ON  FUSED  CYANIDE  OE  POTASSIUM. 
235 
covered  with  a  clear  liquid,  which,  on  cooling,  solidifies  to  a  white 
(not  at  all  yellow)  mass.  When  this  point  is  attained,  the  cru- 
cible is  removed  from  the  fire,  over  which  it  is  held  for  a  few 
minutes  to  allow  the  black  particles  swimming  in  it  to  subside 
the  more  readily ;  the  clear  liquid  poured  on  a  clean  iron  dish, 
broken  into  small  pieces  so  soon  as  it  has  solidified,  and  kept  in 
well  closed  vessels.    The  yield  will  he  from  6  to  6|  parts. 
Hecajritulation. — Ferrocyanide  of  potassium,  deprived  of  its 
water  of  crystallization,  consists  of  2KCy-f-Fe0.y.  By  fusing 
this  with  an  equivalent  of  carbonate  of  potash,  the  oxygen  of 
half  the  potash  combines  with  half  the  cyanogen  of  the  cyanide 
of  iron  to  cyanic  acid,  which,  with  the  other  half  of  the  potash, 
forms  cyanate  of  potash,  =  KO-j-CyO  ;  the  potassium  liberated, 
with  the  other  half  of  the  cyanogen  of  the  cyanide  of  iron,  forms 
cyanide  of  potassium  ;  the  iron  separates,  in  a  metallic  state,  as 
grayish-black  flakes,  and  the  carbonic  acid  is  evolved  : 
2  at.  2KCy+FeCy,  and  2  at.  KO+C02,  form 
5  at.  KCy,  1  at.  KO+CyO,  2  at  Fe,  and  2  at  G02. 
4610  parts  of  anhydrous,  or  5285  parts  of  crystallized  (contain- 
ing three  at.  of  water)  ferrocyanide  of  potassium  require  1730 
parts  of  carbonate  of  potash,  which  nearly  agree  with  the  pro- 
portions given — eight  and  three  parts.  The  above  explanation 
of  the  process  is  not  perfectly  correct ;  for,  instead  of  five  at.  of 
cyanide  of  potassium  and  one  at.  of  cyanate  of  potash,  I  find 
that  the  salt  has  pretty  constantly  the  formula,  7KCy-f  3  (KO-f 
CyO.)*  The  reason  of  it  is  most  likely  this,  that  the  greater 
part  of  carbonic  acid  liberated  becomes  deprived  of  half  its  oxy- 
gen by  a  portion  of  the  cyanide  of  potassium,  and  is  conse- 
quently evolved  as  carbonic  oxide.  One  and  three-fifths  parts 
of  every  two  at.  of  carbonic  acid  are  thus  reduced ;  (to  avoid 
fractions,  we  will  suppose  at  first  25  at.  KCy  and  five  at.  KO-f- 
CyO  are  formed,  and  10  at.  of  carbonic  acid,  of  which  eight  at. 
give  up  half  their  oxygen  —  eight  at.  to  four  at.  cyanide  of  po- 
*  The  portions  of  salt  prepared  at  three  different  times  gave,  on  precipitation 
with  nitrate  of  silver,  from  20  grains  26*4,  2G  5,  and  26-75  grains  cyanide  of 
silver,  the  mean  =  26-55  grains.  These  26  5  grains  cyanide  of  silver  correspond 
to  12  93  grains  cyanide  of  potassium,  consequently  from  20  grains  of  the  salt 
there  remain  7-07  grains  for  cyanate  of  potrsb.  The  compound  l7KOy+3{KO-J- 
CyO)  consists  in  20  parts  of  13-04  KCy  and  6-96  KO-f-CyO. 
