SENNA. 
69 
acids  were  not  precipitable  from  liquor  sennse  by  acids  in  the 
cold,  I  at  once  suspected  that  they  derived  their  origin  from  the 
slow  decomposition  of  an  unstable  glucoside.  Another  supposi- 
sition  that  they  were  products  of  oxidation  was  negatived  by  the 
fact,  that  the  precipitation  occurred  in  perfectly  closed  vessels. 
An  examination  of  liquor  sennge  presented  the  following  reac- 
tions : — It  was  acid  to  test-paper.  When  treated  in  the  cold 
with  weak  hydrochloric  acid  it  did  not  deposit  anything  material 
before  ten  or  twelve  hours  had  elapsed.  Boiled  with  any  mineral 
acid  it  deposited  a  considerable  amount  of  dark  resin,  leaving 
the  fluid  nearly  colorless.  Comparative  tests  before  and  after 
boiling  with  acid,  with  Fehling's  liquor  showed  that  the  propor- 
tion of  glucose  had  been  increased  by  that  treatment.  Neutral 
acetate  of  lead  threw  down  an  abundant  pale  precipitate.  No 
precipitate  of  consequence  was  obtained  by  using  either  tannin, 
ammonia,  or  iodo-hydrargyrate  of  potash.  Basic  acetate  of  lead 
applied  to  the  filtrate  from  the  neutral  acetate,  produced  an 
abundant  orange  precipitate,  leaving  the  liquid  to  all  appearance 
destitute  of  any  active  principle  of  senna.  This  lead  precipitate, 
treated  with  cold  dilute  sulphuric  acid,  yielded  a  dark  solution, 
that  when  boiled  with  a  mineral  acid  yielded  a  resinous  precipi- 
tate, and  a  disagreeable  smell  of  stale  senna.  The  lead  was 
therefore  in  combination  with  the  glucoside,  for  which  I  was  in 
search.  Guided  by  these  results,  my  experiments  were  resumed 
on  a  larger  scale. 
A  quart  of  Liquor  Sennse,  that  within  a  fortnight  of  its  pre- 
paration had  commenced  to  deposit  resin,  was  neutralized  with 
ammonia.  The  precipitate  obtained  consisted  mainly  of  phos- 
phate of  lime. 
Neutral  acetate  of  lead  being  added  in  excess  to  the  filtrate  a 
precipitate  was  obtained,  consisting  of  certain  organic  acids  in 
combination  with  oxide  of  lead.  This  precipitate  washed,  sus- 
pended in  water,  and  decomposed  by  sulphuretted  hydrogen 
furnished  a  brown  acidulous  liquid,  which  was  decolorized  to 
some  extent  by  animal  charcoal,  and  then  neutralized  with  baryta 
water.  Of  the  baryta  compounds  one  part  was  soluble,  the  other 
not.  The  insoluble  part  was  treated  with  sulphuric  acid,  which 
eliminated  the  organic  acid.   The  soluble  part  was  reprecipitated 
