22 
Note  on  Sulphur  Dioxide. 
3  Am.  Jour.  Phann. 
1    January,  1911. 
as  the  ultimate  standard  and  the  suhsequent  checking  of  the  equiva- 
lencies thus  found,  by  means  of  the  reaction  between  sulphur  dioxide 
and  iodine.  All  the  solutions  were  prepared  in  the  ordinary  way 
except  the  iodine  solution,  in  the  case  of  which  an  accurately  weighed 
amount  of  pure  KI,  16.602  Gm.  per  litre,  was  used  instead  of  about 
18  Gm."  which  is  ordinarily  used.  Of  this  KI,  0.5442  Gm.  was 
found  equivalent  to  32.7  c.c.  of  the  n/io  AgNO.^  solution.  This 
would  make  the  iodine  solution  99.85  per  cent,  tenth-normal  with 
reference  to  its  KI  content,  which  value  was  used  in  the  subsequent 
calculations.  The  water  used  was  free  from  oxygen  and  carbon 
dioxide.  When  a  fairly  rapid  current  of  SO2  is  available,  the 
time  required  for  obtaining  about  50  c.c.  of  the  sulphur  dioxide  solu- 
tion, of  a  strength  suitable  for  the  present  purpose,  need  not  exceed 
fifteen  seconds ;  hence  no  special  care  was  taken  to  entirely  avoid 
contact  of  the  liquid  with  the  atmosphere,  but  the  SOo  solution  thus 
obtained  was  quickly  transferred  to  a  burette  and  used  immediately 
for  decolorizing  the  iodine  solution.  The  following  results  were 
obtained  by  working  according  to  the  plan  above  outlined. 
1.  Used  0.4287  Gm.  of  the  pure  metallic  silver  (equivalent  to 
39.74  c.c.  n/io  AgNO.,)  and  found  it  to  require  39.62  c.c.  of  the 
n/io  NH.CNS.  Therefore,  the  normality  of  the  NH.CNS  solu- 
tion, expressed  in  percentage  of  an  exact  n/io  solution,  is  100.30. 
2.  Found  that  50  c.c.  of  the  n/io  AgNO..  are  equivalent  to  49.9 
c.c.  of  the  above  n/io  NH^CNS.  Therefore,  the  normality  of  the 
AgNOo  solution,  expressed  as  above,  is  100.10. 
3.  Found  that  45  c.c.  of  the  n/io  HCl  are  equivalent  to  45.25 
c.c.  of  the  above  n/io  AgNOo.  Therefore,  the  normality  of  the 
HCl  solution,  expressed  as  above,  is  100.65. 
4.  Found  that  45  c.c.  of  the  above  n/io  HCl  are  equivalent  to 
45.05  c.c.  of  the  n/io  NaOH.  Therefore,  the  normahty  of  the 
NaOH  solution,  expressed  as  above  is  100.54. 
5.  Found  that  45  c.c  of  the  n/io  oxalic  acid  are  equivalent  to 
44.7  c.c.  of  the  above  n/io  NaOH.  Therefore,  the  normality  of 
the  oxalic  solution,  expressed  as  above,  is  99.86. 
6.  Found  that  45  c.c.  of  the  above  n/io  oxalic  acid  are  equivalent 
to  45.15  c.c.  of  the  n/io  KMn04.  Therefore,  the  normality  of  the 
KMn04  solution,  expressed  as  above,  is  99.53. 
7.  Found  that  45  c.c.  of  the  above  n/io  KMnO^  are  equivalent 
to  45.45  c.c.  of  the  n/io  NaoSoO..  Therefore,  the  normahty  of 
the  thiosulphate  solution,  expressed  as  above,  is  98.55. 
