^usust*  fm™' }  Physiological  Characteristics  of  Acetylene.  367 
past  he  has  accomplished  so  much  under  the  conditions  of  poor 
illumination  and  soot-laden  atmosphere  which  the  use  of  the  oil 
lamp  has  meant.  The  use  of  the  miner's  acetylene  lamp  affords  an 
illumination  that  is  wonderfully  efficient  and  entirely  soot- free.  Its 
use  raises  some  questions  that  we  may  answer  at  this  time.  Before 
considering  these,  let  us  look  at  some  of  the  problems  which  the 
miner  has  to  face,  upon  which  the  choice  of  an  illuminant  may  have 
some  bearing.  Of  first  importance  is  the  composition  of  the  air  which 
he  breathes. 
For  our  present  purpose  we  may  regard  the  atmospheric  air  as 
a  mixture  of  21  parts  of  oxygen  and  79  parts  of  inert  gas,  mostly 
nitrogen.  It  is  the  oxygen  that  supports  life.  The  proportion  of 
oxygen  may  be  diminished  to  a  certain  extent  without  noticeable 
effect,  especially  if  the  difference  is  made  up  by  inert  nitrogen.  Under 
these  conditions  a  reduction  to  14  per  cent,  produces  little  or  no 
physiological  effect.  When  the  reduction  reaches  12  per  cent., 
there  is  apt  to  be  slightly  deeper  breathing,  while  10  per  cent,  is  an 
amount  distinctly  below  what  is  physiologically  advisable.  Seven 
per  cent,  may  be  regarded  as  the  fatal  point.  It  is  an  amount  too 
small  to  support  the  life  of  animal  or  man  for  any  considerable 
time.  It  must  be  kept  in  mind  that  these  figures,  10  per  cent,  the 
physiological  insufficiency  and  7  per  cent,  the  fatal  point,  are  for 
oxygen  with  inert  nitrogen,  and  without  the  admixture  of  poisonous 
gases. 
There  is  always  present  in  atmospheric  air  a  small  amount  of 
carbon  dioxide  gas,  commonly  known  as  carbonic  acid.  This  amount 
is  very  small,  ordinarily  not  over  5  parts  in  10,000.  It  is  a  product 
of  the  combustion  of  organic  matter  and  is  present  in  air  exhaled 
from  the  body  in  breathing.  As  we  shall  see  later,  it  is  also  a  con- 
stituent of  mine  gases  and  so  is  of  particular  interest  to  us.  I  will 
call  attention  to  what  happens  when  it  is  added  to  the  air. 
To  answer  this  question  I  have  myself  made  direct  observations. 
The  apparatus  employed  was  a  closed  cabinet,  the  inside  measure- 
ments of  which  were  approximately  67  x  30  x  69  in.,  having  a  capa- 
city of  80  cu.  ft.  It  was  provided  with  a  sliding  door.  Into  the 
top  a  pipe  entered  and  connected  with  three  "  sprays,"  one  in  each 
third  of  the  top.  Through  this  system  gases  were  introduced.  There 
was  a  small  sample  tube,  easily  movable,  so  that  gas  was  withdrawn 
from  any  position  desired  within  the  cabinet,  which  was  connected 
outside  with  (a)  an  exhaust  bottle  for  withdrawing  residual  air 
