318  Bichloride  of  Mercury  Tablets.       { Am'jui°y  r*i9Pi4arm' 
of  red,  have  led  to  the  use  of  other  colors.  The  British  Pharma- 
ceutical Codex  directs  methyl  violet,  which  in  this  combination  gives 
a  blue-purple  solution.  The  Swiss  Pharmacopoeia  orders  Eriocy- 
anin  A,  the  sodium  salt  of  a  sulphonated  dye  of  the  triphenyl- 
methane-carbinol  type  that  colors  silk  and  wool  a  bright  blue  and 
is  only  slightly  affected  by  10  per  cent,  hydrochloric  acid.  The 
French  Codex  directs  indigo  carmine  for  this  purpose. 
A  number  of  the  manufacturers  are  already  giving  preference  to 
the  blue  tablets.  One  of  these  writes :  "  Green  and  red  colored 
tablets  are  not  at  all  satisfactory.  I  believe  that  you  will  agree  with 
me  that  a  sombre  blue  would  prove  the  most  desirable.  Confections 
are  made  in  red,  green,  yellow,  white,  and  every  conceivable  color, 
but  the  blue  is  not  attractive  and  therefore  would  in  all  probability 
prove  the  safest.  On  the  question  of  coloring  for  mercuric  chloride, 
Dr.  A.  G.  Rosengarten,  whose  firm  prepares  large  quantities  of 
mixed  salts  already  colored  for  the  manufacturers,  writes  me ; 
"  The  only  satisfactory  color  that  we  have  found  is  the  blue  dye, 
called  indigo  carmine.  We  have  not  yet  found  a  satisfactory  red  or 
green  dye,  but  I  can  highly  recommend  indigo  carmine  for  consistent 
results,  and  a  definite  weight  of  that  dye  added  to  a  definite  weight 
of  corrosive  sublimate  mixture  will  produce  definite  results.  I  can- 
not say  the  same  about  the  other  dyes,  and  I  think  it  will  be  most 
desirable  to  confine  the  dyes  for  corrosive  sublimate  mixture  to 
the  one  color,  blue,  and  the  one  dye,  indigo  carmine." 
My  own  experiments  confirm  these  statements  as  to  the  avail- 
ability of  indigo  carmine  for  this  purpose.  2.5  mg.  per  tablet  is  ' 
sufficient  to  color  500  c.c.  of  water  a  distinct  blue.  If  a  more 
intense  color  be  desired,  this  can  be  increased  up  to  5  mg.,  and  the 
quantity  to  be  specified  in  the  formula  for  100  tablets  should  not 
exceed  .5  Gm.  In  my  experiments  with  red  dyes,  iod-eosin  and 
alizarin  carmine  (sodium  alizarin  sulphonate)  appear  to  have  given 
the  best  results  with  the  Wilson  type,  but  the  color  of  the  solutions 
is  not  as  bright  a  red  as  might  be  desired.  With  the  Bernay"  formula 
containing  citric  acid,  methyl  orange  has  shown  the  best  results. 
The  official  tablet  should  be  adjusted  to  the  basis  of  one  tablet  to 
500  c.c.  of  water,  yielding  a  1  in  1000  solution,  instead  of  one  tablet 
to  the  pint,  as  has  been  the  custom.  This  will  necessitate  only  a 
slight  increase  in  the  weight. 
