§ 04. ALKALOIDS NOT ISOLATED BY AGITATION. 57 



To confirm the presence of an alkaloid, advantage may also be 

 taken of the fact that they all contain nitrogen, and, therefore, 

 yield Prussian blue with Lassaigne's test (heating with metallic 

 sodium, etc.). This test Avill be specially valuable if another 

 peculiarity of most, but not all, alkaloids — viz., the alkaline 

 reaction towards litmus and capability of forming salts — be not 

 well defined (colchicine), or if a compound be obtained which 

 must be referred to the group of amido-acids (colchicine) or 

 glucosidal alkaloids (solanine). It must not, however, be for- 

 gotten that some of the glucosides already mentioned contain 

 nitrogen (§ 167). For tables of the colour-reactions characteristic 

 of many alkaloids see § 171. 



§ 64. Alkaloids not Isolated hj the Metliod of Agitation ; Purifica- 

 tion. — In cases in which an alkaloid is present that cannot be 

 separated in this way or purified as recommended in § 63, the 

 foUo'wing method may be tried. The alkaloid is precipitated by 

 l^otassio-mercuric iodide from its solution in water acidulated with 

 dilute sulphuric acid, the precipitate filtered off, washed, sus- 

 pended in water and decomposed by sulj^huretted hydrogen. On 

 filtering off" the sulphide of mercury, a solution of the hydriodate 

 of the alkaloid together with free hydriodic acid is obtained. Sul- 

 phate of silver is then added as long as it causes a precipitate, and 

 the iodide of silver filtered off. After removing the siüphuric acid 

 by addition of caustic baryta and filtration, a solution of the 

 alkaloid may be obtained by freeing the filtrate from excess of 

 baryta by carbonic-acid gas. The last separation of baryta, 

 however, is not always quite complete. It might be better there- 

 fore in many cases to remove the sulphuric acid hj carbonate 

 instead of hydrate of barium. The former, moreover, Avould be 

 less likely to decompose the alkaloid. 



In following this method, inconvenience is occasionally experi- 

 enced in filtering off the sulphide of mercury, Avhich sometimes 

 separates in a very finely-divided state. To obtain a clear filtrate, 



clxxiv. 143 ; [3], v. 504 ; xiii. 25 ; Hesse, ibid. xii. 313 ; xiii. 481 ; 

 Godeffroy, Oesterr. Zeitschr. f. Pharm. 1878, Nos. 1 to 12 (Am. Journ. 

 Pharm. 1878, 178). For the action of silico-tungstic acid on alkaloids see 

 Godeffroy, Archiv d. Pharm, ix. 434 ; chloride of antimony and stannous 

 chloride see Godeffroj', ibid. 147, and Smith, Jahresb. f. Pharmacie, 1879, 166 ; 

 arseno-molybdic acid, selenic and telluric acid, Brandt, Jahresb. f. Pharmacie, 

 1875, 341. Smith heats trichloride of antimony and projects the alkaloid into 

 the fused mass. Morphine and codeine produce a greenish, narcotine olive- 

 green, thebaine, brucino and veratrine, red colouration. 



