DIYISIOIS^ III. 



GENERAL SYSTEMATIC COURSE OF PHYTO- 

 CHEMICAL ANALYSIS. 



Ether, alcohol, and water, are, as recorded, the most important 

 solvents, respectively extracting agents used in phy to-chemical 

 analysis; acids, alkalies, &c., being of less importance. 



In using the above three liquids, it would appear at first of 

 little consequence in what order they are applied to the su.bstance 

 under investigation, as, after all, the parts soluble in them must 

 enter these liquids as extracts; but taking into consideration all 

 circumstances for the purpose, it soon becomes evident that a 

 certain order has to be adhered to. Those special cases are of 

 course excepted wliei-e it is required to obtain or to recognise only 

 one constituent, and when the choice of the solvent depends 

 already on the nature of the particular constituent, as for 

 example, when ether is required for extracting a fixed oil, and 

 water for gum. Still, if a thorough investigation of the chemical 

 constitution of plants should be intended, then I would recom- 

 mend to follow the practice adopted by me since many years, — 

 to treat the substance first with ether, then with alcohol, and last 

 with water, the reasons for which treatment I shall give 

 j)resently. 



1. By treating the generality of vegetable substances with 

 ether the latter dissolves fat and wax readily and completely; 

 alcohol dissolves these bodies also, but less readily, and only at 

 the boiling heat, and as it deposits them again on cooling, and as 

 filtering is retarded thereby, it becomes necessary to employ ether 

 for removing the rest of fat or wax. These two substances, thei-e- 

 fore, are passing into two difierent solvents. If the analysis is 

 commenced with alcohol, this inconvenience increases when, as in 

 seeds, the quantity of fat or wax pi-edominates, and it can only be 

 avoided by the previous treatment with ether. 



2. Certain alkaloids, bitter substances or resins, dissolve in 

 alcohol and in ether, others only in alcohol. Now, by commencing 



