222 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



the conception of an ELEMENT. The four elements of 

 Aristotle : 



earth, air, fire, and water, 

 and the three principles of the alchemists : 



mercury, sulphur, and salt, 



served rather to describe the qualities than the actual com- 

 position of the bodies in which their presence was implied. 

 The first conception of an element as a substance which 

 cannot be decomposed into simpler substances was given 

 by Boyle. But no clearer statements of this view can be 

 found in the whole of the literature of chemistry than those 

 made by Davy in his controversy with the French chemists, and 

 afterwards with Berzelius. Two of these may be quoted : 



" Some authors continue to write and speak with scept- 

 icism on the subject, and demand stronger evidence of 

 chlorine being undecompounded. These evidences it is 

 impossible to give. It has resisted all attempts at decom- 

 position. In this respect it agrees with gold, and silver, and 

 hydrogen, and oxygen. Persons may doubt whether these 

 are elementary bodies ; but it is not philosophical to doubt 

 whether they have not been resolved into other forms of 

 matter " (A.C.R. IX. 73). 



" It is possible that oxymuriatic gas may be compound, 

 and that this body and oxygen may contain some common 

 principle ; but at present we have no more right to say that 

 oxymuriatic gas contains oxygen than to say that tin contains 

 hydrogen ; . . . and till a body is decompounded, it should 

 be considered as simple" (A.C.R. IX. footnote, p. 61). 



Davy (1810) determines the composition by volume of 

 hydrogen chloride. Until the year 1810 muriatic acid gas 

 was regarded either as a simple substance (Berthollet) or as a 

 compound of the unknown muriatic radical with one-third or 

 one-fourth of its weight of water (Davy ; Gay Lussac ; A.C.R. 

 XIII. 49). x In that year, however, Davy, having proved it 



1 Berzelius (Chemical Proportions, 1819, 125) assumed that 442-65 

 parts of chlorine contained 142*65 parts of the muriatic radical and 300 

 parts of oxygen. 



