CHAPTER III. 



THE "CONSTITUTION," OR "STRUCTURE," OF SOME OF THE 

 SIMPLER ORGANIC COMPOUNDS. 



Introduction. 



IN the foregoing chapter the methods of ascertaining the 

 composition of a given organic compound have been dis- 

 cussed, and it has been shown that analytical results alone 

 are not sufficient for the determination of its correct 

 formula, for different substances may contain the same 

 relative proportions of constituent elements and yet differ 

 from one another in their molecular complexity. The 

 axiom that substances of the same composition should 

 possess the same chemical properties was completely over- 

 thrown, and methods of fixing with certainty the true 

 formulae of organic substances were gradually established. 

 It was found, finally, that by the determination of molec- 

 ular weights, in addition to that of the composition of a 

 substance, its correct formula could be definitely fixed. 



The question which next arises is the following : Are 

 all substances with the same chemical composition and of 

 the same molecular complexity identical ? Experience 

 has shown that this question must be answered in the 

 negative. As long ago as 1823 Liebig found that a sub- 

 stance, silver fulminate, prepared by him, was identical 

 in chemical composition with, although totally different 



