98 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



being fixed air, was even more respirable, more combustible, 

 and consequently more pure even than the air in which we 

 live." 



The calx heated alone gave oxygen and mercury ; when 

 heated with charcoal it gave fixed air and mercury. Fixed 

 air was therefore evidently a compound of charcoal with 

 oxygen. Lavoisier argued that 



" Since carbon disappeared entirely in the revivification of 

 mercury from its calx, and since there result from this 

 operation only mercury and fixed air, one is forced to 

 conclude that the principle which has hitherto been known 

 as fixed air is the result of the combination of eminently 

 respirable air with charcoal" ("On the Nature of the 

 Principle which combines with metals during their Calcina- 

 tion and increases their Weight," Works, II. 122-128). 



The charcoal (French charbon) used in experiments such 

 as these always left behind when burnt a larger or smaller 

 proportion of ash. Lavoisier and his colleagues, therefore, 

 introduced in 1787 "the modified name of CARBON/ which 

 indicates the pure and essential principle of charcoal," thus 

 "distinguishing it from charcoal according to the vulgar 

 acceptation " and isolating it "from the small quantity of 

 foreign matter which it generally contains and which 

 constitutes the ash" (Method of Chemical Nomenclature, 

 tr. 1 788, p. 32). 



In their system of nomenclature, fixed air became an 

 OXIDE OF CARBON : its production during the burning of 

 charcoal was represented by the equation : 

 carbon + oxygen = fixed air 



(oxide of 



carbon) 



whilst the reduction of a calx was shown by the equation : 

 carbon + calx fixed air + metal. 



(oxide of (oxide of 



metal) carbon) 



French carbone. 



