There are two main divisions of chemistry--inorganic and organic; that is to say, the chemistry of “dead” matter, and the chemistry of “living” or organic substances. Chemical experiments may be for the purpose of _analysis_--discovering the constituents of a given substance; _synthesis_, in which a compound substance is “created” from several simpler ones; or purely _experimental_, in which certain tests are made, and the results or reäctions noted. 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 though the 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....”