478 
The  Chemistry  of  Milk. 
/Am.  Jour.  Pharm. 
1     Oct,  1,  1874. 
ing  the  number  of  spaces  occupied  by  the  cream  after  it  is  allowed 
sufficient  time  to  settle.  Tubes  intended  for  this  purpose  are  sold 
under  the  name  of  creamometers. 
Casein  is  the  name  applied  to  the  nitrogenous  constituents  of  milk, 
which  are  coagulated  by  acids,  and  which  have  received  this  name 
from  their  use  in  the  manufacture  of  cheese.    A  portion  of  the  nitro- 
genous substance,  knowTn  as  albumen,  is  coagulated  by  boiling,  and 
then  forms  those  repulsive  little  films  generally  met  with  in  boiled 
milk.    Casein  is  soluble  in  fresh  milk,  but  insoluble  in  milk  which 
has  "turned."     Wanklyn  attributes  this  to  a  molecular  change, 
resembling  the  change  from  soluble  silica  to  insoluble  silica.  This 
change,'  as  we  have  said  above,  is  produced  by  the  presence  of  any 
acid  ;  in  "  sour  milk  "  it  is  caused  by  the  lactic  acid  (C3H603)  formed 
by  the  incipient  decomposition  of  the  milk  sugar.    In  the  manufac- 
ture of  cheese,  the  milk  is  curdled  by  means  of  rennet ;  but,  before 
doing  this,  more  or  less  of  the  cream  is  removed,  rendering  the  cheese 
less  nutritious  than  the  milk  from  which  it  was  formed.  A  skim-milk 
cheese  contains  but  6  per  cent,  of  fat,  while  some  rich  English  cheeses 
contain  30  per  cent.    The  ultimate  composition  of  casein  is  the  same 
as  albumen  and  fibrin.    Milk  from  which  both  fat  and  casein  have 
been  removed  as  far  as  practicable  is  known  as  whey,  and  is  essen- 
tially a  solution  of  milk  sugar  with  some  mineral  salts.    Milk  sugar 
can  be  prepared  by  coagulating  the  casein,  and  removing  that  along 
with  the  fat,  and  then  evaporating  the  whey  to  crystallization  and 
purifying  by  filtration  through  animal  charcoal.    It  is  manufactured 
principally  in  Switzerland,  and  comes  into  market  crystallized  on 
strings,  when  it  somewhat  resembles  an  ear  of  corn.    It  has  the 
composition  C12H24012,  dried  at  212°  F.    It  is  much  less  soluble  than 
cane  sugar,  dissolving  in  5  or  6  parts  of  cold  water,  and  2J  parts  of 
boiling  water.    It  is  not  so  heavy  as  cane  sugar,  and  reduces  the 
oxide  of  copper  like  grape  sugar.    Its  principal  use  is  in  the  prepa- 
ration of  homoeopathic  medicines,  as  envelope  and  dilutant. 
The  ash,  or  mineral  matter,  which  remains  when  milk  is  dried  up 
and  the  residue  incinerated,  consists  mainly  of  phosphate  of  lime  and 
alkaline  chlorides.  The  quantity  of  mineral  matter  in  cows'  milk  is 
but  three-fourths  of  one  per  cent.  ;  in  human  milk  it  is  much  less,  or 
about  one  seventh  of  one  per  cent. 
Testing  Milk. — Since  it  has  become  customary  for  milk  dealers  to 
endeavor  to  palm  off  on  their  customers  a  minimum  quantity  of  real 
