546  Salicylate  and  Sulpho salicylate  of  Sodium,  { AmbJe0cu,r x8P76ariri 
A  blistering  plaster  may  sometimes  fail  from  the  bad  quality  of  the 
flies,  and  in  this  matter  if  there  is  any  suspicion,  I  think  the  judgment 
would  be  much  aided  by  the  use  of  a  microscope.  There  are  other 
causes  of  failure,  such  as  the  plaster  being  insecurely  applied,  or  the 
patient's  skin  may  be  of  that  nature  that  vesicants  will  not  affect  it ; 
these  matters  are  outside  our  control.  I  have  only  attempted  that 
which  is  within  it,  and  believe  the  form  I  have  given  for  cantharides 
plaster  will  be  found  an  improvement  on  that  to  which  we  have  been 
accustomed. 
NOTE  ON  SALICYLATE  AND  SULPHOSALICYLATE  OF  SODIUM.1 
BY  JOHN  WILLIAMS,  F.C.S. 
Salicylate  of  sodium  has  been  much  employed  lately  as  an  internal 
remedy. 
It  is  made  by  neutralizing  a  solution  of  salicylic  acid  with  caustic 
soda,  and  evaporating  to  dryness.  It  can  be  purified  by  crystallization 
from  alcohol  ;  the  crystals  formed  are,  however,  very  small  and  indis- 
tinct, and  this  method  of  purification  is  not  generally  adopted. 
Complaints  have  appeared  in  the  medical  journals  that  the  salt  some- 
times produces  irritative  effects  when  administered  medicinally,  and  it  has 
been  suggested  that  probably  a  trace  of  carbolic  acid  may  occasionally 
be  retained  by  the  salicylic  acid  made  by  artificial  means,  and  thus  the 
salt  prepared  from  such  acid  is  impure. 
An  examination  of  the  salicylic  acid  made  from  carbolic  acid  by 
Kolbe's  process  soon  proves  that  the  product  is  not  always  to  be 
depended  upon  as  a  pure  homogeneous  article  ;  indeed  it  can  hardly  be 
otherwise,  when  we  consider  that  the  carbolic  acid  from  which  it  is 
made  is  itself  not  an  absolutely  pure  or  definite  article.  Still,  I  must 
observe  that  the  salicylic  acid  now  being  supplied  is  much  purer  and 
more  definite  than  that  which  was  at  first  sent  into  the  market  by  the 
German  makers. 
Thus  salicylate  of  sodium — made  from  the  artificial  acid — and  from 
the  great  difficulty  of  purifying  it  by  recrystallization — is  liable  to  be 
more  or  less  impure,  and  indefinite  in  composition.  It  thus  appears 
desirable,  if  possible,  to  obtain  a  salt  which  can  be  purified,  and  obtained 
of  definite  constitution. 
Sulphosalicylic  acid  appeared  to  offer  such  a  compound.    It  was 
1  Read  before  the  British  Pharmaceutical  Conference. 
