ON THE STATE OP ORGANIC CHEMISTRY. 11 



inula, C* H 3 , O 3 . HO*, indicates its connexion with C x H 3 CP* (the old ter- 

 chloride of acetvl), aldehyde and other substances containing C x H 3 * (3)f- 

 Reactions of the kind mentioned in (4) led Kolbe to adopt the formula 



H 

 HO . ( C 2 ifyC 2 , O 3 *. Dumas wrote acetic acid C HO 3 . HO *, to express 



H 

 that that portion of the hydrogen which cannot be replaced by metals, can 

 be removed and replaced by other elements, e. g. chlorine (5, 6, and 7). 

 The formula which we have given as the most general of all is nothing more 

 than a combination of all these, and therefore enables us to recognize the 



value of each J. 



Similar considerations applied to any of the derivatives of acetic acid would 

 lead us to adopt for them formulae of the same degree of generality ; for 

 instance, for chloride of acetyl, — 



H| 



H l( C )iv H J ( W 



H J , and for acetamide (C) iv {}(0)" . 



And in proportion as our knowledge of the genetic relations of any class 

 of compounds is increased, so will their rational formulse approach more and 

 more nearly to the same form. All formulae which come short of this are 

 but imperfect descriptions of the bodies which they represent; for it is 

 evident that a formula containing a compound radicle cannot represent re- 

 actions in which the elements composing that radicle are separated from 

 each other. Nevertheless, for the expression of those relations with which 

 we are most frequently concerned, and for the purposes of classification, it 

 would be of no advantage that the most general formulse should be employed. 

 The relation between any two compounds is best expressed by whatever 

 particular abbreviations of the general formulas represent most simply and 

 distinctly the extent of their similarity and difference ; while, for purposes 

 of classification, it is essential that all bodies should receive formulae of a 

 comparable degree of generality ; and in the majority of cases, the possible 

 degree of generality is but small. Hence Gerhardt's formulae, since they 

 express just those reactions with which we are most familiar, and can be 

 applied to every compound of which we can be said to have any chemical 

 knowledge at all, are better adapted than any others to the ordinary require- 

 ments of science in its present state. 



On the other hand, it cannot be doubted that the chemical character of 

 every substance is affected in a certain definite degree by each separate atom 

 that it contains. And the only way by which we can hope ultimately to 

 ascertain the true chemical value of the elements, or, in other words, to trace 

 the full connexion between the properties and composition of compounds, is 

 by comparing, when possible, (what we may call) their elementary formula. 

 Moreover, we ought not to forget that any classification of chemical com- 

 pounds, which is not founded upon the consideration of their elementary 

 formulae, that is, upon the consideration of their total reactions, however 



t Schischkoff, Ann. Chim. Phys. [3] xlix. 355, has represented acetic acid by precisely 

 the same formula as that given in (3). 



X For a list of nineteen different formulae for acetic acid, see Kekulc, Lehrb. d. Organ. 



Chem., p. 58. 



