Am.  Jour.  Pharm.\ 
Nov.,  1889.  / 
Sulphites  and  Thiosulphates. 
585 
The  compound  HNaK2(S03)2-f-3H20  separates  in  transparent 
prisms  when  a  concentrated  solution  of  equivalent  quantities  of 
sodium  potassium  sulphite  and  potassium  hydrogen  sulphite  is  evap- 
orated over  sulphuric  acid ;  it  behaves  like  the  double  salts  described 
above. 
A  compound,  H(NH4)Na2(S03)2+4H20,  separates  in  colorless  crys- 
tals when  ammonia  is  passed  into  a  concentrated  solution  of  sodium 
hydrogen  sulphite,  or  when  a  concentrated  solution  of  ammonium 
hydrogen  sulphite  is  partially  saturated  with  sodium  carbonate. 
Tauber  (Jahresb.  Chem.  Techn.,  1888.  444),  by  the  latter  method, 
obtained  a  salt  to  which  he  assigned  the  formula  2Na2S03,(NH4)2S2 
O5+10H2O,  and,  in  fact,  all  the  double  salts  described  above  may 
be  regarded  as  pyrosulphites  of  analogous  constitution.  It  crystal- 
lizes in  large  plates,  and  is  moderately  stable  at  the  ordinary  tem- 
perature, but  at  120°  it  is  quickly  decomposed  with  evolution  of  water, 
ammonia,  and  sulphurous  anhydride.  It  is  readily  (48'5  per  cent, 
at  15°,  42#3  per  cent,  at  12'4°)  soluble  in  water,  and  the  solution  has 
an  acid  reaction.  It  seems  to  be  identical  with  the  double  salt 
described  by  Marignac  (Jahresb.  Chem.,  1857,  118). 
Sodium  potassium  thiosulphate,  SNa,S02,OK+2H20,  is  obtained  in 
large,  transparent  plates,  when  a  freshly  prepared,  concentrated  solu- 
tion of  ammonium  pentasulphide  is  added  to  a  solution  of  sodium 
potassium  sulphide  (see  above)  until  a  permanent  yellow  coloration  is 
produced,  the  ammonia  expelled  by  boiling,  and  the  filtered  solution 
evaporated  on  the  water-bath.  It  is  very  readily  (213*7  per  cent,  at 
15°)  soluble  in  water,  melts  at  about  57°,  and  when  heated  with 
ethyl  bromide  in  aqueous  solution  it  yields  colorless  crystals  of 
potassium  ethyl  thiosulphate. 
Potassium  sodium  thiosulphate,  SK*S02,ONa+2H20,  prepared  from 
potassium  sodium  sulphite  (see  above)  in  like  manner,  crystallizes  in 
small,  colorless  plates,  melts  at  about  62°,  and  is  very  readily  (105'3 
per  cent,  at  15°)  soluble  in  water.  When  an  aqueous  solution  is 
heated  with  ethyl  bromide,  sodium  ethyl  thiosulphate  is  obtained ;  the 
last-named  compound  crystallizes  from  dilute  alcohol  in  long,  transpa- 
rent needles,  which  seem  to  contain  1  mol.  H20. 
Potassium  tetrathionate  is  obtained  when  either  sodium  potassium 
or  potassium  sodium  thiosulphate  is  treated  with  iodine;  this  abnor- 
mal behavior  is  owing  to  the  fact  that  potassium  iodide  decomposes 
sodium  tetrathionate  with  formation  of  the  more  stable  and  more 
