42  Physiological  Action  of  Salicylic  Acid.  {A^Ja^Sarm' 
ber  30,  1889,  as  the  result  of  trying  the  impurity  obtained  from 
salicylic  acid,  which  Dr.  Henderson  had  isolated  by  Mr.  Williams' 
method  but  had  not  further  examined.  The  meta-cresotic  acid  was 
innocuous. 
The  conclusion  from  all  these  experiments  seems  to  be  that  a  high 
melting-point  is  not  the  only  or  the  best  test  for  purity.  Something 
more  is  required,  and  this  is  that  the  artificial  crystals  should  be 
identical  with  those  of  the  natural  variety,  for  similarity  of  crystal- 
lization seems  to  be  absolutely  essential  to  secure  a  uniform  and 
harmless  physiological  action.  Pharmaceutical  chemists  may  not 
have  the  apparatus  or  the  time  for  applying  the  melting-point  test, 
but  they  can  all  easily  observe  the  difference  between  well-defined 
crystals,  like  those  of  strychnine,  and  others  which  present  an 
appearance  like  quinine. 
The  well-defined  crystalline  form  of  the  acid  with  a  melting-point 
of  almost  1 570  C,  should  be  the  official  form  of  artificial  salicylic 
acid,  and  from  this  alone  should  the  salicylate  of  sodium  be  prepared. 
I  may  add  that  if  salicylic  acid  be  prepared  from  synthetic  car- 
bolic acid,  having  a  melting-point  of  420  C,  it  then  contains  no 
impurity.  Its  melting-point  is  1 57°  C,  and  its  physiological  action 
is  in  every  way  satisfactory.  This  pure  carbolic  acid  is  about  three 
times  the  price  of  the  ordinary  form,  and  until  this  can  be  reduced 
the  more  economical  plan  will  be  to  produce  salicylic  acid  from  ordi- 
nary carbolic  acid  and  subsequently  to  purify  it. 
I  would  recommend  as  additions  to  the  forthcoming  Addendum 
of  the  British  Pharmacopoeia — 
ACIDUM  SALICYLICUM  PURIFICATUM. 
Characters. — White,  separate,  large,  prismatic  crystals,  inodorous, 
taste  at  first  sweetish,  then  acid.  Soluble  in  about  500  parts  of  cold 
water  and  15  of  boiling  water  ;  readily  soluble  in  hot  chloroform; 
soiuble  in  alcohol  and  ether.  Melting-point  about  1 57°  C.  Dose, 
10  to  30  grains 
SODII  SALICYLAS  PURIFICATA. 
Obtained  by  the  action  of  purified  salicylic  acid  on  carbonate  of 
sodium. 
Characters. — Well  defined  white  odorless  crystalline  scales,  having 
a  sweetish  saline  taste ;  soluble  in  nine-tenth  part  of  its  weight  in 
water,  or  in  6  parts  of  rectified  spirit.    Dose,  10  to  30  grains. 
