ON  A  NEW  TEST  FOR  POTASH. 
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ON  A  NEW  TEST  FOR  POTASH. 
By  W.  Plunkett. 
Student  in  the  Evening  Class  for  Practical  Chemistry,  Museum  of  Irsh  Industry. 
The  two  reagents,  tartaric  acid  and  bichloride  of  platinum, 
used  by  chemists  for  the  detection  of  potash  in  its  salts,  do  not 
either  of  them  fulfil  all  the  conditions  required  of  a  good  test. 
Tartaric  acid  is  neither  sufficiently  delicate  nor  sufficiently  speedy 
in  its  action  to  render  it  a  satisfactory  test,  whilst  bichloride  of 
platinum  requires  to  be  evaporated  to  dryness  along  with  the 
solution  under  examination  to  render  it  sufficiently  delicate  in  all 
cases ;  this  requirement,  together  with  its  costliness,  prevents  it 
being  employed  by  students  in  analytical  classes. 
In  Mr.  Galloway's  "  Manual  of  Qualitative  Analysis,"  the  fact 
is  noticed  that  bitartrate  of  potash  is  soluble  in  acids  ;  Fresenius 
also,  in  his  "  Qualitative  Analysis,"  notices  the  fact,  and  adds 
that  in  the  case  of  acid  solutions  the  free  acid  must,  if  practica- 
ble, be  expelled  by  evaporation  and  ignition,  or  the  solution  must 
be  neutralized  with  soda  or  carbonate  of  soda,  before  we  can  pro- 
ceed to  test  for  potash  with  tartaric  acid.    It  is  evident,  that 
whether  we  have  a  free  acid  or  not,  an  acid  must  be  set  free 
whenever  we  add  tartaric  acid  to  a  salt  of  potash,  thus  : — 
KO,  S03  +  2HO,  T=KO,  HO,  T+HO,  SO3. 
I  was  led  by  these  two  facts — 1st,  that  a  free  acid  is  set  free 
whenever  tartaric  acid  is  added  to  a  salt  of  potash,  and  2ndly. 
that  bitartrate  of  potash  is  soluble  in  free  acids — to  try  bitartrate 
of  soda  in  place  of  tartaric  acid.    I  anticipated  that  bitartrate 
of  soda  would  prove  a  much  more  delicate  and  speedy  test,  be- 
cause I  considered  that  the  liberation  of  a  free  acid  was  the  cause 
of  the  want  of  delicacy  and  the  slowness  of  action  of  tartaric 
acid,  and  in  these  anticipations  I  have  not  been  disappointed,  as 
the  following  experiments  show. 
Four  solutions  of  sulphate  of  potash  containing  the  following 
quantities  were  prepared  ; — the  first  contained  10  parts,  the 
second  5  parts,  the  third  2-5  parts,  and  the  fourth  1-25  part  of 
the  salt  in  1000  parts  of  water.  The  bitartrate  of  soda  solution 
employed  was  prepared  by  dissolving  a  quantity  of  tartaric  acid 
in  water,  dividing  the  solution  into  two  equal  parts,  neutralizing 
one  exactly  with  carbonate  of  soda,  and  then  mixing  the  two 
