198 
AN  ESSAY  ON  SENNA. 
ing  in  this  all  important  respect  from  chrysophanic  acid.  These 
coloring  matters  had  hot  been  in  combination  with  the  oxide  of 
lead  in  the  precipitate,  but  had  been  rendered  insoluble  in  the 
infusion,  and  had  been  carried  down  mechanically  and  diffused 
throughout  the  precipitate.  The  lead  precipitate  was  suspended 
in  water,  and  decomposed  by  a  current  of  HS,  the  liquid  removed 
from  the  precipitate  Pb,S  and  evaporated.  This  mass  did  not 
possess  any  peculiar  taste,  was  of  a  gummy  nature,  and  an  acid 
reaction,  owing  to  the  presence  of  the  vegetable  acids  existing  in 
the  drug,  such  probably  as  gallic,  malic  or  citric.  The  sulphide 
of  lead,  instead  of  being,  as  usual,  rejected,  was  collected,  dried 
and  boiled  in  alcohol.  This  liquid  became  of  a  brownish  color, 
and  left,  on  evaporation,  a  resinous  substance,  extremely  nauseous, 
and  similar  in  taste  to  the  inert  resin  extracted  directly  from 
Senna  by  stronger  alcohol.  It  is  insoluble  in  water,  but  readily 
soluble  in  alcohol  and  ether. 
The  power  of  sulphide  of  lead  as  an  absorbent  was  in  this  ex- 
periment somewhat  exemplified  ;  and  it  occurred  to  the  writer  of 
this,  that  this  property  might  be  taken  advantage  of  in  some 
earlier  steps  of  the  experiment. 
JSxp.  VI.  Eight  ounces  of  Senna  were  infused  in  boiling  water 
for  fifteen  minutes,  the  liquid  strained,  precipitated  by  liq. 
plumbi  subacetatis,  filtered,  and  the  excess  of  lead  removed  by 
HS.  The  sulphide  of  lead  was  collected,  dried,  and  boiled  in 
ether.  This,  upon  spontaneous  evaporation,  yielded  interlaced, 
acicular  crystals  of  a  dirty  white  color.  These  gave  on  first  trial 
no  impression  of  taste  to  the  palate  ;  but  in  a  few  moments  there 
became  evident  a  nauseous,  bitter  and  extremely  persistent  taste. 
They  proved  to  be  insoluble  in  water,  hot  or  cold,  insoluble  in 
cold  alcohol,  but  were  soluble  in  hot  alcohol,  ether,  and  especi- 
ally in  chloroform.  The  ethereal  solution  was  neither  acid  nor 
alkaline  to  test  paper.  They  were  insoluble  in  dilute  acetic 
acid,  and  also  in  alkaline  solutions,  thus  proving  the  substance  to 
be  a  neutral  principle. 
The  entire  quantity  which  remained,  amounting  to  nearly  five 
grains,  was  taken  at  once,  and  proved  actively  purgative  in  five 
hours.  A  small  proportion  of  animal  charcoal  was  added  to  the 
liquid  which  had  yielded  the  crystalline  matter  to  the  sulphide 
