Am.  Jour.  Pharm.  ) 
Oct.  1,  1874.  j 
Vie  Chem  istry  of  Milk. 
479 
milk,  mixed  with  a  maximum  quantity  of  water,  under  the  name  of 
milk,  it  is  sometimes  interesting  to  compare  different  samples  of  such 
milk  for  the  purpose  of  determining  the  amount  of  water  added. 
English  chemists  have  devoted  considerable  attention  to  this  subject, 
because  there  a  law  exists  punishing  adulterations  in  food  and  medi- 
cine, and  we  shall  frequently  have  occasion  to  refer  to  their  observa- 
tions. The  specific  gravity  of  milk,  as  indicated  by  hydrometers 
made  for  the  purpose,  does  not  serve  to  detect  carefully-conducted 
watering.  The  average  density  of  good,  pure  milk  is  about  1*032. 
Since  milk  fat  is  lighter  than  water,  the  more  cream  the  milk  contains 
the  lower  its  specific  gravity,  while  skimmed  milk  has  a  higher  spe- 
cific gravity  than  unskimmed  milk.  Hence  it  is  possible  to  preserve 
the  normal  density  in  watered  milk  by  first  removing  a  portion  or  all 
of  the  cream,  and  then  adding  just  enough  water  to  bring  it  back  to 
its  original  density.  To  ascertain  the  quantity  of  water  -added,  it  is 
necessary  to  determine  by  analysis  the  quantity  of  fat  present  in  the 
milk.  John  Horsley,  F.  C.  S.,  accomplishes  this  in  the  following 
manner:*  A  glass  tube,  11  inches  long,  and  three-fourths  of  an  inch 
in  diameter,  is  graduated  from  10  inches  down,  one-fifth  of  its  length, 
into  per  cent.,  or  hundredths.  A  tablespoonful,  15  c.c,  or  250  grs. 
of  milk  are  first  poured  into  the  glass  tube  ;  a  smilar  bulk  of  ether 
is  next  poured  in,  and  the  tube  closed  with  the  thumb  or  a  cork,  and 
agitated  for  four  or  five  minutes.  An  equal  measure  of  alcohol  is 
next  added  and  the  whole  well  shaken  for  at  least  five  minutes  more, 
when,  on  placing  it  in  an  upright  position  on  a  stand,  the  oily  or  fatty 
matter  will  rise  to  the  surface,  and  can  be  easily  read  off.  Each  line 
will  correspond  to  4-15  grains  of  solid  butter,  as  proved  by  experi- 
ment. Milk  which  has  10  per  cent,  of  cream  will  show  two  lines  of 
butter  oil,  or  8-3  grains,  for  250  grains  of  milk.  If  desired,  the  but- 
ter may  be  drawn  off  and  weighed  in  a  small  platinum  capsule. 
Mr.  Wanklyn  prefers  to  evaporate  5  c.c.  of  the  milk  to  dryness  in 
a  weighed  platinum  dish  over  a  water-bath.  The  operation  requires 
at  least  three  hours.  The  residue  equals  the  total  milk  solids,  and 
averages,  with  a  sample  of  good  country  milk,  12-45  per  cent.  This 
residue  is  treated  with  ether  and  heated  to  boiling,  and  the  solution 
poured  through  a  small  filter,  the  operation  of  boiling  and  pouring  off 
the  ethereal  solution  being  repeated  three  times.    The  solution  of  fat 
*  Chemical  News,  May  2,  1874,  p.  224. 
