A  salt  is  one  of  the  products  obtained  by  the  interaction  of
acids  with  (1)  metals,  (2)  metallic  oxides,  (3)  metallic  hydroxides,
(4)  metallic  carbonates.  The  salt  obtained  is  in  each  case  a
compound  of  the  metal  with  the  elements  of  the  acid  except
hydrogen,  or,  as  is  usually  said,  with  the  acid  radicle.
*  It  is  assumed  that  the  student  has  become  acquainted  with  the  use
of  chemical  formulae,  s.  ELEMENTARY  CHEMISTRY,  Chap.  VI.
38


PRACTICAL   CHEMISTRY.
[CHAP.  vin.
But  more  than  one  salt  is  sometimes  obtained  by  the
reaction  between  a  specified  acid  and  the  same  metallic  oxide
or  hydroxide.
Ex  p.  4.  You  are  given  two  exactly  equal  quantities  of  a
solution  of  oxalic  acid  in  water,  and  a  quantity  of  a  solution  of
potassium  hydroxide*.  To  one  of  the  quantities
of  oxalic  acid  add  the  potash  solution  very  cauti-
ously, from  a  graduated  tube  with  a  stopcock  (a
burette)  (Fig.  17)  until  the  liquid  is  exactly  neutral
(s.  Exp.  2,  Chap.  VII.).  Read  off,  on  the  burette,
the  number  of  cubic  centimetres  of  potash  solution
added.  To  the  other  quantity  of  oxalic  acid  add
exactly  half  as  much  potash  as  you  have  added
to  the  first  quantity  of  the  acid.  Evaporate  both
solutions  over  low  flames  until  a  drop  taken  out
on  a  rod  solidifies  on  cooling ;  allow  to  cool ;
collect,  dry,  and  recrystallise  the  solids  from  as
little  water  as  possible;  collect,  dry,  and  re-
crystallise  each  again.
Prove  that  each   solid  is   (1)  a  compound  of
potassium,  (2)  an  oxalate.
The,  production  of  a  white  pp.  (calcium  oxalate)
when  calcium  chloride  is  added  to  a  solution,  which
pp.  is  insoluble  in  acetic  acid,  is  a  test  for  the  presence
.  ^~~ of  an  oxalate  in  that  solution.
