The  error  (owing  to  imperfect  removal)
only  amounts  to  one  or  two  tenths  per
cent,  of  the  batter  taken.  As  the  salt  is
accurately  estimated  afterwards,  the  loss  falls
on  the  curd.  The  salt  may  be  determined  by
careful  ignition  of  the  filter  and  residue,  the
incombustible  matter  consi^ting  almost  wholly
of  common  s^alt,  while  the  curd  is  ascertained
by  loss  of  weight.  This  method  is  not  to  be
recommended  ;  for  without  great  care  some  of
the  salt  will  be  volatilised  and  lost,  the  error
causing  the  amount  of  curd  to  appear  excessive.
Ignition  al^o  renders  any  further  examina-
tion of  the  curd  an  impossibility.  A  far
preferable  plan  is  to  return  the  weighed  curd
and  salt  to  the  filter,  and  to  wash  them  with
cold  water.  The  filtrate  is  made  up  to  100
c.  c,  and  the  salt  is  estimated  in  a  half  of  it
by  titrating  with  decinormal  nitrate  of  silver.
The  remaining  portion  of  the  solution  can  be
employed  for  the  estimation  of  6U2;ar,  if  de-
sired. This  is  effected  by  inverse  titration
with  Fehling's  copper  solution,  in  the  same
way  as  grape  sugar.  The  estimation  of  sugar
may  sometimes  be  of  interest,  as  a  means  of
ascertaining  whether  the  aqueous  portion  of
the  butter  consisted  of  mere  water  or  of  serum
of  milk.  In  other  words,  the  estimation  of
the  sugar  may  famish  a  means  of  ascertaining
whether  an  excess  of  water  in  the  butter  is
due  to  insufficient  removal  of  the  bntter-milk,
or  to  subsequent  incorporation  of  water.  Every
0-001  gram  of  milk  sugar  represents  about
0022  of  average  milk  serum.
