88       PURIFICATION  OF  SULPHURIC  ACID  FROM  ARSENIC. 
ON  THE  PURIFICATION  OF  SULPHURIC  ACID  FROM  ARSENIC. 
By  Q.  Frederking,  of  Riga. 
The  statement  which  appeared  in  the  Journals  last  year,  that 
sulphuric  acid  may  be  entirely  purified  by  heating  it  with  chloride 
of  sodium,  recommends  a  process,  apparently  very  easy,  but 
which  cannot  be  carried  out  in  practice. 
Sulphuric  acid,  when  brought  in  contact  with  common  salt  or 
sal  ammoniac,  evolves  much  muriatic  acid  gas  ;  one  drachm  of  chlo- 
ride of  ammonium  was  therefore  introduced  into  a  small  retort, 
together  with  15  grs.  arsenious  acid  and  half  oz.  water,  to  which 
three  oz.  suphuric  acid  were  gradually  added ;  muriatic  acid  gas 
was  evolved,  but  not  in  very  large  quantity.  Heat  was  now  ap- 
plied, and  each  half  ounce  of  the  distillate  was  tested  for  arsenic 
in  Marsh's  apparatus.     The  following  was  the  result : 
1st.  The  first  half-ounce  contained  so  much  arsenic,  that  a 
metallic  mirror  was  separated  on  the  introduction  of  a  zinc  rod 
into  the  distillate. 
2d.  The  second  half-ounce  contained  yet  chlorine  and  arsenic. 
3d.  The  third  and  fourth  half-ounces  contained  both  in  small 
proportion. 
4th.  The  fifth  half-ounce  was  free  of  chloride,  and  contained 
a  minute  quantity  of  arsenic. 
5th.  The  residue  of  sulphuric  acid,  about  one  third  of  the 
original  weight,  held  much  arsenic  in  solution. 
This  behaviour  may  be  explained  in  this  way,  that  an  excess 
of  sulphuric  acid  prevents  the  formation  of  chloride  of  arsenic  ; 
it  may  even  be  easily  proven,  that  the  latter  compound,  when 
treated  with  concentrated  sulphuric  acid,  is  decomposed  into 
muriatic  and  arsenious  acids,  the  latter  of  which  remains  behind 
on  distillation. 
It  is  worth  mentioning  that  I  obtained  English  oil  of  vitriol 
(not  the  rectified)  from  a  manufacturer  of  Moscow,  which  was 
free  of  arsenic,  nitrous  acid  and  lead,  and  left  a  residue  consist- 
ing of  the  sulphate  of  potassa  and  of  earthy  matter. 
In  the  "  Archiv"  for  September,  1858,  Neese  proposes  the 
distillation  of  sulphuric  acid  from  a  retort  bedded  in  ashes  ; 
I  can  recommend  this  precaution  from  my  own  observations,  in- 
asmuch as  I  have  been  rectifying  the  acid  in  the  manner  indi- 
cated for  the  last  twelve  years.—. Archiv  d.  Pharm.  Aug.  1859. 
