INTRODUCTION.  13 
3.  Cut  a  channel  perpendicularly  across  the  face  of  the  coal  bed  from  roof  to  floor, 
with  the  exceptions  noted  in  paragraph  4,  and  of  such  a  size  as  to  yield  at  least  5  pounds 
of  coal  per  foot  of  thickness  of  coal  bed — that  is,  5  pounds  for  a  bed  1  foot  thick,  10 
pounds  for  a  bed  2  feet  thick,  20  pounds  for  a  bed  4  feet  thick,  etc. 
4.  All  material  encountered  in  such  a  cut  should  be  included  in  the  sample,  except 
partings  or  binders  more  than  three-eighths  inch  in  thickness  and  lenses  or  concretions 
of  sulphur  or  other  impurities  greater  than  2  inches  in  maximum  diameter  and  one-half 
inch  in  thickness. 
5.  If  the  sample  is  wet  it  should  be  taken  out  of  the  mine  and  dried  until  all  sensi  I  >le 
moisture  has  been  driven  off. 
6.  If  the  coal  is  not  visibly  moist,  it  should  be  pulverized  and  quartered  down  inside 
the  mine  to  avoid  changes  in  moisture,  which  take  place  rapidly  when  fine  coal  is 
exposed  to  different  atmospheric  conditions.  The  coal  should  be  pulverized  until  it 
will  pass  through  a  sieve  with  |-inch  mesh,  and  then,  after  thorough  mixing,  it  should 
be  divided  into  quarters  and  opposite  quarters  rejected.  The  operation  of  mixing 
and  quartering  should  be  repeated  until  a  sample  of  the  desired  size  is  obtained.  When 
the  work  has  been  properly  done  a  quart  sample  is  sufficient  to  send  for  chemical  analy- 
sis. This  should  be  sealed  in  either  a  glass  jar  or  a  screw-top  can  with  adhesive  tape 
over  the  joint,  and  sent  to  the  chemical  laboratory  for  analysis. 
All  chemical  analyses  were  made  at  the  laboratory  of  the  fuel- test- 
ing plant  of  the  Geological  Survey,  located  at  the  Carnegie  Technical 
Schools,  Pittsburg,  Pa.  The  analytical  work  was  under  the  imme- 
diate charge  of  F.  M.  Stanton,  who  conducted  the  laboratory  under 
the  general  direction  of  N.  W.  Lord,  of  the  Ohio  State  University, 
Columbus,  Ohio.  Professor  Lord's  high  standing  as  a  coal  chemist 
is  sufficient  guaranty  of  the  accuracy  of  the  analyses  contained  in  this 
bulletin. 
When  a  sample  reached  the  chemical  laboratory,  it  was  given  a 
serial  number  by  which  it  could  be  recognized,  and  was  pulverized 
and  quartered  down  in  the  ordinary  way  for  analysis.  As  the  sam- 
ples were  taken  in  the  mines  and  not  allowed  to  dry  before  they  were 
pulverized  and  quartered  down,  it  is  generally  true  that  they  con- 
tained more  moisture  than  the  commercial  coal.  Before  attempting 
to  analyze  a  sample  it  was  deemed  desirable  to  eliminate  some  of  this 
excess  moisture,  and  for  this  purpose  the  following  apparatus  was 
used:a 
In  order  to  make  determinations  of  the  loosely  held  moisture  more  uniform  and 
definite,  a  special  drying  oven  has  been  designed  and  introduced  into  the  laboratory. 
In  this  oven  samples  of  several  pounds  weight  can  be  dried  in  a  gentle  current  of  air 
raised  from  10°  to  20°  above  the  temperature  of  the  laboratory.  In  this  way  the  coal 
is  air  dried  in  an  atmosphere  with  a  very  low  dew-point  and  not  subject  to  large 
percentage  variations,  and  the  results  obtained  are  considerably  more  concordant. 
The  sample  was  then  weighed,  and  the  loss  in  weight  is  given  as  the 
"air-drying  loss."  The  results  of  the  analysis  of  this  sample  are  the 
best  for  ordinary  purposes,  and  are  generally  spoken  of  as  l  lie  analysis 
of  the  air-dried  sample.  From  this  set  of  figures  1  he  analysis  is  easily 
recalculated   back   to   the   theoretical   condition    of    the    sample    as 
a  Bull.  U.  S.  Geol.  Survey  No.  290,  1906,  pp 
