All  this  was  a  very  different  process,  however,  from  a  conscious
movement  for  reduction  of  hours.  The  only  clear  eight-hour  move-
ment in  the  iron  industry  that  ever  became  important  was  in  the
sheet  mills,  under  circumstances  so  peculiar  that  it  may  well  be
recorded.  It  is  interesting  both  in  its  relation  to  the  movement  for
a  shorter  work  day,  and  as  throwing  light  upon  the  psychology  of
the  members  of  the  Amalgamated  Association  at  that  time.
As  improvements  in  sheet  mill  construction  made  it  possible
to  finish  a  turn's  work  in  a  shorter  time  than  twelve  hours,  there
came  to  be  periods  of  idleness  between  shifts.  This  is  unde-
sirable in  a  mill  of  this  character,  for  sheet  iron  is  rolled  so  thin
that  good  results  can  be  obtained  only  when  the  rolls  are  ex-
panded by  the  heat.  The  rolls  are  so  shaped  that  when  cold  they
cannot  turn  out  a  sheet  of  uniform  thickness;  consequently
after  a  period  of  idleness  hot  scrap  is  sent  through  them  until
they  reach  the  correct  expansion.  To  avoid  these  periods  of  idle-
ness, the  manufacturers  tried  to  introduce  an  eight-hour  day.
