PREPARATION  OF  SULPHOCYANIDE  OF  POTASSIUM.  307 
suit  of  which  is  the  following  method,  which  has  been  found 
uniformly  to  give  good  results,  a  large  yield,  and  to  require  far 
less  alcohol  than  any  other  process  known  to  the  writer. 
The  saving  in  alcohol,  where  the  quantity  prepared  is  large,  is 
of  course  of  considerable  importance. 
The  process  is  as  follows : 
Take  of  cyanide  of  potassium,  in  small  pieces  of  about  the 
size  of  a  pea,  two  parts  by  weight ;  sulphur  one  part. 
Mix  thoroughly,  and  fuse  gently  in  an  iron  pan  over  a  Bun- 
sen's  burner,  until  the  cyanide  is  entirely  fused  and  mixed  with 
the  melted  sulphur,  and  the  blue  flame  of  sulphur,  and  the  scin- 
tillation caused  by  the  burning  of  minute  particles  of  iron,  have 
ceased ;  and  allow  the  whole  to  cool,  until  a  drop  let  fall  into 
water  no  longer  produces  a  hissing  sound. 
Then  pour  the  still  soft  mass  into  three  parts  of  water,  in 
which  it  immediately  dissolves ;  filter,  to  separate  impurities, 
particles  of  sulphuret  of  iron,  etc.  The  filtrate  contains  a  large 
amount  of  sulphocyanide  of  potassium,  mixed  with  sulphide, 
hyposulphite,  cyanate,  etc.  ;  the  next  step  is  for  the  removal  of 
these. 
This  is  simply  and  perfectly  attained  by  the  addition,  with 
constant  stirring,  of  dilute  sulphuric  acibl  (1  to  4),  until  the  re- 
action is  slightly  acid.  This  operation  should  be  performed  un- 
der a  hood,  or  in  some  place  where  the  gases  evolved  may  be 
removed. 
Sulphocyanide  of  potassium  is  neutral  to  test  paper,  and  not 
affected  by  dilute  sulphuric  acid  in  the  cold,  while  all  the  other 
substances  mentioned  above  are  at  once  decomposed,  evolving 
sulphuretted  hydrogen  and  cyanogen  compounds,  and  depositing 
a  considerable  amount  of  sulphur. 
The  liquid  is  filtered  to  separate  this,  and  then  contains  only 
sulphocyanide  of  potassium  and  sulphate  of  potassa  ;  the  quan- 
tity of  the  latter  depends  upon  the  purity  of  the  cyanide  of 
potassium  employed,  since  any  carbonate  present  forms  direct 
sulphur  compounds,  which  are  afterwards  decomposed  by  the 
sulphuric  acid  added.  Where  the  amount  of  sulphate  formed  is 
large,  it  may  partially  separate  with  the  sulphur,  as  a  dirty, 
white,  crystalline  powder. 
