. Optical projection : a treatise on the use of the lantern in exhibition and scientific demonstration. Fig. 211 Fig. 212 225. Convection Currents.—The simplest apparatus forprojecting currents produced by the lowering of specificgravity, is a mere test-tube held in a Bunsen holder andheated as in fig. the tube be flattened,the effect will be betterstill; or a flattened flaskcan be similarly pro-jected. To make thecurrents more visible, afew particles of exceed-ingly fine sawdust fromheavy wood may beplaced in the water, orparticles of blotting-paper rubbed up in a mortar with water ; M
. Optical projection : a treatise on the use of the lantern in exhibition and scientific demonstration. Fig. 211 Fig. 212 225. Convection Currents.—The simplest apparatus forprojecting currents produced by the lowering of specificgravity, is a mere test-tube held in a Bunsen holder andheated as in fig. the tube be flattened,the effect will be betterstill; or a flattened flaskcan be similarly pro-jected. To make thecurrents more visible, afew particles of exceed-ingly fine sawdust fromheavy wood may beplaced in the water, orparticles of blotting-paper rubbed up in a mortar with water ; Mr. H. Gr. Madanuses a crystal or two of magenta coated with gum-water and cc 2. Pig. 213 388 OPTICAL PROJECTION dropped into the vessel, from which coloured streams willproceed. The little apparatus shown in fig. 213 will both showconvection currents, and illustrate their every-day applica-tion to hot-water systems of heating. A few small bubblesor particles of sawdust show the movement well in thisapparatus. 226. Evaporation.—Boiling in a small flask is easily pro-jected, and by the well-known apparatus in fig. 214, boiling up a flask of water, which isclosed with a cork and theninverted in the field of thelantern, the familiar experi-ment of producing ebullitionby the application of coldwater, is also shown. Theloss of heat in evaporationmay be projected either bywrapping the bulb of athermometer in a piece ofrag moistened with the liquid,or by applying a moistenedplate to the face of a thermo-pile, the galvanometer inconnection with which isprojected direct, or by a re-flected pencil. (See § 240.)227. Conductivity.—Toshow the different conducting power of
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Keywords: ., bookauthorwrightle, bookcentury1900, bookdecade1900, bookyear1906
