182 



ALKALOIDS. 



174. Estimation of Alkaloids. In estimating the alkaloid in 

 leaves or easily pulverizable stalks, it will frequently be found 

 practicable to exhaust the powdered substance with spirit, 

 evaporate the tincture, and extract the residue with acidulated 

 water. The solution thus obtained may then be titrated with 

 potassio-mercuric iodide, as directed in 65. But if the material 

 contains much starch, or is difficult to powder (as, for instance, 

 ' aconite root), it is better to allow it to soak in about twice its 

 weight of dilute sulphuric acid (1 in 30) before extracting with 

 alcohol, as, otherwise, larger fragments of the substance are not 

 uniformly penetrated by the spirit. 



In estimating atropine, the drop-test (that is, the addition of a 

 drop of the precipitating solution to a filtered drop of the liquid 

 to be precipitated) cannot be used. It will be found advanta- 

 geous to add at once sufficient of the reagent to precipitate the 

 greater part of the alkaloid ; after standing several hours, until 

 the supernatant liquid has become clear, more of the reagent may 

 be added, and so on as long as a precipitate is produced. The 

 liquid clears more rapidly as the end is approached, till at last an 

 interval of five to ten minutes is sufficient. 



Atropine may also be estimated gravimetrically by adding 



