\ 
294  Acetic  Acid,  Pure.  {An,j&8^rnu 
the  discovery  of  any  acid  except  those  which  exist  ready  formed  in  the 
vegetable  kingdom.  Having  an  organic  origin,  that  is,  being  a  resultant 
from  changes  produced  in  organic  substances,  by  heat  or  otherwise,  it 
is  naturally  rather  troublesome  to  deprive  it  of  some  of  the  other 
simultaneously-produced  compounds,  such  as  empyreumatic  oils,  etc., 
without  effecting  a  partial  decomposition  of  the  acid  itself. 
One  method  is  to  combine  it  with  a  base,  such  as  soda  or  lime,  and 
to  maintain  the  resulting  salt  at  a  temperature  sufficiently  elevated 
partially  to  carbonize  the  empyreumatic  substance.  Even  by  this 
method,  however,  the  desired  result  is  not  realized  with  economy,  for 
if  heated  until  complete  carbonization  of  foreign  matter  is  effected,  the 
acetate  also  is  partially  sacrificed,  and  proves  a  loss. 
In  some  parts  of  France  and  Germany  the  carbonate  of  baryta  is 
used,  instead  of  the  corresponding  soda  salt,  to  produce  the  acetate,  as 
acetate  of  baryta  is  more  stable  under  the  influence  of  high  tempera- 
tures than  acetate  of  soda. 
Some  of  the  acetic  acid  manufactured  in  this  country  is  derived  from 
the  distillation  of  acetate  of  lime  with  a  stronger  acid,  or  is  produced 
from  pyroligneous  acid  of  home  manufacture.  The  former  is  generally 
of  a  better  quality,  and  has  a  more  acceptable  odor. 
As  a  perfect  carbonization  of  empyreumatic  oils  cannot  be  effected 
without  endangering,  to  some  extent,  the  acetate,  an  acid  perfectly  free 
from  them  is  rarely  met  with. 
I  have  examined  various  samples  of  this  acid  and  have  found  that 
all  of  them,  after  being  neutralized  and  then  mixed  with  a  dilute  solu- 
tion of  permanganate  of  potassa,  would  discolor  this  reagent  from  the 
presence  of  these  oils.  A  very  delicate  test  is  the  odor  of  the  acid, 
which,  if  fragrant  and  pungent,  without  a  smoky  or  empyreumatic 
smell,  generally  indicates  that  the  acid  is  free  from  any  large  quantity 
of  these  substances. 
However,  when  used  in  delicate  operations,  as  in  photography,  it 
should  be  tested  by  adding  to  it  an  equal  bulk  of  pure  sulphuric  acid, 
and  if  this  does  not  color  within  a  few  hours  the  acetic  acid  may  be 
considered  pure. 
The  Dispensatory  and  the  U.  S.  Pharmacopoeia  give,  as  a 
test  for  the  presence  of  nitric  acid,  to  digest  the  acid  with  silver,  and 
then  add  chloro-hydric  acid,  when,  if  any  be  present,  a  precipitate  of 
chloride  of   silver  will  be  formed.    I  have,  on  several  occasions, 
