Am.  Jour.  Pharm 
Sept.,  1889. 
The  Salts  of  Milk 
477 
whilst  the  other  compound  does  not  react  either  with  litmus  or  with 
phenolphthalein,  and  contains  only  1*55  per  cent,  of  lime.  The 
basicity  of  casein  was  also  determined  by  titration  with  soda,  using 
phenolphthalein  as  indicator.  Neutral  or  slightly  alkaline  solutions 
of  calcium-casein,  prepared  by  rubbing  together  the  corresponding 
amounts  of  casein  and  calcium  carbonate,  become  turbid  only  when 
kept  for  some  time  ;  but  when  an  alkaline  calcium-casein  solution  is 
neutralized  or  acidified  it  at  once  becomes  turbid.  Alkaline,  neutral, 
or  just  perceptibly  acid  solutions  of  calcium -casein  do  not  curdle 
when  boiled  ;  the  addition  of  more  acid  causes  the  solutions  to  curdle, 
the  temperature  required  becoming  lower  as  the  amount  of  acid  pre- 
sent increases.  The  calcium-derivative  which  reacts  alkaline  with 
litmus  is  not  curdled  with  rennet.  Hence  it  is  probable  that  casein  is 
present  in  milk  as  neutral  calcium  salt  (with  1*55  per  cent,  of  lime). 
Assuming  this  to  be  the  case,  and  making  the  correction  for  phos- 
phoric acid  already  given,  a  litre  of  milk  will  contain  in  grams — 
CaO  fin 
NaCl.       KC1.      K3P04.     K20.   Ca3P208.  Mg3P208.  casein). 
I.. .0'877        0-603        1-653        0*405        2*315        0447  0-465 
II.  ..0*962        0*830        0*903        0595        2793        0436  0*465 
The  excess  of  base  is  probably  present  in  the  milk  as  organic  salts, 
Henkel  having  shown  that  citric  acid  is  a  constant  constituent  of  milk 
to  the  extent  of  at  least  1  gram  per  litre.  There  is  reason  to  suppose 
that  milk  contains  a  still  greater  amount  of  organic  acid,  and  this  is 
assumed,  for  the  present  purpose,  to  be  citric  acid. 
Analyses  of  milk  serum,  prepared  by  Zahn's  method,  by  filtering 
milk  through  porous  battery  cells,  showed  that  the  whole  of  the 
potash,  most,  if  not  all,  of  the  soda,  and  the  greater  part  of  the 
magnesia  present  in  milk  are  in  the  form  of  soluble  salts,  so  that  the 
casein  salt  can  only  be  a  calcium-derivative.  The  acidity  of  milk  to 
phenolphthalein  is  probably  due  to  the  presence  of  acid  phosphates, 
and  to  the  power  of  casein  of  uniting  with  a  further  amount  of  base 
without  becoming  alkaline  towards  phenolphthalein.  Calculated  from 
the  results  of  Series  II,  the  salts  present  in  the  milk  may  be  grouped 
as  follows  (in  grams  per  litre): — 
Sodium  chloride   0-962 
Potassium  chloride   0*830 
Monopotassium  phosphate..  1*156 
Dipotassium  phosphate         0  853 
Potassium  citrate   0*495 
Dimagnesium  phosphate       0  336 
Magnesium  citrate   0*367 
Dicalcium  phosphate   0*671 
Tricalcium  phosphate   0*806 
Calcium  citrate  :   2*133 
Lime  (in  casein)   0*465 
