A August]  ^a£^m•}     Caustic  Soda  Sold  as  Caustic  Potash.  395 
The  quantities  of  hydrate  and  carbonate  are  then  calculated  in 
the  following  manner  :  If,  for  example,  15-5  ex.  of  normal  acid  be 
required  for  the  titration  with  phenolphthalein,  and  0-35  c.c.  in 
addition,  to  render  the  solution  neutral  to  methyl  orange,  then  15-5 
—  0-35  =  15-15  c.c.  is  the  volume  required  for  the  hydrate  and 
0-35  X  2  =  07  c.c.  for  the  carbonate  in  the  sample,  each  cubic 
centimeter  corresponding  to  0  056  gramme  of  potassium  hydrate  or 
0*069  gramme  of  potassium  carbonate. 
The  objection  has  been  made  to  this  method  of  titrating  mix- 
tures of  alkali  hydrates  and  carbonates,  that  it  is  untrustworthy 
because  of  loss  of  carbon  dioxide  during  the  titration  with  phenol- 
phthalein. This  loss  can  readily  be  avoided,  as  the  writer  has 
determined,  by  diluting  the  solution  to  250  c.c.  for  each  gramme  of 
sample,  running  in  the  volumetric  acid  slowly  and  stirring  continu- 
ously and  gently  to  the  end  of  the  titration. 
Somewhat  less  care  is  required  in  this  regard  when  an  excess  of 
barium  chloride  is  added  to  the  solution  before  titrating,  to  precipi- 
tate the  carbonate  present.  In  this  case  all  of  the  volumetric  solu- 
tion required  to  render  the  solution  neutral  to  phenolphthalein  is 
calculated  as  hydrate.  The  precipitated  carbonate  may  then  be 
readily  estimated  by  continuing  the  titration  after  addition  of 
methyl  orange,  shaking  thoroughly  after  each  addition  of  acid. 
The  barium  chloride  used  must  be  neutral  to  both  indicators  used, 
and  at  least  enough  to  precipitate  all  carbonate  must  be  added. 
Chloride  is  most  conveniently  estimated  by  supersaturating  the 
sample  with  nitric  acid,  adding  an  excess  of  decinormal  silver 
nitrate,  and  titrating  the  excess  with  decinormal  sulphocyanate, 
with  ferric  alum  as  indicator.  Each  cubic  centimeter  of  the  silver 
solution  is  equivalent  to  0  00354  gramme  of  chlorine,  or  0  00744 
gramme  of  potassium  chloride. 
Sulphate  is  determined  gravimetrically  as  barium  sulphate,  when- 
ever great  accuracy  is  necessary,  but  very  serviceable  results  may 
be  obtained  by  titration  with  barium  chloride.  The  normal  solu- 
tion of  the  U.S. P.  of  1890,  containing  122  grammes  of  pure  crystal- 
lized salt  per  liter,  may  be  used.  The  sample  is  dissolved  in  dilute 
hydrochloric  acid,  avoiding  a  large  excess,  which  retards  precipita- 
tion of  barium  sulphate.  After  heating  the  solution  to  near  boil- 
ing, the  barium  chloride  solution  is  added  a  drop  at  a  time,  shaking 
after  each  addition,  so  long  as  each  drop  can  be  seen  to  cause 
