This near approach to the truth was thrown into discredit by the more brilliant and imposing theory of Stahl, who captivated the imaginations of chemists by his doctrine of phlogiston, the principle or element of fire, a sort of metaphysical something, which conferred the property of being combustible. Stahl taught that the process of combustion deprived bodies of their phlogiston, which, in the act of separation, exhibited its latent energies in the evolution of light and heat. This wild chimera long maintained its ground, and received successive modifications in the hands of several distinguished chemists, the most important of which was that of Kirwan; but these all retained the fundamental error that something was _abstracted from_ the burning body. Yet Rey, so early as 1630, and Bayer afterwards, had both shown that metals by calcination _increase_ in weight, or have something _added_ to them. Lavoisier turned his attention to the defects of the existing theory about 1770; and the last-named experiments probably directed him more specifically to the essential point of the inquiry. He pursued his researches with unwearied industry; and by a long series of experiments of the most laborious and precise nature, he succeeded in determining that, in all cases of combustion, that substance which is the _real_ combustible invariably receives _an addition_, or enters into a new combination; and the matter with which it combines is in all cases that same substance which had now been shown by Priestley to be one of the constituents of the atmosphere, and which was then known by the name of _vital air_. It was however long before Lavoisier gained a single convert. At length M. Berthollet, at a meeting of the Academy in 1785, publicly renounced the old opinions and declared himself a convert. Fourcroy followed his example. In 1787, Morveau, during a visit to Paris, became convinced, and declared the conclusions of Lavoisier irresistible. The younger chemists speedily embraced the new views; and their establishment was thus complete. There only remained some lurking prejudices in England, where the Essay of Kirwan retained its credit. Lavoisier and his coadjutors translated this essay into French, accompanying each section by a refutation. So completely was this done, that the author himself was convinced; and, with that candour which distinguishes superior minds, gave up his views as untenable, and declared himself a convert. These discoveries introduced Lavoisier to the notice of the most eminent persons in the State; and in 1776, Turgot engaged him to superintend the manufacture of gunpowder for the Government. He introduced many valuable improvements in the process, and many judicious reforms into the establishment.