Mariottesche bottle
The Mariottesche bottle (after Edme Mariotte ) is used to maintain an even pressure and thus an even flow rate from a container. The apparatus is an airtight bottle with a lateral discharge opening into which a glass tube, open at both ends, protrudes from above.
Working principle
If liquid flows out of the bottle, the volume of the air space above the liquid is increased in the bottle, so that the pressure drops until the external air pressure acting in the glass tube overcomes the internal pressure, including the pressure of the water column from the lower end of the tube to the water level can and air bubbles rise from the lower end of the tube.
Then the external air pressure prevails at level b of the lower end of the tube, as long as the water level c does not drop below b ; and the outflow of the liquid takes place only under the pressure of the water column a b , which extends from the outflow mouth to the level of the lower end of the tube. You can therefore let the liquid flow out with the help of the Mariotte bottle, although the water level is falling, under constant pressure and therefore with constant speed. The deeper you push the tube in, the slower the discharge becomes and stops completely when you place the end of the tube at the level of the mouth.
This system is used in chemistry to keep a filter evenly filled. The device consists of a large two-necked bottle, one opening of which is straight and the other a tube that is bent twice at right angles and acts like a lifter. Both tubes reach almost to the bottom of the bottle, the free end of the siphon tube is immersed in the liquid on the filter, and the bottle is level with the edge of the filter in the funnel. Move the straight tube until air bubbles enter through the tube and therefore water flows out of the siphon as soon as the liquid in the funnel sinks.
