Am.  Jour.  Pharm. 
March,  1888. 
Formic  Acid  in  Acetic  Acid. 
131 
FORMIC  ACID :  ITS  DETECTION  AND  ESTIMATION  IN 
ACETIC  ACID  AND  ACETATES. 
A  Contribution  from  the  Chemical  Laboratory  of  the  Philadelphia  College  of 
Pharmacy. 
By  Frank  X.  Moerk,  PiiG. 
Read  at  the  Pharmaceutical  Meeting,  February  21. 
Id  a  paper  on  mercurammonium  chlorides  published  in  the  recent 
issue  of  the  American  Journal  of  Pharmacy,  the  peculiar  effect 
of  acetic  acid  on  these  compounds,  as  also  on  mercuric  chloride,  was 
noticed.  The  peculiarity  was  the  reduction  of  the  mercuric  salt  and 
formation  of  mercurous  chloride.  This  reaction  has  since  been  in- 
vestigated, and  is  caused  by  the  presence  of  formic  acid  in  the  acetic 
acid  used. 
A  solution  of  mercuric  chloride  was  boiled  for  one  hour  with  a  por- 
tion of  the  acetic  acid,  at  the  end  of  which  time  the  odor  and  reactions 
of  acetic  acid  were  easily  recognizable.  The  mixture  was  filtered,  to 
remove  the  mercurous  chloride  which  was  deposited,  and  to  the  filtrate 
added  carbonate  of  sodium,  effervescence  occurred  showing  the  presence 
of  free  acid ;  to  another  portion  was  added  potassium  iodide,  a  red 
precipitate  of  mercuric  iodide  indicating  the  presence  of  mercuric  salt. 
This  proves  that  acetic  acid,  if  pure,  will  not  reduce  mercuric  chloride, 
and  that  the  reduction  was  due  to  a  foreign  substance,  as  was  shown 
by  adding  a  fresh  portion  of  the  acetic  acid  to  some  of  the  filtrate  and 
boiling;  it  again  yielded  a  white  precipitate  of  calomel. 
To  ascertain  the  effect  of  pure  acetic  acid  upon  the  mercurammonium 
chloride,  commercial  acetic  acid  (No.  8)  was  boiled  with  mercuric 
chloride,  the  calomel  filtered  off,  and  a  portion  of  this  filtrate  was 
taken  and  added  to  mercurammonium  chloride ;  it  did  not  dissolve  an 
appreciable  quantity  without  application  of  heat,  but  with  the  aid  of 
the  latter  agent  took  up  considerable  of  it,  and  even  protracted  boiling 
caused  no  separation  of  calomel. 
In  the  preparation  of  pyroligneous  acid,  there  are  produced  in 
addition  to  acetic  acid,  smaller  quantities  of  formic  and  other  acids. 
In  the  purification  of  this  crude  acid  it  is  presumed  that  all  acids  other 
than  the  acetic  are  destroyed  or  separated.  Not  one  of  the  standard 
works  intimates  the  presence  of  formic  acid  either  in  the  commercial 
or  so-called  chemically  pure  acetic  acids. 
The  formation  of  mercurous  chloride  from  the  mercuric  chloride  is 
