Am*  /me,'  i9i4.rm' }   Volumetric  Estimation  of  Sulphates.  251 
Measure  4  c.c.  HQ  (sp.  gr.  1.12),  40  c.c.  water  and  10  c.c. 
barium  chloride  solution  (about  43  gms.  BaCL  +  2HLO  in  1000  c.c.) 
into  a  100  c.c.  glass-stoppered  volumetric  flask,  heat  the  liquid  to 
boiling,  run  in  10  c.c.  n/i  K2Cr207,  rinse  down  the  neck  of  the 
flask  with  10  c.c.  water  and  without  further  heating  add  drop  by 
drop  with  constant  shaking  a  mixture  of  15  c.c.  ammonia  water  (sp. 
gr.  0.98)  and  2  c.c.  36  per  cent,  acetic  acid.  Cool  the  mixture  to  the 
normal  temperature,  make  up  to  the  mark  and  filter  with  the  aid  of 
suction  through  an  asbestos  felt  previously  formed  in  the  usual  man- 
ner, then  dried  at  about  no°  C.  Titrate  40  c.c.  of  the  filtrate  under 
the  conditions  specified  in  the  standardization  of  the  n/io  Na2S203, 
except  that  40  c.c.  water  are  used  in  place  of  60  c.c,  the  total  volume 
of  the  solution  during  the  six-minute  period  of  standing  being 
100  c.c.  Divide  20,000  by  the  number  of  c.c.  n/io  Na2S2Oa  re- 
quired, and  dilute  each  litre  of  the  BaCL  solution  to  the  volume  in- 
dicated. A  new  trial  is  then  to  be  made  with,  if  necessary,  the 
slight  readjustment  required. 
An  estimation  of  S04  is  carried  out  as  follows : 
Transfer  the  sulphate  solution  containing  about  0.16  gm.  S04  to 
a  100  c.c.  glass-stoppered  volumetric  flask,  dilute  to  a  volume  of 
30  c.c,  add  sufficient  HC1  (sp.  gr.  1.12)  so  that  the  total  amount, 
present  is  4  c.c  (if  acidity  is  unknown,  first  neutralize  with  am- 
monia), heat  the  liquid  to  boiling,  run  in  20  c.c  N/3  BaCl2,  again 
heat  to  boiling,  run  in  10  c.c.  n/i  K2Cr207,  rinse  down  the  neck  of 
the  flask  with  10  c.c.  water  and  without  further  heating  add  drop 
by  drop  with  constant  shaking  a  mixture  of  15  c.c  ammonia  water 
(sp.  gr.  0.98)  and  2  c.c.  36  per  cent,  acetic  acid.  Complete  the 
experiment  as  specified  under  the  standardization  of  the  N/3  BaCl2. 
C.c.  n/io  Na2S203  required  X 0.008  =  gm.  S04  originally  taken. 
The  reaction  between  equivalent  solutions  of  K2Cr207  and 
BaCL  is  -expressed  by  the  equation :  K2Cr207  +  BaCL  +  H20  = 
BaCr04  +  K2Cr04  +  2HCI.  The  resulting  HC1  retains  in  solu- 
tion a  considerable  portion  of  the  Ba.  On  neutralizing  with  am- 
monia all  of  the  Ba  is  thrown  out  as  chromate  and  half  the  Cr 
originally  taken  remains  in  solution. 
A  large  number  of  preliminary  experiments,  the  details  of  which 
it  is  hardly  necessary  to  give,  demonstrated  the  following  points : 
(1)  When  cold  solutions  of  K2Cr2Q7  and  BaCL  are  mixed  and 
neutralized,  the  precipitate  of  BaCrQ4  carries  down  soluble  chro- 
mate in  considerable  and  variable  amounts. 
