102  Volumetric  Solution  of  Iodine.  {AmFeb'i^arm' 
strength  of  the  latter,  and  from  this  hyposulphite  of  sodium  solution 
a  weak  or  unknown  solution  of  iodine  might  be  at  once  corrected 
or  standardized. 
Arsenious  oxide  might  also  be  used,  and  it  has  the  advantage  of 
being  permanent  and  nonhygroscopic. 
The  defect  in  the  Pharmacopoeia  to  which  Mr.  Hoseason  directed 
attention  was  this :  The  standard  iodine  used  to  fix  the  value  of 
the  hyposulphite  of  sodium  solution,  is  the  one  which  answers  the 
"  characters  and  tests  "  of  the  Pharmacopoeia.  This  official  "  iodine  " 
is  tested  by  using  solution  of  sodium  hyposulphite.  It  is  evident, 
therefore,  that  the  true  value  of  the  iodine  can  never  be  ascertained  in 
this  way,  which  is  simply  a  case  of  reasoning  in  a  circle.  He  sug- 
gested that  the  following  should  be  the  directions  for  preparing  the 
volumetric  solution  of  iodine  :  "  Mix  intimately  in  a  mortar,  in  the 
proportion  of  one  of  potassium  iodide  to  four  of  iodine ;  place  in  a 
suitable  arrangement  and  sublime.  When  cool  place  the  sublimate 
in  a  desiccator  for  two  hours.  Of  this  chemically  pure  iodine,  weigh 
off  quickly  on  a  paraffined  paper  the  quantity  required,  or  an 
unknown  quantity  may  be  weighed  from  weighing  tubes  and  made 
up  to  the  proper  volume  with  water,  so  that  each  ioo  cc.  contain 
1-27  grain  of  pure  iodine."  He  had  examined  some  commercial 
and  resublimed  samples  of  iodine  with  the  following  result  : 
No 
Quality. 
Description. 
Iodine 
per  cent. 
Moisture  per  cent. 
1 
Resublimed. 
Fine  lustrous  scales 
thin,  dry. 
IOD 
0"0 
2 
Resublimed. 
Small  crystalline 
fragments  and 
dry  dust. 
99  "5 
o-5 
3 
Commercial. 
Fine   scales  and 
(-slight 
dust. 
99 '4 
100 
o-6 
<  fixed 
4 
Resublimed. 
Very  small  crys- 
tals; lustrous,  dry. 
o-o 
(.residue. 
5 
Resublimed. 
Very  large  thick 
scales  and  crys- 
talline masses, 
very  moist. 
96-6 
99  '2 
3 '4 
6 
Resublimed. 
Very   large  thick 
crystalline  scales, 
moist. 
o-8 
r  slight 
7 
Commercial. 
Dry  powdery  mass. 
2*4 
<  fixed 
97  6 
(  residue. 
