156  Standardization  of  Sodium  TJiiosuIphate.  ^Am-J^{- ^Tm- 
Another  lot  of  N/10  K2Cr207  made  up  by  the  same  method, 
using  Baker's  salt,  the  same  Na2S203  A'.  S..  had  the  factor  noted 
below. 
Small  amounts  of  iodine  prepared  as  directed  under  A'.  S.  iodine 
were  weighed  off  and  after  solution  in  water  with  the  aid  of  KI 
employed  to  standardize  the  Na2S2Oa  solution  :  the  factor  is  recorded 
below. 
Iodine  prepared  as  directed  by  the  U.  S.  P.  under  Y.  S.  Iodine 
was  mixed  with  KI  placed  in  a  small  porcelain  crucible,  heated  on  a 
sand-bath  until  copious  evolution  of  iodine  fumes,  when  one  of  a  set 
of  watch-glasses  with  ground  edges,  which  were  tared  with  a  clip, 
was  slipped  over  the  top  of  the  crucible  until  a  sufficient  amount  of 
iodine  had  sublimed,  when,  after  cooling,  the  watch-glasses,  clip,  and 
iodine  were  weighed  again,  the  increase  being  iodine.  The  watch- 
glasses  and  iodine  without  clip  were  then  put  into  a  .few  cubic 
centimetres  KI  solution,  and  when  the  iodine  was  dissolved  the 
Na2S2Oa  V.  S.  was  run  in  until  the  reaction  was  complete.  The 
factor  for  the  Na2S2Os  solution  is  noted  below. 
Factor  employing  Kahlbaum's  chemical — 1  Cc.  =  0.011342 
gramme  iodine;  1  Cc.  =  0.9009  Cc.  X  10  Na2S203  A'.  S. 
Baker's  chemical — 1  Cc.  =  0.011362  gramme  iodine;  1  Cc.  = 
0  9025  Cc.  X  10  XaoS20:3  A'.  S. 
Iodine  resublimed  on  funnel — 1  Cc.  =0.011539  gramme  iodine: 
1  Cc.  =  0.91652  Cc.  Xyio  Na2S203  V.  S. 
Iodine  resublimed  on  watch-glass — 1  Cc.  =  0.011533  gramme 
iodine;  1  Cc.  =  0.91604  Cc.  X/10  X'a2S2Oo  A'.  S. 
These  results  indicate  that  the  use  of  resublimed  iodine  gives 
higher  and  probably  more  accurate  results  than  the  potassium 
dichromate  method. 
I  am  fully  aware  of  the  fact  that  the  potassium  dichromate  used 
for  standardization  is  usually  directed  to  be  checked  against  pure 
iron,  as  is  evidenced  by  the  following  citation  from  page  136,  U.  S. 
Department  of  Agriculture,  Division  of  Chemistry.  Bulletin  107, 
revised,  under  the  determination  of  the  iodine  number  of  fats 
and  oils  : 
"  Decinormal  Potassium  Bichromate. — Dissolve  4.9083 
grammes  of  chemically  pure  potassium  bichromate  in  dis- 
tilled water  and  make  the  volume  up  to  1  litre  at  the  tem- 
perature at  which  the  titrations  are  to  be  made.  The 
bichromate  solution  should  be  checked  against  pure  iron  "  : 
