PURIFICATION  OF  SULPHURIC  ACID  FROM  ARSENIC  417 
ON  AN  EASY  METHOD  TO  PURIFY  SULPHURIC  ACID  FROM 
ARSENIC. 
By  L.  A.  Buchner. 
[From  Buchner's  Repertorium,  1855,  p.  124.    By  J.  M.  Maisch.] 
It  is  a  well  known  fact  that  arsenious  acid  by  aid  of  hydro- 
chloric acid  is  transformed  into  chloride  of  arsenic.  Liebig 
(Jahresbericht,  1851,  p.  630)  has  found,  that  chloride  of  arsenic 
is  separated  in  oily  drops,  and  may  be  distilled  off,  when  arseni- 
ous acid  is  dissolved  in  hydrochloric  acid,  or  on  the  mixture  of 
this  with  a  liquid  containing  arsenious  acid,  afterwards  adding 
concentrated  sulphuric  acid.  Chloride  of  arsenic  boils  at  132°  C,, 
(270Q  F.,)  and  evaporates  very  easily  with  the  vapors  of  hydro- 
chloric acid,  under  its  own  boiling  point,  whilst  concentrated 
sulphuric  acid  does  not  evaporate  until  it  has  reached  its  boiling 
point,  at  325-327°  C,  ("617-620°  F.) 
I  do  not  know  that  these  facts  have  been  employed  for  the  re- 
moval of  arsenic  from  sulphuric  acid ;  but  that  this  acid  may  be 
purified  by  a  method  founded  on  them,  I  have  conclusively  shown 
by  experiments.  A  little  muriatic  acid  added  to  a  sulphuric  acid 
containing  arsenic,  and  heating,  or,  what  is  better  and  preferable, 
hydrochloric  acid  gas  passed  into  such  heated  acid,  separates  all 
arsenic  as  chloride  of  arsenic.  Intentionally  I  have  dissolved  a 
large  quantity  of  arsenious  acid  in  concentrated  sulphuric  acid, 
and  treated  this  solution  in  the  above  manner.  In  a  short  time 
the  arsenic,  in  connection  with  the  hydrochloric  acid,  was  so 
completely  driven  off  that  not  the  smallest  possible  trace  could 
be  detected  in  Marsh's  apparatus,  even  after  operating  for  half 
an  hour.  The  heating  of  the  acid  need  not  be  continued  but  a 
short  time  after  stopping  the  steam  of  hydrochloric  acid,  and 
every  trace  of  it,  if  necessary,  will  be  driven  off. 
This  I  believe  to  be  the  only  reliable  mode  of  making  sulphuric 
acid  free  of  arsenic  in  a  short  time  and  at  little  expense,  for 
chemico-legal  investigations  and  medicinal  pharmaceutical  pur- 
poses. It  is  well  known,  that  this  cannot  be  achieved  by  rectifica- 
tion of  an  impure  oil  of  vitriol,  inasmuch  as  its  point  of  sublima- 
tion is  not  far  enough  from  the  boiling  point  of  sulphuric  acid, 
and  even  lower  than  this,  it  being  at  218°  C,  (425y  F.  Mitchell) 
and  to  dilute  the  acid,  precipitate  by  sulphuretted  hydrogen,  de- 
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