AmAp0rUii,'i9oi?rm'}  Indicators  in  Nature.  177 
Class  III — In  this  class  the  materials  give  extracts  which  are 
red  or  a  shade  of  red  when  acid,  yellow  or  a  shade  of  yellow  when 
alkaline.  All  the  colors  are  fairly  sensitive,  being  changed  by  at 
least  two  drops  of  tenth-normal  ammonia.  Twenty-one  of  the  81 
materials  examined  fall  into  this  group,  11  being  originally  red  or 
pink  flowers,  4  orange  or  yellow,  5  purple  or  violet,  1  green  (coleus 
leaf).  The  red  and  pink  flowers  were  the  pink,  rose  (faint  pink, 
rose  and  wild  rose),  pink  larkspur,  crimson  clover,  phlox  (faint 
pink,  light  claret,  rose,  scarlet,  magenta),  begonia  (2  varieties), 
double  oleander,  a  variety  of  Euphorbia,  Spensonia  goligefolia  rosa, 
Clerodendrum  and  Silene  Virginica.  With  the  exception  of  Clero- 
dendrum,  which  gave  a  well-colored,  orange-pink  solution,  all  of  the 
flowers  above  named  were  bleached  when  boiled  with  water, 
giving  a  colorless  or  faintly  colored  solution,  which,  however, 
became  colored  on  the  addition  of  acid  or  ammonia.  Verbena 
flowers  gave  extracts  yellow  with  caustic  soda,  but  green  with 
ammonia,  and  the  extract  from  sweet  peas,  green  when  first  made 
alkaline,  became  yellow  on  standing.  These  two  are  included  in 
Class  IV. 
The  purple  or  violet  flowers  were  the  vetch,  Mexican  sage,  helio- 
trope, Clematis  ochroleuca  and  Solatium  Carolinensis.  They  were 
bleached  by  the  boiling.  The  orange  or  yellow  flowers  were  orange 
nasturtium  and  canna,  Asclepias  tuberosa,  yellow  Allamanda  vereo- 
folia.  The  yellow  color  of  the  flower  was  unaffected,  but  a  color- 
less or  faintly  colored  extract  was  formed  which  became  colored  on 
addition  of  acid  or  ammonia.  A  red-orange  extract  was  obtained 
from  the  green  part  of  the  leaf  of  a  red  and  green  coleus,  which 
was  red  with  acid  and  brown-yellow  with  ammonia. 
Class  IV. — This  includes  those  coloring  matters  which  are  a  shade 
of  red  when  acid,  a  shade  of  green  when  alkaline.  The  greens 
are  at  times  of  a  beautiful  emerald  color,  sometimes  of  a  yellowish 
tinge.  Most  of  the  colors  are  very  sensitive  to  the  reagents,  being 
affected  by  less  than  one  drop  of  tenth-normal  ammonia. 
Thirty  of  the  materials  examined  fall  into  this  class,  15  being 
originally  a  shade  of  red,  9  violet  or  purple,  3  blue,  I  lilac,  I  black 
(bean),  1  yellow.  The  flowers  a  shade  of  red  were :  red  clover, 
scarlet  sage,  Canterbury  bell,  red  zinnia,  rose  geranium,  crimson 
honeysuckle,  California  poppy,  verbenas  (faint  pink  and  rose),  sweet 
peas  (faint  pink,  rose,  maroon,  magenta,  lavender),  gladiolus  (rose), 
