602 
Lactic  Acid. 
/Am.  Jour,  Pharm. 
\  November,  1897. 
As  the  fermentation  progresses,  the  solution  must  be  neutralized 
with  milk  of  lime,  or  chalk  in  suspension.  The  limits  of  acidity  in 
which  lactic  bacteria  are  healthy  are  rigidly  confined  between  o  02 
and  0  5  of  1  per  cent.  Keeping  the  acidity  of  the  fermentation 
between  these  limits  is  the  main  preventive  against  butyric  fer- 
mentation, as  the  regulating  of  the  temperature  is  the  preventive 
against  alcoholic  fermentation.  If  the  fermenting  solution  is  over- 
neutralized,  the  butyric  ferment  will  at  once  begin  to  act,  and,  once 
active,  is  very  difficult  to  control.  It  is  the  greatest  enemy  to  the 
lactic  fermentation,  destroying  the  lactic  acid  that  has  been  made, 
and  devouring  new  quantities  as  fast  as  they  can  be  produced.  In 
twenty-four  hours  one-third  of  the  lactic  acid  may  be  destroyed  by 
the  butyric  bacillus.  Anti-ferments  cannot  be  used  with  much 
safety  in  lactic  fermentation.  The  lactic  bacillus  is  more  susceptible 
than  other  ferments,  and  is  killed  while  others  are  only  stagnated. 
Mustard-seed  oil  is  about  the  only  exception  that  I  know.  This 
has  apparently  a  deadening  effect  on  butyric  fermentation,  with  no 
serious  effect  on  the  lactic  fermentation.  The  lactic  fermentation  is 
best  completed  in  from  three  to  six  days,  although  its  life  may  be 
prolonged  up  to  a  fortnight.  Any  prolongation  of  life  is  attended 
with  danger  of  butyric  invasion.  When  the  fermentation  is  ended, 
the  liquor  must  be  heated  sharply  to  kill  all  bacteria  and  spores 
and  prevent  subsequent  fermentation. 
The  fermented  liquor,  which  is  now  a  solution  of  calcium  lactate, 
with  a  multitude  of  dead  lactic  bacteria  floating  in  it,  is  filtered  and 
evaporated.  If  a  pure  lactic  acid  is  desired,  the  calcium  lactate  is 
allowed  to  crystallize  and  purified  by  repeated  crystallization.  For 
a  commercial  lactic  acid,  decomposition  by  sulphuric  acid  of  the 
dense  uncrystallized  solution  of  calcium  lactate  gives  an  acid  of 
sufficient  purity.  The  free  acid  obtained  from  this  decomposition  is 
further  concentrated  to  such  strength  as  the  market  demands.  In 
evaporating  free  lactic  acid  there  is  danger  of  forming  lactic  anhy- 
dride. It  is  possible  to  have  conditions  such  that  the  longer  evapo- 
ration takes  place  the  less  percentage  of  lactic  acid  is  obtained.  In 
concentrated  solutions  very  little  lactic  acid  is  lost  by  volatilization. 
In  dilute  solutions  much  acid  may  be  mechanically  carried  away  with 
steam,  especially  if  a  blast  is  used.  A  50  per  cent,  solution  is  about 
.as  concentrated  as  it  is  economical  to  manufacture.  This  appears 
-on  the  market  as  a  syrupy  liquid,  with  more  or  less  brown  color, 
