600  Blue  Coloring  Matter  of  Flowers.     i^"^' b^^'S^^""- 
even  Fownes'  Manual  is  entirely  silent  on  the  coloring  matter  of 
flowers,  carmin  and  carthamin  excepted,  though  a  number  of  other 
vegetable  coloring  matters  have  been  described.  The  cause  for  this 
disregard  is  evidently  to  be  looked  for  in  the  unsatisfactory  results 
thus  far  obtained,  and  these  are  very  easily  explained  by  the  difficul- 
ties surrounding  an  investigation  of  substances,  which  are  apparently 
not  crystallizable,  and  are  known  to  be  very  readily  altered  under  the 
influence  of  various  physical  and  chemical  agencies.  It  may, 
therefore,  be  of  interest  to  give  a  brief  summary  of  what  is  known 
concerning  the  nature  of  the  blue  coloring  matter  of  flowers. 
The  influence  of  woodash  and  similar  alkaline  substances  upon  cer- 
tain vegetable  colors  was  known  at  an  early  period  ;  but  these  charac- 
teristic reactions  were  first  studied  by  Eobert  Boyle  (1627-1691),  who 
was  "  the  first  chemist,  whose  investigations  in  chemistry  emanated 
solely  from  the  noble  impulse  to  explore  nature."^  He  observed  that 
the  alkalies  change  the  blue  vegetable  colors  to  green,  several  red 
ones  to  purple,  the  yellow  colors  to  red,  and  that  the  vegetable  colors 
altered  by  acids  are  restored  by  the  alkalies.^ 
Since  that  time,  and  more  particularly  during  the  past,  and  the 
early  part  of  the  present  century,  the  coloring  matter  of  blue  flowers 
has  been  frequently  used  as  a  reagent  for  alkalies  and  acids,  until  it 
has  been  entirely  supplanted  by  litmus,  turmeric  and  several  artificial 
coloring  matters.  Thus  we  find,  for  instance,  in  "  Cooley's  Cyclo- 
pedia of  Practical  Receipts,'^  under  the  heading  Paper,  Test, 
directions  for  the  preparation  of  test  papers,  and  among  other 
varieties  the  following  in  which  the  blue  coloring  matter  of  flowers 
and  fruits  is  utilized  : 
Dahlia  Paper ;  Georgina  Paper. — From  an  infusion  of  the  petals 
of  the  violet  dahlia  ( Georgina  purpurea),  alkalies  turn  it  green  ; 
acids  red  ;  strong  alkalies  turn  it  yellow.    Very  delicate. 
Elderberry  Paper, — From  the  juice  of  the  berries,  as  the  last. 
Mallow  Paper. — From  an  infusion  of  the  purple  flowers  of  the 
common  mallow  ;  aflected  like  dahlia  paper. 
In  some  localities  the  flowers  of  the  blue  violet  were  employed  as  a 
reagent,  and  a  permanent  solution  of  the  coloring  matter,  adapted  for 
the  purpose  indicated,  was  recommended  in  1810  by  Descroizilles,^  to  be 
^Kopp,  Geschichte  der  Chemie  I,  163. 
2Ibid.  Ill,  p.  27. 
^Trommsdorff,  Jour,  der  Phar.  xvii,  2,  p.  304. 
