BIRTH OF MODERN CHEMISTRY Boyle.—A new era began with Robert Boyle. In early life, a member of the "Invisible College" (the germ from which the Royal Society sprang), he was drawn in 1654 to Oxford where several of the members were in residence. Here he spent his most active years in experimental research. He established by careful experiments the law known by his name—that the volume of a given mass of air varies inversely as the pressure upon it. He determined the density of air and pointed out that bodies altered in weight according to the varying buoyancy of the atmos phere; and he compared the lower strata of the air to a number of sponges or small springs compressed by the weight of the layers above them. It is notable that not only the facts published by Boyle on the "Spring of the Air," but the very images he used were repeated by Mariotte 14 years later.
In 1661 Boyle published the Sceptical Chymist, in which he gravely questions the tria prima : "There are some bodies from which it has not yet been made to appear that any degree of fire can separate either salt, or sulphur or mercury, much less all three. Gold may be heated for months in a furnace without losing weight or altering, and yet one of its supposed constituents is volatile and another combustible. Neither can solvents separate any of the three principles from gold ; the metal may be added to, and so brought into solution . . . but the gold particles are present all the time : and the metal may be reduced to the same weight, of yellow, ponderous malleable substance it was before." Boyle gives many instances in which metals, such as lead or copper, may be dissolved in acids and their properties entirely disguised in the compound. The corpuscles of which the metal is composed, meeting with corpuscles of another kind, may be more disposed to unite with them than with the particles forming their original metallic cluster. From the coalition of two different corpuscles a new body may be formed "as really one as either of the corpuscles before they were confounded." We can trace here the modern idea of chemical affinity uniting atoms into compounds. Boyle devised a method for extracting the element phosphorus, which was long known as Boyle's phosphorus; he made many experiments on air and other gases. He prepared hydrogen by the action of acids on steel filings and on iron nails, and showed that it would burn with a strong flame though with little light. He collected the gas in an inverted glass flask over dilute acid, and showed that the imprisoned gas was permanent and "dilated itself" like air when the vessel was warmed.
In his "New Experiments touching the Relation betwixt Flame and Air" he showed that the flames of hydrogen, of sulphur, and of a candle were extinguished in the receiver of his air-pump when the air was rarified. But, finding that gunpowder and fulminating gold would burn in his vacuum, he was forced to conclude that flame may exist without air : it was left to his assistant Hooke to make the next advance.
By observing that wood-charcoal was immediately dissipated into white ashes if the retort was opened in the air while still red-hot, Hooke grasped the fact that the air "preyed upon" or "dissolved" the charcoal ; and he compared the active constituent of the air with that which is fixed in saltpetre. The oil rising as vapour from a lighted wick is not burnt inside the flame (which is dark) but only as it reaches the surrounding atmosphere where it meets the "nitre-air." Mayow made careful experiments on the burning of combustible bodies in air confined over water. He showed that part of the air disappeared both in combustion and respiration, and that the residue left would not support flame or life. This residue differed then from ordinary air. He did not isolate his nitre-air, nor show what became of it.