NEW  METHODS   FOR  MANUFACTURING  PURE  ACETIC  ACID.  49 
liquid,  and  may  be  skimmed  off,  and  likewise  decomposes  the  com- 
pounds of  lime  with  kreosote  and  some  other  imperfectly  known 
volatile  substances,  which  are  driven  off  by  further  evaporation. 
As  these  volatile  substances  have  little  or  no  action  upon  litmus- 
paper,  its  being  reddened  by  the  liquor  is  a  sign  that  not  only  are 
ihe  lime  compounds  of  these  substances  decomposed,  but  also  a 
small  quantity  of  acetate  of  lime.  The  quantity  of  acid  necessary 
for  this  purpose  varies  and  depends  upon  the  nature  of  the  pyrol ig- 
neous acid,  which  is  again  dependent  upon  the  quantity  of  water 
in  the  wood  from  which  it  is  obtained.  150  litres  of  wood  liquor 
require  from  4  to  6  lbs.  of  hydrochloric  acid. 
The  solution  of  acetate  of  lime  is  evaporated  to  dryness,  and  a 
tolerably  strong  heat  applied  at  last,  in  order  to  remove  all  vola- 
tile substances.  Both  operations  may  be  performed  in  the  same 
iron  pans,  but  when  the  quantity  of  salt  is  large,  the  latter  may  be 
more  advantageously  effected  upon  cast  iron  plates.  The  drying 
of  the  salt  requires  very  great  care,  for  the  empyreumatic  substan- 
ces adhere  very  strongly  the  acetate  of  lime,  as  well  as  to  the  com- 
pound of  resin  and  acetic  acid  mixed  with  it,  and  when  not  per- 
fectly separated,  pass  over  with  the  acetic  acid  in  the  subsequent 
distillation  with  an  acid  communicating  to  it  a  disagreeable  odor. 
The  drying  must  therefore  be  continued  until  upon  cooling  the 
acetate  does  not  smell  at  all,  or  but  very  slightly.  It  then  has  a 
dirty  brown  color.  The  acetic  acid  is  obtained  by  distillation  with 
hydrochloric  acid  in  a  still  with  a  copper  head  and  leaden  conden- 
ser when  proper  precautions  are  taken,  the  acetic  acid  does  not 
contain  a  trace  of  either  metal.  The  quantity  of  hydrochloric  acid 
required  cannot  be  exactly  stated,  because  the  acetate  of  lime  is 
mixed  with  resin,  and  already  formed  chloride  of  calcium.  In 
most  instances  90  or  95  parts  by  weight  of  acid,  1.16  spec,  grav.^ 
are  sufficiently  to  decompose  completely  100  parts  of  the  salt? 
without  introducing  much  hydrochloric  acid  into  the  distillate. 
The  distilled  acetic  acid  possesses  only  a  very  faint  empyreuma- 
tic odor,  very  different  from  that  of  the  raw  pyroligneous  &cid  ;  it  is- 
perfectly  colorless,  and  should  only  become  slightly  turbid  on  the  ad- 
dition of  nitrate  of  silver.  If  the  acid  has  a  yellowish  color,  this  is 
owing  to  resin  having  been  spirited  over  in  the  distillation.  It  is 
therefore  advisable  to  remove  the  resin  which  is  separated  on  the  ad- 
dition of  hydrochloric  acid,  and  floats  upon  the  surface  of  the  liquid 
