MEDIAEVAL CHEMISTRY
As before stated, Chemistry is more or less the direct child of Alchemy; but before the modern, scientific period of chemical research had been reached, two transitional stages were first of all passed through. These were (1) The so-called “Iatro-Chemical” period—the period of medical mysticism; and (2) the “phlogistic” period. A few words will be necessary to explain each of these terms, and the period of chemical development which they covered.
As may be inferred from the name, the iatro-chemical period was one in which attempts were made to combine chemistry and medicine, and make the former serve the latter. All kinds of weird concoctions were tried, and attempts were made to explain, on chemical principles, all the changes and reactions occurring in the body—an attempt which was necessarily futile for the chemistry of that day. However, many important results were achieved, as the consequence of experimentation, and chemical science was on the whole enriched, even thoughthe workers of that day were inspired by totally erroneous views.
The Phlogistic Period takes its name from a hypothetical substance denominated “phlogiston.” This was supposed to be an invisible principle or entity, constituting the basis of Fire, and corresponds to the “pure fire” of Zoroaster. The Phlogiston theory was propounded and championed by Stahl, and it was defined by him as follows:
“Phlogiston is ... a very subtle matter, capable of penetrating the most dense substances; it neither burns, nor glows, nor is visible; it is agitated by an igneous motion, and it is capable of communicating its motion to material particles apt to receive it. The particles when indued with this rapid motion constitute visible fire....”
This conception dominated the whole scientific world for many years. The experimental work undertaken by Scheele and Priestly, however, finally enabled Lavoisier to discover the true nature of “fire”—combustion. In a famous “Memoir,” published in 1783, entitled “Reflections Concerning Phlogiston,” he showed that all the observed phenomena could be accounted for without the presence of any hypothetical phlogiston; in fact, as he himself says, they “can be better explained without phlogiston than by means of it.” His discovery of oxygen, in the atmosphere, was a fundamentally important step in modern chemical science. Hitherto, the air was thought to be a single gas, or a mixture of various gases; but oxygenwas unknown as its most important constituent. Lavoisier’s discovery finally disposed of the phlogiston idea, and ushered in the new era of scientific chemistry.
It may be thought that undue space has been devoted to this theory of Phlogiston; but anyone reading the history of Chemistry will realize the extent to which this idea completely dominated the minds of men at that time, and how all chemical researches were perverted by it. The discovery of the true nature of combustion was one of the fundamental turning-points in the history of scientific thought.
The material world in which we live is very evidently composed of a variety of substances. At least some of these were soon seen to exist in at least three different states—solid, liquid and gaseous. These seemed to differ radically from one another; ice, water and steam are as different as one can imagine; and yet, somehow, they were the same thing after all; for ice melts and becomes water, and water, when heated, becomes steam. On the contrary, steam cools and becomes water again, and when it is sufficiently cold, will again form ice. There must be some fundamental Thing, therefore, of which water is composed. What is this Thing? How many such Things are there in the world? Are there a limitless number, or only a few? If a certain, limited number, how many? And how discover them? These were questions which naturally occupied the minds of men throughout the ages. No answer wasfound, however, and it remained for John Dalton to discover and formulate the Law which enabled men to obtain their first glimpse of the nature of the ultimate constitution of matter.