22 Dr. Be van Lean on the 



Davy, Dulong, and Liebig. It may be remarked, too, that 

 after the work of Kolbe and Frankland, Kekule stated that 

 the basicity of an organic acid was determined solely by the 

 number of carboxyls which it contained — a conclusion 

 which can only be maintained by defining an organic acid 

 as a substance containing carboxyl. The following definition 

 of an acid states as clearly as may be the modern conception 

 of an acid ; it is due to Ramsay : — 



"An acid is a compound of hydrogen, which when mixed with 

 or dissolved in water, is capable of exchanging the whole or a 

 portion of the hydrogen which it contains for a metal, with simul- 

 taneous formation of water, by the action on the aqueous solution 

 of the acid, of a metallic oxide or hydroxide." 



Substances which come under this definition are found to 

 contain hydrogen in intimate combination with one or more 

 of the following : fluorine, chlorine, bromine, iodine, oxygen, 

 sulphur, selenium, tellurium, or certain groups of elements 

 of which carbon is one. Amongst organic compounds there 

 are many besides carboxyl derivatives which can exchange 

 hydrogen for a metal by the action of an oxide or hydroxide. 

 The chief of these are certain acid ethereal salts, the 

 mercaptans, many nitro-derivatives of the alkyl radicals, 

 and phenols. From a consideration of these compounds 

 Ramsay has drawn the following deductions : 



(a) A powerfully electro-negative element such as chlorine 

 bromine, or iodine, confers acid properties on its com- 

 pound with hydrogen. 



(p) In compounds of elements exhibiting less markedly 

 electro-negative properties than the halogens, the presence 

 of an electro-negative element is necessary for the 

 development of acid character. In illustration of this 

 the following series of compounds may be noted : — 

 methane — methyl alcohol — prussic acid, 

 anthracene — anthraquinone — alizarine. 



The study of the basicity of acids has done much to 

 enlarge our knowledge of acids. From the dualistic stand- 



