^""'£^■£8?™"}    Detection  of  Mineral  Acids  in  Vinegar.  101 
The  method  is  to  evaporate  a  portion  (about  one  fluidounce)  of  the 
suspected  vinegar  in  a  glass  or  porcelain  vessel  down  to  a  thick,  syrupy 
extract^  just  capable  of  being  stirred  easily  with  a  glass  rod,  then  let 
the  evaporating  dish  cool  till  the  hand  can  bear  the  heat  without  feel- 
ing unpleasantly  warm,  or  until  the  dish  is  about  blood-warm,  then 
siir  into  the  extract  a  few  grains  of  finely  powdered  chlorate  of  potas- 
sium ;  or  if  there  is  no  organic  extract,  or  very  little,  as  might  result 
if  a  very  pure  article  of  acetic  acid  were  carefully  evaporated,  add  a 
small  percentage  of  sugar  to  the  chlorate  before  mixing  it  as  above 
directed.  If  there  should  be  as  much  as  one  per  cent,  of  sulphuric 
acid,  the  mass  Avould  ignite  vigorously  and  I  feel  confident  much  less 
would  be  indicated  by  fire,  and  a  still  smaller  quantity,  even  quite 
minute,  would  be  made  known  by  the  odor  of  chlorine.  Muriatic  acid 
would  evolve  the  same  odor  but  produce  no  fire. 
After  mixing  the  chlorate  and  the  extract  thoroughly  with  a  glass 
rod  wait  a  minute  or  two,  stirring  the  mass  occasionally,  if  it  does  not 
immediately  ignite.  Be  careful  not  to  place  the  face  too  near  the 
mixture  until  several  minutes  have  elapsed,  or  the  ignition  may  do 
harm  to  the  eyes.  Afterwards  the  mass  may  be  smelt,  to  detect  the 
chlorine  odor,  and  if  the  quantity  of  mineral  acid  is  minute  the  dish 
with  its  contents  may  be  carefully  warmed  or  even  gradually  heated, 
smelling  occasionally,  not  too  closely,  until  the  dish  cools.  The 
extract  from  pure  vinegar  does  not  ignite  until  the  heat  is  quite  painful 
to  the  hand  if  the  dish  be  felt ;  whereas  if  sulphuric  acid  be  present 
the  heat  will  not  be  very  great  before  the  mass  burns  up  with  a  flare. 
I  am  not  sure  that  this  test  can  conveniently  be  used  for  the  quantita- 
tive determination  of  free  mineral  acid,  but  think  that  a  method  might 
be  devised  for  conducting  the  gaseous  chlorine  into  a  solution  of  nitrate 
of  silver,  collecting,  washing,  drying  and  weighing  the  precipitated 
chloride  of  silver,  and,  by  appropriate  calculation,  estimating  the 
amount  of  free  acid,  having  first  determined  the  kind  and,  if  necessary, 
made  a  separation  of  them  by  available  methods  which  it  is  not  within 
the  scope  of  this  article  to  detail. 
Nitric  acid  would  not  be  so  easily  detected,  though  in  skillful  hands 
I  think  it  would  appear  by  manifesting  an  odor  somewhat  similar  to 
chlorine  (the  nitro-muriatic  acid  odor).  But  this  acid  could  more 
advantageously  be  detected  by  its  action  on  copper,  in  the  form  of 
clean  wire  or  strips,  which  should  be  used  without  the  addition  of  the 
chlorate  of  potassium.  The  above  test  is  very  easily  made  and  the 
<;hemistry  of  it  is  so  well  understood  as  to  need  no  further  explanation. 
Nashville,  February  2,  1882. 
