Text-book of medical and pharmaceutical chemistry . ough the rarefiedgas (pressure one millionth of an atmosphere), the charged mole-cules, in the case of electricity, seem to launch forth in a directline from the negative pole toward the positive. If a light discbe placed in this path, it is bombarded by the molecules on theside presented to the negative pole, and thus it receives a suffi-cient impulse to render the motion visible to the eye. The radiometer (Fig. 4) consists of a glass globe as cornpletely 22 MEDICAL CHEMISTRY. exhausted of air as possible, containing a vane holding four disc
Text-book of medical and pharmaceutical chemistry . ough the rarefiedgas (pressure one millionth of an atmosphere), the charged mole-cules, in the case of electricity, seem to launch forth in a directline from the negative pole toward the positive. If a light discbe placed in this path, it is bombarded by the molecules on theside presented to the negative pole, and thus it receives a suffi-cient impulse to render the motion visible to the eye. The radiometer (Fig. 4) consists of a glass globe as cornpletely 22 MEDICAL CHEMISTRY. exhausted of air as possible, containing a vane holding four discsof mica, blackened on one side, and delicately suspended upona point, so as to revolve with as little friction as possible. Onbringing the globe into a strong light, or near a source of heat,it begins to revolve, because of the bombardment of the dark surface moves in the path of the light. 20. Diffusion of Gases.—If two gases be brought in contactwith one another, by inverting one jar over the other, as repre- FlG. 4. Fig. 5. Fig. sented in Fig. 5, the gases will not long remain separate but willquickly mingle, so as to make a uniform mixture throughout bothjars. This property of gases is called diffusion. The diffusionof gases will also take place if they are separated by a porous wallof earthenware, stone, or parchment, by the passage of the gasthrough the pores. A convenient method of illustrating thisphenomenon is to take an unglazed earthenware cup, such as isused in a Bunsens battery cell, invert it in a funnel provided CHEMICAL PHYSICS. 23 with a long stem, and fasten it in place by a paste made of plaster-of-Paris. Tlie lower end of the funnel tube is passed through aperforated cork into a bottle containing water, as shown in theaccompanying figure. (See Fig. 6.) On bringing a bell-jar ofhydrogen or illuminating gas over the porous cup, the air in thefunnel will be forced out below, and may be seen to escapein bubbles through the water. 21. Grahams Law
Size: 909px × 2749px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1, booksubjectpharmaceuticalchemistry
