68 
PREPARATION  OF  PURE  SULPHATES. 
color  are  obtained,  containing  no  trace  of  iron.  Deutoxyd  of 
lead  is  prepared  for  this  purpose  by  boiling  minium  with  dilute 
nitric  or  acetic  acid  in  the  usual  way,  but  minium  itself,  if  free 
from  soluble  impurities,  may  be  used  directly  in  ordinary  cases, 
although  a  portion  of  the  oxyde  of  copper  also  is  thereby  precipi- 
tated.   Deutoxyd  of  barium  is  of  course  also  applicable. 
In  cases  where  the  presence  of  a  little  lime  in  the  product  is 
of  no  moment,  as  for  the  use  of  the  calico-printer  and  manufac- 
turer of  pigments,  carbonate  of  lime  may  be  substituted  for  that 
of  baryta. 
In  addition,  it  may  be  remarked  that  if  the  blue  vitriol  con- 
tains traces  of  manganese,  as  is  extremely  liable  to  occur,  this 
contamination,  as  would  appear  from  the  observations  of  Schon- 
bein  and  Wolcott  Gibbs,  must  also  be  entirely  removed. 
The  same  treatment  is  evidently  applicable  to  some  other  sul- 
phates, and  I  therefore  present  it  as  a  general  method  for  the  re- 
moval of  iron  from  the  sulphates  of  bases  precipitated  with  dif- 
ficulty by  carbonate  of  baryta,  namely,  those  of  the  alkalies, 
magnesia,  manganese,  zinc,  cadmium,  mercury,  nickel,  cobalt  and 
protoxyd  of  iron.  Of  these  the  most  important  one  practically 
is  the  sulphate  of  magnesia.  The  mode  of  proceeding  with  this 
would  be  precisely  similar  to  that  with  the  copper  salt,  as  it 
would  be  also  with  the  sulphates  of  zinc,  cadmium,  mercury,  nickel 
and  the  alkalies.  With  regard  to  the  manganous  sulphate  it 
must  be  remembered  that  deutoxyd  of  lead,  as  observed  by  Schon- 
bein,  wholly  precipitates  sulphate  of  manganese  from  its  boiling 
solution  ;  so  that  the  deutoxyd  must  be  used  only  in  small  excess 
over  the  necessary  quantity.  The  same  precaution  applies,  in 
a  modified  manner,  to  the  treatment  of  the  cobaltous  sulphate, 
because  Gibbs  states  that  the  salts  of  this  metal  are  also  partial- 
ly precipitated  by  long  boiling  with  an  excess  of  the  deutoxyd, 
passing  first  to  a  higher  state  of  oxydation. 
As  to  the  protosulphate  of  iron,  I  have  already  (New  York 
Jour.  Pharmacy,  i.  229)  recommended  the  use  of  carbonate  of 
baryta  for  the  removal  from  it  of  sesquioxyd  of  iron.  In  the 
same  paper  (which  has,  I  believe,  entirely  escaped  notice  from 
other  Journals,  owing  to  the  irregularity  with  which  the  ex- 
changes of  that  publication  were  effected)  I  have  given,  among 
other  observations  upon  the  purification  of  copperas,  another 
