57, 58. DIRECT TESTS FOR ALKALOIDS, ETC. 51 



this method of agitation is doubtless very large, and by making 

 the required experiments the list given in the preceding section 

 might be rendered far more complete. It is this very fact 

 that renders the method so suitable for the qualitative exami- 

 nation of those plants and parts of plants the constituents 

 of which are at present unknown. Of course, it is possible to 

 employ infusions which have been prepared by digesting the 

 material under examination with water on the water-bath, instead 

 of aqueous solutions from the ethereal or alcoholic extracts. This 

 would especially be the case if acids, bitter principles and gluco- 

 sides are to be looked for. Alkaloids may likewise be tested for 

 by digesting the material with water acidulated with sulphuric 

 acid (1 in 50). In both cases, however, it must be remembered 

 that by thus directly extracting the substance with aqueous liquids 

 many bodies, such as mucilage, etc., are dissolved, and that this 

 is avoided by treating them according to the method first de- 

 scribed. The presence of such substances is disadvantageous, 

 inasmuch as they sometimes render the extraction of a principle 

 from aqueous solution by the method of agitation more difficult, 

 and always act injuriously in rendering the separation of the two 

 liquids after shaking almost impossible. It is therefore advisable 

 to remove all matter tending to increase the viscosity of the 

 aqueous infusion by concentrating to a syrupy consistence (if 

 necessary, after having previously nearly neutralized with ammonia 

 or magnesia), precipitating with about three volumes of spirit, 

 filtering after standing twelve to twenty-four hours in a cold place, 

 and distilling off the alcohol. 



58. Alkaloids, etc., not Removable ly Agitation. Some bitter 

 principles, glucosides and alkaloids cannot, however, be removed 

 from solution by agitation, either because they have less tendency 

 to pass into any other known liquid than to remain in aqueous 

 solution, or because they are insoluble in water. The latter is 

 the case, for instance, with the glucosidal resins which occur in 

 the convolvulaceaB. Such substances are generally isolated with 

 the resins. (Cf. 153.) 



The purification of bitter principles and glucosides that are 

 soluble in water, but cannot be removed by shaking, may be 

 effected by evaporating the aqueous solutions prepared from the 

 ethereal or alcoholic extracts, and repeatedly dissolving the sub- 

 stance in chloroform, alcohol, or ether. It will be found easier to 



42 



