a glass, filled and inverted it under water, and lifted it inverted so that it remained full on the surface of the water. Then he made the new gas pass through a tube and rise under the glass; the ascending bubbles soon filled the vessel with the pure gas. Thus he had oxygen collected in a glass of water; he held the microcosm in his grasp, and could investigate its properties. Almost at the same time the gas was discovered by the Swede Scheele, who prepared it by heating oxide of manganese. This was but one step, however; the substance that was to initiate a new era in the world was discovered but not yet recognized. As yet an error swayed the mind of man.
The phenomenon of combustion which, at the present time, is ascribed to the chemical union of oxygen with combustible bodies, was at that time explained as due to the escape of an unknown fire-substance called phlogiston. The products of combustion were said to be dephlogisticated. That substance was thought to escape from the burning body during the act of combustion; and yet experience demonstrated that the result of the combustion, such as, for example, the rusts of lead, zinc, and copper, had more weight than the original metals. In reply to this, it was maintained that the phlogiston possessed negative weight (that it buoyed up the substances on account of its levity). Thus error begat error. At length the mystery was solved by Lavoisier. He distinctly recognized the nature of oxygen as that of a simple body, and asserted that combustion was the combination of a substance with oxygen. This introduced the element into chemistry, a conception which formed at once the basis of an exact science. Priestley was the Copernicus of Chemistry, Lavoisier became its Kepler.
An immense number of familiar facts now easily clustered around this fundamental conception; and the so-called antiphlogistic system sprang into life, a system which has prevailed up to this day, although its name is no longer in use, there being no purpose in maintaining a term that would perpetuate the memory of an error.
The system met with the fate of that of Copernicus; after a protracted struggle it came out victorious, the tenet of every naturalist now living. Oxygen being the most frequently-occurring substance, entering into combinations with all bodies, forming eight-ninths of the weight of water, and over one-half the mass of our globe, and being the conspicuous element ever present in the phenomena of combustion and respiration—it was eminently the substance to establish the new system everywhere. More than half the science of chemistry is taken up by oxygen and its compounds. Priestley and Scheele, its discoverers, remained to the ends of their lives enemies to the new theory. On the 16th of Floreal, in the year II. of the French Republic, Lavoisier was compelled to lay his head under the guillotine.
The composition of water was discovered by Cavendish. This completed the antiphlogistic system. Water consists of two gases,
