Am.  Jour.  PJiarm. ) 
March,  1906.  / 
Estimation  of  Caseine. 
12$ 
Thus,  in  one  sample  of  milk,  there  was  twice  as  much  sugar  as  in 
the  other,  and  yet  the  amount  of  thiosulphate  required  was  practi- 
cally the  same  in  both  cases. 
In  connection  with  this,  Long  (Jour.  Am.  Chem.  Soc,  Vol.  XIX, 
p.  683)  has  published  elaborate  work,  showing  that  sugar  eventually 
reduces  ferric  salts  to  the  ferrous  state. 
However,  he  notes  that  the  change  is  first  noted  after  standing 
forty-eight  hours,  and  in  the  present  process,  the  entire  time  from 
adding  ferric  alum  to  milk  to  the  final  titration,  need  not  exceed  six 
hours;  hence  the  results  given  above  in  no  way  run  counter  to  Dr. 
Long's  statement. 
As  to  influence  of  fat : 
20  c.c.  milk,  plus  20  c.c.  ferric  alum  solution  required  12  c.c.  thio.  solution. 
20  c.c.     "       "    20  c.c.     "       "         "  "     11. 6  c.c.    "  " 
20  c.c.     "       "    o*6  gm.  butter,  plus  20  c.c.  ferric  alum  solution,  required 
1 1 '6  c.c.  thiosulphate  solution. 
20  c.c.  milk,  plus  o-6  gm.  butter,  plus  20  c.c.  ferric  alum  solution,  required 
ii*66  c.c.  thiosulphate  solution. 
Thus,  double  the  theoretical  amount  of  fat  does  not  affect  the 
results.  As  already  mentioned,  the  question  of  the  temperature  of 
the  milk  is  of  the  greatest  importance,  and  the  figures  of  a  large 
amount  of  preliminary  work  with  ferric  alum  were  rendered  useless 
for  this  paper,  because  the  mixture  of  milk  and  ferric  alum  were 
warmed  before  filtration.  Later  experiment  showed  that,  unlike  the 
precipitation  of  caseine  with  potassa  alum,  heat  was  not  necessary  to 
facilitate  the  filtration  of  whey  and  led  to  the  variation  in  the  figures 
obtained. 
Heat  affects  the  coagulation  of  ferric  albuminate,  while  in  cases  of 
cold  admixture  it  remains  in  solution  or  at  most  in  soluble  colloidal 
form.  Thus,  if  the  filtrate  from  a  ferric  alum  precipitate  is  divided 
into  two  portions,  and  one-half  is  titrated  just  as  it  is  while  the  other 
half  is  boiled  and  filtered,  and  the  second  filtrate  titrated  ;  the  latter 
requires  much  less  thiosulphate  solution  than  the  first  half. 
Time  has  prevented  careful  investigation  of  this  important  point 
within  which  possibly  lies  the  germ  of  a  volumetric  estimation  of 
total  proteids  in  milk,  even  as  does  the  cold  process  give  us  the 
amount  of  caseine. 
It  will  be  noticed  that  with  practically  all  samples  of  milk  reported 
in  Table  I,  10  c.c.  milk  required  4  c.c.  decinormal  ferric  alum  solu- 
