EFFECT OF HEAT ON SUBSTANCES 



lamp can be used, but where a gas supply is available it is cheaper and 

 more economical to use a Bunsen burner, which fulfils the above con- 

 ditions. It will be noticed on 

 reference to Fig. 70 that at the 

 bottom of the tube A there is a 

 collar B, which can be turned so 

 as to uncover two holes in the 

 tube by which air may be allowed 

 to enter and mix with the gas 

 before ignition. When the collar 

 is in the position described the 

 flame is non-luminous, and if a 

 cold body, such as a porcelain 

 basin, be placed in it, no soot is 

 deposited. But when the collar 

 is rotated so as to close the holes, 

 an ordinary luminous flame is 

 produced, and it is found that a 

 cold body placed in it becomes 

 coated with soot. The real nature 

 of the Bunsen flame will be better 

 understood after the question of 

 combustion has been dealt with. F- TO.-A Bunsen burner. 



