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erature¡¡which¡¡is¡¡necessary¡¡for¡¡continuing¡¡combustion¡£¡¡When¡¡this¡¡is¡¡not¡¡the¡¡casethat¡¡is£»¡¡when¡¡the¡¡disengaged¡¡caloric¡¡is¡¡not¡¡sufficient¡¡for¡¡keeping¡¡up¡¡the¡¡necessary¡¡temperaturethe¡¡combustion¡¡ceases¡£¡¡This¡¡circumstance¡¡is¡¡expressed¡¡in¡¡the¡¡common¡¡language¡¡by¡¡saying¡¡that¡¡a¡¡body¡¡burns¡¡ill¡¡or¡¡with¡¡difficulty¡£¡¨£§10£§


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III¡£¡¡CHEMISTRY¡¡SINCE¡¡THE¡¡TIME¡¡OF¡¡DALTON

JOHN¡¡DALTON¡¡AND¡¡THE¡¡ATOMIC¡¡THEORY

Small¡¡beginnings¡¡as¡¡have¡¡great¡¡endingssometimes¡£¡¡¡¡As¡¡a¡¡case¡¡in¡¡point£»¡¡note¡¡what¡¡came¡¡of¡¡the¡¡small£»¡¡original¡¡effort¡¡of¡¡a¡¡self¡­trained¡¡back¡­country¡¡Quaker¡¡youth¡¡named¡¡John¡¡Dalton£»¡¡who¡¡along¡¡towards¡¡the¡¡close¡¡of¡¡the¡¡eighteenth¡¡century¡¡became¡¡interested¡¡in¡¡the¡¡weather£»¡¡and¡¡was¡¡led¡¡to¡¡construct¡¡and¡¡use¡¡a¡¡crude¡¡water¡­gauge¡¡to¡¡test¡¡the¡¡amount¡¡of¡¡the¡¡rainfall¡£¡¡The¡¡simple¡¡experiments¡¡thus¡¡inaugurated¡¡led¡¡to¡¡no¡¡fewer¡¡than¡¡two¡¡hundred¡¡thousand¡¡recorded¡¡observations¡¡regarding¡¡the¡¡weather£»¡¡which¡¡formed¡¡the¡¡basis¡¡for¡¡some¡¡of¡¡the¡¡most¡¡epochal¡¡discoveries¡¡in¡¡meteorology£»¡¡as¡¡we¡¡have¡¡seen¡£¡¡¡¡But¡¡this¡¡was¡¡only¡¡a¡¡beginning¡£¡¡The¡¡simple¡¡rain¡­gauge¡¡pointed¡¡the¡¡way¡¡to¡¡the¡¡most¡¡important¡¡generalization¡¡of¡¡the¡¡nineteenth¡¡century¡¡in¡¡a¡¡field¡¡of¡¡science¡¡with¡¡which£»¡¡to¡¡the¡¡casual¡¡observer£»¡¡it¡¡might¡¡seem¡¡to¡¡have¡¡no¡¡alliance¡¡whatever¡£¡¡¡¡The¡¡wonderful¡¡theory¡¡of¡¡atoms£»¡¡on¡¡which¡¡the¡¡whole¡¡gigantic¡¡structure¡¡of¡¡modern¡¡chemistry¡¡is¡¡founded£»¡¡was¡¡the¡¡logical¡¡outgrowth£»¡¡in¡¡the¡¡mind¡¡of¡¡John¡¡Dalton£»¡¡of¡¡those¡¡early¡¡studies¡¡in¡¡meteorology¡£

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It¡¡was¡¡about¡¡the¡¡year¡¡1803¡¡that¡¡Dalton¡¡first¡¡gained¡¡a¡¡full¡¡grasp¡¡of¡¡the¡¡conception¡¡of¡¡the¡¡chemical¡¡atom¡£¡¡¡¡At¡¡once¡¡he¡¡saw¡¡that¡¡the¡¡hypothesis£»¡¡if¡¡true£»¡¡furnished¡¡a¡¡marvellous¡¡key¡¡to¡¡secrets¡¡of¡¡matter¡¡hitherto¡¡insolublequestions¡¡relating¡¡to¡¡the¡¡relative¡¡proportions¡¡of¡¡the¡¡atoms¡¡themselves¡£¡¡It¡¡is¡¡known£»¡¡for¡¡example£»¡¡that¡¡a¡¡certain¡¡bulk¡¡of¡¡hydrogen¡¡gas¡¡unites¡¡with¡¡a¡¡certain¡¡bulk¡¡of¡¡oxygen¡¡gas¡¡to¡¡form¡¡water¡£¡¡If¡¡it¡¡be¡¡true¡¡that¡¡this¡¡combination¡¡consists¡¡essentially¡¡of¡¡the¡¡union¡¡of¡¡atoms¡¡one¡¡with¡¡another¡¡£¨each¡¡single¡¡atom¡¡of¡¡hydrogen¡¡united¡¡to¡¡a¡¡single¡¡atom¡¡of¡¡oxygen£©£»¡¡then¡¡the¡¡relative¡¡weights¡¡of¡¡the¡¡original¡¡masses¡¡of¡¡hydrogen¡¡and¡¡of¡¡oxygen¡¡must¡¡be¡¡also¡¡the¡¡relative¡¡weights¡¡of¡¡each¡¡of¡¡their¡¡respective¡¡atoms¡£¡¡If¡¡one¡¡pound¡¡of¡¡hydrogen¡¡unites¡¡with¡¡five¡¡and¡¡one¡­half¡¡pounds¡¡of¡¡oxygen¡¡£¨as£»¡¡according¡¡to¡¡Dalton's¡¡experiments£»¡¡it¡¡did£©£»¡¡then¡¡the¡¡weight¡¡of¡¡the¡¡oxygen¡¡atom¡¡must¡¡be¡¡five¡¡and¡¡one¡­half¡¡times¡¡that¡¡of¡¡the¡¡hydrogen¡¡atom¡£¡¡Other¡¡compounds¡¡may¡¡plainly¡¡be¡¡tested¡¡in¡¡the¡¡same¡¡way¡£¡¡Dalton¡¡made¡¡numerous¡¡tests¡¡before¡¡he¡¡published¡¡his¡¡theory¡£¡¡He¡¡found¡¡that¡¡hydrogen¡¡enters¡¡into¡¡compounds¡¡in¡¡smaller¡¡proportions¡¡than¡¡any¡¡other¡¡element¡¡known¡¡to¡¡him£»¡¡and¡¡so£»¡¡for¡¡convenience£»¡¡determined¡¡to¡¡take¡¡the¡¡weight¡¡of¡¡the¡¡hydrogen¡¡atom¡¡as¡¡unity¡£¡¡¡¡The¡¡atomic¡¡weight¡¡of¡¡oxygen¡¡then¡¡becomes¡¡£¨as¡¡given¡¡in¡¡Dalton's¡¡first¡¡table¡¡of¡¡1803£©¡¡5¡£5£»¡¡that¡¡of¡¡water¡¡£¨hydrogen¡¡plus¡¡oxygen£©¡¡being¡¡of¡¡course¡¡6¡£5¡£¡¡The¡¡atomic¡¡weights¡¡of¡¡about¡¡a¡¡score¡¡of¡¡substances¡¡are¡¡given¡¡in¡¡Dalton's¡¡first¡¡paper£»¡¡which¡¡was¡¡read¡¡before¡¡the¡¡Literary¡¡and¡¡Philosophical¡¡Society¡¡of¡¡Manchester£»¡¡October¡¡21£»¡¡1803¡£¡¡¡¡I¡¡wonder¡¡if¡¡Dalton¡¡himself£»¡¡great¡¡and¡¡acute¡¡intellect¡¡though¡¡he¡¡had£»¡¡suspected£»¡¡when¡¡he¡¡read¡¡that¡¡paper£»¡¡that¡¡he¡¡was¡¡inaugurating¡¡one¡¡of¡¡the¡¡most¡¡fertile¡¡movements¡¡ever¡¡entered¡¡on¡¡in¡¡the¡¡whole¡¡history¡¡of¡¡science£¿

Be¡¡that¡¡as¡¡it¡¡may£»¡¡it¡¡is¡¡certain¡¡enough¡¡that¡¡Dalton's¡¡contemporaries¡¡were¡¡at¡¡first¡¡little¡¡impressed¡¡with¡¡the¡¡novel¡¡atomic¡¡theory¡£¡¡Just¡¡at¡¡this¡¡time£»¡¡as¡¡it¡¡chanced£»¡¡a¡¡dispute¡¡was¡¡waging¡¡in¡¡the¡¡field¡¡of¡¡chemistry¡¡regarding¡¡a¡¡matter¡¡of¡¡empirical¡¡fact¡¡which¡¡must¡¡necessarily¡¡be¡¡settled¡¡before¡¡such¡¡a¡¡theory¡¡as¡¡that¡¡of¡¡Dalton¡¡could¡¡even¡¡hope¡¡for¡¡a¡¡bearing¡£¡¡¡¡This¡¡was¡¡the¡¡question¡¡whether¡¡or¡¡not¡¡chemical¡¡elements¡¡unite¡¡with¡¡one¡¡another¡¡always¡¡in¡¡definite¡¡proportions¡£¡¡Berthollet£»¡¡the¡¡great¡¡co¡­worker¡¡with¡¡Lavoisier£»¡¡and¡¡now¡¡the¡¡most¡¡authoritative¡¡of¡¡living¡¡chemists£»¡¡contended¡¡that¡¡substances¡¡combine¡¡in¡¡almost¡¡indefinitely¡¡graded¡¡proportions¡¡between¡¡fixed¡¡extremes¡£¡¡He¡¡held¡¡that¡¡solution¡¡is¡¡really¡¡a¡¡form¡¡of¡¡chemical¡¡combinationa¡¡position¡¡which£»¡¡if¡¡accepted£»¡¡left¡¡no¡¡room¡¡for¡¡argument¡£

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More¡¡than¡¡that¡£¡¡¡¡As¡¡the¡¡analysts¡¡were¡¡led¡¡to¡¡weigh¡¡carefully¡¡the¡¡quantities¡¡of¡¡combining¡¡elements£»¡¡it¡¡was¡¡observed¡¡that¡¡the¡¡proportions¡¡are¡¡not¡¡only¡¡definite£»¡¡but¡¡that¡¡they¡¡bear¡¡a¡¡very¡¡curious¡¡relation¡¡to¡¡one¡¡another¡£¡¡If¡¡element¡¡A¡¡combines¡¡with¡¡two¡¡different¡¡proportions¡¡of¡¡element¡¡B¡¡to¡¡form¡¡two¡¡compounds£»¡¡it¡¡appears¡¡that¡¡the¡¡weight¡¡of¡¡the¡¡larger¡¡quantity¡¡of¡¡B¡¡is¡¡an¡¡exact¡¡multiple¡¡of¡¡that¡¡of¡¡the¡¡smaller¡¡quantity¡£¡¡This¡¡curious¡¡relation¡¡was¡¡noticed¡¡by¡¡Dr¡£¡¡Wollaston£»¡¡one¡¡of¡¡the¡¡most¡¡accurate¡¡of¡¡observers£»¡¡and¡¡a¡¡little¡¡later¡¡it¡¡was¡¡confirmed¡¡by¡¡Johan¡¡Jakob¡¡Berzelius£»¡¡the¡¡great¡¡Swedish¡¡chemist£»¡¡who¡¡was¡¡to¡¡be¡¡a¡¡dominating¡¡influence¡¡in¡¡the¡¡chemical¡¡world¡¡for¡¡a¡¡generation¡¡to¡¡come¡£¡¡¡¡But¡¡this¡¡combination¡¡of¡¡elements¡¡in¡¡numerical¡¡proportions¡¡was¡¡exactly¡¡what¡¡Dalton¡¡had¡¡noticed¡¡as¡¡early¡¡as¡¡1802£»¡¡and¡¡what¡¡bad¡¡led¡¡him¡¡directly¡¡to¡¡the¡¡atomic¡¡weights¡£¡¡So¡¡the¡¡confirmation¡¡of¡¡this¡¡essential¡¡point¡¡by¡¡chemists¡¡of¡¡such¡¡authority¡¡gave¡¡the¡¡strongest¡¡confirmation¡¡to¡¡the¡¡atomic¡¡theory¡£

During¡¡these¡¡same¡¡years¡¡the¡¡rising¡¡authority¡¡of¡¡the¡¡French¡¡chemical¡¡world£»¡¡Joseph¡¡Louis¡¡Gay¡­Lussac£»¡¡was¡¡conducting¡¡experiments¡¡with¡¡gases£»¡¡which¡¡he¡¡had¡¡undertaken¡¡at¡¡first¡¡in¡¡conjunction¡¡with¡¡Humboldt£»¡¡but¡¡which¡¡later¡¡on¡¡were¡¡conducted¡¡independently¡£¡¡In¡¡1809£»¡¡the¡¡next¡¡year¡¡after¡¡the¡¡publication¡¡of¡¡the¡¡first¡¡volume¡¡of¡¡Dalton's¡¡New¡¡System¡¡of¡¡Chemical¡¡Philosophy£»¡¡Gay¡­Lussac¡¡published¡¡the¡¡results¡¡of¡¡his¡¡observations£»¡¡and¡¡among¡¡other¡¡things¡¡brought¡¡out¡¡the¡¡remarkable¡¡fact¡¡that¡¡gases£»¡¡under¡¡the¡¡same¡¡conditions¡¡as¡¡to¡¡temperature¡¡and¡¡pressure£»¡¡combine¡¡always¡¡in¡¡definite¡¡numerical¡¡proportions¡¡as¡¡to¡¡volume¡£¡¡Exactly¡¡two¡¡volumes¡¡of¡¡hydrogen£»¡¡for¡¡exam

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