INTEODÜCTION. 



The chemical analysis of a plant is distinguished from that of a 

 mineral in several ways. 



1. With a minei-al the object of the analysis is the investigation 

 of the nature of its elements or of their simplest binary combi- 

 nations. 



With a plant it is otherwise, because the elements, constituting 

 the same,* are few in number and always the same, namely, car- 

 bon, hydrogen, nitrogen and oxygen, f 



It is true, all organic bodies do not contain these four elements 

 together ; but to all of them belongs carbon, with which in most 

 cases is combined oxygen and hydrogen, in some hydrogen, oxygen 

 and nitrogen, in others hydrogen and nitrogen, in others again 

 only hydrogen, and in a very small number only oxygen. Accord- 

 ing to the nature of their elements, the organic bodies form there- 

 fore the following five groups : 



Fh'st group, carbon combined with oxygen. 



Second „ „ „ „ hydrogen, 



Thii-d ,, „ „ „ „ and oxygen. 



Fourth „ „ „ „ „ „ nitrogen. 



Fifth „ „ „ „ „ „ „ and oxygen, 



of which the third group in regard to members greatly excels the 

 other four groups. 



* Once for all be it here remarked, that the investigation of plants in 

 regard to their inorganic constituents — the ash-analysis — is excluded from 

 this book, since I have published regarding this branch of science special 

 instructions already several years ago. 



t Sulphur, present in a very few proximate constituents of plants, may 

 here remain unconsidered. 



