HISTORY OF CHEMISTRY: Sir Isaac Newton (1642-1727). Stephen Hales (1677-1761). Joseph Black (1728-99).

Early in the 18th century Newton in his Opticks indicated the nature and the modes of formation of gases. "Dense bodies," he tells us, "by fermentation rarely into several sorts of air; and this air by fermentation, and sometimes without it, returns into dense bodies;" and further on he remarks that the particles shaken off from bodies by heat or fermentation, so soon as they are beyond the reach of the attraction of the body, recede from it, and also from one another with great strength, so as sometimes to take up above a million of times more space than they did before in the form of a dense body. This vast contraction and expansion seem to him unintelligible by feigning the particles of air to be springry and ramous, or rolled up like hoops, or by any other means than a repulsive poweer; the particles of fluids which do not cohere strongly are most easily rarefied into vapour; but those which are grosser, or cohere by a stronger attraction, are not separated without a stronger heat, or perhaps not without fermentation; being rarefied by fermentation they become true permanent air, those particles receding from one another with the greatest force, and being most difficulty brought together, which upon contact adhere most firmly. -- (Opticks, bk. Iii. qu. 30 and 31, 1730.)

In 1727 Dr Stephen Hales (1677-1761), who had for some years been engaged in investigations similar to those of Mayow, gave to the world in his Statical Essays the collective results of his observations. The atmosphere he describes in this work as a fine elastic fluid, with particles of very different natures floating in it, whereby it is fitted to be the breath of life of vegetables as well as of animals. The effect of respiration and of the burning of sulphur in air is to deprive it of its elasticity; and country air is cleaner and more elastic than that of towns. Elasticity, we read, is not an essential immutable property of air particles; "they are easily changed from an elastic to a particles; "they are easily changed form an elastic to a fixed state by the strong attraction of the acid, sulphureous,a and saline particles, which abound in the air. Whence it is reasonable to conclude that our atmosphere is a chaos, consisting not only of elastic, but also of unelastic air particles, which in great plenty float in it." – (Stat. Ess., vol. i. 4th ed., 1769) Hales did not, however, attempt to determine the distinctive properties of the various gaseous constituents of the atmosphere, and of the substances on which he experimented; all are indiscriminately designated "air." It is air that is generated by fermentation, and that contributes to the briskness of Pyrmont and other mineral waters; 108 cubic inches of air are procured from a cubic inch of iron filings and the same quantity of oil of vitriol; and 33 cubic inches of air are the result of distilling a cubic inch of dog’s blood. Hales determined also the volume of air to be obtained by distilling certain quantities of amber, chalk, coal, grey pyrites, aqua-fortis, antimony, tobacco, and other materials, but apparently with no other end in view than the establishment of the fact that air is contained in a great number of substances. He had learned to interrogate, but not cross-examine nature.

The first important step towards a knowledge of the specific properties of the various gaseous bodies was that made in the middle of the various gaseous bodies was that made in middle of the 18th century by Dr. Black, who experimentally proved that the causticity acquired on iguition by mild magnesia and lime was attributable not to the entrance into them of ponderable caloric, but to the expulsion of a peculiar kind of air, which occurred fixed, or in a state of combination, in the unburnt or mild earths, and caused them to be heavier before than after exposure to heat. He found it possible, in facts, to impart to these substances a large amount of heat, which became latent, whilst at the same time their weight was lessened by the loss of "fixed air" (carbon dioxide). It was discovered by Black that alkalies in contact with quicklime became caustic by giving up their fixed air to the lime, which was thereby increased in weight and rendered mild. It was thus, by employing the balance as an experimental test of the composition of bodies, that Black laid the foundation of quantitative chemistry, and in so doing gave the first occasion to the strife that twenty years later began to rage between the followers of Stahl and the antiphlogistians.






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