METHOD  OF  PREPARING  LACTATE  OF  ZINC. 
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lactate  of  potassa,  which  is  separated  by  filtration.  The  carbon- 
ate of  potassa  should  be  in  excess,  and  the  precipitate  carefully 
washed,  so  as  to  extract  the  last  traces  of  soluble  lactate.  On 
saturating  the  excess  of  carbonate  of  potassa  with  lactic  acid,  we 
obtain  by  evaporation  pure  lactate  of  potassa,  in  deliquescent 
crystallised  masses,  soluble  in  alcohol .  But  for  the  preparation 
of  lactate  of  zinc,  it  is  not  necessary  to  use  so  pure  a  product ; 
it  is  only  necessary  to  take  a  liquid  containing  at  once  the  lactate 
and  carbonate  of  lime,  produced  by  the  precipitation  of  the 
lactate  of  lime ;  by  pouring  it  in  excess,  without  heat,  into  a  con- 
centrated solution  of  acetate  of  zinc,  it  forms  a  precipitate  of 
lactate  and  carbonate  of  zinc. 
After  having  collected  this  mixture  it  is  subjected  to  pressure ; 
it  is  treated  with  distilled  water,  and  by  filtering  while  hot,  the 
insoluble  carbonate  is  easily  separated  from  the  lactate  of  zinc 
which  remains  in  solution.  The  liquor  is  evaporated  and  crys- 
tallised, and  the  salts  obtained  are  purified  by  fresh  crystallisa- 
tions. If  we  are  careful  in  the  two  successive  operations  to  use 
the  carbonate  of  potassa  and  the  lactate  of  the  same  base  in  ex- 
cess, we  shall  have  no  reason  to  fear  the  presence  of  any  salt  of 
zinc  besides  the  lactate. 
The  lactate  of  zinc  is  most  frequently  found  in  the  form  of 
white  plates,  formed  by  the  union  of  small  prismatic  crystals  of 
four  sides,  terminated  by  summits  truncated  obliquely.  It  is 
inodorous,  of  a  slightly  saccharine  taste,  afterwards  styptic.  It 
is  sparingly  soluble  in  water,  at  the  ordinary  temperature  ;  in 
fact  it  requires  to  dissolve  it,  sixty  times  its  weight  of  water.  It 
is,  on  the  contrary,  very  soluble  in  hot  water,  for  it  dissolves  in 
six  times  its  weight  of  boiling  water. 
Lactate  of  zinc  is  insoluble  in  alcohol ;  this  property  may  be 
made  available  in  its  separation  from  the  acetate  of  the  same 
base.  On  treating  two  alcoholic  solutions  of  lactate  of  potassa, 
and  acetate  of  zinc  with  each  other,  we  obtain  instantaneously 
a  precipitate  of  lactate  of  zinc. 
The  medical  properties  of  lactate  of  zinc  had  not  been  ascer- 
tained, when  Dr.  Herpin  undertook  the  study  of  this  salt.  The 
stability  of  composition  and  the  solubility  of  this  compound,  have 
induced  him  to  substitute  lactate  of  zinc  for  the  oxide,  in  the 
treatment  of  epilepsy. 
He  prescribes  it  in  the  following  forms  : — 
