; and, when converted into vapour, it spreads through the air, or other gase ous mass, passively, filling up the vacuities, and oc cupying exactly the same space, vellich it would leave done, if the medium of its expansion had been entirely removed. But these assertions Al ill be found to be grounded on vague experiments, and supported only by very crude and unphilosophical Ieasouings. We de cline entering on the consideration of the question at present, but propose to give it a thorough discussion in some future article.
About the year 1746, M. Dalihard, (:rem. des -vans Etrangers, i. p. 212, et seq.) at the request of the comte de Buffon, made sonic curious obseevations uu the variable weight of a piece of wood, which was kept plunged under water. It was discovered, when taken out, and its surface w iped, to be SOIllell hat bean k r or lighter, according to the state of the atmosphere, es pecially in regard to temperature. Similar results v ere obtained from horn; marble and other granular stones. All those substances, being kept immersed in water, were found to gain uniformly more weight in winter than during the months of summer; and, in general, to absorb the fluid more copiously in cold than in hot weather. But when the cold became intense, a singu lar anomaly took place. The dilatation, which always accompanies the act of freezing, communicates a mu tual repulsive force to the particles of water, that seems, in a certain degree, to overcome the opposite attraction of the hygroscopic substances. A piece of wood suffered a sudden and very material diminution of weight, when the surrounding liquid was converted into solid ice. A mass of copper, penetrated by sub mersion in mercury, is liable also to very sensible varia tion of weight, according to the temperature in which it is exposed—being always heavier when cold, and lighter when subjected to heat. These remarkable facts
throw new light on the nature and modifications of che mical affinity. But the subject would require a nicer and more elaborate investigation.
On the faculty of the different earths to abstract moisture from the air, professor Leslie has given us a very interesting sketch in Nicholson's Journal for the year 1800. By help of that delicate instrument—his hygrometer—he found, that earthy substances, after being intensely dried, showed a remarkable disposition to attract moisture again, and to desiccate the air in which they are included ; not inferior, indeed, to that possessed by sulphuric acid and the most deliquescent salts. The several primitive earths exhibit that ab sorbent power in v cry different degrees ; silica having the smallest energy, and alumina the greatest. The effects are much augmented, in a higher temperature. Of the compound bodies, basalt has, in every state, the strongest attraction for humidity. This fact perfectly agrees with the known property, that basalt, or whin stone, by its decomposition, forms the most fertile soil ; for garden, or vegetable, mould showed the most ener getic absorption. Hence, perhaps, a method is furnish ed, much easier, and more satisfactory, than any che mical analysis, for ascertaining the relative values of different soils. We trust, that a subject so novel will not he suffered to rest, but will Le pursued with that ardour which its importance demands. 'We shall have occasion, in the subsequent parts of our work, to treat of chemical absorption with inure detail. See At .1 iui (lie mica! ; CAPILLARY 3Cti9// ; EAR1 HS .3689rb.. rta ; 8ublitancrx ; and Solis. (y)