372  Physiological  Characteristics  of  Acetylene.  { AlAUgS'  mi""" 
With  the  production  of  a  strong  movement  of  the  air,  by  direct 
fanning  of  the  lamps,  in  two  experiments  the  acetylene  lamps  were 
extinguished  when  the  air  contained  9.4  per  cent,  and  9,9  per  cent, 
carbon  dioxide,  respectively,  while  the  oil  lamps  were  extinguished 
by  the  same  breeze  in  atmospheric  air. 
'The  movement  of  the  lamps  worn  on  the  heads  of  the  miners 
would  produce,  in  quiet  air,  the  effects  that  result  from  a  breeze  with 
the  lamps  stationary.  We  may  conclude,  therefore,  that  in  the  case 
of  the  acetylene  lamp  the  extinction  point  is  lower  than  25  per  cent., 
in  proportion  to  the  rapidity  of  motion;  and  with  the  oil  lamps, 
correspondingly  lower  than  14  per  cent. 
C.  Oxygen  Proportion. — In  the  experiments  mentioned,  the  oxy- 
gen was  reduced  only  moderately  by  the  admixture  of  the  carbon 
dioxide  in  the  form  of  pure  gas.  Undoubtedly,  such  reduction  tends 
to  lower  the  carbon  dioxide  extinction  point.  The  effect,  however, 
is  only  moderate,  since  the  oxygen  in  all  experiments  was  distinctly 
more  than  would  sustain  the  flame  if  the  specific  effect  of  the  carbon 
dioxide  were  neglected. 
When  the  admixture  of  carbon  dioxide  is  in  the  form  of  black- 
damp,  however,  the  question  of  the  oxygen  proportion  becomes  an 
important  factor  for  consideration.  In  these  preliminary  investiga- 
tions, we  were  not  able  to  study  the  effect  of  black-damp,  since  with 
the  use  of  so  large  a  cabinet,  the  quantity  of  nitrogen  required  would 
be  much  greater  than  it  was  practical  to  obtain. 
D.  Humidity. — In  a  number  of  experiments,  water  vapor  was 
introduced  into  the  gas  mixture  by  blowing  over  the  surface  of  water 
within  the  cabinet.  In  this  way,  the  humidity  was  raised  from 
approximately  35  to  65  or  80.  Any  effect  upon  flame  extinction  by 
carbon  dioxide  that  may  have  resulted  was  within  the  limits  of  varia- 
tion from  the  other  factors  considered.  The  conclusion  is  therefore 
reached  that  humidity  affects  the  proportion  of  carbon  dioxide 
required  to  produce  flame  extinction  only  within  relatively  narrow 
limits. 
Comparing  now  the  effects  of  carbon  dioxide  increase  on  flame 
extinction  and  respiration,  we  note  that  the  first  effect  is  a  physio- 
logical one,  when  the  proportion  reaches  3  to  4  per  cent.,  there  being 
an  increase  in  the  respiratory  rate  that  is  entirely  adequate  to  warn 
persons  of  the  atmospheric  condition.  Flame  extinction  occurs  with 
oil  at  13  per  cent,  and  acetylene  at  26  per  cent,  in  still  atmosphere, 
but  at  10  per  cent,  and  17  per  cent,  with  moderate  motion.  With 
