142  INDUSTRIAL  APPLICATION  OF  BARYTA. 
The  acetate  of  baryta  thus  obtained  is  decomposed  by  1  equiv. 
of  sulphuric  acid ;  the  decomposition  is  only  complete  when  the 
solution  of  the  acetate  is  not  too  much  concentrated.  The  re- 
sult is  artificial  sulphate  of  baryta  and  weak  acetic  acid,  which, 
however,  is  strong  enough  to  be  applied  in  various  ways  in  the 
arts.  Thus  it  may  be  employed  directly  in  the  manufacture  of 
white  lead,  acetate  of  lead,  and  other  acetates. 
When  the  solution  of  acetate  of  baryta  is  too  concentrated, 
the  sulphate  of  bartya  does  not  separate  in  the  ordinary  form  ; 
it  then  retains  some  acetic  acid,  and  presents  a  gelatinous, 
semitransparent  appearance,  which  is  not  got  rid  of  without 
difficulty. 
To  obtain  a  purer  acid  the  acetate  of  baryta  may  be  converted 
into  acetate  of  soda,  by  the  addition  of  sulphate  of  soda.  In 
this  way  the  formation  of  the  double  sulphate  of  soda  and  lime, 
which  usually  occurs  in  the  ordinary  process  with  lime,  is 
avoided. 
Chromic  acid,  hydroferrocyanic  acid,  $c. 
Db'bereiner  had  employed  baryta  in  the  preparation  of  chromic 
acid,  and  Porret  in  that  of  hydroferrocyanic  acid. 
I.  The  usual  process  employed  in  the  laboratory  for  the  isola- 
tion of  chromic  acid,  consists  in  the  action  of  an  excess  of  sul- 
phuric acid  upon  chromate  of  potash.  To  prepare  this  acid  for 
use  in  the  arts,  the  author  employs  chloride  of  barium  and  neu- 
tral chromate  of  potash,  the  double  decomposition  of  which 
furnishes  chloride  of  potassium  and  chromate  of  baryta.  The 
latter  is  treated  with  1  equiv.  of  sulphuric  acid,  diluted  with  ten 
times  its  volume  of  water,  and  the  action  is  aided  by  heat ;  the 
insoluble  sulphate  of  baryta  is  rapidly  deposited  and  the  solu- 
tion of  chromic  acid  marks  10°  B.  The  chromic  acid  may  be 
concentrated  to  50°  or  60°  B.,  by  evaporation  in  earthenware 
vessels,  or  even  in  leaden  cauldrons.  The  sulphate  of  baryta, 
even  when  washed,  retains  some  chromic  acid;  it  may  be  used 
in  the  preparation  of  colors. 
Chromate  of  baryta  may  be  substituted  for  chromate  of  lead 
in  painting  ;  it  is  of  a  bright  yellow  color,  but  less  intense  than 
that  of  chromate  of  lead.  Its  economy  and  inalterability  give 
it  a  preference  over  the  lead-salt. 
