ON  THE  USES  OF  HYPOSULPHITE  OF  SODA, 
125 
ON  THE  USES  OF  HYPOSULPHITE  OF  SODA. 
By  W.  A.  Froehde. 
The  author  has  found  this  salt  to  be  a  very  delicate  test  for 
cyanides.  In  all  cases  sulphocyanide,  sulphuret  and  sulphate 
are  formed.  With  cyanide  of  potassium  the  reaction  is  as  follows  : 
2KCy+4(NaO,S202)=2  NaCyS2+2(KO,S03)-f-NaO,S03+NaS. 
The  following  shows  the  decomposition  of  ferrocyanide  of  potas- 
sium :  2K2FeCy3  +  l2(NaO,S,02)  =6NaCyS2  +  4(KO,S03) 
+  5(NaO,S03)  -h  NaS  +  2FeS.  With  an  insufficient  quantity 
of  the  soda  salt,  cyanate  is  formed  which  is  decomposed  by  the 
heat,  carbonic  acid  being  evolved  and  ammonia  found  in  the 
residue.  With  ferridcyanide  of  potassium,  after  the  previous 
desiccation  of  the  salts,  the  result  is  similar,  some  sulphurous 
acid  being  evolved ;  otherwise  sulphur  and  sulphurous  acid  are 
liberated,  and  sulphate  and  ferrocyanide  formed  according  to 
the  following  equation:  K3Fe2Cy6  +  2NaO,Sa02=K2FeCy3 + 
Na2FeCy3  -f  KO,S03  +  S2  +  S02.  Prussian  blue  and  Turn- 
bull's  blue  yield  with  the  hyposulphite  sulphuret  of  iron  and 
sulphocyanide  of  sodium. 
For  detecting  cyanogen  in  the  solid  cyanides,  the  operation 
is  as  follows  :  a  little  hyposulphite  of  soda  is  fused  to  a  bead  ; 
after  the  desiccation  of  the  salt,  a  minute  quantity  of  suspected 
cyanide  is  added,  and  heat  applied.  If  the  bead  of  the  pla- 
tinum wire  is  now  placed  in  a  few  drops  of  ferric  chloride,  an 
intense  blood-red  coloration  will  be  produced  around  the  wire, 
which  gradually  spreads  over  the  whole  liquid.  If  not  heated 
long  enough,  some  hyposulphurous  acid  may  remain  undecom- 
posed  and  produce  with  the  ferric  chloride  the  well  known 
violet  color,  which,  however,  disappears,  the  ferric  salt  being  de- 
oxidized to  ferrous  chloride.  On  the  other  hand,  too  long  con- 
tinued a  heat  will  decompose  and  burn  sulphocyanide  with  a 
peculiar  red  flashing  flame.  This  process  allows  to  distinguish 
cyanide  of  silver  from  chloride,  bromide  and  iodide,  or  to  detect 
it  when  mixed  with  the  latter. 
The  above  reaction  furnishes  a  ready  means  for  preparing 
sulphocyanides.  One  part  of  ferrocyanide  of  potassium  is  mix- 
ed with  3«5  parts  crystallized  hyposulphite  of  soda,  the  mixture 
desiccated  and  then  heated  to  the  complete  decomposition  of  the 
hyposulphite  ;  hot  alcohol  dissolves  from  the  residue  sulphocyan- 
ide of  sodium. 
