M&xwell Simpson. 177 



C 4 H 6 3 , H 2 0, Acetic acid 

 C 4 H 4 05, H 2 O, Tartaric acid 

 C 4 H 4 4 , H 2 0, Citric acid 



To Gerhardt is due the merit of having shown, in 1851, that the 

 formulae of acids ought to represent molecular and not equivalent 

 weights, and of having given definitions of mono- and poly basic acids, 

 which are still considered to be correct. These definitions, together 

 with Gerhardt's- Williamson's theory of types, led to the recognition of 

 the chemical values of compound radicals. 



Nitric acid N ^ j C ^ } 0, Acetic acid. 



Sulphuric acid S ^ j Q 2 G ^^ 1 2 , Succinic acid. 



It is at once seen that the chemical value of S0 2 is twice that of 

 N0 2 , or, if acetyl is called monovalent, succinyl must be regarded as 

 divalent. N0 2 and C 2 H 3 each replace one atom of hydrogen in one 

 molecule of water, S0 2 and C 4 H 4 O 2 , each two atoms of hydrogen in two 

 molecules of water. A monobasic acid is derived from one, a dibasic 

 acid from two molecules in water. 



The important discovery of the anhydrous acids R 2 and KE^O, 

 by Gerhardt, and the results of Berthelot's* investigation of the action 

 of acids on glycerine, confirmed these views. 



Berthelot concluded from his results that glycerine stood to a 

 monovalent alcohol in the same relation as a tribasic acid did to a 

 monobasic acid. Wurtz more fully explained this view. Hence, if 

 there are alcohols of the structure of monobasic and tribasic acids, 

 then there ought to be likewise alcohols corresponding to dibasic acids. 

 Berzelius had pointed out, in 1839, that probably an alcohol C 2 H 6 O 2 

 could be prepared from ethylenic chloride C 2 H 4 C1 2 . No notice was 

 taken of this suggestion until Wurtz, prompted by the above con- 

 siderations, successfully carried out the idea of Berzelius by using 

 C 2 H 4 I 2 instead of the chloride : 



C 2 H 4 I 2 -^ C 2 H 4 (C 2 H 3 2 ) 2 >- C 2 H 4 (OH) 2 -*- C 2 Q 2 (QH) 2 

 Ethy- Ethylenic Glycol Oxalic 



lenic Acetate Acid 



iodide 



* 



About the time when Simpson arrived in Paris Wurtz was engaged 



with the aforesaid investigations, which suggested the further question : 



can an alcohol of the structure of glycerine be prepared from C 2 Hsl3 or 



another halogen compound of vinyl ? Simpson undertook to answer 



* Compt. Eend., xxxviii, 668. 



