48 SUBSTANOES 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. §§ lol, 16.5.) 



The weight of the dried residue frequently indicates with 

 toleiublft 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 maybe verified by titration with permanganate 

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

 ether 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 FOH GLUOOSIDES, BITTER PRINCIPLES, 

 ALKALOIDS, ETC. 



j 64. Extraction by AgitcAi<m.-^\i 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 . priuciple, 

 glucoside or alkaloid insoluble in ether but soluble in water is 

 suspected, the watery solution prepared from the evaporation 

 residue of the alcoholic tincture may be subjected to consecutive 

 treatment with various liquids which, being themselves insoluble 

 in water, are adapted for removal of substaiices in solution by 

 agitation and separation. The aqueous solution from the ethereal 

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

 petroleum spirit, benzene, and chloroform may be especially recom- 

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

 in which thej' .are named, and the Uquid should be rendered first 

 slightly acid with sulphuric acid, and subsequently alkaline. with 

 ainniouia ; I have spoken at length on this Subject in my ' Ermit- 

 teluiig 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 



' P. 119. Compare also Russ. Arohiv furgerichtl. Med. J, i. und Pharni. 

 Zeitschr. I. Russland, v. 85 ; vi. 663. 



