48 SUBSTANCES SOLUBLE IN ALCOHOL. 



tion (§ 48) directly with ether, renewing the solvent four or five 

 times. On evaporating the ethereal solution, both gallic and 

 catechuic acids remain behind in a crystalline form, generally 

 needles felted together. (Cf. §§ 151, 165.) 



The weight of the dried residue frequently indicates with 

 tolerable accuracy the quantity of the substance present ; but if 

 the residue be mixed with much colouring or amorphous matter, 

 so as to cause some hesitation in accepting the weight as correct, 

 the result obtained may be verified by titration with permanganate 

 of potash. (See above.) If the material has been extracted with 

 «ther previous to treating with alcohol, gallic and catechuic acids 

 ■will be found in the aqueous solution from the ethereal extract. 

 <Cf. §§ 38, 151.) 



For the free vegetable acids which may occur in the alcoholic 

 extract see § 82. (See also in § 159.) 



EXAMINATION FOR GLUCOSIDES, BITTER PRINCIPLES, 

 ALKALOIDS, ETC. 



§ 54. Extraction h?j Agitation. — If no tannic acid or allied sub- 

 stance has been found in the aqueous liquid (§ 48), but by the 

 bitter taste or other properties the presence of a bitter principle, 

 i^lucoside or alkaloid insoluble in ether but soluble in water is 

 suspected, the watery solution prej)ared from the evaporation 

 residue of the alcoholic tincture may be subjected to consecutive 

 treatment with various liquids which, being themselves insoluble 

 in water, are adajited for removal of substances in solution by 

 agitation and separation. The aqueous solution from the ethereal 

 extract (§ 38) may also be treated in a similar manner. The use of 

 petroleum s})irit, benzene, and cliloroform may be especially recom- 

 mended for this purpose ; they should be employed in the order 

 in which they are named, and the liquid should be rendered first 

 slightly acid with sulphuric acid, and subsequently alkaline with 

 ammonia; I have spoken at length on this subject in my 'Ermit- 

 telung der Gifte.'^ After each agitation, the solvent should be 

 separated, washed once by shaking with pure water, again 

 separated, evaporated to dryness, and the residue examined. If a 

 solvent, as for instance petroleum spirit, removes any appreciable 

 quantity of a substance, the agitation with this liquid should be 



1 P. 119. Compare also Russ. Archiv f lir ^'erichtl. Med. J. i. und riiaim, 

 Zuitischr. f. Ptussland, v. 85 ; vi. 663. 



