120 CHEMICAL PROPERTIES AND COMPOSITION 



(b) Influence of Oxygen. 



(a) Oxygen intensifies acidity. No element possesses this 

 property in so high a degree as oxygen, which indeed owes 

 its name to the favouring influence it exerts on the intro- 

 duction of metal. In inorganic chemistry the instances are 

 so common that there is no need to quote any, for every 

 oxyacid is evidence of the influence of oxygen in the sense 

 considered. The influence may be followed in detail in the 

 region of organic chemistry. 



Facility of carbon for combination with metals. Organic 

 compounds are comparatively rare which are capable of 

 exchanging any of their hydrogen atoms, which are directly 

 united with carbon, for metals. Still such derivatives are 

 well known to be important for synthetic purposes. 

 A case was mentioned on p. 114, in connexion with the 

 effect of hydrogen, viz. that of the acetylides. The 

 majority of others depend on the presence of oxygen. 



In carbonic oxide an unmistakable tendency of the 

 carbon to combine with metals is seen, as is proved by the 

 existence of nickel carbonyl, Ni(CO) 4 , and the corresponding 

 iron derivative. 



Secondly, it may be noted that in the group 



OC-C CO, 



the middle carbon atom has regularly the faculty of com- 

 bining with metals, e. g. aceto-acetic and malonic esters 1 . 



H 3 CCOCH 2 C0 2 C 2 H 5 , H 5 C 2 OCOCH 2 C0 2 C 2 H 5 , 



in each of these an atom of hydrogen in the CH 2 group 

 may be replaced by sodium, with the aid either of the 

 metal itself or of sodium ethylate. 



The same result follows from the combined withdrawal 

 of hydrogen and introduction of oxygen in the group : 



HC = CH CO, 



1 Berl. Ber. 32. 1876, p. 3398. The constitution of the metal derivative 

 in question is still somewhat uncertain ; see inter alia A. Claisen's remarks 

 to the German Chemical Society, Dec., 1899. 



