A juneui J7harm' )        Methods  of  Studying  Coal  269 
of  softening  and  bleaching  these  carbonized  remains,  it  has  been 
found  possible  to  add  very  largely  to  our  knowledge  of  the  organiza- 
tion of  ancient  plants,  particularly  of  the  Mesozoic  Age,  concerning 
which  our  information  has  been  most  meager.  Methods  developed 
first  for  the  investigation  of  isolated  members  and  parts  of  plants, 
by  modification  have  proved  serviceable  in  the  study  of  that  struc- 
turally almost  unknown  mineral  coal.  Our  ignorance  of  the  or- 
ganization of  coal  is  not  due  at  all  to  the  neglect  of  mineralogists,  but 
rather  to  the  unsuitability  of  the  approved  methods  of  their  science 
in  the  case  of  a  substance  at  once  so  opaque  and  so  friable.  The 
advantages  of  the  methods  recorded  here  may  be  judged  from  the 
fact  that  they  permit  the  cutting  of  large  quantities  of  sections,  which 
average  one  tenth  of  the  thickness  of  the  few  and  laboriously  secured 
preparations  resulting  from  the  grinding  processes  of  the  mineralogist. 
Moreover  it  is  possible  to  render  the  sections  even  more  favorable 
for  study  for  bleaching,  which  is  inapplicable  to  ground  sections.  It 
should  be  added  that  the  successful  manipulation  of  the  processes 
described  in  the  subsequent  paragraphs  involves  a  considerable  ex- 
perience in  the  use  of  the  microtome,  the  slicing  mechanism  of  the 
biologist. 
The  more  recent  and  less  modified  coals  are  treated  for  sectioning 
with  comparative  ease.  Alcohol  alone  is  frequently  sufficient  to 
bring  about  the  necessary  degree  of  softening  for  successful  slicing. 
Such  coals  are  of  relatively  light  hue,  and  sections  need  not  be  so 
thin  as  is  essential  in  the  case  of  the  older  and  more  highly  car- 
bonized coals.  In  general,  however,  somewhat  vigorous  softening 
agents  must  be  used  in  the  investigation  of  combustible  minerals, 
since  pressure  and  temperature  have  often  brought  about  a  con- 
siderable degree  of  modification  even  in  coals  of  tertiary  and  sec- 
ondary origin.  Caustic  soda  or  potash  dissolved  in  alcohol  of  about 
70  per  cent,  strength  in  the  proportion  one  part  in  ten  is  a  very  useful 
preliminary  reagent  but  has  been  found  for  various  reasons,  less 
valuable  in  use  than  phenol.  This  substance  has  unfortunately  ad- 
vanced immeasurably  in  cost  on  account  of  its  employment  as  a  basis 
for  the  manufacture  of  high  explosives  in  the  present  European  war. 
The  phenol  or  carbolic  acid  is  melted  and  the  selected  coal  samples 
(which  must  ordinarily  not  be  more  than  a  centimeter  in  length 
and  breadth  by  half  a  centimeter  in  thickness  vertically)  are 
subjected  to  its  action.  The  material  is  to  be  kept  hot  in  a 
water  bath  for  a  number  of  days,  usually  as  long  as  a  week.  The 
