A text-book on chemistryFor the use of schools and colleges . e-Winds.—Land and Sea Breezes.—Ap-plications of the Mon-conducting Power of Air. The conducting power of most liquids, such as water,is very low; a thin stratum is sufficient almost entirelyto cut off the passage of heat. This may be shown bythe apparatus Fig. 57, consisting of a funnel partly fill-ed with water, with an air-thermometer included insuch a manner that the bulb is within a short distanceof the surface, a depth of a quarter of an inch or less in-tervening. The tube of the thermometer may be pass-ed through the lower mou
A text-book on chemistryFor the use of schools and colleges . e-Winds.—Land and Sea Breezes.—Ap-plications of the Mon-conducting Power of Air. The conducting power of most liquids, such as water,is very low; a thin stratum is sufficient almost entirelyto cut off the passage of heat. This may be shown bythe apparatus Fig. 57, consisting of a funnel partly fill-ed with water, with an air-thermometer included insuch a manner that the bulb is within a short distanceof the surface, a depth of a quarter of an inch or less in-tervening. The tube of the thermometer may be pass-ed through the lower mouth of the funnel, water-tightby means of a cork, and the position at which the index-liquid stands having been marked, some ether is pouredon the surface of the water, upon which it readily floats,and set on fire. A voluminous flame is the result, and Do solids conduct equally in all directions ? Describe Fig. effect has pressure on conduction? How does the conductingpower of liquids compare with that of solids ? Describe Fig. 57. CONVECTION. IS. a great deal of heat is evolved; and since the bulb ofthe thermometer is apparently sep- ^ 5T arated from the flame by a thin filmof water only, if the heat traversedthat film the thermometer shouldrapidly move, but it does not; wetherefore conclude that water is avery bad conductor of heat. But the experiment is very de-ceptive ; for as the flame is hollow,and only incandescent on its sur-face, it is really a great distancefrom the thermometer bulb, and,in addition, the evaporation of theether is a cooling operation. Theconclusion is nevertheless true. To a certain extent all liquidsconduct. Mercury is a good conductor; but, in thoseof which water is the type, the dissemination is chieflyeffected by a process called convection or circulation,which depends on the free mobility of their particles. * The apparatus Fig. 58 illustrates this process. It con-sists of a wide tube, into Avhich the water pig, be poured ; the
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