AGRICULTURAL CHEMISTRY 



bustion. The outer portion of the flame is a non-lumi- 

 nous envelope of gases undergoing perfect combustion; 

 within this is a layer of gases undergoing partial combus- 

 tion, and constituting the light-giving part of the flame ; 

 while in the center is a zone which is more perfectly cut 

 off from the supply of air, and little or no combustion is 

 taking place. The combustion of a gas or candle flame 

 can be studied from the following experiment : 



Experiment 6. Structure of the flame. Unscrew the top 

 of a Bunsen burner and make a drawing showing how the burner 



works, and the workings 

 of the orifices at the bot- 

 tom of the burner. Re- 

 place the parts of the 

 burner, open the air-holes 

 at the base, and light the 

 gas. Hold a sheet of paper 

 back of the flame and try 

 to distinguish the three 

 parts : ( i ) the outer non 

 luminous envelope of per- 

 fect combustion ; (2) the 

 inner luminous zone of 

 partial combustion ; (3) 

 the central blue cone of 

 unburned gas. Make a drawing of the flame. Press a piece of card- 

 board or paper down upon the flame for an instant and remove it 

 before it takes fire. Observe the result. Hold a piece of wire close 

 to the burner and observe that at first the wire does not become red 

 at the center of the flame. Thrust the head of a match into the 

 center of the flame for an instant and then remove it. If this is 

 done quickly, the match can be removed before combustion takes 

 place. Place a piece of wire gauze above the flame as shown in Fig. 

 23. Observe the result. Extinguish the gas. Hold the wire gauze 



Fig. 22. Combustion. 



