216 THE FITNESS OF THE ENVIRONMENT 



a carbon atom is attached to four hydrogen 

 atoms, or to one carbon and three hydrogens, 

 or to two carbons and two hydrogens, or to 

 three carbons and one hydrogen, or to four 

 carbon atoms ; in all such cases the effect 

 of the radical upon the general characteristics 

 of the molecule varies very little. 



There are a great number of phenomena 

 which might be employed further to illustrate 

 the nature of the case, but two will suffice. 

 The acidity of acetic acid, CH 3 *COOH, is 

 only slightly and slowly changed by the 

 accumulation of hydrocarbon radicals ; thus 

 the compounds propionic acid, CH 3 *CH 2 ' 

 COOH, and butyric acid, CHg-CHa'CHv 

 COOH, are only a little less acid than acetic 

 acid itself, because nearlv all the effect of 

 such larger radicals as they contain is already 

 exerted by the methyl group. 



Ionization Constants of Acids 



