Pneumatic trough

A Pneumatic trough is a piece of laboratory apparatus used for collecting gases. The gas may be heavier or lighter than air but it must be insoluble, or only slightly soluble, in water. Examples include hydrogen, oxygen, nitrogen.

Equipment

Three items are required:
* a pneumatic trough, which is a large glass dish
* a beehive shelf, which is an inverted ceramic dish with holes in the side and top
* a gas jar

et up

The beehive shelf is placed in the pneumatic trough and enough water is poured into the trough to cover the shelf. The outlet tube from the gas-generating apparatus is inserted into the side hole of the beehive shelf so that gas bubbles up through the top hole. A gas jar is filled with water, covered with a glass plate, inverted, and placed on the beehive shelf. The glass plate is carefully removed so that gas can bubble up into the jar. When the jar is full of gas it is again covered by a glass plate, removed, and replaced by another jar. The process is repeated until the required volume of gas has been collected.