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SCIENCE 



[N. S. Vol. XXXIV. No. 871 



the like. Stahl, however false his theory, 

 had at least the merit of having con- 

 structed a reversible chemical equation : 

 Metal — phlogiston = calx ; calx + phlogis- 

 ton = metal. 



It is difficult to say when the first ele- 

 ment was known to be an element. After 

 Lavoisier's overthrow of the phlogistic hy- 

 pothesis, the part played by oxygen, then 

 recently discovered by Priestley and 

 Scheele, came prominently forward. Loss 

 of phlogiston was identified with oxidation ; 

 gain of phlogiston, with loss of oxygen. 

 The scheme of nomenclature ( ' ' Methode de 

 Nomenclature chimique"), published by 

 Lavoisier in conjunction with Guyton de 

 Morveau, Berthollet and Foureroy, 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 'ele- 

 ments' the simple and indivisible mole- 

 cules 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 ele- 

 ment; 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 separated, or 

 rather, because we have no means of sepa- 

 rating them, they act, so far as we car 

 judge, as elements; and we can not call 

 them 'simple' until experiment and obser- 

 vation 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 form- 



ing salts must also possess a metallic sub- 

 stratum. In October, 1807, Sir Humphry 

 Davy proved the correctness of this view 

 for soda and potash by his famous experi- 

 ment of splitting these bodies by a power- 

 ful electric current into oxygen and hydro- 

 gen 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, lime, barytes, strontia, and mag- 

 nesia. Some years later Scheele 's "de- 

 phlogisticated marine acid," obtained by 

 heating pyrolusite with "spirit of salt," 

 was identified by Davy as in all likelihood 

 elementary. His words are : ' ' All the con- 

 clusions which I have ventured to make 

 respecting the undecompounded nature of 

 oxymuriatie gas are, I conceive, entirely 

 confirmed by these new facts." "It has 

 been judged most proper to suggest a name 

 founded upon one of its obvious and char- 

 acteristic properties, its color, and to call 

 it chlorine." The subsequent discovery of 

 iodine by Courtois in 1812, and of bromine 

 by Balard in 1826, led to the inevitable con- 

 clusion that fluorine, if isolated, should 

 resemble the other halogens in properties, 

 and much later, in the able hands of Mois- 

 san, this was shown to be true. 



The modern conception of the elements 

 was much strengthened by Dal ton's re- 

 vival of the Greek hypothesis of the atomic 

 constitution of matter, and the assigning 

 to each atom a definite weight. This mo- 

 mentous step for the progress of chemistry 

 was taken in 1803 ; the first account of the 

 theory was given to the public with Dal- 

 ton 's consent in the third edition of Thomas 

 Thomson's "System of Chemistry" in 

 1807 ; it was subsequently elaborated in the 

 first volume of Dalton's own "System of 

 Chemical Philosophy," published in 1808. 

 The notion that compounds consisted of 

 aggregations of atoms of elements, united 



