A^;nJu0aryV^9Sm•}  Digitalis  Glucosides  and  Allied  Drugs.  43 
stituent  of  digitalin  Homolle  this  coloration  is  due  is  uncertain ; 
it  may,  however,  be  pointed  out  that  among  the  digitalis  glucosides 
which  have  since  been  studied  in  detail  the  only  one  which  gives 
this  reaction  is  digitoxin.  Digitalinum  verum  is  colored  yellow 
by  hydrochloric  acid,  digitonin  remains  colorless  and  on  heating 
with  this  acid  it  becomes  red. 
Later  on  Homolle's  reaction  underwent  several  modifications, 
some  of  which  were  quite  unnecessary,  with  the  intention  of  render- 
ing it  more  characteristic.  Thus  Jorissen  18  used  a  solution  of  1 
gramme  of  zinc  chloride  in  30  grammes  of  water  and  30  grammes 
of  hydrochloric  acid.  As  might  have  been  expected,  it  gave  a 
green  color  with  digitalin.19  The  second  part  of  Jorissen's 
reaction,  namely  that  digitalin  when  evaporated  with  the  zinc 
chloride  solution  mentioned  above  assumes  a  brown  or  black  color, 
cannot  be  considered  characteristic  for  digitalin,  even  though 
Czumpelitz 20  attributes  the  chestnut-brown  color  obtained  on 
evaporating  to  dryness  to  be  due  to  the  condensing  action  of  the 
zinc  chloride.  O.  Pape 21  varied  Homolle's  reaction  by  mixing 
digitalin  19  with  ten  times  the  amount  of  starch,  adding  sufficient 
concentrated  sulphuric  acid  to  form  a  thick  paste  and  then  diluting 
with  hydrochloric  or  nitric  acid.  The  starch  is  said  to  be  colored 
green  by  this  method.  Lafon  22  heated  digitalin  19  with  a  mixture 
of  alcohol  and  sulphuric  acid  (1:1)  until  it  became  yellow  and 
then  added  a  drop  of  very  dilute  iron  chloride  solution.  This 
also  gave  a  green  color.  This  color  is  probably  produced  by 
all  mineral  acids  under  suitable  conditions,  and  also  by  sulphuric 
acid,  provided  it  is  not  masked  by  secondary  reactions  giving  dark 
colored  or  black  products,  or  by  the  brown  coloration  resulting 
from  its  mixture  with  the  red  digitalin  reaction  described  below. 
Fliickiger 23  modifies  the  test  as  follows :  he  concentrated  phos- 
phoric acid  (25  p.  c.)  by  heating  on  a  watch  glass,  and  added 
digitalin  Nativelle  to  the  warm  acid.    The  digitalin  was  colored 
38  Jorissen,  Chemisches  Zentralblatt  1880,  p.  376. 
19  This  must  be  a   French  digitalin,   such  as  digitalin  Homolle,  digitalin 
Nativelle,  or  digitalin  amorph.  Gallicum,  for  digitalinum  verum  never 
gives  a  green  coloration. 
20  Czumpelitz,  Pharmazeutische  Post  1881,  p.  47. 
21  Pape,  Archiv  der  Pharmazie,  1876,  p.  233. 
22  Lafon,   Comptes  rendus   de  l'academie   des   sciences  Vol.   100,  p.  1463. 
—  Bulletin  de  la  societe  chimique  Vol.  44,  p.  18. 
23Fliickiger,  Neues  Jahrbuch  der  Pharmazie  Vol.  39,  p.  129. 
