578  Pharmacopceial  Standard  for  {ADeoJemberP^™' 
with  a  N/io  sodium  thiosulphate  solution.  In  the  proposed  method 
for  the  determination  of  chlorine  in  chlorides  the  sample  is  mixed 
with  finely  powdered  manganese  dioxide,  and  treated  with  sulphuric 
acid  (i  :  i  by  vol.)  in  a  distilling  apparatus,  as  in  the  Mn02  deter- 
mination, and  the  chlorine,  produced  by  the  interaction  of  Mn02 
and  the  HC1  set  free  from  the  chloride  sample  by  the  action  of 
H2S04,  is  conducted  into  a  KI  solution  and  the  liberated  iodine  ti- 
trated as  usual  with  N/io  Na2S2Os.  In  this  reaction  between  sul- 
phuric acid  and  a  chloride  in  the  presence  of  Mn02,  the  chlorine  from 
the  chloride  is  all  distilled  off,  the  spent  liquor  showing  no  chlorine 
when  tested  with  AgN03.  The  reaction  appears  to  be : 
2NaCl  +  2H2S04  +  Mn02  =  Na2SO,  +  MnSO,  +  2H20  +  Cl2. 
Method. 
The  Reagents  Required. —  (1)  Finely  ground  Mn02  (passing 
100-mesh  sieve). 
(2)  Sulphuric  acid  (1:1  by  vol.)  free  from  nitric,  hydrochloric 
acids,  nitrates  and  nitrous  fumes,  etc. 
(3)  Potassium  iodide  solution,  25  grams  per  liter. 
(4)  N/10  sodium  thiosulphate  solution. 
The  Apparatus  used  is  the  same  as  in  the  case  of  Mn02  deter- 
mination by  distillation  with  hydrochloric  acid  and  is  shown  in  the 
accompanying  sketch. 
The  Sampling  in  this  method  is  very  important.  In  the  case  of 
solids  the  sample  must  be  finely  powdered  to  insure  intimate  mixing 
with  the  manganese  dioxide.  If  this  is  not  done,  there  may  occur 
a  loss  of  chlorine  during  the  operation  or  incomplete  decomposition 
of  the  chloride.  In  the  case  of  liquids  the  sample  must  be  measured 
from  a  burette  if  percentage  of  volume  is  required  or  weighed  in  the 
flask  directly  without  adding  any  water.  The  amount  of  sample 
to  be  taken  for  the  analysis  varies  from  0.12  to  5  Gm.,  depending  on 
the  amount  of  chlorine  present.  For  liquids,  from  0.5  to  5  Cc,  or 
weights  corresponding  to  these  figures,  are  taken. 
Procedure. — The  weighed  sample  is  thoroughly  mixed  on  the 
weighing  glass  with  about  2  G.  of  finely  powdered  manganese 
dioxide2  and  transferred  into  the  round-bottomed  flask  A;  50  Cc. 
of  sulfuric  acid  (1:1  by  vol.)  are  added  and  at  once  the  flask  is  at- 
tached to  the  glass  tubing  B,  which  is  inserted  into  the  larger  glass 
tube  C  containing  100  Cc.  of  KI  solution  and  surrounded  with  cold 
2  For  larger  samples  the  amount  of  Mn02  can  be  increased. 
