ON  RESINS  OF  JALAP  AND  SCAMMONIUM. 
447 
Kayser  and  Wm.  Mayer,  is  by  the  action  of  alkalies  converted 
into  an  acid  insoluble  in  water,  to  which  was  given  the  name^of 
rhodeoretic  acid.  That  part  of  the  resin  which  is  soluble  in  ether 
is  changed  the  same  way ;  for  if  the  resin  is  dissolved  under  ap- 
plication of  heat  in  diluted  caustic  potassa,  and  an  excess  of  sul- 
phuric or  muriatic  acid  then  added,  the  liquor  will  remain  undis- 
turbed, or  become  a  little  opalescent  without  any  precipitate, 
according  to  the  discoloration  of  the  resin  by  charcoal. 
On  this  property  a  method  may  be  founded  to  prove  the  purity 
of  the  commercial  resin  of  jalap  by  a  single  experiment,  as  the 
common  adulterations,  rosin,  resins  of  guaiacum  and  agaric,  are 
precipitated  by  acids  from  their  alkaline  solutions.  A  little  of 
the  resin  is  to  be  dissolved  in  diluted  caustic  potassa  or  soda,  the 
solution  heated,  filtered,  if  necessary,  and  then  diluted  sulphuric 
acid  added  in  excess.  The  pure  resin,  as  stated  above,  will  to 
the  utmost  produce  a  slight  opalescence ;  an  adulteration  of  but 
a  very  small  quantity  of  a  common  resin  will  instantly  form  a 
thick  resinous  precipitate. 
In  this  manner  it  cannot  be  detected,  if  the  resin  of  the  tubers 
of  the  genuine  jalap  be  substituted  by  that  of  the  spindle-shaped 
root  of  Ipomsea  (convolvulus)  orizabensis,  which,  according  to 
Dr.  Mayer,  is  acted  upon  analogous  to  rhodeoretin.  But  this  is 
entirely  and  easily  soluble  in  ether,  the  resin  of  the  genuine 
jalap  only  to  the  smaller  part. 
Experiments  made  in  my  laboratory  by  Dr.  Spirgatis,  show 
that  scammony,  like  rhodeoretin,  by  alkalies  is  changed  into  an 
acid,  very  soluble  in  water  and  therefore  not  precipitated  by 
acids.  The  above  method  may  also  be  adopted  for  the  detection 
of  adulterations  of  scammony  with  any  of  the  common  resins. 
The  powdered  scammony  is  heated  with  solution  of  potassa,  fil- 
tered, and  an  excess  of  diluted  sulphuric  acid  added.  Genuine 
Aleppo  scammony  produces  only  an  opalescence  or  a  slight  tur- 
bidness,  but  a  considerable  resinous  precipitate  will  appear  if  the 
drug  be  adulterated  with  rosin  or  another  of  the  common  resins. 
The  experiment  will  be  still  more  satisfactory  if  the  scammony 
is  extracted  with  alcohol,  the  solution  dissolved  by  shaking  it 
with  animal  charcoal,  filtered,  evaporated  and  treated  as  above ; 
for  the  alcoholic  solution  of  the  decolorized  scammony,  like  that 
of  the  purified  resin  of  jalap,  is  not  affected  by  acids, — (Buck- 
ner's  Repertorium  f.  Pharm.  iii.  1.) 
