CHAPTER II. 



THE IDENTIFICATION AND ANALYSIS OF ORGANIC 

 COMPOUNDS. 



THE bodies of plants and animals are composed for the 

 most part of highly complex substances, the structures of 

 which, even after several decades of investigations, have 

 not yet been elucidated in a perfectly satisfactory manner. 

 The chief reason for the delay in acquiring a more com- 

 plete knowledge of such complex substances lies, apart 

 from the fact of their complexity, in the circumstance that 

 no definite criteria of their purity exists, and the investi- 

 gator is often at a loss to know whether the product in 

 his hands is a chemical entity or a mixture of different 

 substances. As the first stage in the investigation of an 

 organic substance is the determination of its exact chemical 

 composition, it follows that the product submitted to 

 chemical analysis should be perfectly pure and free from 

 all contaminating admixtures. Now although it is often 

 impossible to attain such a standard of purity in the 

 case of very complex substances, it is generally possible, 

 by means of some chemical process, to degrade them into 

 simpler products, which can be readily obtained in a pure 

 state, and of which the chemical constitution, or structure, 

 can be determined. By a knowledge, then, of the nature 

 of the chemical process by means of which the degradation 

 lias been brought about, and by a knowledge, furthermore, 



