Am'jirer'i9ihrm'}   Volumetric  Estimation  of  Sulphates.  249 
THE  VOLUMETRIC  ESTIMATION  OF  SULPHATES. 
By  Horace  North. 
Although  S04  is  easily  the  most  important  acidic  ion  concerned 
in  the  operations  of  industrial  chemistry,  there  is  at  the  present  time 
no  satisfactory  method  of  general  application  for  its  volumetric 
estimation.  A  method  is  proposed  which,  in  the  light  of  numerous 
experiments,  promises  to  be  widely  useful.  Subject  to  certain  limita- 
tions which  will  be  considered  in  due  course,  the  method  is  applicable 
in  the  presence  of  the  ions  Li,  Na,  K,  NH4,  Cu  -,  Mg,  Ca,  Sr,  Zn, 
Cd,  Hg-,  Al,  Ni,  Co,  CI,  P04,  B407.  All  data  are  referred  to  one 
standard  solution  which  is  readily  prepared  of  exact  strength  and 
which  is  permanent.  The  end  point  of  the  titration  is  clearly  defined. 
When  all  is  in  readiness  an  estimation  requires  fifty  minutes. 
In  1877  Hinman  1  proposed  to  determine  sulphuric  acid  as  fol- 
lows:  To  a  slightly  acid  solution  of  a  sulphate  heated  to  boiling 
is  added  a  small  excess  of  a  solution  of  barium  chromate  in  hydro- 
chloric acid,  barium  sulphate  is  precipitated,  then  the  solution  is 
neutralized  with  ammonia  which  precipitates  the  remaining  barium 
chromate,  the  precipitates  of  barium  sulphate  and  chromate  are 
filtered  off,  and  the  chromic  acid,  determined  in  the  filtrate  by 
means  of  stannous  chloride,  is  equivalent  to  the  sulphuric  acid  in 
the  original  solution. 
This  method  is  limited  in  its  application ;  in  particular,  metals 
forming  chromates  insoluble  in  the  presence  of  ammonia  as  well  as 
phosphates  and  borates  interfere.  Various  modifications  2  designed 
to  correct  its  inherent  defects  have  been  suggested  without,  however, 
1  Amer.  Journ.  Science  and  Arts,  114,  478. 
2  Andrews,  Am.  Chem.  Journ.,  2,  567;  32,  476-480. 
Marboutin  and  Molinie,  Bull.  Soc.  Chim.,  17,  950-955  ;  19,  713-717.  Journ. 
Soc.  Chem.  Ind.  (1897),  1041;  (1898)  874. 
Reuter,  Chem.  Ztg.  (1898),  357. 
Telle,  /.  Pharm.  Chim.,  7,  165-170. 
Bruhns,  Z.  anal.  Chem.  (1906),  573. 
Komarowsky,  Chem.  Zcit.,  32,  770. 
Mitchell  and  Smith,  Chem.  Soc.  Proc,  25,  291. 
Repiton,  Monit:  Sclent.,  24,  382-384. 
Holliger,  Stahl  u.  Eiscn,  30,  1376-1378;  Z.  Anal.  Chem.,  49,  84-93; 
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