What is "pneumatic trough"

Pneumatic \Pneu*mat"ic\, Pneumatical \Pneu*mat"ic*al\, a. [L. pneumaticus, Gr. ?, fr. ?, ?, wind, air, ? to blow, breathe; cf. OHG. fnehan: cf. F. pneumatique. Cf. Pneumonia.]

1. Consisting of, or resembling, air; having the properties of an elastic fluid; gaseous; opposed to dense or solid.

   The pneumatical substance being, in some bodies, the native spirit of the body.
   --Bacon.

2. Of or pertaining to air, or to elastic fluids or their properties; pertaining to pneumatics; as, pneumatic experiments. ``Pneumatical discoveries.''
   --Stewart.

3. Moved or worked by pressure or flow of air; as, a pneumatic instrument; a pneumatic engine.

4. (Biol.) Fitted to contain air; Having cavities filled with air; as, pneumatic cells; pneumatic bones.

5. Adapted for containing compressed air; inflated with air; as, a pneumatic cushion; a pneumatic tire, a tire formed of an annular tube of flexible fabric, as India rubber, suitable for being inflated with air.

   Pneumatic action, or Pneumatic lever (Mus.), a contrivance for overcoming the resistance of the keys and other movable parts in an organ, by causing compressed air from the wind chest to move them.

   Pneumatic dispatch, a system of tubes, leading to various points, through which letters, packages, etc., are sent, by the flow and pressure of air.

   Pneumatic elevator, a hoisting machine worked by compressed air.

   Pneumatic pile, a tubular pile or cylinder of large diameter sunk by atmospheric pressure.

   Pneumatic pump, an air-exhausting or forcing pump.

   Pneumatic railway. See Atmospheric railway, under Atmospheric.

   Pneumatic syringe, a stout tube closed at one end, and provided with a piston, for showing that the heat produced by compressing a gas will ignite substances.

   Pneumatic trough, a trough, generally made of wood or sheet metal, having a perforated shelf, and used, when filled with water or mercury, for collecting gases in chemical operations.

   Pneumatic tube. See Pneumatic dispatch, above.

n. (context chemistry English) a piece of laboratory apparatus used for collecting gases

A pneumatic trough is a piece of laboratory apparatus used for collecting gases, such as hydrogen, oxygen, and nitrogen. Pneumatic troughs require a liquid such as water. Scientists also have used mercury in pneumatic troughs, but usually only for the collection of water-soluble gases. Health-and-safety issues surrounding mercury generally prohibit its use in modern-day pneumatic troughs.

Four items are required for gas collection with a pneumatic trough:

• The trough itself, which is a large glass dish or a similar container
• A gas bottle (or bulb), to hold the gas collected
• A way to support the gas bottle or bulb, such as a Beehive shelf or a hanger (see picture)
• A liquid in the trough

The bottle is filled with water, inverted, and placed into the pneumatic trough already containing water. The outlet tube from the gas-generating apparatus is inserted into the opening of the bottle so that gas can bubble up through it, displacing the water within.