A 5^SS^-wSni' }  Digitalis  Glucosides  and  Allied  Drugs.  45 
explained,  the  blue  coloration  is  probably  due  to  the  splitting  up 
of  the  digitoxin,  by  which  digitoxose  is  formed.  This  latter  most 
probably  causes  the  blue  ring,  for  Kiliani 28  has  found  that  digi- 
toxose yields  a  blue  color  when  dissolved  in  acetic  acid  containing 
iron  oxide  and  sulphuric  acid. 
In  analytical  practice,  the  following  reaction  for  the  three  most 
important  digitalis  glucosides  have  been  extensively  adopted,  being 
founded  on  the  observations  detailed  above : 
Digitalinum  verum  (and  digitalinum  Germanicum)  dissolves  in 
pure  concentrated  hydrochloric  acid,  or  sulphuric  acid,  giving  a 
yellow  color.  If  a  drop  of  dilute  ferric  chloride  solution  is  added 
to  the  solution  in  sulphuric  acid,  a  red  color  containing  a  touch 
of  blue  is  immediately  produced;  the  depth  of  the  red  coloration 
varies  according  to  the  amount  of  digitalin  present,  and  it  remains 
constant  for  days.  This  coloration  is  most  probably  due  to  digi- 
taligenin,  a  product  of  decomposition  of  digitalin.  If  sulphuric 
acid  containing  iron  oxide  is  used  for  this  reaction,  a  yellow  colora- 
tion often  appears  at  first,  which  lasts  for  a  short  time  and  very 
soon  changes  to  red.  Digitonin  is  not  altered  by  a  similar  test ; 
digitoxin  is  colored  a  dirty  greenish-brown  or  brown. 
Digitoxin  is  most  easily  recognized  by  Keller's  reaction  de- 
scribed above ;  it  may  also  be  carried  out  in  the  following  modifica- 
tion. To  100  c.c.  of  concentrated  sulphuric  acid  about  1  c.c.  of  a 
5  p.c.  aqueous  solution  of  ferric  sulphate  is  added,  while  a  mixture  of 
1  c.c.  of  the  same  ferric  sulphate  solution  with  100  c.c.  of  glacial 
acetic  acid  is  also  prepared.  If  now  a  trace  of  digitoxin  is  dis- 
solved in  about  5  c.c.  of  this  glacial  acetic  acid  containing  iron 
oxide,  and  this  solution  is  layered  on  to  5  c.c.  of  the  sulphuric 
acid  containing  iron  oxide,  the  coloration,  especially  the  bluish- 
green  band,  will  become  more  evident.  The  green  coloration 
referred  to  above,  formed  by  the  action  of  concentrated  hydrochloric 
acid  on  the  glucoside,  is  also  characteristic  of  digitoxin. 
Digitonin  is  not  colored  either  by  hydrochloric  acid  or  by  . 
sulphuric  acid  in  the  cold.  On  boiling  with  hydrochloric  acid, 
or  with  sulphuric  acid  which  is  not  too  dilute,  a  red  solution 
results  the  intensity  of  which  gradually  increases.  (Compare 
Cloetta,  Archiv  fur  experimentelle  Pathologie  1901,  Vol.  45,  p. 
4350 
The  reactions  given  above  suffice  as  a  means  of  identification  for 
pharmaceutical  purposes ;  they  are  not  conclusive  for  forensic 
28  Kiliani,  Berichte  der  deutschen  chemischen  Gesellschaft  Berlin  1898,  p.  2454. 
