XVII MOLECULAR ARCHITECTURE 419 



Gerhardt (1843) halves the formulae of organic com- 

 pounds. Further important developments were made in 

 Gerhardt's " Investigations on the Chemical Classification of 

 Organic Compounds " (fourn. prakt. Chem., 1842, 27, 439- 

 464; 1843, 28, 34-53, 65-100, 30, i-io). His theory of 

 copulation had compelled him to bring together into one 

 equation both complex organic products and simple in- 

 organic substances. He therefore soon discovered "that 

 the formula of most organic substances are too great by half 

 in comparison with the formula of inorganic chemistry" 

 (Journ. prakt. Chem., 1843, 30, 8). In inorganic chemistry. 

 (following Berzelius), water, ammonia and hydrogen chloride 

 were written as H 2 O, NH 3 , and HC1 ; but as products of 

 the copulation of organic compounds they always appeared 

 as H 4 O 2 , N 2 H 6 , and H 2 C1 2 . Gerhardt was therefore led to 

 fall back again upon Avogadro's hypothesis as a valid guide 

 to the molecular formulae of organic compounds, and re- 

 wrote them as follows : 



These formulae were only rendered possible by the fact that 

 Gerhardt had abandoned the older form of the theory of 

 radicals, according to which silver acetate was a binary 

 compound of silver oxide and "anhydrous acetic acid" 

 (acetic anhydride), whilst " hydrated acetic acid " (acetic 

 acid) was a binary compound of water with the anhydrous 

 acid, thus (in modern formulae) 



Silver acetate = C 4 H 6 O 3 ,Ag 2 O = Ag 2 C 4 H 6 O 4 . 

 Acetic acid = C 4 H 6 O 3 ,H 2 O = C 4 H 8 O 4 . 



To the student of this bewildering period of chemical 

 history nothing is more refreshing than to find once more 

 in Gerhardt's papers the simple formulae, based upon 



E E 2 



