REMARKS  ON  SOME  CHEMICAL  PROCESSES. 
139 
have  found  that  if  it  was  checked  at  this  stage,  a  comparatively 
•  small  amount  of  water  would  answer,  but  if  allowed  to  react 
violently  a  much  larger  quantity  of  water  was  necessary.  The 
evaporation  of  the  acid,  after  the  phosphorus  is  all  oxidized,  is 
conducted  in  a  porcelain  capsule  ;  towards  the  end  of  this  process 
it  will  froth  up,  owing  to  the  rapid  disengagement  of  nitric  oxide. 
The  dish  must  therefore  have  about  three  times  the  capacity  of 
the  acid  when  concentrated,  and  a  little  distilled  water  should  be 
kept  conveniently  near,  to  add  in  case  there  is  danger  of  froth- 
ing over.  It  is  scarcely  necessary  to  add  that  the  operation 
should  be  conducted  under  a  good  furnace  hood,  or  otherwise  the 
beak  of  the  retort  should  be  introduced  into  a  good  flue. 
Sulpliate  of  Manganese.  Wishing  to  make  some  of  this  salt, 
I  adopted  the  following  formula,  which  gives  an  abundant  yield 
of  the  pure  salt : 
Introduce  into  an  iron  crucible  a  mixture  of  five  parts  of  \ 
peroxide  of  manganese  and  three-fourth  parts  of  coarsely 
powdered  charcoal.  Cover  the  crucible  and  heat  to  redness 
until  all  the  charcoal  is  consumed.  Allow  the  contents  of  the 
crucible  to  cool,  place  in  a  porcelain  dish  and  add  6J  parts  of 
sulphuric  acid.  Evaporate  nearly  to  dryness,  return  the  mass 
to  the  crucible  and  heat  to  redness.  When  cool  rub  to  powder, 
if  necessary,  and  treat  twice  successively  with  eight  parts  of  boil- 
ing water ;  mix  the  liquors,  filter  and  evaporate  until  a  pellicle 
begins  to  form,  when  set  aside  to  crystallize. 
If  evaporated  too  far  an  insoluble  sulphate  is  deposited,  (pro- 
bably in  a  peculiar  state  of  hydration),  hence  care  must  be  taken 
to  remove  it  from  the  sand-bath  as  soon  as  a  pellicle  begins  to 
form.  When  a  good  article  of  peroxide  of  manganese  is  used, 
this  formula  will  give  an  abundant  yield  of  perfectly  pure  sul- 
phate of  manganese.  Any  iron  or  copper  present  is  destroyed 
by  heating  the  crude  salt  to  redness. 
Ammonio-ferric  Alum.  In  making  this  salt  according  to  the 
U.  S.  Pharm.  formula  I  found  that,  instead  of  obtaining  crystals 
of  a  clear  violet  tinge,  they  had  a  brownish  color.  I  first  ascribed 
it  to  unskilful  manipulation,  but  on  repeated  trials  met  with 
similar  results,  sometimes,  however,  approaching  in  appearance  to 
