576 
Neutral  Oxalate  of  Potassium. 
f  Am.  Jour.  Pharm. 
1       Nov.,  1881. 
PKEPAEATION  of  XEUTRAL  OXALATE  of  POTASSIUM. 
By  E.  B.  Shuttleworth. 
The  rapid  dry-plate  processes  in  photography,  which  are  at  present 
exciting  considerable  attention  among  the  more  advanced  classes  of 
those  engaged  in  the  art,  have  created  a  demand  for  neutral  potassium 
oxalate  that  cannot  be  supplied  through  the  ordinary  trade  channels. 
The  writer  has  frequently  been  asked  for  this  salt,  as  doubtless  have 
many  of  the  readers  of  the  Journal,  and  as  the  preparation  is  simple, 
involving  no  special  apparatus,  a  few  notes  on  the  subject  may  prove 
opportune. 
There  are  three  oxalates  of  potassium  known  to  chemists — the  neu- 
tral salt  to  which  this  paper  refers,  and  which  contains  two  atoms  of 
potassium  to  one  molecule  of  acid ;  the  binoxalate,  the  ordinary  salt  of 
sorrel  of  the  drug  stores,  and  that  which  is  found  in  many  plants,  con- 
taining one  atom  of  potassium  to  one  of  acid ;  and  the  quadroxalate,  a 
salt  not  frequently  prepared  or  used,  in  which  the  proportion  of  potas- 
sium and  acid  ar^as  1  to  2. 
The  neutral  salt  is  the  only  one  used  in  photography.  It  crystal- 
lizes in  rhombic  prisms,  is  stable  in  the  air,  contains  two  molecules  of 
water  of  crystallization  which  may  be  driven  off  by  heat,  and  is  solu- 
ble in  about  three  times  its  weight  of  cold  water. 
It  is  evident  that  the  easiest  mode  of  preparing  this  salt  is  by  neu- 
tralizing a  solution  of  carbonate  of  potassium  by  oxalic  acid.  Some 
have  recommended  that  the  ordinary  salt  of  sorrel,  sal  aeetosellce,  be 
rendered  neutral  by  the  addition  of  the  carbonate,  but  this  is  certainly 
a  roundabout  and  expensive  plan,  not  only  as  involving  the  use  of 
more  costly  material,  but  unnecessary  evaporation.  The  most  expedi- 
tious method  will  be  found  co  be  as  follows : 
Dissolve  a  quantity — say  one  pound — of  carbonate  of  patassium  in 
an  equal  weight  of  cold  water,  decanting  the  clear  solution  from  any 
undissolved  sediment,  if  such  should  remain.  This  residue  consists  of 
potassium  sulphate  or  silicate,  and  is  commonly  present  in  the  ordi- 
nary salts  of  tartar  of  commerce.  Put  the  clear  solution  into  an 
enameled  iron,  porcelain,  or  wedgwood  dish,  add  a  quantity  of  water 
equal  to  that  first  employed,  and  heat  to  the  boiling  ])oint.  Add  care- 
fully, and  by  small  portions,  avoiding  mishap  by  effervescence,  suffi- 
cient powdered  oxalic  acid  to  neutralize  the  carbonate,  testing  carefully 
towards  the  close  with  test  paper.    If  necessary  filter  the  solution 
