Am-sTe°pT"i^i9rm'  }    Assay  of  Hypochlorite  Solutions.  593 
In  titrating  the  Dakin's  solution  by  following  the  above  direc- 
tions the  permanent  discharge  of  the  blue  color  required  the  repeated 
addition  of  sodium  thiosulphate  and  the  sum  total  of  the  volumetric 
solution  agreed  very  closely  with  that  required  when  the  2  Cc.  of 
glacial  acetic  acid  were  replaced  by  10  Cc.  sulphuric  acid  (10  per 
cent.)  or  10  Cc.  hydrochloric  acid  (5  per  cent.).  In  the  latter  cases, 
titration  was  complete  with  the  first  decolorization. 
By  omitting  the  water  used  for  dilution,  it  was  found  that  2  Cc, 
or  even  1.5  Cc,  glacial  acetic  acid  gave  a  definite  end  reaction,  the 
results  agreeing  with  those  obtainable  with  dilute  sulphuric  acid. 
While  the  neutralizing  power  of  2  Cc  of  glacial  acetic  acid  is  con- 
siderably greater  than  that  of  10  Cc.  of  dilute  sulphuric  acid  (10  per 
cent.)  or  10  Cc.  hydrochloric  acid  (5  per  cent.),  dilution  of  the  latter 
does  not  affect  its  action,  whilst  dilution  of  the  acetic  acid  consid- 
erably retards  its  action.  To  illustrate — 10  Cc.  hydrochloric  acid 
(5  per  cent.)  (equal  to  0.8  Cc.  glacial  acetic  acid)  or  10  Cc.  sul- 
phuric acid  (10  per  cent.)  (equal  to  1.2  Cc.  glacial  acetic  acid)  will 
give  a  permanent  end  reaction,  even  if  diluted  with  50  Cc  of  water. 
2  Cc  glacial  acetic  acid  (equal  to  24  Cc.  hydrochloric  acid  5  per 
cent,  or  16  Cc.  sulphuric  acid  10  per  cent.)  will  not  give  a  permanent 
end  reaction  unless  the  50  Cc  of  water  be  omitted. 
The  Eighth  Revision  of  the  U.  S.  P.  directed  the  use  of  10  Cc.  of 
hydrochloric  acid  in  the  assay  of  Labarraque's  solution,  while  in  the 
Ninth  Revision,  5  mils  of  acetic  acid  are  directed ;  the  substitution  of 
acetic  for  hydrochloric  acid  in  the  assay  suggested  the  possible  in- 
definiteness  of  the  end  reaction  as  noticed  in  the  Dakin's  solution. 
In  titrations  made  with  a  deteriorated  sample  of  Labarraque's 
solution  (1  per  cent,  available  chlorine),  by  the  U.  S.  P.  process, 
several  additions  of  sodium  thiosulphate  volumetric  solution  were 
necessary  for  a  permanent  end  reaction,  but  if  the  quantity  of  acetic 
acid  was  increased  to  10  mils  the  first  decolorization  was  permanent 
and  corresponded  to  that  obtained  with  diluted  hydrochloric  acid  or 
dilute  sulphuric  acid. 
The  results  of  the  experiments  warrant  the  following  sugges- 
tions—  (1)  That  the  prepared  test  be  allowed  to  stand  one  hour 
before  titrating;  (2)  to  increase  the  quantity  of  glacial  acetic  acid  to 
3  Cc.  for  immediate  titration  ;  or  (3)  to  replace  the  acetic  acid  by  a 
diluted  hydrochloric  or  sulphuric  acid. 
Chemical  Laboratory, 
Philadelphia  College  of  Pharmacy. 
