Am.  Jour.  Pharm.  ) 
January,  1911.  j 
Note  on  Lactic  Acid. 
15 
acids  by  boiling  with  aqueous  solutions  of  alkalies,  it  would  seem 
that  a  much  better  plan  for  recovering  the  acid  value  of  such  anhy- 
drides is  to  boil  with  a  measured  excess  of  a  standard  solution  of 
alkah  and  determine  the  amount  of  alkali  which  remains  uncom- 
bined  by  titration  (at  ordinary  temperature)  with  a  standard  solu- 
tion of  acid.  On  looking  into  the  matter,  it  was  found  that  in  the 
French  Pharmacopoeia  (1908)  such  a  plan  has  actually  been  adopted, 
the  procedure  consisting  essentially  in  adding  a  measured  excess  of 
alkali,  boihng  for  fifteen  minutes,  cooling,  and  then  titrating  the 
residual  alkali.  It  was  thought  desirable,  therefore,  to  obtain  some 
comparative  data  concerning  both  this  residual  titration  process  and 
that  in  which  the  titration  is  carried  out  at  a  boihng  temperature. 
On  titrating  a  dilute  aqueous  solution  of  lactic  acid  at  a  boiling 
temperature  it  was  found  that  the  result  thus  obtained  may  vary 
within  comparatively  wide  limits,  depending  on  what  is  taken  as 
indicating  the  end-reaction,  whether  the  coloring  of  the  solution  by 
the  phenolphthalein  indicator  and  its  remaining  on  mixing  the  solu- 
tion (first  indication  of  neutrality),  or  whether  the  boiHng  is  to  be 
continued  for  some  time  after  that  point  has  been  reached,  and  the 
length  of  time  the  boiling  is  continued  after  the  first  indication  of 
neutrality.  In  the  following  work,  therefore,  two  procedures  were 
used  in  carrying  out  the  titration  at  a  boiling  temperature.  In  one 
of  these  (designated  as  No.  2  in  the  Tables),  the  solution  was  first 
titrated  to  neutrality  at  ordinary  temperature  and  the  standard 
alkali  then  added  in  small  portions  (three  drops)  at  a  time  and 
boiled  after  each  such  addition  of  the  alkali  until  a  decided  pink 
color  remained  after  the  boiling  had  continued  for  one  minute  longer. 
The  other  procedure  in  which  the  titration  was  completed  at  a  boiling 
temperature  (designated  as  No.  3  in  the  Tables)  was  carried  out  in 
exactly  the  same  way,  but  the  titration  was  not  considered  ended 
until  a  decided  pink  color  had  remained  after  the  boiling  had  been 
continued  for  ten  minutes  longer.  Likewise,  in  the  case  of  the  resid- 
ual titration  after  treatment  with  an  excess  of  alkali,  two  procedures 
were  used.  In  one  of  these  (designated  as  No.  4  in  the  Tables), 
the  stated  amounts  of  the  acid  and  alkali  were  well  mixed  and 
allowed  to  stand  thirty  minutes  at  ordinary  temperature  before 
titrating  the  excess  alkali.  In  the  other  (designated  as  No.  5  in 
the  Tables),  the  mixture  was  boiled  for  fifteen  minutes,  cooled,  and 
the  excess  alkali  then  titrated  with  the  standard  acid.  And  in  the 
latter  case,  in  order  to  avoid  any  possibility  of  the  alkali  becoming 
