SOAP  AND  SOAP  MAKING

Properties  of  Soap. — Garments  of
linen  and  other  fabrics  become  soiled
principally  by  the  oily  exudations  of
the  bbdy,  as  in  perspiration  and  the
natural  oil  of  the  hair,  and  in  the
case  of  table  linen,  by  animal  fats,
etc.  The  skin  itself,  of  course,  re-
tains a  considerable  part  of  the  oily
substances  not  absorbed  by  the  cloth-
ing. These  greasy  substances  by
their  adhesive  quality  attract  and
hold  particles  of  dirt.  When  soap  is
dissolved  in  water,  the  neutral  alkali
salts  become  in  part  separated  into
alkali  which  dissolves,  and  free  fatty
acid  which  precipitates.  This  ex-
plains why  the  transparency  of  clear
water  is  disturbed  by  the  use  of  soap
even  of  the  purest  kind.
The  detergent  or  cleansing  proper-
ties of  soap  are  due  to  the  presence
of  free  alkali,  either  caustic  potash
or  soda  liberated  in  the  soapsuds.
This  attacks  and  decomposes  the
grease  contained  in  soiled  linen,  in
perspiration,  and  in  dishwater,  unites


with  the  fatty  acids,  and  in  turn  sa-
ponifies them.  The  process  is  pre-
cisely similar  to  that  of  soap-making.
The  union  of  the  alkali  set  free  in
soapsuds  with  the  grease  of  garments
or  dishwater  produces  a  soapy  sub-
stance which  is  readily  soluble,  and
hence  is  easily  removed  by  rinsing.
