132 
Formic  Acid  in  Acetic  Acid. 
( Am.  Jour.  Pharm. 
I     March,  1888. 
a  very  sensitive  test  for  formic  acid^  and  it  is  not  shared  by  oxalic, 
citric,  or  tartaric  acids  either  free  or  combined,  as  was  found  by 
experiment.  A  solution  of  ammonium  oxalate,  however,  is  prone  to 
decomposition,  and  after  decomposition  has  set  in  the  solution  will 
give  the  reduction  test  with  mercuric  chloride.  The  reaction  for  this 
decomposition  is  as  follows  : 
(NH^)^  C2  +  H2O  =  NH,  HCO3  -f-  NH,  CHO2 ;  the  bicarbo- 
nate is  shown  by  the  effervescence  with  acids  and  the  evolution  of 
ammonia  vapors  on  heating. 
"  Other  tests  to  prove  the  presence  of  formic  acid,  which  were  carried 
out  with  the  acetic  acid,  are  : 
1.  Boiling  with  silver  nitrate,  a  black  precipitate  consisting  of  me- 
tallic silver. 
2.  Mercuric  oxide  dissolved  in  the  acid  on  boiling  separated  mercu- 
rous  formate,  which,  on  further  boiling,  decomposed  yielding  metallic 
mercury. 
3.  The  decolorizing  of  potassium  permanganate  in  cold  acid  solution. 
The  estimation  of  formic  acid  was  next  attempted,  but  here  the  lack 
of  processes  was  encountered.  Only  one  method  was  found,  and  that 
in  Watt's  dictionary,  the  process  consists  in  the  precipitation  of  mer- 
curous  chloride  from  mercuric  chloride  in  the  presence  of  sodium 
acetate  by  boiling  in  dilute  solution,  and  after  filtration  estimating  the 
excess  of  mercuric  chloride  volumetrically  with  potassium  iodide 
solution. 
To  ascertain  if  the  use  of  sodium  acetate  did  not  furnish  a  source  of 
error  in  that  it  was  contaminated  with  formate,  a  specimen  of  chemi- 
cally pure  (so  labelled)  sodium  acetate  was  boiled  with  mercuric  chlo- 
ride; a  decided  precipitate  of  calomel  was  obtained.  This  was  suffi- 
cient to  cause  the  rejection  of  the  method  as  published. 
The  reaction  for  the  reduction  of  mercuric  chloride  is  given  in 
Kiliani  and  Miller.'' 
2  HgCl2-f2  NaCH02=Hg2Cl2-l-2  NaCl+HCH02-|-C02,  in  which 
only  one-half  of  the  formic  acid  is  decomposed.  The  following  may 
represent  the  action  of  formic  acid :  2  HgCl2+HCH02=Hg2Cl2+2 
HCI+CO2.  The  presence  of  free  hydrochloric  acid  and  of  large  quan- 
tities of  chloride  is  stated  to  j)revent  the  complete  decomposition  of 
formic  acid ;  the  results  of  two  analyses  sustain  this.  Ten  cc.  of  the 
acid  were  weighed  and  diluted  to  150  cc.  with  water;  in  this  was  dis- 
solved 2  gm.  of  mercuric  chloride,  and  the  mixture  boiled  for  one 
