GENERAL VIEWS. 339 



cules themselves. A more satisfactory idea of this sub- 

 ject can be obtained after reading what follows, on the 

 subject of organic radicals. 



Give an in- 858. SUBSTITUTION. A still more re- 



stance of sub- ma rkable evidence of the influence of ar- 



stitution titat 



does not affect rangement or grouping of atoms, remains 

 P 10 P C ^ to be mentioned. The internal arrange- 



ment of a molecule remaining the same, it seems to 

 matter little, in many cases, of what it is composed. 

 Hydrogen may even be replaced by chlorine, a body 

 as widely different from it as anything which nature 

 affords. By this means, ordinary acetic acid is con- 

 verted into chloracetic acid, a body remarkably anal- 

 ogous in its properties to the acid from which it is 

 formed. From this, again, by withdrawing the chlo- 

 rine and restoring the hydrogen, the original acetic acid 

 is reproduced. 



859 TYPES. The last example will 



What in said . , 



of the doctrine serve as an illustration of the doctrine of 



cnem i ca l types and substitution, which cer- 

 tain chemists have endeavored to extend to 

 all organic bodies. It has been maintained that the 

 properties of these bodies depend solely upon arrange- 

 ment, without any reference to the nature of the ele- 

 ments combined. The fact is, that while there are 

 many cases of such substitution without essential 

 change of properties, it is always attended by more or 

 less modification of the original substance. The 

 properties of a compound are therefore to be regarded 

 as depending neither upon the nature or arrangement 

 of atoms alone, but upon both causes combined. The 



