176 
Indicators  in  Nature. 
Am.  Jour.  Pharm. 
April,  1901. 
The  colors  of  the  coleus,  especially,  depend  on  the  degree  of 
acidity  of  the  leaf  as  well  as  on  the  kinds  and  distribution  of  the 
colors.  With  coleus  colors  there  is  a  regular  change  in  color  from 
acid  to  alkaline,  or  the  reverse,  passing  through  several  stages.  It 
is  easy  to  see  that  a  slight  change  in  the  acidity  of  the  sap  of  the 
leaf  will  affect  the  color  and  give  rise  to  some  of  the  manifold 
variations  that  are  observed  in  the  coleus.  The  same  may  be  said 
of  some  flowers. 
METHODS  OF  EXAMINATION. 
Two  methods  were  adopted  for  testing  the  color.  In  the  one, 
small  portions  of  the  material  were  placed  into  two  test-tubes  with 
alcohol,  a  few  drops  of  fifth-normal  hydrochloric  acid  added  to  one, 
of  tenth-normal  caustic  soda  to  the  other,  and  the  changes  noted. 
It  usually  requires  some  time  for  the  effect  to  be  visible.  In  the 
second  method  the  material  was  boiled  in  a  large  test-tube  with 
about  20  c.c.  of  water,  to  which  a  little  alcohol  was  often  addedr 
cooled,  the  extract  poured  off,  and  titrated  with  fifth-normal  acid 
and  tenth-normal  ammonia.  The  two  methods  usually  gave  the 
same  results,  though  they  were  sometimes  different,  as  was  to  be 
expected,  as  in  the  one  case  all  of  the  color,  soluble  and  insoluble, 
was  subjected  to  the  action  of  caustic  soda ;  in  the  other  case  only 
the  soluble  part  was  treated  with  ammonia.  Method  2  allowed 
some  conclusion  as  to  the  sensitiveness  of  the  color  to  be  made. 
Class  I. — Color  unaffected  by  acid  or  alkali.  This  includes  the 
orange  flowers  of  StyJosanthus  biflora,  the  yellow  ones  of  CJirysogo- 
num  Virginianum,  and  the  leaves  of  a  smooth,  red  variety  of  coleus. 
Three  materials  not  containing  indicators  were  found  out  of  eighty- 
one  examined. 
Class  II. — The  flowers  in  this  class  give  a  colorless  extract  which 
becomes  yellow  when  made  alkaline. 
The  color  is  moderately  sensitive.  All  of  the  flowers  but  one — 
t*he  white  petals  of  the  wild  daisy — are  yellow  or  orange.  Yellow 
is  a  color  which  cannot  be  extracted  by  boiling  water.  In  some 
cases  it  goes  into  solution  with  the  tenth-normal  caustic  soda. 
This  class  comprises  10;  stamens  of  begonia  and  Solanum  Caro- 
linense;  petals  of  canna,  Oenothera  sinuata,  Hypoxis  erecta,  butter- 
cups, allamanda,  wild  daisy,  a  yellow  wild  flower,  and  leaves  of  the 
yellow  coleus. 
