A boiling tube looks much like a test tube.
A boiling tube is a large cylindrical vessel used to strongly heat substances in the flame of a bunsen burner. A boiling tube is essentially a scaled-up test tube, being about 50% larger in every aspect.
They are designed to be wide enough to allow substances to boil violently as opposed to a test tube which is too narrow for this task; boiling liquid can explode out of the end of test tubes when they are heated as there is no room for the bubbles of gas to escape independently of the surrounding liquid. They can also be used as a general test tube substitute particularly when a larger volume is desired. They can be used as an ignition chamber for gases where their large volume allows for a more effective gas air mixture compared to that possible in a test tube.
Boiling tubes are commonly made from Pyrex glass which can withstand high temperatures.
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