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ine¡¡always¡¡in¡¡definite¡¡numerical¡¡proportions¡¡as¡¡to¡¡volume¡£¡¡Exactly¡¡two¡¡volumes¡¡of¡¡hydrogen£»¡¡for¡¡example£»¡¡combine¡¡with¡¡one¡¡volume¡¡of¡¡oxygen¡¡to¡¡form¡¡water¡£¡¡¡¡Moreover£»¡¡the¡¡resulting¡¡compound¡¡gas¡¡always¡¡bears¡¡a¡¡simple¡¡relation¡¡to¡¡the¡¡combining¡¡volumes¡£¡¡In¡¡the¡¡case¡¡just¡¡cited£»¡¡the¡¡union¡¡of¡¡two¡¡volumes¡¡of¡¡hydrogen¡¡and¡¡one¡¡of¡¡oxygen¡¡results¡¡in¡¡precisely¡¡two¡¡volumes¡¡of¡¡water¡¡vapor¡£

Naturally¡¡enough£»¡¡the¡¡champions¡¡of¡¡the¡¡atomic¡¡theory¡¡seized¡¡upon¡¡these¡¡observations¡¡of¡¡Gay¡­Lussac¡¡as¡¡lending¡¡strong¡¡support¡¡to¡¡their¡¡hypothesisall¡¡of¡¡them£»¡¡that¡¡is£»¡¡but¡¡the¡¡curiously¡¡self¡­reliant¡¡and¡¡self¡­sufficient¡¡author¡¡of¡¡the¡¡atomic¡¡theory¡¡himself£»¡¡who¡¡declined¡¡to¡¡accept¡¡the¡¡observations¡¡of¡¡the¡¡French¡¡chemist¡¡as¡¡valid¡£¡¡Yet¡¡the¡¡observations¡¡of¡¡Gay¡­Lussac¡¡were¡¡correct£»¡¡as¡¡countless¡¡chemists¡¡since¡¡then¡¡have¡¡demonstrated¡¡anew£»¡¡and¡¡his¡¡theory¡¡of¡¡combination¡¡by¡¡volumes¡¡became¡¡one¡¡of¡¡the¡¡foundation¡­stones¡¡of¡¡the¡¡atomic¡¡theory£»¡¡despite¡¡the¡¡opposition¡¡of¡¡the¡¡author¡¡of¡¡that¡¡theory¡£

The¡¡true¡¡explanation¡¡of¡¡Gay¡­Lussac's¡¡law¡¡of¡¡combination¡¡by¡¡volumes¡¡was¡¡thought¡¡out¡¡almost¡¡immediately¡¡by¡¡an¡¡Italian¡¡savant£»¡¡Amadeo£»¡¡Avogadro£»¡¡and¡¡expressed¡¡in¡¡terms¡¡of¡¡the¡¡atomic¡¡theory¡£¡¡The¡¡fact¡¡must¡¡be£»¡¡said¡¡Avogadro£»¡¡that¡¡under¡¡similar¡¡physical¡¡conditions¡¡every¡¡form¡¡of¡¡gas¡¡contains¡¡exactly¡¡the¡¡same¡¡number¡¡of¡¡ultimate¡¡particles¡¡in¡¡a¡¡given¡¡volume¡£¡¡¡¡Each¡¡of¡¡these¡¡ultimate¡¡physical¡¡particles¡¡may¡¡be¡¡composed¡¡of¡¡two¡¡or¡¡more¡¡atoms¡¡£¨as¡¡in¡¡the¡¡case¡¡of¡¡water¡¡vapor£©£»¡¡but¡¡such¡¡a¡¡compound¡¡atom¡¡conducts¡¡itself¡¡as¡¡if¡¡it¡¡were¡¡a¡¡simple¡¡and¡¡indivisible¡¡atom£»¡¡as¡¡regards¡¡the¡¡amount¡¡of¡¡space¡¡that¡¡separates¡¡it¡¡from¡¡its¡¡fellows¡¡under¡¡given¡¡conditions¡¡of¡¡pressure¡¡and¡¡temperature¡£¡¡The¡¡compound¡¡atom£»¡¡composed¡¡of¡¡two¡¡or¡¡more¡¡elementary¡¡atoms£»¡¡Avogadro¡¡proposed¡¡to¡¡distinguish£»¡¡for¡¡purposes¡¡of¡¡convenience£»¡¡by¡¡the¡¡name¡¡molecule¡£¡¡¡¡It¡¡is¡¡to¡¡the¡¡molecule£»¡¡considered¡¡as¡¡the¡¡unit¡¡of¡¡physical¡¡structure£»¡¡that¡¡Avogadro's¡¡law¡¡applies¡£

This¡¡vastly¡¡important¡¡distinction¡¡between¡¡atoms¡¡and¡¡molecules£»¡¡implied¡¡in¡¡the¡¡law¡¡just¡¡expressed£»¡¡was¡¡published¡¡in¡¡1811¡£¡¡Four¡¡years¡¡later£»¡¡the¡¡famous¡¡French¡¡physicist¡¡Ampere¡¡outlined¡¡a¡¡similar¡¡theory£»¡¡and¡¡utilized¡¡the¡¡law¡¡in¡¡his¡¡mathematical¡¡calculations¡£¡¡And¡¡with¡¡that¡¡the¡¡law¡¡of¡¡Avogadro¡¡dropped¡¡out¡¡of¡¡sight¡¡for¡¡a¡¡full¡¡generation¡£¡¡¡¡Little¡¡suspecting¡¡that¡¡it¡¡was¡¡the¡¡very¡¡key¡¡to¡¡the¡¡inner¡¡mysteries¡¡of¡¡the¡¡atoms¡¡for¡¡which¡¡they¡¡were¡¡seeking£»¡¡the¡¡chemists¡¡of¡¡the¡¡time¡¡cast¡¡it¡¡aside£»¡¡and¡¡let¡¡it¡¡fade¡¡from¡¡the¡¡memory¡¡of¡¡their¡¡science¡£

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At¡¡least¡¡two¡¡great¡¡chemists¡¡of¡¡the¡¡time£»¡¡however£»¡¡adopted¡¡the¡¡atomic¡¡view¡¡with¡¡less¡¡reservation¡£¡¡¡¡One¡¡of¡¡these¡¡was¡¡Thomas¡¡Thomson£»¡¡professor¡¡at¡¡Edinburgh£»¡¡who£»¡¡in¡¡1807£»¡¡had¡¡given¡¡an¡¡outline¡¡of¡¡Dalton's¡¡theory¡¡in¡¡a¡¡widely¡¡circulated¡¡book£»¡¡which¡¡first¡¡brought¡¡the¡¡theory¡¡to¡¡the¡¡general¡¡attention¡¡of¡¡the¡¡chemical¡¡world¡£¡¡The¡¡other¡¡and¡¡even¡¡more¡¡noted¡¡advocate¡¡of¡¡the¡¡atomic¡¡theory¡¡was¡¡Johan¡¡Jakob¡¡Berzelius¡£¡¡¡¡This¡¡great¡¡Swedish¡¡chemist¡¡at¡¡once¡¡set¡¡to¡¡work¡¡to¡¡put¡¡the¡¡atomic¡¡theory¡¡to¡¡such¡¡tests¡¡as¡¡might¡¡be¡¡applied¡¡in¡¡the¡¡laboratory¡£¡¡¡¡He¡¡was¡¡an¡¡analyst¡¡of¡¡the¡¡utmost¡¡skill£»¡¡and¡¡for¡¡years¡¡be¡¡devoted¡¡himself¡¡to¡¡the¡¡determination¡¡of¡¡the¡¡combining¡¡weights£»¡¡¡¨equivalents¡¨¡¡or¡¡¡¨proportions£»¡¨¡¡of¡¡the¡¡different¡¡elements¡£¡¡These¡¡determinations£»¡¡in¡¡so¡¡far¡¡as¡¡they¡¡were¡¡accurately¡¡made£»¡¡were¡¡simple¡¡expressions¡¡of¡¡empirical¡¡facts£»¡¡independent¡¡of¡¡any¡¡theory£»¡¡but¡¡gradually¡¡it¡¡became¡¡more¡¡and¡¡more¡¡plain¡¡that¡¡these¡¡facts¡¡all¡¡harmonize¡¡with¡¡the¡¡atomic¡¡theory¡¡of¡¡Dalton¡£¡¡¡¡So¡¡by¡¡common¡¡consent¡¡the¡¡proportionate¡¡combining¡¡weights¡¡of¡¡the¡¡elements¡¡came¡¡to¡¡be¡¡known¡¡as¡¡atomic¡¡weightsthe¡¡name¡¡Dalton¡¡had¡¡given¡¡them¡¡from¡¡the¡¡firstand¡¡the¡¡tangible¡¡conception¡¡of¡¡the¡¡chemical¡¡atom¡¡as¡¡a¡¡body¡¡of¡¡definite¡¡constitution¡¡and¡¡weight¡¡gained¡¡steadily¡¡in¡¡favor¡£

From¡¡the¡¡outset¡¡the¡¡idea¡¡had¡¡had¡¡the¡¡utmost¡¡tangibility¡¡in¡¡the¡¡mind¡¡of¡¡Dalton¡£¡¡¡¡He¡¡had¡¡all¡¡along¡¡represented¡¡the¡¡different¡¡atoms¡¡by¡¡geometrical¡¡symbolsas¡¡a¡¡circle¡¡for¡¡oxygen£»¡¡a¡¡circle¡¡enclosing¡¡a¡¡dot¡¡for¡¡hydrogen£»¡¡and¡¡the¡¡likeand¡¡had¡¡represented¡¡compounds¡¡by¡¡placing¡¡these¡¡symbols¡¡of¡¡the¡¡elements¡¡in¡¡juxtaposition¡£¡¡Berzelius¡¡proposed¡¡to¡¡improve¡¡upon¡¡this¡¡method¡¡by¡¡substituting¡¡for¡¡the¡¡geometrical¡¡symbol¡¡the¡¡initial¡¡of¡¡the¡¡Latin¡¡name¡¡of¡¡the¡¡element¡¡representedO¡¡for¡¡oxygen£»¡¡H¡¡for¡¡hydrogen£»¡¡and¡¡so¡¡ona¡¡numerical¡¡coefficient¡¡to¡¡follow¡¡the¡¡letter¡¡as¡¡an¡¡indication¡¡of¡¡the¡¡number¡¡of¡¡atoms¡¡present¡¡in¡¡any¡¡given¡¡compound¡£¡¡This¡¡simple¡¡system¡¡soon¡¡gained¡¡general¡¡acceptance£»¡¡and¡¡with¡¡slight¡¡modifications¡¡it¡¡is¡¡still¡¡universally¡¡employed¡£¡¡Every¡¡school¡­boy¡¡now¡¡is¡¡aware¡¡that¡¡H2O¡¡is¡¡the¡¡chemical¡¡way¡¡of¡¡expressing¡¡the¡¡union¡¡of¡¡two¡¡atoms¡¡of¡¡hydrogen¡¡with¡¡one¡¡of¡¡oxygen¡¡to¡¡form¡¡a¡¡molecule¡¡of¡¡water¡£¡¡¡¡But¡¡such¡¡a¡¡formula¡¡would¡¡have¡¡had¡¡no¡¡meaning¡¡for¡¡the¡¡wisest¡¡chemist¡¡before¡¡the¡¡day¡¡of¡¡Berzelius¡£

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Here£»¡¡then£»¡¡were¡¡two¡¡utterly¡¡novel¡¡and¡¡independent¡¡sets¡¡of¡¡empirical¡¡facts¡¡which¡¡harmonize¡¡strangely¡¡with¡¡the¡¡supposition¡¡that¡¡substances¡¡are¡¡composed¡¡of¡¡chemical¡¡atoms¡¡of¡¡a¡¡determinate¡¡weight¡£¡¡This¡¡surely¡¡could¡¡not¡¡be¡¡coincidenceit¡¡tells¡¡of¡¡law¡£¡¡And¡¡so¡¡as¡¡soon¡¡as¡¡the¡¡claims¡¡of¡¡Dulong¡¡and¡¡Petit¡¡and¡¡of¡¡Mitscherlich¡¡had¡¡been¡¡substantiated¡¡by¡¡other¡¡observers£»¡¡the¡¡laws¡¡of¡¡the¡¡specific¡¡heat¡¡of¡¡atoms£»¡¡and¡¡of¡¡isomorphism£»¡¡took¡¡their¡¡place¡¡as¡¡new¡¡levers¡¡of¡¡chemical¡¡science¡£¡¡¡¡With¡¡the¡¡aid¡¡of¡¡these¡¡new¡¡tools¡¡an¡¡impregnable¡¡breastwork¡¡of¡¡facts¡¡was¡¡soon¡¡piled¡¡about¡¡the¡¡atomic¡¡theory¡£¡¡And¡¡John¡¡Dalton£»¡¡the¡¡author¡¡of¡¡that¡¡theory£»¡¡plain£»¡¡provincial¡¡Quaker£»¡¡working¡¡on¡¡to¡¡the¡¡end¡¡in¡¡semi¡­retirement£»¡¡became¡¡known¡¡to¡¡all¡¡the¡¡world¡¡and¡¡for¡¡all¡¡time¡¡as¡¡a¡¡master¡¡of¡¡masters¡£


HUMPHRY¡¡DAVY¡¡AND¡¡ELECTRO¡­CHEMISTRY

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What¡¡Davy¡¡really¡¡had¡¡done¡¡was¡¡to¡¡decompose¡¡the¡¡potash£»¡¡which¡¡hitherto¡¡had¡¡been¡¡supposed¡¡to¡¡be¡¡elementary£»¡¡liberating¡¡its¡¡oxygen£»¡¡and¡¡thus¡¡isolating¡¡its¡¡metallic¡¡base£»¡¡which¡¡he¡¡named¡¡potassium¡£¡¡The¡¡same¡¡thing¡¡was¡¡done¡¡with¡¡soda£»¡¡and¡¡the¡¡closely¡¡similar¡¡metal¡¡sodium¡¡was¡¡discoveredmetals¡¡of¡¡a¡¡unique¡¡type£»¡¡possessed¡¡of¡¡a¡¡strange¡¡avidity¡¡for¡¡oxygen£»¡¡and¡¡capable¡¡of¡¡seizing¡¡on¡¡it¡¡even¡¡when¡¡it¡¡is¡¡bound¡¡up¡¡in¡¡the¡¡molecules¡¡of¡¡water¡£¡¡Considered¡¡as¡¡mere¡¡curiosities£»¡¡these¡¡discoveries¡¡were¡¡interesting£»¡¡but¡¡aside¡¡from¡¡that¡¡they¡¡were¡¡of¡¡great¡¡theoretical¡¡importance£»¡¡because¡¡they¡¡showed¡¡the¡¡compound¡¡nature¡¡of¡¡some¡¡familiar¡¡chemicals¡¡that¡¡had¡¡been¡¡regarded¡¡as¡¡elements¡£¡¡¡¡Several¡¡other¡¡elementary¡¡earths¡¡met¡¡the¡¡same¡¡fate¡¡when¡¡subjected¡¡to¡¡the¡¡electrical¡¡influence£»¡¡the¡¡metals¡¡barium£»¡¡calcium£»¡¡and¡¡strontium¡¡being¡¡thus¡¡discovered¡£¡¡Thereafter¡¡Davy¡¡always¡¡referred¡¡to¡¡the¡¡supposed¡¡elementary¡¡substances¡¡£¨including¡¡oxygen£»¡¡hydrogen£»¡¡and¡¡the¡¡rest£©¡¡as¡¡¡¨unde¡­compounded¡¨¡¡bodies¡£¡¡These¡¡resist¡¡all¡¡present¡¡efforts¡¡to¡¡decompose¡¡them£»¡¡but¡¡how¡¡can¡¡one¡¡know¡¡what¡¡might¡¡not¡¡happen¡¡were¡¡they¡¡subjected¡¡to¡¡an¡¡influence£»¡¡perhaps¡¡some¡¡day¡¡to¡¡be¡¡discovered£»¡¡which¡¡exceeds¡¡the¡¡battery¡¡in¡¡power¡¡as¡¡the¡¡battery¡¡exceeds¡¡the¡¡blowpipe£¿

Another¡¡and¡¡even¡¡more¡¡important¡¡theoretical¡¡re

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