yellow when fully open if on a bunson burner
The flame itself will get bigger/hotter, and the amount of 'blue' increases. Depending on the type of burner, it may or may not increase proportionately with the total flame size.
A Bunsen flame is hottest when the air hole is open. When the air hole is open, more oxygen can mix with the gas, resulting in a hotter and more efficient flame. Closing the air hole restricts the amount of oxygen, leading to a cooler flame.
To properly light a Bunsen burner, first ensure the air hole is open and the gas valve is closed. Use a striker to ignite the gas as you slowly open the valve. Adjust the flame by controlling the air hole and gas valve until you have a blue, steady flame.
A Bunsen burner flame with the air hole half open is typically called a "luminous flame." It appears yellow and produces soot due to incomplete combustion, indicating a fuel-rich environment. Adjusting the air hole allows for better control of the flame temperature and combustion efficiency.
A hot flame is obtained (but not the hottest) with a color violet-white.
To adjust the flame on a Bunsen burner, first make sure the gas is turned on. Then, slowly open the air vent to let in more oxygen, which will produce a blue, hotter flame. Conversely, closing the air vent will produce a yellow, cooler flame.
To change the flame of a Bunsen burner you must open or close the air valve, usually this is done by rotating the barrel.
Increase the air flow by opening the circular valve on the stem of the burner. This will cause the flame to burn more intensely and with a blue flame. When the valve is closed, the flame will burn yellow and cooler - more like a wax candle's flame.
To increase the height of a Bunsen burner flame, you can open the air valve to allow more air to mix with the gas before it ignites. This will result in a hotter and taller flame. Adjusting the gas flow rate higher can also increase the flame height.
Air hole fully open gives a 'roaring blue flame'
The most stable flame is a blue flame (produced when air valve is open)
To heat chemicals or substances in science lab for experiment. There is an air hole in the Bunsen burner where you can screw loose to have open air hole that is the blue flame which is hotter. When there is a close air hole then the flame would be orange in color which is not as hot compared to the blue flame.