188 ALKALOIDS. 



the alkaloi(-l from the precipitate. Ten grams of the substance 

 are rubbed down with water to a fine paste, then exhausted by- 

 boiling -n-ith the same menstruum, filtered and washed with 

 boiling water (700 to 800 cc), as long as alkaloid can be detected 

 in the washings. Tlie mixed aqueous solutions ai'e precipitated 

 "with ammoniacal acetate of lead and filtered. The filtrate is made 

 alkaline with caustic soda, evaporated to 50 cc, acidified with 

 sulphuric acid, and again filtered. From the acid solution, which 

 should contain about 6 per cent, of free sulphuric acid, the theo- 

 bromine may be precijiitated by warming with jihosphomolybdic 

 acid. The precipitate is collected when cool, washed Avith water- 

 acidified Avith sulphuric acid, and decomposed by warming with 

 caustic baryta ; the excess of the latter is removed hy sulphuric acid 

 and the sulphuric acid by carbonate of barium. The mixture is- 

 then filtered whilst hot, evaporated to dryness, and Aveighed. By 

 deducting the ash the amount of j)ure theobromine is found. 



§ 178. Estimation of Piperine. — The folloAving is Cazeneuve- 

 and Caillot's method : ^ 10 grams of finely-ground pepper are 

 mixed Avith 20 of slaked lime, and enough Avater to form a thin 

 paste, boiled for fifteen minutes, and then evaporated to dryness 

 on a A\'ater-bath ; the residue is finely poAvdered and exhausted Avith 

 ether. The pipeline obtained by evaporating the ethereal solution 

 is recrystallized from alcohol and weighed. It Avoukl, I think, be 

 better if the powdered pepper Avere first freed from fat by treat- 

 ment Avith petroleum spirit. Possibly the alkaloid might then be 

 jmrified by Avashing Avith petroleum spirit and Avater instead of 

 recrystallizing from alcohol. (Compare also >5 64.) 



§ 179. AcidimetricEstiiiiafiim of Nicotine. — Schloessing's process, 

 mentioned in § Q^, consists in extracting the nicotine by passing 

 the vapour of ether and ammonia through the tobacco, condensing 

 the distillate, alloAving the ether and ammonia to evaporate, and 

 titrating the residual nicotine Avith dilute sulphuric acid. But 

 the alkaloid retains ammonia, and the amount found is conse- 

 quently too high. (Compare Kosutany and my ' Werthbestim- 

 mxuig.') 



Wittstein, Biandl, and Liccke, all extract the tobacco Avith 

 water acidified Avith sulphuric acid. liiccke evaporates to a 

 syru}), prcci])itates Avith 2 volumes of alcohol, Avashes, and again 

 evaporates. The I'csiduc is made alkaline Avith excess of potash,, 



Zeitschr. f. anal. Clicm. xvii. :j1'.\ 187S (Vear-book of riiann. 42, 1878). 



