AmDe°cU,r*x8P76?rm'}  Salicylate  and  Sulphosalicylate  of  Sodium.  547 
discovered  many  years  back  by  Cahours,and  has  been  further  investigated 
by  Mendius.  The  process  described  for  its  production  is,  however,  one 
of  considerable  practical  difficulty. 
The  vapor  of  anhydrous  sulphuric  acid  is  passed  over  salicylic  acid 
kept  cool ;  gradually  a  sticky,  gummy  mass  is  produced,  which  contains 
the  new  acid,  and  can  be  separated  by  appropriate  means. 
I  have  made  several  attempts  to  produce  this  conjugated  acid  by 
means  of  ordinary  sulphuric  acid,  and  have  at  length  succeeded  in  doing 
so,  but  not  without  several  failures.  I  find  the  following  process  to 
answer  : 
The  salicylic  acid  must  be  very  pure  ;  the  unpurified  commercial 
acid,  when  treated  with  sulphuric  acid,  simply  yields  a  black  mass, 
giving  off  sulphurous  acid,  and  yielding  no  sulpho-salt  capable  of  giving 
definite  crystals. 
If  pure  acid  is  employed,  then  about  twice  its  weight  of  sulphuric 
acid  is  quite  sufficient.  The  mixture  must  be  gently  heated  in  a  sand- 
bath  up  to  about  ioo°  C,  when  action  will  commence  in  the  liquid,  and 
•considerable  heat  be  developed.  The  beaker  must  be  removed  from 
the  sand-bath,  and  the  contents  stirred,  so  as  to  regulate  and  keep  down 
the  temperature  ;  but  the  cooling  must  not  be  sufficient  to  altogether 
check  the  reaction.  If  the  temperature  exceeds  the  proper  point,  little 
or  no  sulphosalicylic  acid  is  produced,  but  apparently  bisulpho-carbolic 
acid,  which  does  not  yield  definite  crystallizable  salt. 
When  the  reaction  has  been  properly  maintained,  at  the  end  of  ten 
minutes  or  a  quarter  of  an  hour  the  temperature  begins  to  fall  and  in  a 
short  time  the  whole  becomes  a  solid  mass,  generally  of  a  light  brown 
color  ;  this  will  speedily  deliquesce  if  left  exposed  to  the  air ;  but  it 
can  be  dissolved  in  water  at  once,  and  treated  with  carbonate  of  barium 
in  the  usual  way.  I  may  mention  that  as  the  sulphosalicylate  of  barium 
is  not  a  very  soluble  salt,  it  is  necessary  to  employ  a  considerable  quan- 
tity of  water,  and  filter  the  liquid  while  still  hot.  This  solution  of  the 
barium  salt,  decomposed  by  an  equivalent  quantity  of  sulphate  of  sodium, 
which  yields  a  solution  of  the  sulphosalicylate  of  sodium  upon  evapo- 
ration to  a  small  bulk,  yields  crystals  ;  these  crystals  must  be  pressed 
from  the  mother  liquor  and  purified  by  recrystallization  two  or  three 
times  from  hot  water. 
When  pure,  sulphosalicylate  of^sodium  forms  hard  white  prisms  ;  it 
is  not  deliquescent,  although  very  soluble  in  water.    It  is  almost  insol- 
