258  PRODUCING  HIGH  TEMPERATURES  BY  COAL  GAS  AND  AIR. 
the  possibility  of  producing  high  temperatures  by  its  simple 
combustion  in  air  is  proved.  It  is  a  question  of  apparatuses, 
which  I  propose  to  resolve  as  follows  : — 
I  considered  that  there  were  two  principal  conditions  to  be 
fulfilled :  1.  Combustion,  without  excess  of  air  or  gas,  effected 
entirely  in  the  space  to  be  heated ;  2.  Sufficiently  rapid  supply 
of  the  burning  gases  to  keep  up  the  high  temperature,  in  spite 
of  the  losses  by  the  casings,  or  any  other  expenditure  of  heat. 
With  respect  to  this  second  condition,  in  most  of  the  operations 
requiring  a  high  temperature,  the  loss  of  heat  through  the  casings 
is  the  chief  cause  of  cooling,  and  it  is  in  proportion  to  their  size  ; 
hence  the  advantage  of  large  furnaces  over  small  ones — taking 
into  account  only  the  better  employment  of  the  heat. 
These  two  conditions  I  found  to  be  realized  by  the  following 
arrangement ; — -Air  is  forced  into  a  copper  pipe  of  from  three  to 
four  decimetres  long,  through  a  tube  running  a  few  centimetres 
into  the  pipe ;  two  opposite  holes  are  pierced  into  the  pipe  a  little 
behind  the  orifice  of  the  tube  ;  at  this  point  the  pipe  is  sur- 
rounded by  a  muff  supplied  with  gas,  which  is  drawn  into  the 
current  of  air,  and  becomes  mixed  with  it.  The  action  of  this 
apparatus  cannot  be  better  described  than  by  supposing  a  Bun- 
sen's  jet  with  the  air,  and  the  gas  entrances  reversed,  the 
gas  entrance  much  enlarged  and  admitting  air,  and  the  air 
holes  admitting  gas.  The  delivery  of  gas  is  of  course 
regulated  by  a  cock,  that  of  the  air  by  a  given  pressure. 
On  igniting  in  the  air  the  gaseous  mixture  thus  produced 
a  large  blue  flame  is  the  result,  the  heat  of  which  does  not 
appear  to  be  more  intense  than  that  of  an  ordinary  blowpipe  of 
equal  expenditure;  but  if  the  jet  penetrates  a  refractory  en- 
velope, without  taking  the  outer  air  with  it,  the  flame,  which  I 
suppose  to  be  produced  by  a  mixture,  in  theoretical  proportions, 
of  gas  and  air,  becomes  very  short,  and  the  combustion  takes 
place  entirely  in  a  confined  space  ;  this  is  doubtless  caused  by 
the  previous  condition  of  the  mixture  of  fluids,  due  to  their  simul- 
taneous entrance  into  the  same  pipe.  It  does  not  follow  that 
this  fixture  of  explosive  gases  is  dangerous.  In  fact,  from  the 
researches  made  both  by  M.  Demondesir  and  myself,  on  the  com- 
bustion *of  gaseous  mixtures,  it  has  been  found  that  the  velocity 
