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SUGGESTIONS FOR DEMONSTRATIONS' WALTER 5. LAPP Overbrook High School, Philadelphia, Pennsylvania
C a t h o d i c Protection qf Iron .from Corrosion. In 1824 Sir Humphry Davy first demonstrated the principle of the rathodir protertion of met,als from rorrosion. This ides may hr demonstrated before a class as follows: Half fill two 250-ml. beakers with tap water. Add a few drops of phenolphthalein to each. In one of the heakers stand a clean strip of iron (a strip measuring about 1 cm. by 15 cm. is sat,isfactory). Into the other b a k e r place a couple made by attaching a coil of freshly cleaned magnesium ribbon 25 om. long t o a strip of iron of the same size used in the first beaker. The effect is evident within a fen. minutes and shows how an expendable anode of magnesium or aluminum ic of ferrous met,als, may prevent loral g a l v a ~ ~corrosion such as soil pipes and hot water storage t,anks. 1;sc o f Lithium in Preparing Hydrogen. Wit,hin P ~ w m t e dat the S,vrnposiurn on Lerture Dornonst.rstiona at the 120t,h Mcatingof the Arnrrirm Chrmiesl Society, Ncw York, Septtmlm 7, 1051. For othur pnpcrs in this ~ymporiomsee Trm J O ~ N A 2L9 , 288 (1052).
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the past decade metallic lithium has become availahle in a variet,y of forms, such as cup, rod, ~vire,ribbon, cartridge, and shot.. Hydrogen may be conveniently and safely prepared by t,he a(%ion of lithium shot on water. Place about 15 shot in a 250-ml. wide-mouth hottle full of water, rover with a glass plat,e, immediately invert in a trough of wat,er, and remove the glass plate. The lithium flame may be demonstrated by pirking up a single shot wit,h all ice pick and holding it in the non-luminous flame of the Bunsen burner. Diffusion in a solntion may be shown by placing a few shot in a large cylinder of water to which some phenolphthalein has been added. A n Easily Constructed Conductivity Kit. Remove t,he switch from a plug-in bakelite night lamp. Rewire the lamp in series and at,taeh alligator clamps to the plugs. Pencil leads are used as electrodes (Figure 1). Support for Rubber Stoppers. A support for rubber stoppers (Figure 2) has been found useful, to make a few of any size or form readily availahle.
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