PREPARATION  OF  LACTATE   OF  PROTOXIDE    OF  IRON.  557 
The  following  is  the  mode  of  operating  if  the  former  of  the  two 
processes  indicated  above  be  adopted: — 
After  having  prepared  lactate  of  lime  in  the  usual  way,  by  ar- 
tificial means,  it  is  necessary  to  test  the  degree  of  purity  of  the 
salt,  as  it  is  difficult  to  get  it  always  in  the  same  state,  for  not 
only  does  it  frequently  contain  carbonate  of  lime,  but  the  amount 
of  water  present  is  always  variable.  It  should  be  ascertained, 
therefore,  what  quantity  of  sulphuric  acid  of  a  definite  strength 
is  required  for  the  complete  decomposition  of  a  given  quantity 
of  the  lactate. 
For  the  preparation  of  lactate  of  iron  a  certain  quantity  of  the 
lactate  of  lime  is  mixed  with  the  required  quantity  of  sulphuric 
acid  for  its  decomposition,  the  latter  being  mixed  with  ten  or 
twelve  times  its  weight  of  water,  and  allowed  to  stand  in  contact 
with  it,  without  heat,  for  forty-eight  hours,  the  mixture  being 
stirred  from  time  to  time.  It  may  then  be  filtered  through  a 
cloth  to  separate  the  sulphate  of  lime,  when  a  solution  of  lactic 
acid,  sufficiently  pure  for  the  purpose  intended,  will  be  obtained. 
If  it  be  desired  to  get  the  lactic  acid  in  a  greater  state  of  pu- 
rity, the  decomposition  of  the  lactate  of  lime  may  be  effected 
with  oxalic  acid  instead  of  sulphuric  acid,  but  for  the  purpose  re- 
ferred to  this  is  unnecessary,  as  the  small  quantity  of  sulphate 
of  lime  which  it  would  retain  when  sulphuric  acid  is  used  would 
be  deposited  during  the  concentration  of  the  solution. 
Two-thirds  of  the  lactic  acid,  obtained  in  the  manner  indicated, 
is  to  be  added  to  iron  filings  in  an  iron  vessel,  and  the  action 
promoted  by  the  application  of  heat.  When  the  iron  ceases  to  be 
acted  upon,  the  liquor  is  to  be  filtered,  and  if  the  directions  above 
given  have  been  followed  it  will  be  in  a  condition  favorable  to 
crystallization.  The  solution,  as  it  filters,  should  be  received  in 
a  vessel  immersed  in  warm  water,  and  should  be  subsequently 
covered.  After  five  or  six  days  the  sides  of  the  vessel  will  be 
found  to  be  covered  with  a  crystalline  coat  of  lactate  of  iron.  It 
only  remains  to  dry  the  salt,  which  is  very  easily  effected  by 
first  washing  it  with  a  mixture  of  one  part  of  lactic  acid  and 
eight  parts  of  spirit,  and  afterwards  exposing  it  to  a  tempera- 
ture of  from  60°  to  70°  Fahr.,  on  filtering  paper  or  on  a  chalk- 
stone. 
In  order  to  effect  the  crystallization  of  the  mother-liquor  some 
of  the  free  lactic  acid,  which  was  kept  in  reserve,  is  to  be  added 
