128 
Estimation  of  Caseinc. 
( Am.  Jour.  Pharm. 
1      March,  1906. 
measure  more  than  50  c.c.  The  distilled  water  used  for  washing 
the  precipitate  should  be  added  before  all  of  the  preceding  liquid 
has  run  through ;  for  the  drained  precipitate  becomes  a  firm  mass 
through  which  liquid  passes  with  difficulty.  The  filtrate  is  usually 
free  from  iron  when  it  measures  200  c.c.  (at  times  it  is  iron  free  when 
1 50  c.c.  have  passed  through),  and  either  the  total  filtrate  or  an 
aliquot  part  can  be  titrated  with  thiosulphate  solution.  The  titration 
is  carried  on  as  provided  in  the  assay  of  ferric  alum  given  in  U.S.P., 
1900. 
In  passing  it  might  be  noted  that  the  strength  of  ferric  alum  and 
thiosulphate  solutions  used  in  this  work  are  based  on  the  molecular 
weights  of  the  U.S.P.,  1890,  since  experiments  were  started  before 
the  appearance  of  our  present  standard. 
In  filtration,  care  must  be  taken  that  the  liquid  as  it  drops  from 
the  funnel  is  clear  and  if  it  is  cloudy  it  must  be  returned  until  it 
does  drop  clear.  Shortly  after  the  filtration  the  liquid  becomes 
slightly  turbid,  due  undoubtedly  to  separated  ferric  albuminate.  It 
was  feared  that  the  precipitate  might  be  caseine  instead  of  ferric 
albuminate  and  thus  prove  a  source  of  error.  That  there  was  little 
danger  of  this,  provided  the  filtrate  was  originally  clear,  seemed 
shown  by  the  uniformity  of  figures  in  Tables  I  and  II,  but  to  settle 
the  question,  six  samples  of  the  same  milk, — a,  b,  c,  d,  e,  and  f — 
were  assayed.  One  set — a,  c,  and  e — the  originally  cloudy  liquid 
was  refiltered  before  titration ;  while  their  duplicates,  b,  d,  and  f, 
were  titrated  in  cloudy  condition,  with  the  following  results : 
Tabids  III. 
All  with  20  cubic  centimeters  decinormal  ferric  alum  solution. 
Cubic  centimeters  deci-     Cubic  centimeters  deci- 
Milk  sample.       Amount  milk  used.       normal    thiosulphate        normal    ferric  alum 
required.  used  by  milk. 
a  5  c.c.  18  2*o 
b  5  c.c.  18  2*0 
c  10  c.c.  16  4*o 
d  10  c.c.  16  4'o 
e  20  c.c.  12  8*o 
f  20  c.c.  12  8*o 
As  the  results  of  titration  in  both  cases  were  identical,  the  amount 
of  separated  substance  must  be  insignificant. 
Pharmaceutical  Laboratory, 
Cleveland  School  of  Pharmacy. 
August,  1905. 
