(8)  Alkalies. — The  filtrate  and  washings  from  7  (=100  grn.  soil)
containing  the  alkalies  as  chlorides,  together  with  ammonic  chloride
and  a  small  quantity  of  ammonic  arsenate,  are  evaporated  to  dryness
on  the  water  bath,  then  ignited  gently  and  carefiilly  under  a  chim-
ney to  volatilize  all  the  arsenate  and  other  salts  of  ammonia.  The
alkalies  are  then  left  nearly  pure  as  chlorides.  The  residue  is
dissolved  in  a  very  little  water,  filtered  through  a  small  filter  into  a
small  crucible,  evaporated  to  dryness,  and  weighed  direct.  If  it
be  desirable  to  ascertain  the  amount  of  potash,  it  may  be  separated
by  weight  as  potassio-platinic  chloride,  or  the  indirect  method  of
calculation,  as  in  §  38,  may  be  adopted.
(9)  Phosphoric  Acid. — The  remainder  of  the  acid  solution,  viz.
300  dm.  (=150  gra  soil),  is  mixed  with  a  little  nitric  acid,  heated
and  precipitated  with  ammonia,  as  in  5,  the  precipitate  collected  on
a  filter  and  washed  with  boiling  water  (filtrate  and  washings  set
aside).  The  precipitate  is  then  dissolved  on  the  filter  with  dilute
nitric  acid,  the  filter  slightly  washed;  and  the  solution  so  obtained
digested  in  the  water  bath  for  24  hours  with  about  two  ounces  of
molybdic  solution,  prepared  as  directed  in  §  69.5a.
If  any  precipitate  occurs,  it  will  contain  all  the  phosphoric  acid
(unless  it  should  exist  in  large  quantity,  which  is  not  probable)
as  ammonic  phospho-molybdate,  which  is  to  be  collected  on  a  small
filter,  well  washed  with  the  same  fluid,  then  redissolved  in  am-
monia, and  a  portion  of  the  magnesia  mixture  added  (§  69.  5a)
to  precipitate  the  phosphoric  acid  as  double  ammonio- magnesic
phosphate ;  the  precipitate  so  produced  is  dissolved  in  acetic  acid,
and  titrated  with  uranium  as  in  §  69.
