3o6  Fluorescence  for  Detecting  Adulteration,  {^"'jify/is^s^'"'- 
matter  soluble  in  spirit  of  wine,  which  is  devoid  of  flourescence.  Tur- 
meric is  always  present  in  the  inferior  qualities  of  this  condiment,  be- 
cause the  actual  adulterant  is  wheaten  flour  or  rice,  the  turmeric  being 
necessary  to  bring  the  white  adulterant  up  to  the  same  shade  as  the 
ground  mustard  seeds,  therefore,  the  samples  vary  from  0*5  per  cent,  to 
O'05  per  cent,  of  turmeric.  Now,  with  such  minute  quantities  of  tur- 
meric, the  alkaline  test  is  very  unsatisfactory — in  fact,  all  chemical  re- 
actions are  unsatisfactory  when  dealing  with  such  a  minimum  of  adul- 
teration. 
But  the  great  elegance  of  this  fluorescent  test  consists  in  the  fact, 
that  within  reasonable  limits,  the  more  dilute  the  solution^  the  more  strongly 
does  the  fluorescence  test  come  out.  The  non-fluorescence  of  the 
coloring  matter  of  all  substances  that  are  adulterated  with  a  fluorescent 
substance  should,  in  the  first  instance,  be  exactly  and  scientifically  de- 
termined. This  is  easily  done  by  any  one  who  has  the  necessary  ar- 
rangements. In  the  case  of  the  mustard  yellow,  Mr.  H.  Draper  kindly 
-examined  it  for  me,  by  the  light  of  the  spark  formed  between  two  steel 
wires  (such  a  spark  being  the  best  for  the  purpose). 
The  steel  points  were  placed  in  connexion  with  a  four-inch  intensity 
-coil  and  a  small  Leyden  jar  was  interposed  in  the  circuit.  The  battery 
used  consisted  of  three  Groves  elements.  In  examining  by  this  method, 
ordinary  glass  vessels  must  be  discharged,  because  even  the  strongly 
marked  fluorescence  of  turmeric  is  more  or  less  masked  by  the  blue 
fluorescence  of  the  glass. 
In  a  quartz  cell  (two  plates  of  quartz  in  a  frame  of  gutta  percha), 
these  observations  can  be  carried  on  with  the  greatest  accuracy.  Mr. 
Draper's  observations  prove  that,  whilst  the  coloring  matter  of  the  true 
seeds  gave  no  fluorescence,  the  presence  of  so  small  a  quantity  of  tur- 
meric as  -005  per  cent,  could  be  readily  detected. 
Before  we  are  justified,  however,  in  using  this  phenomenon  as  the 
test  for  the  presence  of  any  substance,  it  is  necessary  to  put  it  to  a  cru- 
cial examination,  such  as  that  detailed  above  to  find  out  how  far  the 
particular  substance  under  examination  is  capable  of  giving  fluorescence. 
But  it  is  not  at  all  necessary  that  we  should  sumbit  it  to  the  light  of  a 
spark  in  the  practical  application  of  the  test.  The  fluorescence  of  an 
ordinary  white  glass  flask  is  not  observable  under  the  ordinary  diffused 
light  of  a  laboratory,  but  the  ordinary  fluorescent  substances  (so  called), 
are  easily  recognized  under  such  conditions.  It  is  only  necessary,  there- 
fore, to  form  a  tincture  of  the  substance  to  be  examined.    The  obser- 
