68 SUBSTANCES SOLUBLE IN ALCOHOL. 



evaporation with white bole and re-solution in water may be tried. 

 The iodide of silver and sulphate of barium are also at times \«ry 

 difficult to remove, and clear liquids can only be obtained by 

 repeated filtration through double filters. 



Should the alkaloid, after liberation with caustic baryta, be 

 sparingly soluble in water, it may be precipitated simultaneously 

 with the sulphate of barium. In this case it may be extracted 

 from the dry precipitate by treatment with alcohol or other 

 suitable solvent. But those alkaloids that resist extraction by 

 the method of agitation are generally freely soluble in water. 



Many alkaloids, too, are easily attacked by alkalies, splitting up, 

 on boiling, into acids and new complex amides. Atropine under 

 such circumstances yields tropine and tropic acid ; hyoscyamine 

 is resolved into the same two substances. (Cf. § 65.) How easily 

 errors are thus caused may be seen from the number of Mkaloidal 

 substances that have been described in text-books as special 

 alkaloids, and which arc in reality nothing but products of decom- 

 position (acolyctine and jiapeIline = aconiiie; lycoctonine = pseud- 

 aconine).^ Curarine is another alkaloid easily • decomposed by 

 alkalies. Certain members of this ' class are also decomposed by 

 boiling with dilute acids. 



If the alkaloid under examination is not easily attacked by 

 baryta or lime, it may be precipitated by phoqihomoiybdic or jphps- 

 pho-tungstw acid (§ 63), and separated from its combination with 

 either of these acids by baryta or lime, the excess of alkaline 

 earth being removed by carbonic acid. These methods, which 

 are sometimes of use in the quantitative estimation of certain 

 alkaloids, will be discussed in detail in § 177. 



§ 65. Estimation. — For the quantitative determination of alka- 

 loids, one of the following methods may be feasible : 



1 . The alkaloid obtained in § 64. may be dried and weighed. 



2. The substance removed by agitation according to ^ 55, 56, 

 may be weighed, care being taken to avoid loss.* 



' I avail myself of this opportunity to draw attention to the more recent 

 researches of Wright and Luff on the aconite-alkaloids. See Jahresb. I. Fharm. 

 1873, 131; 1874, 135; 1876, 169 j 1877, 434 J 1879, 189 ; and in Pharm. 

 Joum. and Trans. Pn atesin of Aconitum heterophylluin see Wasowicz, Arcbi v 

 d. Fharm. xiv. 193 (1879) (Pharm. Joom. and Trans. [31, x. 310). See papers 

 by Wright and Luff, etc., in Pharm. Joum. and Trans. [3], vols. ix. x. and xi. 

 ^ Compare the methods I have proposed for the quantitative estimation of 

 trychnine, brueine, and veratrine, in § 174. Gunther has successfully era- 



