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DIFFUSION
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EQUIPMENT
    redball.gif (326 bytes) Diffusion Apparatus
    



NARRATIVE
               The Diffusion Apparatus is designed to show the principle of diffusion of gasses. To demonstrate the phenomenon with this apparatus, set up the porous cup, rubber stopper, and glass tube. A bell jar, battery jar, or beaker may be placed over the porous cup. A supply of hydrogen from a hydrogen generator os a supply of illuminating gas from the gas jet should be introduced by means of a length of rubber tubing placed into the jar. The gas will diffuse through the walls of the porous cup, and the increased pressure due to this gas will force bubbles of the gas out of the water in the beaker below. This is due to the fact that the gas, which is introduced under the jar, is lighter than the air, and diffuses into the porous cup faster than the denser air diffuses outward form the cup into the jar.

            If the jar is removed, the reverse will happen. The light gas will defuse out of the porous cup faster than the air passes in, and since a diminished pressure will result, the water will start rising in the glass tube.

            Any gas lighter than air can be used to make this demonstration. Hydrogen is perhaps more effective, but illuminating gas is more convenient.

            Do not force the rubber stopper into the lower cup with a force sufficient to break the cup. A porous cup is necessarily somewhat fragile and can be easily broken by forcing the rubber stopper into it.

            Another more effective method of making this demonstration is to have the long glass tube extend downward into a 2 hole rubber stopper, which in turn is fitted into a Florence flask. The Florence flask is filled partly full of water, and another glass tube is fitted in the other hole of the 2 hole stopper, and extends down into the water. The upper end of this glass tube should be drawn into a jet. When the gas diffuses through the cup and exerts its pressure on the water, the water will then be forced out of the glass jet tube into a fine spray.