Boyle then proceeds to collect and comment on the effluvia from volcanoes and from decaying vegetables and animals, and proposes tests for the presence of such ingredients. He even attributes the darkening of silver chloride to its being a reagent for certain salts present in air at one time and not at another, and draws attention to the sulphurous smell produced by “thunder.” Farther on (p. 61) he writes:
“The generality of men are so accustomed to judge of things by their senses, that because the air is invisible they ascribe but little to it, and think it but one remove from nothing. And this fluid is even by the Schoolmen considered only as a receptacle of visible bodies, without exerting any action on them unless by its manifest qualities, heat and moisture; tho’, for my part, I allow it other faculties, and among them, such as are generative, maturative, and corruptive; and that, too, in respect not only of animals and bodies of a light texture, but even of salts and minerals.”
In another place (p. 17) he states:
“I conjecture that the atmospherical air consists of three different kinds of corpuscles: the first, those numberless particles which, in the form of vapours or dry exhalations, ascend from the earth, water, minerals, vegetables, animals, etc.; in a word, whatever substances are elevated by the celestial or subterraneal heat, and thence diffused into the atmosphere. The second may be yet more subtile, and consist of those exceedingly minute atoms the magnetical effluvia of the earth, with other innumerable particles sent out from the bodies of the celestial luminaries, and causing, by their impulse, the idea of light in us. The third sort is its characteristic and essential property, I mean permanently elastic parts.”
Boyle also relates experiments designed to “produce what appears to be air”; and he describes the production, by the action of oil-of-vitriol on steel filings, of “air” (now known as hydrogen) which possessed the property of elasticity; although he failed to notice its inflammability. He further obtained carbon dioxide by the fermentation of raisins, and probably also hydrogen chloride in the gaseous form by breaking a bulb containing “some good spirit-of-salt” in a vacuous receiver.
The result of shrewd reasoning power, applied, however, to imperfect observations, is well illustrated by the following passages:
“For tho’, by reason of its great thinness and of its being, in its usual state, devoid both of taste and smell, air seems wholly unfit to be a menstruum [or solvent]; yet it may have a dissolving, or at least a consuming, power on many bodies, especially such as are peculiarly disposed to admit its operations. For the air has a great advantage by the vast quantity of it that may come to work, in proportion to the bodies exposed thereto.... Thus we find a rust on copper that has been long exposed to the air.”[2]
Boyle, shortly after, describes the production of “an efflorescence of a vitriolic nature” on marcasite (or sulphide of iron) which has been exposed to the air; and he relates that the “ore of alum, robb’d of its salt, will in tract of time recover it by being exposed to the air, as we are assured by the experienced Agricola.”
To account for such actions, and for combustion, he proceeds (p. 81):
“The difficulty we find in keeping flame and fire alive, tho’ but for a little time, without air, renders it suspicious that there may be dispersed thro’ the rest of the atmosphere some odd substance, either of a solar, astral, or other foreign nature; on account whereof the air is so necessary to the subsistance of flame.... It also seems by the sudden wasting or spoiling of this fine substance, whatever it be, that the bulk of it is but very small in proportion to the air it impregnates with its vertue; for after the extinction of the flame, the air in the receiver was not visibly alter’d; and for ought I could perceive by several ways of judging, the air retained either all, or at least the far greatest part, of its elasticity; which I take to be its most genuine and distinguishing property. And this undestroyed springyness of the air, with the necessity of fresh air to the life of hot animals, suggest a great suspicion of some vital substance, if I may so call it, diffused thro’ the air; whether it be a volatile nitre, or rather some anonymous substance, sidereal or subterraneal; tho’ not improbably of kin to that which seems so necessary to the maintenance of the other flames.”