Stahl’s writings evince the great progress which chemistry had made even since the time of Beccher. But it is difficult to say what particular new facts, which appear first in his writings were discovered by himself, and what by others. I shall not, therefore, attempt any enumeration of them. His reasoning is more subtile, and his views much more extensive and profound than those of his predecessors. The great improvement which he introduced into chemistry was the employment of _phlogiston_, to explain the phenomena of combustion and calcination. This theory had been originally broached by Beccher, from whom Stahl evidently borrowed it, but he improved and simplified it so much that the whole credit of it was given to him. It was called the Stahlian theory, and raised him to the highest rank among chemists. The sole objects of chemists for thirty or forty years after his time was to illucidate and extend his theory. It applied so happily to all the known facts, and was supported by experiments, which appeared so decisive that nobody thought of calling it in question, or of interrogating nature in any other way than he had pointed out. It will be requisite, therefore, before proceeding further with this historical sketch, to lay the outlines of the phlogistic theory before the reader. It was conceived by Beccher and Stahl that all _combustible_ bodies are compounds. One of the constituents they supposed to be dissipated during the combustion, while the other constituent remained behind. Now when combustible bodies are subjected to combustion, some of them leave an acid behind them; while others leave a fixed powdery matter, possessing the properties of an _earth_, and called usually the _calx_ of the combustible body. The metals are the substances which leave a calx behind them when burnt, and sulphur and phosphorus leave an acid. With respect to those bodies that would not burn, chemists did not speculate much at first; but afterwards they came to think that they consisted of the fixed substance that remained after combustion. Hence the conclusion was natural, that they had already undergone combustion. Thus quicklime possessed properties very similar to the calces of metals. It was natural, therefore, to consider it as a calx, and to believe that if the matter dissipated during combustion could be again restored, lime would be converted into a substance similar to the metals.