In  this  way  the  acids  when  once  in  the  flask
are  not  taken  out  until  their  weight  has  been
taken,  thus  reducing  the  risk  of  loss  to  a
minimum.  Meanwhile  the  acidity  of  the
aqueous  filtrate  and  washings  is  estimated  by
decinormal  soda  solution.  Subtracting  from
the  amount  required  to  the  proportion  neces-
sary to  neutralise  the  excess  of  acid  added  in
decomposing  the  soap,  the  rest  represents  the
soluble  fatty  acids  contained  in  the  butter
taken,  and  on  the  assumption  of  its  being
butyri    acid,  we  can,  of  course,  calculate  the


amount  of  this  acid  present.  When  once  the
equivalent  of  the  soluble  acids  present  in
butter  is  fairly  determined,  this,  of  course,
will  have  to  be  substituted  for  that  of  butyric
acid.  The  results  thus  obtained  are  very
accurate,  and  the  process  is  very  simple  in
execution.
The  author  has  satisfied  himself  by  repeated
experiments  that  the  alkalinity  of  the  alcoho-
lic soda  solution  by  itself  is  not  altered  by  tlie
process.  The  author  places  no  reliance  on  the
specific  gravity  test,  as  he  fi  nds  that  mutton
dripping,  and  other  fats  likely  to  be  used  as
adulterants  of  butter,  may  acquire  a  specific
gravity  above  '911  by  being  strongly  and  re-
peatedly heated.  He  thinks,  however,  that
any  sample  of  butter  below  "911  may  safely  be
pronounced'  adulterated.
