4.  Milk  of  lime.     This  is  a  valuable  disinfectant  for  the  body
wastes  and  is  perhaps  the  cheapest  to  be  obtained.     To  make  the
solution,  add  one  part  by  weight  of  freshly  slacked  lime  to  four
parts  of  water  and  stir  the  whole  until  it  has  the  appearance  of  milk.
Only  fresh  lime  should  be  used;    that  exposed  to  the  air  for  some
time  loses  its  strength  and  is  worthless.     It  should  not  be  emptied
into  sinks,  as  the  solid  particles  will  clog  the  pipes.
5.  Formaldehyde,  or  formalin.   This  may  be  used  in  solutions
(six  ounces  of  the  forty  per  cent  solution  to  one  gallon  of  water)  for
the  same  purposes  as  carbolic  acid,  although  it  is  somewhat  injuri-
ous to  the  hands.     Its  more  frequent  use,  however,  is  for  fumigation,
as  explained  in  the  section  on  Health  Work.
6.  Several  preparations  from  coal  tar  containing  cresol  —  lysol,
chloro-naphthalene,  cresoline,  etc. —  are  disinfectants  of  recognized
merit  and  are  said  to  be  more  powerful  and  safe  in  their  use  than
carbolic   acid.     They   are   used   in   solutions   varying   in   strength
from  one-half  of  one  per  cent  to  three  per  cent  for  all  the  purposes
mentioned    above.     Complete     directions    are    supplied    by    the
manufacturers.
All  of  these  disinfectants  except  the  milk  of  lime  are  poisonous
and  should  be  so  labeled.  They  should  for  obvious  reasons  be
kept  away  from  substances  used  as  food  or  medicine.
