6 HISTORY OF CHEMISTRY. [LECTURE I. 



This theory was applied to all combustible substances. 

 Thus, according to StahFs views, sulphur consists of sul- 

 phuric acid and phlogiston ; a metal, of its metallic calx (of 

 its oxide we should say) and phlogiston. According to Stahl, 

 sulphur was not identical with phlogiston, but, as with Pliny, 

 it was rich in the principle of inflammability, which he did not 

 know in a separate state. Soot appeared to be the substance 

 richest in phlogiston ; in fact as almost pure phlogiston. It 

 was in consequence of this that the conversion of the metallic 

 calx into the metal by heating it with soot succeeded so well ; 

 for the soot handed over its phlogiston to the metallic calx, so 

 that a metal was produced again. In his experimentum novum 

 Stahl tries to prove that the phlogiston in soot and in sulphur 

 is identical. He shows here, how a sulphate can be converted 

 by means of charcoal into liver of sulphur, from which sulphur 

 is precipitated by the action of an acid. From the reduction 

 of the metallic calces by means of soot, Stahl further infers the 

 identity of the phlogiston of the metals with the inflammable 

 principle in soot and in sulphur ; and thus he arrives at a 

 proof that there exists only one such principle, which he calls 

 simply Phlogiston (from <XoyrTo<?, combustible). 



The phlogiston theory was, for a century, the basis of all 

 chemical considerations ; nevertheless we shall find that during 

 this time the conception of phlogiston did not always retain its 

 first signification, and that the whole mode of regarding it was 

 altered in consequence. 



We can understand Stahl and his immediate followers quite 

 well if we assume a loss of oxygen in every place where they 

 speak of the taking up of phlogiston, and vice versa ; a phlogisti- 

 cated substance is, with us, a substance free from or poor in 

 oxygen. It might perhaps be said, in short, that phlogiston is 

 negative oxygen. 



Stahl borrowed from the ancients the view that combustion 

 is accompanied by destruction, or decomposition. This he 

 retained, although, even in his time, facts were well known 

 which proved an increase of weight on combustion. Even 

 Geber, an alchemist of the eighth century, appears to have 



