334  Alkaloidal  Color  Tests.  {Amiuiy;fm.cm' 
ethereal  or  chloroformic  extraction  directly  with  the  original 
material. 
F.  Selmi 1  further  purifies  the  alkaloids,  as  usually  obtained  in 
the  ethereal  extractive,  by  precipitating  them  from  this  ethereal 
solution,  both  with  and  without  an  excess  of  water,  by  means  of 
carbon  dioxide.  This  method  is  said  to  possess  certain  merits,  but 
on  account  of  the  uncertainties  usually  encountered,  the  method  has 
gained  very  little  prestige. 
Notwithstanding  such  elaborate  and,  apparently,  faultless  schemes, 
this  department  of  chemistry  presents  many  complex  problems. 
When  it  is  remembered  that  nearly  2,000  substances,  with  definite 
chemical  individualities,  have  been  separated  from  plant  tissues,  and 
there  is  scarcely  a  line  of  demarcation  anywhere  between  them,  but 
they  imperceptibly  grade  into  one  another ;  then  add  to  this  the 
host  of  synthetic  bodies,  which  are  employed  as  medicinal  remedies, 
the  difficulties  to  be  encountered  in  isolating  in  a  pure  state,  even 
some  of  the  most  characteristic  ones  from  a  heterogeneous  mixture, 
becomes  quite  apparent. 
ANALYTICAL  REACTIONS  OF  STRYCHNINE. 
Most  alkaloids  are  precipitated  from  aqueous  solutions,  acidulated 
with  a  mineral  acid,  by  a  number  of  reagents,  such  as  Mayer's, 
Wagner's,  Scheibler's,  Sonnenschein's,  etc.,  and  they  serve  very  well 
as  general  reagents  for  establishing  the  presence  of  alkaloids ;  but 
further  than  this,  little  has  been  done  with  these  reagents  which  is 
of  distinct  service  in  establishing  the  individuality  of  an  alkaloid 
either  qualitatively  or  quantitatively.  We  must,  therefore,  look  for 
other  information  leading  up  to  the  identification  of  the  various  alka- 
loids, and  this  has  been  largely  supplied  by  way  of  color  reaction. 
But  can  these  color  reactions  be  utilized  as  the  basis  of  a  positive 
opinion?  Blyth  says,  in  substance,  fairly  pure  alkaloids  give  cer- 
tain color  reactions  more  or  less  characteristic,  but  they  are  gener- 
ally untrustworthy  and  must  be  looked  upon  as  useful  guides  only, 
to  be  confirmed  by  other  characteristics  of  the  substance  in  quest. 
There  are  probably  very  few,  if  any,  of  the  many  alkaloidal  color  re- 
actions that  can  be  ascribed  to  definite  chemical  changes.  In  many 
cases,  the  color  reactions  are  probably  due  to  the  presence  of  minute 
quantities  of  associated  impurities,  rather  than  the  pure  material 
itself.    Again,  the  various  shades  of  color  are  usually  difficult  to 
1  1877,  Gazett.  Chim.  Ital.,  6,  153  ;  Jour.  Chetn.  Soc,  1,  93. 
