Getting to know your Bunsen burner
The Bunsen or Tirrell burner is commonly used in laboratory heating operations. While the details of construction vary among burners, each has a gas inlet located in the base, a vertical tube or barrel in which the gas is mixed with air, and an adjustable opening or ports in the base of the barrel to introduce air into the gas stream. The burner may have an adjustable needle valve to regulate the supply of gas, or adjusting the valve on the supply line may regulate the gas supply simply. The burner is always turned off at the gas valve, never at the needle valve.
Take your burner apart and examine it. Compare the parts with the drawing in Fig. 1-1.
Put the parts together again and note particularly how you can control the amount of air admitted near the base of the burner. In lighting the burner, partially close the ports at the base of the barrel, turn the gas full on, and hold the lighted match about 5 cm above the top of the burner. If you are using a torch lighter place the torch lighter next to and slightly above the burner, apply a downward pressure of the flint towards the plate and strike the lighter.
The gas may then be regulated until the flame has the desired height. If a very low flame is needed, the ports should be kept partly closed when the gas pressure is reduced. Otherwise the flame may "strike back" and burn inside the base of the barrel. If this happens, turn off the gas, decrease the amount of air admitted, and re-light.
Relight the Bunsen burner. Close the airports or inlets as completely as possible and note the color and shape of the flame which is now luminous.
Pass your hand quickly through the flame, which can be done without discomfort.
Using crucible tongs, hold a dry porcelain-evaporating dish in the flame for a few seconds. Examine the dish and record your observations. After the dish cools, clean and dry the evaporating dish.
Sketch the luminous flame and show its structure as far as you can see.
Using a test tube holder, hold one end of a glass tube about 15 cm long and inclined at a 45 degree angle just inside the barrel and attempt to light the gas which escapes from the other end of the glass tube. If unsuccessful with lighting the gas at the end of the glass tube, then increase the flow of gas slightly and try again. Record your observations.
Extinguish the burner flame.
NON LUMINOUS FLAME
For laboratory work, you should adjust the burner so that the flame will be free of yellow color, and also free from the "roaring" sound caused by admitting too much air. Regulate the flow of gas to give a flame extending roughly 8 cm above the barrel. Slowly open the airports and notice that the flame loses its luminosity and two well-defined regions appear in the flame. The two distinct regions of the flame are called the oxidizing and reducing regions. This is the so-called Bunsen flame, and it should always be used for heating purposes. You may have to adjust the amount of air admitted and the amount of gas mixing with the air. A yellow flame yields much light but little heat. Such a flame is the mark of an amateur. Obtain a flame which is quiet, steady, and does not go out.
Insert a wooden splint in the reducing region across the flame near the base of the blue inner region, resting on the top of the barrel for a few seconds. Remove from the flame, extinguish, examine and record observations.
Repeat the process, but place the splint one cm above the oxidizing region.
Using tongs, hold a cool, dry porcelain-evaporating dish above the top of the reducing region for about ten seconds. Do not permit the evaporating dish to incandesce. Remove from the flame, place on a wire gauze, and allow the dish to cool. Then examine and record your...
Please join StudyMode to read the full document