252 
MANUFACTURE  OF  SULPHATE  BARYTA. 
pieces  of  carbonate  of  baryta,  no  matter  how  large,  are  acted 
upon  and  completely  transformed  into  a  fine  white  power  en- 
tirely composed  of  sulphate  of  baryta,  and  of  the  greatest  tenuity. 
If  the  same  experiment  is  made  without  the  addition  of  hy- 
drochloric acid,  the  carbonate  is  acted  upon  very  slowly.  The 
part  which  hydrocholoric  acid  plays  in  this  reaction  is  easily  un- 
derstood. It  forms  a  soluble  chloride  of  barium  which  sulphu- 
ric acid  decomposes,  reproducing  hydrochloric  acid  always  in 
the  same  quantity,  so  that  it  is  in  fact  the  latter  acid,  not  the 
sulphuric  acid,  which  acts  upon  the  carbonate  of  baryta. 
This  experiment  becomes  still  more  interesting  if  dilute  sul- 
phuric acid  be  placed  with  a  few  pieces  of  carbonate  of  baryta 
in  two  matrasses,  and  brought  to  a  boiling-point  ;  then  with  the 
end  of  a  glass  rod  introduce  into  one  of  them  a  few  drops  of  hy- 
drochloric acid.  A  white  powder  will  be  seen  to  detach  itself  in 
increasing  quantity  from  the  pieces  of  carbonate,  and  at  the  same 
time  an  effervescence  will  take  place  owing  to  the  disengage- 
ment of  the  carbonic  acid.  In  the  other  matrass  nothing  of  the 
kind  takes  place ;  the  liquid  is  hardly  rendered  turbid  by  a 
scarcely  perceptible  trace  of  sulphate  of  baryta. 
In  this  case  a  similar  phenomenon  takes  place,  as  in  the  man- 
ufacture of  white  lead  by  the  Dutch  process,  in  which  a  trace  of 
vinegar  is  sufficient  to  determine  the  oxidation  of  an  enormous 
quantity  of  lead.  Without  the  agency  of  that  acid  the  lead 
would  not  be  acted  upon  by  air  or  carbonic  acid.  In  like  man- 
ner, although  in  a  lesser  degree,  carbonate  of  baryta  resists  the 
action  of  sulphuric  acid  without  the  presence  of  hydrochloric 
acid. 
I  thought  that  marble  would  be  acted  upon  still  more  easily 
than  carbonate  of  baryta  by  a  mixture  of  diluted  sulphuric  acid 
and  a  small  quantity  of  hydrochloric  acid ;  but  my  experiments 
have  given  a  result  contrary  to  my  expectations.  Under  the 
same  conditions  as  those  pointed  out  for  carbonate  of  baryta, 
marble  is  acted  upon  with  more  difficulty  and  more  slowly  than  the 
last  named  salt.  The  addition  of  a  relatively  large  quantity  of 
hydrochloric  acid  shortens  very  little  the  time  it  takes  to  be  con- 
verted into  sulphate  of  lime.  The  pieces  of  marble  are  deeply 
impregnated  with  sulphate  of  lime.  I  do  not  know  the  cause  of 
this  difference  of  action  ;  but,  at  all  events,  I  have  been  obliged 
