184 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1911. 



element the meaning that it now possesses — the constituent of a 

 compound. But in the middle of the seventeenth century chem- 

 istry had not advanced far enough to make his definition useful; for 

 he was unable to suggest any particular substance as elementary. 

 And, indeed, the main tenet of the doctrine of phlogiston, promul- 

 gated by Stahl in the eighteenth century, and widely accepted, was 

 that all bodies capable of burning or of being converted into a calx, 

 or earthy powder, did so in virtue of the escape of a subtle fluid 

 from their pores; this fluid could be restored to the calces by heating 

 them with other substances rich in phlogiston, such as charcoal, oil, 

 flour, and the like. Stahl, however false his theory, had at least the 

 merit of having constructed a reversible chemical equation: 



Metal — phlogiston = Calx ; Calx + phlogiston = Metal. 



It is difficult to say when the first element was known to be an 

 element. After Lavoisier's overthrow of the phlogistic hypothesis, 

 the part played by oxj'gen, then recently discovered by Priestley and 

 Scheele, came prominently forward. Loss of phlogiston was identi- 

 fied with oxidation; gain of phlogiston with loss of oxygen. The 

 scheme of nomenclature (Methode de Nomenclature chimique), 

 published by Lavoisier in conjunction with Guy ton de Morveau, 

 Berthollet, and Fourcroy, created a system of chemistry out of a 

 wilderness of isolated facts and descriptions. Shortly after, in 1789, 

 Lavoisier published his Traite de Chimie, and in the preface the 

 words occur: "If we mean by elements the simple and indivisible 

 molecules of which bodies consist, it is probable that we do not 

 know them; if, on the other hand, we mean the last term in analysis, 

 then every substance which we have not been able to decompose is 

 for us an element; not that we can be certain that bodies which we 

 regard as simple are not themselves composed of two or even a larger 

 number of elements, but because these elements can never be sepa- 

 rated, or rather because we have no means of separating them, they 

 act, so far as we can judge, as elements, and we can not call them 

 simple until experiment and observation shall have furnished a proof 

 that they are so." 



The close connection between crocus of Mars and metallic iron, 

 the former named by Lavoisier oxyde de fer, and similar relations 

 between metals and their oxides, made it likely that bodies which 

 reacted as oxides in dissolving in acids and forming salts must also 

 possess a metallic substratum. In October, 1807, Sir Humphry 

 Davy proved the correctness of this view for soda and potash by his 

 famous experiment of splitting these bodies by a powerful electric 

 current into oxygen and hydrogen, on the one hand, and the metals 

 sodium and potassium, on the other. Calcium, barium, strontium, 

 and magnesium were added to the list as constituents of the oxides, 



