^Mirch,f899rm'}  Syrup  of  Hydriodic  Actd.  129 
The  proportion  of  animal  charcoal  is  directed  by  Mr.  D.  Cameron 
to  be  y2  ounce  of  animal  charcoal  to  the  pint  of  syrup. 
In  the  writer's  experience  the  amount  necessary  is  dependent 
upon  the  degree  of  discoloration,  very  dark  syrups  requiring  greater 
amounts. 
The  following  process  has  been  found  to  give  satisfactory  re- 
sults : 
Mix  the  discolored  syrup  with  from  3  to  5  per  cent,  its  weight  of 
powdered  purified  animal  charcoal  jn  a  bottle,  allow  to  stand  from 
two  to  three  hours  with  frequent  agitation  and  filter. 
Should  the  filtrate  not  be  perfectly  colorless,  an  additional  amount 
of  charcoal  must  be  used. 
PERCENTAGE  ESTIMATION. 
The  Pharmacopoeia  gives  the  following  directions  for  valuation  : 
If  32  (31-88)  grammes  of  the  syrup  be  exactly  neutralized  by 
ammonia  water  and  then  mixed  with  two  drops  of  potassium  chro- 
mate  T.  S.,  it  should  require  about, 25  c.c.  of  decinormal  silver 
nitrate  V.  S.  to  produce  a  permanent  red  tint  (corresponding  to 
about  I  per  cent,  of  absolute  hydriodic  acid).  Extreme  care  must 
be  used  in  neutralizing  the  syrup  with  ammonia  water. 
Theoretically  calculated,  only  -425  grammes  of  the  official  aqua 
ammoniae  are  required  to  exactly  neutralize  the  stated  quantity. 
The  end  of  the  reaction  depends  upon  the  formation  of  red 
silver  chromate. 
Errors  may  be  made  either  in  the  case  of  incomplete  neutraliza- 
tion or  trifling  excess  of  ammonia. 
Silver  chromate  is  soluble  both  in  diluted  nitric  acid  and  ammonia 
water. 
In  the  case  of  incomplete  neutralization,  addition  of  silver  nitrate 
V.  S.,  while  precipitating  silver  iodide,  will  cause  a  corresponding 
amount  of  nitric  acid  to  be  liberated,  which  redissolves  the  silver 
chromate  formed  with  destruction  of  the  red  color. 
An  excess  of  ammonia  water  produces  allied  results  and  errors 
amounting  to  several  cubic  centimetres  of  the  —  silver  nitrate  V.  S. 
10 
may  result  therefrom. 
A  slight  error  may  also  take  place  by  the  presence  of  potassium 
bitartrate  in  the  syrup. 
