“The air is very instrumental in the production and growth of animals and vegetables, both by invigorating their several juices while in an elastick active state, and also by greatly contributing in a fix’d state to the union and firm connection of several constituent parts of those bodies, viz. their water, salt, sulphur, and earth. This band of union, in conjunction with the external air, is also a very powerful agent in the dissolution and corruption of the same bodies; for it makes one in every fermenting mixture; the action and re-action of the aerial and sulphureous particles is, in many fermenting mixtures, so great as to excite a burning heat, and in others a sudden flame; and it is, we see, by the like action and re-action of the same principles, in fuel and the ambient air, that common culinary fires are produced and maintained.
“Tho’ the force of its elasticity is so great as to be able to bear a prodigious pressure, without losing that elasticity, yet we have, from the foregoing Experiments, evident proof that its elasticity is easily, and in great abundance destroyed; and is thereby reduced to a fixt state by the strong attraction of the acid sulphureous particles which arise either from fire or from fermentation; and therefore elasticity is not an essential immutable property of air-particles; but they are, we see, easily changed from an elastick to a fixt state, by the strong attraction of the acid, sulphureous, and saline particles which abound in air. Whence it is reasonable to conclude that our atmosphere is a Chaos, consisting not only of elastick, but also of unelastick air-particles, which in plenty float in it, as well as the sulphureous, saline, watery, and earthy particles, which are no ways capable of being thrown off into a permanently elastick state, like those particles which constitute true permanent air. Since, then, air is found so manifestly to abound in almost all natural bodies; since we find it so operative and active a principle in every chymical operation; since its constituent parts are of so durable a nature, that the most violent action of fire or fermentation cannot induce such an alteration of its texture as thereby to disqualify it from resuming, either by the means of fire or fermentation, its former elastick state; unless in the case of vitrification, when, with the vegetable Salt and Nitre in which it is incorporated, it may, perhaps, some of it, with other chymical principles, be immutably fixt—since then this is the case, may we not with good reason adopt this now fixt, now volatile Proteus among the chymical principles, and that a very active one, as well as acid sulphur; notwithstanding it has hitherto been overlooked and rejected by chymists, as no way intitled to that denomination?”
This quotation shows us how little Mayow’s shrewd reasoning and well-devised experiments had impressed the thinkers of his age. While Hales quotes frequently from Boyle’s and Newton’s works, his reference to Mayow is meagre; nor does he adopt any one of Mayow’s conclusions. One would have thought that, having prepared so many gases by means of apparatus well adapted to their purpose, and having observed that certain substances introduced into air produced contraction, he would have drawn the conclusion that such “airs” were essentially different kinds of matter. But the “Proteus” was too much for him; and he left the subject practically in the same state of “Chaos” in which he found it.
CHAPTER II
“FIXED AIR” AND “MEPHITIC AIR”—THEIR DISCOVERY BY
BLACK AND BY RUTHERFORD
Before relating the history of the discoveries of Black, Rutherford, and Priestley, it will be appropriate to give an account of a theory which professed to explain the phenomena of combustion, and with it the conversion of metals into calces, and the reduction of these calces to the reguline or metallic state. Like other theories, it was slow in developing. Its germ is to be traced to the writings of Johann Baptist van Helmont of Brabant, Seigneur of Merode, Royenboch, Oorshot, and Pellines, who was born in Brussels in 1577. He adopted a fantastical creation of Paracelsus, the archaeus, a kind of demon which, by means of fermentation, draws together all the particles of matter. Believing that water was the true principle and origin of everything (for he had succeeded in producing a willow tree, weighing 164 lbs., from water alone, the earth in which it grew having neither gained nor lost appreciably in weight), he conceived that it was acted on by a ferment or principle pre-existing in the seed developed by it, and exhaling an odour by which the archaeus was attracted. Water undergoing the action of this ferment developed a vapour, to which van Helmont gave the name of “gas.” A “gas” was a substance intermediate between spirit and matter, and the word was probably derived from Geist, the common German word for spirit. Another word introduced by him to denote the life-principle of the stars was Blas, connected probably with blasen, to blow, and our English word blast.
It is curious to notice how the idea of an archaeus survived down to later times under the name of a “life-principle”—a conception that all organic substances must necessarily owe their origin to life itself, and not to the usual chemical and physical transformations.
Van Helmont was acquainted with various kinds of gases, as appears from his treatise “De Flatibus.” His gas sylvestre was evolved from fermenting liquors, and he knew that it was formed during the combustion of charcoal, and also that it was present in the Grotto del Cane near Naples. He was likewise acquainted with combustible gases, which he named gas pingue, gas siccum, or gas fuliginosum.
These principles of van Helmont’s apparently suggested to his successors, Becher and Stahl, the notion of a principle inherent in every combustible substance, which was lost during combustion. The development of this—the phlogistic—theory is almost wholly due to the latter chemist, and indeed it is difficult to trace Becher’s share in it.
George Ernest Stahl was born at Anspach in 1660; he studied and graduated in medicine at Halle, and in 1694 he was appointed second professor of medicine at that University, where he continued to teach for twenty-two years. His most important work was his Fundamenta chymiae dogmaticae et experimentale. His theoretical views are contained in the last part of this work. He there treats of zymotechnia, or fermentation; halotechnia, or the production of salts; and pyrotechnia, or the doctrine of combustion. It is the last of these sections which gives an account of the doctrine of phlogiston.
The fundamental conception of this doctrine is that all combustible bodies are compounds. During combustion one of these constituents, common to all, was dissipated and escaped, while the other, sometimes an acid, sometimes an earthy powder or calx, remained behind. Thus sulphur and phosphorus, when burnt, give acids; and the metals form calces. Non-combustible substances, such as lime, were imagined to be calces, and it was supposed that if phlogiston were restored to them, they too would be converted into metals. This combustible principle was thought to be inherent in all combustible bodies whatsoever; it corresponds in kind with the “sulphur” of more ancient writers, but differs from the latter inasmuch as no very precise ideas were entertained of the identity of the “sulphur” which conferred on the substances containing it as a constituent, or possessing it as a property, their power of combustion. It was also made more definite by Stahl that substances capable of burning or conversion into calces are compounds containing phlogiston in combination with other substances.
Stahl can hardly be credited with more than the invention of the term “phlogiston,” and with bringing the subject