346 
TINCTUEA  lODINII  DECOLORATA. 
Now,  the  Tinctura  iodinii,  U.  S.  P.,  contains  30  grains  of 
iodine  per  ounce,  all  of  it  uncombined.  The  Tinctura  Iodinii 
Composita,  U.  S.  P.,  contains  38  grains  of  iodine,  (15  grains  of 
free  iodine,  and  23  grains  of  iodine  combined  with  potassium). 
As  the  iodine  in  the  colorless  preparation  does  not  exist  in  a 
free  state,  but  in  that  of  ammonia  compounds,  which  acts  some- 
what less  energetically  than  the  free  metalloid,  the  proportions 
of  the  compound  tincture,  38  grains  of  iodine  per  ounce,  are 
probably  the  best,  and  this  would  require  about  one  and  one 
quarter  ounces  per  pint. 
To  exactly  convert  this  amount  of  iodine  into  the  colorless 
iodide  of  ammonium  and  iodate  of  ammonia,  309  minims  (about 
five  fluid-drachms)  of  Aqua  Ammonias  fortior  U.  S.  P.  (spec, 
grav.  0-900)  per  pint,  or  about  20  minims  per  ounce  are  requisite. 
The  published  formulse  give  considerably  more  than  that,  some 
of  them  recommending  half  a  pint ;  some  only  four  fluid-ounces 
per  pint  of  tincture,  but  all  of  them  agree  in  using  vastly  more 
than  theory  requires,  and  thereby  make  the  preparation  objec- 
tionable on  account  of  irritating  ammonia  vapor,  which  though 
it  may  prove  very  useful  in  many  cases,  should  certainly 
not  always  be  present ;  at  least  its  addition  should  be  left  to 
extemporaneous  prescription.  On  the  other  hand,  the  employ- 
ment of  only  the  theoretical  quantity  results  in  decoloration  so 
slowly  as  to  be  practically  and  virtually  inapplicable. 
•  Experiments  instituted  to  ascertain  the  least  amount  of  am- 
monia by  which  the  tincture  could  be  rendered  colorless  in  a 
reasonable  space  of  time,  gave  the  following  results.  Into  nine 
vials  the  ingredients  for  the  tincture  were  placed  in  varying  pro- 
portions, thus  : 
I    II  III  IV  y  VI  VII  VIII  IX 
Iodine,  grains  38  38  38  38  38  38  38  38  38 
Alcohol  f5  8     71    7      61    6     51      5     4i  4 
Aqua  Amm.  fort,  f^  J  1  IJ  2  2i  3  31  4 
No  special  precautions  were  taken  in  regard  to  the  regula- 
tion of  light  or  temperature.  The  iodine  was  completely  dis- 
solved in  the  alcohol  before  the  addition  of  ammonia,  which  oc- 
casioned a  copious  dark  precipitate,  re-dissolving  in  a  few  hours. 
No.  1  was  simply  kept  for  comparison  of  color.    Even  during 
