464  Chemical  Analysis  of  Potash,  {^"•Jri8^75.""* 
These,  however,  never  are  found  all  associated  ;  silica  and  chlorine  are 
probably  never  absent  from  the  portion  soluble  in  water,  or  ferric,  ox- 
ide and  silica  from  the  insoluble  portion.  Manganese  generally  manifests 
its  presence  by  the  bluish-green  tinge  it  gives  to  the  potash  but  it  is 
always  present  in  such  small  quantities  that  it  cannot  be  determined 
without  considerable  loss  of  material  ;  the  same  holds  true  of  the  phos- 
phoric acid. 
The  following  treatment  extends  to  all  the  above-mentioned  bodies  : 
Take  200  grams  common  potash,  triturate  to  coarse  powder,  weigh  off 
I  gram  and  20  grams  ;  in  the  first,  find  the  loss  of  water  through  the 
loss  of  weight  by  incandescence  ;  cover  the  second  in  an  evaporating 
dish  with  100  grams  of  distilled  water,  allow  to  boil  slowly  for  10  min- 
utes, filter,  wash  contents  of  filter  until  the  filtrate  does  not  give  an 
alkaline  reaction,  set  contents  of  filter  aside  for  future  experimenting 
(see  b\  and  dilute  the  filtrate  with  sufficient  water  to  make  200  c.c.m. 
J.    The  part  soluble  in  water. 
(a.)  Estimation  of  chlorine:  20  to  40  c.c.m.  are  supersaturated  with 
nitric  acid,  filtered,  if  necessary  (the  turbidness  arises  from  the  silica 
being  set  free),  precipitate  with  nitrate  of  silver,  collect  on  a  previously 
tared  filter,  dry  at  a  temperature  of  100°  C,  weigh  and  calculate  there- 
from the  chlorine.  (100  parts  silver  chloride  contain  24*74  parts 
chlorine.) 
{b.)  Estimation  of  sulphuric  acid  :  20  to  40  c.c.m.  are  super- 
saturated with  HCl,  filtered,  if  necessary,  and  precipitated  with  chloride 
of  barium  ;  calculate  from  the  precipitate  (previously  exposed  to  incan- 
descence) the  amount  of  SO3.  100  parts  barium  sulphate  contain  34*35 
parts  SO3. 
(r.)  Estimation  of  phosphoric  acid  :  50  c.c.m.  are  supersaturated 
with  HCl,  and  filtered,  if  required.  Then  add  about  i  gram  chloride 
of  ammonium  and  a  few  crystals  of  sulphate  of  magnesium,  super- 
saturate with  ammonia,  stir  for  a  few  minutes,  and  set  aside  a  day.  If, 
after  the  expiration  of  that  time,  crystals  of  ammonio-magnesium  phos- 
phate have  formed,  collect ;  lixivate  with  ammoniacal  water,  dry,  heat 
to  redness,  and  calculate  the  phosphoric  acid  from  the  remaining  pyro- 
phosphate of  magnesium.  (100  parts  of  this  combination  are  equivalent 
to  64  parts  phosphoric  acid.) 
{d.)  Estimation  of  the  dissolved  silica  :  50  c.c.m.  are  supersaturated 
with  HCl ;  evaporate  to  dryness,  then  mix  with  water,  decant  the 
supernatant  liquid,  and  collect  the  silica  on  a  filter  ;  heat  to  redness, 
weigh,  and  bring  the  filtrate  back  to  50  c.c.m. 
