A ji^ig^3™' )        Methods  of  Studying  Coal.  271 
repeatedly  with  warm  water  and  then  transferred  to  strong  alcohol 
and  finally  to  absolute  alcohol,  to  remove  all  the  water.  Two  or 
three  changes  of  absolute  alcohol  are  necessary.  After  the  water  is 
entirely  removed  the  specimens  are  exhausted  of  all  air  under  an  air 
pump  of  high  vacuum.  In  order  to  secure  slices  of  the  softened  coal, 
it  must  be  held  together  by  means  of  nitrocelluloses.  The  best  and 
least  explosive  of  these  is  Schering's  Celloidin,  which  is  for  the 
moment  practically  unobtainable  on  account  of  the  war.  It  may  be 
replaced  with  some  degree  of  success  by  Anthony's  photographic 
cotton.  This  is  a  less  pure  nitrocellulose  and  gives  results  which  are 
less  satisfactory.  The  dehydrated  and  air-free  coal  is  transferred 
into  a  2  per  cent,  solution  of  nitrocellulose  in  absolute  alcohol  and 
ordinary  ether  (of  good  quality).  Absolute  methyl  alcohol  gives 
better  results  than  ethyl  alcohol  and  is  sold  by  the  Bausch  &  Lomb 
Optical  Company  under  the  commercial  name  of  Synthol.  The  ma- 
terial is  secured  in  a  strong  bottle  by  means  of  a  good  cork  wired  in 
and  remains  for  a  day  in  a  bath  kept  at  the  temperature  of  700  Cen- 
tigrade. It  is  allowed  to  cool  and  then  transferred  to  a  4  per  cent, 
solution  of  nitrocellulose  in  the  medium  indicated  above.  A  second 
twenty-four  hours  in  the  heat  brings  it  to  a  6  per  cent,  solution. 
After  the  latter  treatment  it  is  enclosed  in  an  air-tight  chamber  made 
from  large  diameter  steam  pipe.  The  corks  are  removed  from  the 
bottles  preliminarily  and  by  means  of  a  valve  in  the  cap  of  the  cham- 
ber and  an  automobile  pump,  pressure  is  raised  to  two  hundred  or 
more  pounds.  The  coal  remains  under  these  conditions  over  night 
and  has  then  become  thoroughly  infiltrated  with  the  solution  of  nitro- 
cellulose. The  next  step  is  to  transfer  it  to  a  thick  solution  of  nitro- 
cellulose. In  this  it  is  placed  again  in  the  warm  bath  and  after  a  time 
still  further  thickening  is  brought  about  by  the  addition  of  dry  frag- 
ments of  nitrocellulose.  After  several  days  of  repeated  thickening 
the  specimens  are  now  ready  for  the  final  process.  This  consists  of 
transferring  them  from  the  thick  nitrocellulose  to  chloroform. 
Chloroform  has  the  valuable  property  of  at  once  hardening  the  nitro- 
cellulose and  further  softening  the  coal.  After  a  stay  of  some  hours 
in  chloroform,  which  must  not  be  used  sparingly,  the  piece  of  coal 
are  transferred  to  a  mixture  of  equal  parts  of  alcohol  and  glycerine, 
where  they  may  remain  indefinitely,  until  needed  for  sectioning. 
The  fragments  of  coal  treated  in  the  manner  described  above  are 
clamped  in  a  heavy  sliding  microtome  (the  Jung-Thoma  modified 
to  the  author's  design  answers  very  well  for  this  purpose).   A  very 
