142 GENERAL SCIENCE 



fire in the colorless cone at the center of the flame. This part of 

 the flame is made up of unburning gases. Hold a piece of glass 

 tubing in the inner cone in such a manner as to allow the gas to 



run through the tubing. Light 

 the gas outside of the flame at 

 c " f\ ^v *%&*** the other end. This inner cone 



A g.^ a ^^-..-cNX "a s made U P of unburning gas 



which diffuses outward to the an\ 

 Around this is a second cone in 

 which oxygen unites with the gas, 

 setting free small particles of car- 

 bon which .are heated to "white 

 FIG. 110. Parts of a Flame. heat." Around this second cone 



is a third cone, bluish in color, 



where complete combustion is taking place. If a large quantity 

 of air is allowed to enter the Bunsen burner a non-luminous flame 

 is produced, with an inner cone of unburning gas, and an outer cone 

 of gas where complete combustion is taking place, resulting in a 

 colorless flame. 



The Action of Wire Gauze upon Gas. Place a piece of fine 

 copper wire gauze over a small gas flame. It will be seen that the 

 gas above the wire gauze does not take fire until the gauze has become 

 red hot. Turn out the gas. Allow the gauze to cool; replace it 

 about 1 inch above the burner, and light the gas above the gauze. 

 The gas will burn on top of the screen and will not take fire under- 

 neath, since the heat is rapidly 'conducted away by the wire screen, 

 preventing the gas from reaching the temperature of kindling point. 

 There are two uses made of this principle. One is in the Davy 

 Safety Lamp in which the flame is enclosed in a screened cylinder. 

 This enables miners to go into a mine without danger of exploding the 

 fire damp (a gas found in mines), since the gas can burn only as fast 

 as it can sift through the screen. A screen is also used in the Bun- 

 sen burner or mantles to prevent the gas from burning back. Often 

 in lighting a gas light the mixture of air and gas is sufficient to 

 cause a slight explosion which often causes the gas to take fire at the 

 spud or base of the burner. The gauze helps to prevent the gas from 

 taking fire at this point. 



