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Updated: May 25, 2025
Now, if the phlogistic hypothesis be true, it would follow that a metal should be the heavier, its oxide the lighter body, for the former contains something phlogiston that has been added to the latter. But, on weighing a portion of any metal, and also the oxide producible from it, the latter proves to be the heavier, and here the phlogistic hypothesis fails.
Lavoisier, for example, believed oxygen gas to be composed of a metal oxygen combined with the alleged element heat; Dr. Priestley thought it a compound of positive electricity and phlogiston; and Humphry Davy, when he entered the lists a little later, supposed it to be a compound of oxygen and light.
It seemed necessary to suppose that not only was phlogiston expelled from mercury during calcination, but that the mercury also imbibed some portion, and that the purest portion, of the surrounding air.
The rudimentary chemistry that overthrew alchemy had nothing so obvious and palpable. The great first step was the substitution of the one principle, phlogiston, for the three principles, salt, sulphur, and mercury.
It is not that there are any very staggering arguments against the immortality of man; but, like electricity, phlogiston, etc., the subject is so involved in darkness, that we want data to go upon. One thing frightens me much: that we are to live for ever seems too good news to be true.
In the course of my inquiries I was, however, soon satisfied that atmospheric air is not an unalterable thing; for that, according to my first hypothesis, the phlogiston with which it becomes loaded from bodies burning in it, and the animals breathing it, and various other chemical processes, so far alters and depraves it as to render it altogether unfit for inflammation, respiration, and other purposes to which it is subservient; and I had discovered that agitation in the water, the process of vegetation, and probably other natural processes, restore it to its original purity....
Newton now renewed his computation, and, as I have related on a previous page, as it drew to a close, foreseeing that a coincidence was about to be established, was so much agitated that he was obliged to ask a friend to complete it. The hypothesis was sustained. A second instance will sufficiently illustrate the method under consideration. It is presented by the chemical theory of phlogiston.
These substances are of two kinds; the one more simple, the other more compound. The most simple kind is composed of two different substances, viz. phlogiston, with certain specific substances; from which result, on the one hand, sulphur, and, on the other, proper coal and metals. The more compound sort, again, is oily matter, produced by vegetables, and forming bituminous bodies.
Besides, in addition to abortive hypotheses, there are dethroned ones. What theory was more clinging, more fascinating in its applications, than that of phlogiston? Kant praised it as one of the greatest discoveries of the eighteenth century. The development of the sciences is replete with these downfalls.
Moreover, the theory asserted that all combustible, or incinerable, things are composed of phlogiston, and another principle, or, as was often said, another element, which is different in different kinds of combustible substances. The metals, for instance, were said to be composed of phlogiston and an earthy principle or element, which was somewhat different in different metals.
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