CHEMISTRY 209 



acteristic. Such compounds, accordingly, 

 supplement those which contain the acid 

 carboxyl group ( — COOH) and make possible 

 the fundamental relations of acid, base, and 

 salt among organic compounds, corresponding 

 to those of inorganic chemistry. 



There exist also many compounds of sul- 

 phur, of chlorine, bromine, and iodine, as 

 well as of various less common elements 

 among organic substances; but in all such 

 cases the complexity and variety of the 

 compounds depend primarily upon the ca- 

 pacity of carbon, hydrogen, and oxygen, or 

 carbon and hydrogen together, to form nu- 

 merous, varied, and complex compounds on 

 which, as it were, the further complexity is 

 superposed. 



E 



THE CHARACTERISTICS OF ORGANIC SUBSTANCES 



Thus the great diversity of organic sub- 

 stances depends in the first instance upon the 

 quadrivalence of carbon, which makes of 

 the carbon atom in the organic molecule a 

 focus, from which chains of atoms may ex- 

 tend in four different directions; or, in the 

 case of double or treble ties, in three directions ; 



t 

 or in but two: <-C->, /C=>, <=C=>, 



v 



