Salts. — Of  these  some  are  soluble  in  alcohol  as  the  lactates  of  pot-
ash,—  the  principal  lactate, —  of  soda,  ammonia,  lime,  and  magnesia;
others  are  soluble  in  water,  but  not  In  alcohol,  as  sulphate  of  potash,
and  the  phosphates  of  potash  and  soda  ;  lastly,  the  phosphates  of  lime,
iron,  and  magnesia  are  insoluble  In  water.
For  all  practical  purposes,  in  order  to  ascertain  whether  a  milk  is
genuine  and  of  good  quality,  it  Is  sufficient  to  take  the  specific  gravity
of  the  milk  by  the  hydrometer  or  galactometer,  and  to  estimate  the
quantity  of  cream  by  the  lactometer.  Should  we  desire  to  institute  a
quantitative  analysis  of  its  chief  constituents,  we  may  then  adopt  the
process  described  by  Haidlen.*

The  Butter.  —  The  weighed  quantity  of  milk  Is  mixed  with  one-
sixth  of  its  weight  of  common  unburnt  gypsum,  previously  reduced  to
a  very  fine  powder.  The  whole  is  then  evaporated  to  dryness,  with
frequent  stirring,  at  the  heat  of  boiling  water  ;  a  brittle  mass  is  ob-
tained, which  is  reduced  to  a  fine  powder.  By  digesting  this  powder
in  ether,  the  whole  of  the  butter  Is  dissolved  out,  and,  after  evaporation
of  the  ether,  may  be  obtained  In  a  pure  state,  and  weighed ;  or  the
powder  itself,  after  being  treated  with  ether,  may  be  dried  and
weighed  ;  the  butter  Is  then  estimated  by  the  loss.
