§§ 2, 3. INTRODUCTION. 3 



Part I, I have not separated the qualitative and the quantita- 

 tive determinations of the more important substances from 

 each other. I have made the method of separation serve as a 

 leading principle, and have therefore grouped together the 

 constituents of plants in such a manner that all those may be 

 considered together that are isolated by the same means. I 

 have then placed in sub-divisions of the principal groups such 

 substances as may be isolated by special methods, and these 

 latter are also discussed. 



The more important peculiarities of the various bodies belong- 

 ing to the different groups, as well as special methods for the 

 estimation of some of them, have been placed in Part IL, which 

 has been so arranged as to follow closely on Part I. in the form 

 of a supplement. In this way I hope to be more easily able 

 to avoid repetition, and especially to facilitate investigations in 

 which the substances that may be found are unknown. Thus a 

 method of analysis, taking account of the more important con- 

 stituents of plants, may be traced through the work. 



§ 3. It has always been accepted, as an important principle, 

 by those who have been engaged in plant analysis, that the 

 constituents present should be separated as far as possible by 

 means of different solvents. I have also followed this plan, 

 which has in many instances proved itself adapted to the attain- 

 ment of the object in view, and I concur Avith those chemists 

 who recommend the use, as far as practicable, of the most in- 

 different solvents. If, in the analyses of vegetable substances 

 I have already made, I have deviated from the course followed 

 by my predecessors, ^ I have done so, first, in increasing the 

 number of solvents ; and secondly, in varying the order in 

 which those solvents were allowed to act upon the substances 

 under examination. I shall subsequently show that this may 

 have a great influence on the result of the analysis. 



^ I draw particular attention here to Rochleder's 'Anleitung zur Analyse 

 von Pflanzen und Pflanzentheilen ' (Würzburg, 1858), which I regard as open- 

 ing up new ground in this subject. See also Wittstein, 'Anleitung zur 

 chemischen Analyse von Pflanzentheilen' (Nördlingen, 1868), and an English 

 translation of the same by Baron von Mueller, ' The Organic Constituents of 

 Plants and Vegetable Substances and their Chemical Analysis ' (Melbourne, 

 1878) ; Arata, ' Guja Paralel Analysis immediato de los Vejetales ' (Buenos 

 Aires, 1869) ; and a paper by Parsons in the American Chemical Journal, 

 vol. i. No. 6. 



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