170 
Assay  Processes. 
Am.  Jour.  Pharm. 
April,  1917. 
are  calcium  carbonate  and  oxide,  solution  lead  subacetate,  lead  ace- 
tate and  oxide  and  manganese  dioxide.  For  example,  calcium  car- 
bonate is  first  converted  into  the  chloride  by  HC1.  To  this,  oxalic 
acid  is  added,  and  sufficient  ammonia  water  to  make  alkaline.  After 
standing  over  night,  the  solution  is  filtered,  washed,  acidified  with 
sulphuric  acid,  and  the  excess  of  oxalic  acid  titrated  with  permanga- 
nate. 
In  the  assay  of  potassium  chlorate  several  new  features  are  in- 
troduced. .1  Gm.  of  potassium  chlorate  is  dissolved  in  10  mils  of 
water,  to  which  is  added  25  mils  acidulated  ferrous  sulphate  T.S. 
The  solution  is  placed  in  a  flask  with  a  valve  stopper,  made  by  cut- 
ting a  longitudinal  strip  15  Mm.  long  in  a  rubber  tube  and  closing 
the  end  with  a  glass  rod.  This  allows  for  the  escape  of  gases  with- 
out permitting  the  air  to  return  to  the  flask.  The  solution  is  boiled 
10  minutes,  cooled,  and  10  mils  manganese  sulphate  solution  added, 
and  the  excess  of  ferrous  sulphate  titrated  with  potassium  perman- 
ganate. A  parallel  is  run  without  potassium  chlorate.  The  result 
of  the  former  is  subtracted  from  that  of  the  latter.  The  reactions 
involved  are  as  follows: 
KCIO3  +  6(FeS04-7H20)  +  3H2S04 
Potassium  Ferrous  Sulphuric 
Chlorate  Sulphate  Acid 
=  3Fe2S04)3  +  KC1  +  45H20. 
Ferric  Potassium 
Sulphate  Chloride 
2KMn04  +  io(FeS04-7H20)  +  8H2S04 
Potassium  Ferrous  Sulphuric 
Permanganate  Sulphate  Acid 
=  5Fe2(S04)3  +  K2S04  +  2MnS04  +  8H2G. 
Ferric  Potassium  Manganese  Sulphate 
Sulphate  Sulphate 
The  assay  of  sodium  peroxide  presents  nothing  of  special  mo- 
ment, except  the  fact  that  when  it  is  dissolved  in  water,  it  decom- 
poses into  H202  and  sodium  metaborate.  The  assay  is  conducted 
by  adding  to  the  weighed  salt  dissolved  in  water,  sulphuric  acid, 
and  titrating  with  potassium  permanganate. 
NaB03-4H20   +   H20   =   H202   +    NaB02   +  4H20. 
Sodium  Perborate  Hydrogen  Sodium 
Dioxide  Metaboratt 
5H202    +    2KMn04    +  3H2S04 
Hydrogen        Potassium  Sulphuric 
Dioxide      Permanganate  Acid 
