Page:Popular Science Monthly Volume 23.djvu/199

Rh often be found in the neighborhood of Hastings, derived from the wealden formation.

The curious so-called mineral beekite is really coral or shelly matter which has been replaced by silica. Researches into the behavior of the colloid form of silica, already spoken of, have shown how in many instances large deposits of silica, such as the flinty bands of the cretaceous formation, may have originated. Mr. Church's experiments, made some years since, proved that the minutest particle of carbonate of lime was sufficient to transform the pure aqueous solution of silica into the solid state in the course of a few minutes; and he was able, by the infiltration of silica in solution, to replace almost entirely the carbonate of lime in recent coral by silica, producing by this means what may be looked upon as a kind of artificial beekite. Thus in the slower, perhaps, but mighty chemistry of nature, marvelous reactions may have taken place, giving rise to some of the multitudinous forms in which silica presents itself to the mineralogical student.—Science-Gossip.



ARBONIC acid, the lung-poisoning residuum of respiration and combustion, is heavier than the atmospheric air, and accumulates in low places—in wells, in cellars, in deep, narrow valleys, etc.—and often mingles with the malarious exhalations of low, swampy plains. On very high mountains, on the other hand, the air becomes too rarefied to be breathed with impunity. It accelerates the respiratory process, as the amount of air inhaled at one inspiration does not contain oxygen enough to supply the wants of the organism at the ordinary rate of breathing, and is therefore especially distressing to diseased (wasted) lungs, whose functions are already abnormally quickened, and can not be further stimulated without overstraining their mechanism.

In the temperate zone, the purest and at the same time most respirable air is found at an elevation of about four thousand feet above the level of the sea, an altitude corresponding to the midway terraces of the European Alps and the average summit-regions of our Southern Alleghanies. The broad table-lands of the Cumberland Range are several hundred feet above the dust- and mosquito level. 