Phlogiston

Phlogiston. During the eighteenth century the whole theory of chemical reactions, more especially in relation to combustion, was founded upon the suppositious existence of an element known as phlogiston. All combustible materials were supposed to contain this substance, and the more they contained the more actively did they burn on ignition. During combustion the phlogiston escaped and a dephlogisticated product was left. By a slight extension it is seen that metals were supposed to consist of their calces - i.e. oxides - with the addition of phlogiston, and the reduction of a metallic oxide by carbon or other reducing agent was regarded as due to the combination of the phlogiston, so plentiful in the latter, with the calx. These views, enunciated first by Stahl, were held by a large number of distinguished chemists, as Black, Scheele, Cavendish, and Priestley, the two latter of whom, it is noticeable, though firm adherents of the theory, contributed much to its overthrow. The fact that the calces weighed more than the metals from which they were produced was explained by the assertion that phlogiston was a "principle of levity." In this fact, however, lay the nucleus of the phlogistic downfall, although the establishment of the oxygen theory of combustion now held -was only brought about after a long and arduous scientific struggle, and chiefly through the instrumentality of the great French chemist Lavoisier.