428 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



But sulphuric acid, H 2 SO 4 , potassium hydrogen sulphate 

 (potassium bisulphate, KHSO 4 ), and potassium sulphate, 

 K 2 SO 4 , could not be represented adequately in this way. 

 Williamson, therefore, who had begun by writing sulphuric 

 acid and ethyl hydrogen sulphate (in his two papers " On 

 Etherification," 1852) as : 



H 



H)S0 4 



and 



was soon led to regard all the sulphates as derived from 

 two molecules of water and to write their formulae (in his 

 paper " On the Constitution of Salts," Journ. Chem. Soc., 

 1852, 4. 353) as : 



The significance of these formulae is shown clearly in a reply 

 to certain criticisms of Kolbe (Journ. Chem. Soc.^ 1855, 7, 

 in), in which Williamson derives the formula of sulphuric 

 acid from that of water by allowing a molecule of sulphur 

 dioxide to " replace two atoms of hydrogen in two of water," 

 thus 



' 



(Journ. Chem. Soc., 1855, 7, 137). In the last formula, the 

 molecule of sulphuric acid is subdivided into five portions, 

 namely, four single atoms and one small radical, SO 2 , the 

 exact structure of which is still doubtful even at the present 

 day. 



Williamson's multiple types were developed by Odling 

 (" On the Constitution of Acids and Salts," 'Journ. Chem. Soc., 



1 In the original papers Williamson writes all his formulae without 

 brackets, whilst Odling writes 2O instead of O 2 in the formulae of 

 multiple types ; for the sake of convenience, one method of representa- 

 tion only is used in this paragraph. 



