GAS  FURNACE  FOE,  GENERAL  CHEMICAL  USE. 
47 
in  the  sketch.  The  gaseous  mixture  passes  up  the  vertical  tube 
b,  and  is  inflamed  at  the  top,  where  it  burns  with  a  single,  tall, 
blue  flame,  which  gives  no  smoke,  very  little  light,  but  much 
heat.  In  this  condition,  the  apparatus  differs  from  »  Bunsen's 
Gas-burner  "  only  in  size,  c  represents  a  thin  brass  cap,  which 
fits  the  air-box  a,  but  moves  easily  round  it.  d  is  a  flat,  cast- 
iron  box,  with  many  holes  round  the  margin,  and  a  few  small 
ones  on  the  top.  This  box  fits  loosely  on  the  upper  part  of  the 
tube  6,  and  when  it  is  placed  upon  it,  and  the  ga3  is  lighted,  the 
flame  produced  consists  of  a  series  of  radiating  jets,  forming  a 
horizontal  circular  flame  of  about  7  inches  in  diameter.  Fig. 
2 — a  shows  a  ring  of  horizontal  flames  thus  produced,  and  b 
shows  the  single  vertical  flame.*  The  ring  of  flame  is  suited 
to  the  purposes  of  boiling  and  evaporation  ;  the  single  flame 
to  ignition  and  fusion.  The  height  of  the  apparatus  repre- 
sented by  Fig.  1  is  12  inches  ;  the  bore  of  the  tube  b  is  1  inch  ; 
and  the  diameter  of  the  fire-box  d  is  4  inches. 
Bunsen's  gas-burner,  whatever  its  size,  is  subject  to  two  de- 
fects :  sometimes  the  flame  burns  white  and  smoky,  and  some- 
times it  blows  down,  the  gaseous  mixture  explodes,  and  the  gas 
then  burns  with  a  smoky  flame  in  the  air-box  a,  Fig.  1.  The 
remedies  for  these  defects  are  as  follows : — If  the  flame  is  white 
only  when  the  gas  is  turned  on  very  full,  the  remedy  is  to  lessen 
the  supply  of  gas  ;  but  if  the  flame  continues  to  burn  white  at 
the  top  when  the  gas  is  gradually  turned  off,  and  the  mass  of 
flame  slowly  sinks,  then  the  holes  which  deliver  the  gas  from 
the  supply  pipe  into  the  air  box  are  too  large,  and  are  placed 
too  directly  under  the  centre  of  the  vertical  tube  5,  Fig.  1,  and 
these  defects  must  be  corrected  in  the  instrument.  Finally, 
when  the  flame  blows  down,  it  is  because  the  supply  of  atmos- 
pheric air  is  too  large  in  proportion  to  the  supply  of  gas,  and 
their  relative  proportions  must  be  altered.    To  effect  this  alter- 
ation, the  cap  c  is  to  be  turned  round  on  the  air-box  a,  so  as 
partially  to  close  the  holes,  and  thus  lessen  the  supply  of  air. 
If,  when  the  gas  is  alight,  the  flame  needs  to  be  lowered,  first 
the  supply  of  air  is  to  be  lessened,  and  then  the  supply  of  gas. 
If  the  flame  is  to  be  enlarged,  first  the  supply  of  gas  must  be 
*  Fig.  2  represents  a  small  variety  of  this  gas-burner,  in  which  the  head 
is  not  removable,  but  the  efflux  of  the  mixed  gases  is  regulated  by  a 
sliding  valve,  which  is  represented  by  b. 
