14  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,   1907,   PART   II. 
received,  and  this  result  is  also  given  in  the  tables  of  analyses.  In 
every  case  the  two  analyses  are  presented  as  a  matter  of  convenience 
to  the  general  reader,  who  may  use  either  the  analysis  that  represents 
coal  as  it  came  from  the  mine,  with  more  or  less  mine  water  in  its  pores, 
or  the  analysis  of  the  sample  dried  under  nearly  ordinary  atmospheric 
conditions.  It  is  believed  that  the  latter  more  nearly  represents  com- 
mercial coal  than  the  former,  and  also  that  it  is  more  nearly  compara- 
ble to  analyses  of  samples  collected  in  the  ordinary  way  from  stock 
piles  or  cars  of  coal  and  shipped  to  a  laboratory  in  canvas  sacks. 
The  heating  power  of  the  coal  sample  was  determined  by  burning  a 
small  briquet  in  a  Mahler  bomb  calorimeter  and  noting  the  amount  of 
heat  given  off  during  the  process.  It  is  expressed  in  both  calories  and 
British  thermal  units  (B.  t.  u.).a  The  calories  may  be  converted  into 
British  thermal  units  by  multiplying  by  1.8. 
A  proximate  analysis  and  a  calorimetric  determination  were  made 
on  each  sample  sent  to  the  chemical  laboratory,  and  in  special  cases 
ultimate  analyses  were  made  in  addition  to  those  specified  above. 
The  comparative  value  of  proximate  and  ultimate  analyses  is  an 
extremely  interesting  subject,  and  it  is  to  be  hoped  that  the  present 
work  will  go  a  long  way  toward  showing  the  inadequacy  and  mislead- 
ing character  of  the  former  and  the  great  value  of  the  latter,  not  alone 
for  comparative  purposes,  but  also  as  a  base  for  economic  calculations. 
Up  to  the  beginning  of  the  fuel-testing  work  by  the  Geological  Sur- 
vey at  St.  Louis  in  1904  very  few  ultimate  analyses  of  coal  had  been 
made  in  this  country.  Fortunately  Professor  Lord,  who  had  charge 
of  all  chemical  work  for  the  fuel-testing  plant,  had  already  learned 
the  unreliable  character  of  proximate  analyses  and  had  determined, 
wherever  practicable,  to  make  ultimate  analyses.  Lack  of  funds 
alone  prevented  him  from  making  ultimate  analyses  of  all  samples 
received,  but  even  with  the  limited  means  at  his  command  several 
hundred  such  analyses  of  coal  have  been  made.  Time  and  space 
forbid  a  full  discussion  of  this  subject,  but  some  of  the  shortcomings 
of  the  proximate  analysis  are  the  variable  amount  of  volatile  matter, 
dependent  on  the  rapidity  with  which  it  is  driven  off  (amounting  in 
some  samples  to  20  per  cent),  and  the  fact  that  in  many  analyses  of 
anthracite  and  other  high-grade  coal  the  total  carbon  in  the  ultimate 
is  less  than  the  so-called  fixed  carbon  in  the  proximate.  These  points 
are  discussed  more  fully  in  Bulletin  323. 
The  final  paper  in  this  volume  is  a  bibliography  by  Willis  T.  Lee 
and  John  M.  Nickles  of  the  reports  of  the  United  States  Geological 
Survey,  exclusive  of  those  on  Alaska,  that  deal  directly  or  indirectly 
with  the  subject  of  coal. 
a  Calory:  Amount  of  heat  required  to  raise  1  kilogram  of  water  1°  C.    British  thermal  unit:  Amount 
of  heat  required  to  raise  1  pound  of  water  1°  F. 
