39, 40. PORTION SOLUBLE IN ALCOHOL. 33 



and other glucosides, and alkaloids may be looked for. The 

 latter, however, may, as a rule, be more easily extracted with 

 water containing acetic or sulphuric acid. A measured portion 

 of the aqueous liquid may be evaporated, and the residue weighed. 

 For the detection of hsematoxylin and allied substances see 150 ; 

 of gallic acid, etc., 151 ; of salicylic and benzoic acid, 26, 34; 

 of glucosides, 54 et seq., 165 et seq. ; of alkaloids especially, 63 

 .et seq., 171 et seq. 



39. Portion Soluble in Alcohol. The part insoluble in water 

 should be again dried and extracted in a similar manner with 

 .absolute alcohol. If the plants under examination contain much 

 resin it will often be observed that a part only of the resinous 

 constituents, etc., dissolves in alcohol. The amount of matter 

 soluble in alcohol, as well as in ether, must then be determined 

 by evaporating the alcoholic solution and weighing the residue. 



We have thus determined (a) the total substances dissolved by 

 ether, (b) any fat that may have been extracted, (c) the substances 

 .soluble in ether and water, (d) substances insoluble in water, 

 .soluble in ether and in alcohol, and (e) substances extracted by 

 ether insoluble in water and alcohol. 



The next step is to obtain a further insight into the nature of 

 the resinous substances soluble in ether alone, as well as those 

 soluble in ether and alcohol. 



40. Microchemical Examination. The microscopical examina- 

 tion shows that the resins are present partly in the cell wall, 

 saturating it as it were, and partly in the form of exudations 

 either within or upon the cells. Special attention should be paid 

 to their insolubility in water, solubility in alcohol or ether, to the 

 red colour which, according to Miiller, is produced with resins by 

 alcoholic tincture of alkanna, violet or blue (Hanstein) by aniline. 

 .Some of the reactions enumerated in 146 might also be made 

 available for microchemical analysis. 



In the macrochemical examination it should first be ascertained 

 whether the resin cannot be separated into different component 

 parts by the use of other solvents, such as chloroform, benzene, 

 bisulphide of carbon, acetone, acetic ether, or boiling absolute 

 alcohol, or finally by precipitating the concentrated ethereal 

 solution with alcohol, petroleum spirit, or other suitable liquid. 

 Similarly, if a substance soluble in ether has not from the tirst 

 been obtained in crystals, slow evaporation of the solution in the 



3 



