260 
Active  Principle  of  Senna  Leaves. 
j  Am.  Jour  Pharm. 
t       May,  1885. 
It  was  again  filtered,  and  as  the  CO2  does  not  decompose  all  the  cath- 
artate  of  baryta  the  cathartic  acid  is  found  partly  free  in  the  filtrate 
and  partly  as  cathartate  of  baryta  in  the  residue  on  the  filter.  The 
latter,  after  treatment  with  sulphuric  acid  and  filtering,  yields  a  light 
brown  colored  filtrate,  which  was  repeatedly  shaken  up  with  ether  to 
remove  the  coloring  matter  arising  from  a  slight  decomposition  of  the 
cathartic  acid.  It  was  then  carefully  neutralized  with  lead  carbonate 
or  oxide  at  a  very  slightly  elevated  temperature,  filtered,  and  so  much 
alcohol  and  ether  added  to  the  filtrate  that  a  moderate  precipitate 
occurred.  After  again  filtering,  the  filtrate  was  treated  with  very 
great  excess  of  alcohol  and  ether,  the  resulting  precipitate  of  cathar- 
tate of  lead  collected  on  a  filter,  washed  with  alcohol,  and  dried  in 
vacuo  over  sulphuric  acid.  There  remains  in  the  alcohol-ether,  how- 
ever, a  considerable  quantity  of  cathartic  acid,  because  the  neutral 
cathartate  of  lead  seems  during  the  precipitation  to  form  both  a  basic 
and  an  acid  salt,  the  latter  of  which  is  not  thrown  down. 
To  obtain  the  baryta  salt,  the  same  method  practically  is  used 
barium  hydrate  being  substituted  for  lead.  The  neutral  solution, 
however,  is  only  very  slightly  precipitated  by  alcohol-ether,  and  hence 
baryta  water  must  be  added  to  it,  thus  greatly  facilitating  the  precipi- 
tation. 
In  the  filtrate  obtained  after  treating  the  original  barium  precipitate 
with  CO2  there  is  also  a  large  amount  of  cathartic  acid,  which  may  be 
recovered  by  adding  acetate  of  lead,  treating  the  precipitate  with  sul- 
phuric acid,  filtering,  and  then  adding  to  the  filtrate  baryta  water. 
The  resulting  precipitate  is  then  washed  and  from  it  either  the  lead  or 
barium  salt  obtained  as  before. 
By  this  method  a  large  quantity  of  th()  cathartic  acid  is  undoubt- 
edly lost,  unless  the  various  filtrates  and  precipitates  be  re- worked,  but 
after  trial  of  many  other  methods  and  modifications  of  this  method,  I 
have  found  that  by  it  the  purest  specimens  of  cathartic  acid  are 
obtained.  The  chief  points  in  it  are:  (1)  that  the  solutions  of  the 
active  substance  must  never  be  evaporated  by,  or  even  exposed  to  heat, 
as  thereby,  whether  the  solution  be  acid,  alkaline  or  neutral,  decompo- 
sition is  certain  to  ensue.  This  was  proved  by  a  series  of  special 
experiments.  And  (2)  the  use  of  must  be  avoided,  as  it  was 
probably  from  this  that  the  sulphur  in  Kubly's  acid  arose. 
The  salts  have  the  following  characteristics :  Cathartate  of  lead  is  a 
non-crystalline,  grayish  powder.    The  neutral  salt  is  readily  soluble 
