244 INORGANIC CHEMISTRY 



working the rare metals, in making enamels by fusion, in producing 

 and fashioning glass, and in preparing fermented liquors. 



On the other hand, a little people, whose part in everything was to 

 throw the most brilliant light on it without inventing new applica- 

 tions, sought to explain, philosophically, these transformations of 

 matter. The Greek philosophers discussed this subject at length. 

 Empedocles reduced all the bodies that nature can present to four 

 elements: fire, air, water, and earth. For him, these elements were 

 composed of a multitude of minute particles, indivisible and insecable. 

 Such a theory leads easily to the atoms of Democritus. Whether 

 these elements were considered as symbols or as a veritable classi- 

 fication of matter, the idea of Empedocles, adopted by Aristotle, and 

 taught by all the schools, was destined to maintain for centuries 

 the position of a doctrine that could not be disputed. 



Later, Epicurus revives the theory of atoms, and Lucretius, in a 

 poetic divination, can write: 



Principio, quoniam terra corpus, et humor 

 Aurarumque leves animae, calidique vapores, 

 E quibus haec rerum consistere summa videtur, 

 Omnia native ac mortali corpore constant, 

 Debet eodem omnis mundi natura putari. 1 



The idea of the four elements reappears unchanged among the 

 Arabian chemists, and among the alchemists of the Middle Ages; 

 though it undergoes various transformations at the hands of Paracel- 

 sus who recognized five elements: spirit; mercury; phlegm or water; 

 salt, sulphur, or oil; and earth, and later at the hands of Beecher 

 who admits the existence of three essences in earth, vitrifiable, 

 inflammable, and mercurial earth. 



The theory of four elements reigns without contest up to the 

 moment when Stahl, professor at the University of Halle, develops 

 his important conception of phlogiston. For Beecher, combustible 

 bodies and metals contained his three sorts of earth combined. 

 For Stahl, "inflammable earth" becomes phlogiston. Carbon, by its 

 combustion, gives heat and light; it therefore contains phlogiston. 

 When a calx, that is to say, a metallic oxide, is heated with carbon, 

 it extracts and fixes the phlogiston, and becomes a metal. These 

 were important conceptions, because they made it possible to unite in 

 one body of doctrine the phenomena of oxidation and of reduction. 



Such was the state of the science when Lavoisier followed up his 

 memorable experiments by developing the notion of simple sub- 

 stances. This great savant showed that the same body could change 

 its state, and he separated clearly, among the phenomena of chemistry, 

 on the one side the weight of the reacting bodies, and on the other 



1 " First, since earth, and water, and the light breath of air, and glowing fire 

 of which our world seems to be composed all consist of matter that is subject 

 to birth and to death, we must think that the whole universe is made up of this 

 same sort of matter." 



