126 
Estimation  of  Caseine. 
/  Am.  Jour.  Pharm. 
X      March,  1906. 
tion  (0-1924  gramme  ferric  alum)  for  precipitation  of  caseine.  This 
factor  is,  however,  insufficient  as  a  standard  of  milk-testing,  and 
therefore  a  line  of  comparative  tests  between  amount  of  ferric  alum  ' 
consumed  and  amount  of  nitrogen  in  the  caseine  by  the  Kjehldahl 
process  was  instituted. 
In  this  line  of  experiments,  20  c.c.  decinormal  ferric  alum  solution 
was  placed  in  a  Kjehldahl  distilling  flask  and  10  c.c.  milk  and  about 
20  c.c.  water  added.  The  precipitate  was  transferred  to  a  filter, 
washed  free  from  soluble  iron  and  the  filtrate  titrated  with  decinor- 
mal thiosulphate  solution.  The  precipitate  and  filter  was  dried, 
placed  in  the  original  dried  Kjehldahl  flask  to  the  walls  of  which 
some  of  the  precipitate  still  remained  clinging.  The  contents  of  the 
flask  were  then  digested  with  sulphuric  acid  and  mercury,  distilled 
with  potassium  sulphide  and  alkali  and  the  liberated  ammonia  was 
titrated  with  decinormal  sulphuric  acid.  Blank  experiments,  includ- 
ing filter-paper,  were  carried  on  at  the  same  time  and  correction 
made  in  the  caseine  estimation.  The  results  are  shown  in  the  table 
appended : 
Tabi^e  II. 
In  all  10  c.c.  milk  was  mixed  with  20  c.c.  decinormal  ferric  alum  solution, 
the  filtrate  titrated  with  decinormal  sodium  thiosulphate  solution,  while  the 
precipitate  was  assayed  for  nitrogen  by  the  Kjehldahl  process.  In  the  columns 
marked  "  Percentage  Caseine"  "  a  "  gives  the  figures  obtained  by  multiplying 
weight  of  nitrogen  by  6*25  x  10,  while  "  b  "  gives  results  in  using  factor  6-38 
x  10. 
Filtrate.  Precipitate. 
Cubic  cen- 
timete  r  s 
dec  mor- 
Cubic  centi- 
Cubic  centime- 
m a  1  fer- 
meters 
ters  decinor- 
r i  c  alum 
decino  r  mal 
Milk 
mal  thiosul- 
used by 
sulphuric 
Am't  of  nitrogen 
Percentage  caseine. 
sample. 
phate  requ'd. 
milk. 
acid  needed. 
in  grammes. 
a 
b 
i  a 
I5'8 
4-2 
25*5 
0-0357 
2-23 
2-28 
1  b 
i6*o 
4'o 
25-0 
00350 
2"I9 
223 
1  c 
i6'o 
26*0 
0-0364 
2  27 
2'33 
2  a 
i6t 
3'9 
24-0 
0-0336 
2*IO 
2'I/L 
2  b 
16- 
4-0 
23-0 
0*0322 
2-or 
2-05 
2  c 
16- 
4-0 
24*0 
0-0336 
2"IO 
2-14 
2d 
I5-9 
4'i 
23-5 
0*0329 
2-05 
2'IO 
3  a 
i6"4 
3'6 
26*0 
O  0364 
2'27 
2-33 
3b 
i6"o 
4'o 
26-6 
0*0372 
2-32 
2-37 
3  c 
i6*o 
4'o 
26-5 
0-0371 
2-32 
2-36 
3d 
16-2 
3'8 
26*0 
0-0364 
2-27 
2'33 
4  a 
I5'9 
4'i 
24-5 
0-0343 
2*14 
2-19 
