It  is  also  good  practice  to  use  coal  which  has  been  crushed,
or  broken,  into  lumps  of  three  or  four  inches  in  diameter,  as
this  exposes  more  fuel  surface,  thereby  aiding  combustion,  and
allays,  to  an  appreciable  extent,  the  formation,  of  clinkers.
Coal  is  often  wet  down  for  the  purpose  of  cleanliness-— to
keep  coal  dust  from  flying — and  to  prevent  fine  coal  from  being
drawn  through  the  tubes,  but,  in  this  connection,  remember
that  it  takes  heat  to  evaporate  the  moisture.  Aside  from  this
fact,  the  steam  generated  thereby  occupies  about  1,800  times  the
volume  of  water  at  atmospheric  pressure.  At  a  reduced  pres-
sure, and  high  temperature,  conditions  existing  in  the  firebox,
the  volume  would  be  correspondingly  larger.  Therefore,  water
introduced  into  the  firebox  through  any  medium,  upon  becom-
ing steam  (and  if  not  dissociated)  occupies  space  that  would
otherwise  be  occupied  by  combustible  gases.  That  is,  the  effi-
ciency of  the  draft  is  impaired.  This  same  effect  manifests
itself  in  firing  oil  damp  or  rainy  days.
By  combining  a  knowledge  of  the  above  facts  with  a  little
sound  judgment,  the  fireman  should  be  enabled  to  fire  his  engine
in  an  efficient,  satisfactory  manner,  and  reduce  greatly  the  fuel
losses  often  prevalent  in  this  connection.
The  Security  Arch.
The  firebox  arch,  as  manufactured  by  the  American  Arch
Company,  of  New  York  City,  has  been  designed  to  do  away
with  a  great  many  of  the  fuel  losses  due  to  improper  firing,
and  to  improve  combustion,  even  when  the  firing  is  accom-
plished as  perfectly  as  is  possible.
