a history of science-4-第6节

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or　which　a　prize　had　been　offered　by　M。　de　Sartine；　the　chief　of　police。　This　prize　was　not　awarded　to　Lavoisier；　but　his　suggestions　were　of　such　importance　that　the　king　directed　that　a　gold　medal　be　bestowed　upon　the　young　author　at　the　public　sitting　of　the　Academy　in　April；　1776。　Two　years　later；　at　the　age　of　thirty…five；　Lavoisier　was　admitted　a　member　of　the　Academy。

In　this　same　year　he　began　to　devote　himself　almost　exclusively　to　chemical　inquiries；　and　established　a　laboratory　in　his　home；　fitted　with　all　manner　of　costly　apparatus　and　chemicals。　Here　he　was　in　constant　communication　with　the　great　men　of　science　of　Paris；　to　all　of　whom　his　doors　were　thrown　open。　One　of　his　first　undertakings　in　this　laboratory　was　to　demonstrate　that　water　could　not　be　converted　into　earth　by　repeated　distillations；　as　was　generally　advocated；　and　to　show　also　that　there　was　no　foundation　to　the　existing　belief　that　it　was　possible　to　convert　water　into　a　gas　so　〃elastic〃　as　to　pass　through　the　pores　of　a　vessel。　He　demonstrated　the　fallaciousness　of　both　these　theories　in　1768…1769　by　elaborate　experiments；　a　single　investigation　of　this　series　occupying　one　hundred　and　one　days。

In　1771　he　gave　the　first　blow　to　the　phlogiston　theory　by　his　experiments　on　the　calcination　of　metals。　It　will　be　recalled　that　one　basis　for　the　belief　in　phlogiston　was　the　fact　that　when　a　metal　was　calcined　it　was　converted　into　an　ash；　giving　up　its　〃phlogiston〃　in　the　process。　To　restore　the　metal；　it　was　necessary　to　add　some　substance　such　as　wheat　or　charcoal　to　the　ash。　　Lavoisier；　in　examining　this　process　of　restoration；　found　that　there　was　always　evolved　a　great　quantity　of　〃air；〃　which　he　supposed　to　be　〃fixed　air〃　or　carbonic　acidthe　same　that　escapes　in　effervescence　of　alkalies　and　calcareous　earths；　and　in　the　fermentation　of　liquors。　He　then　examined　the　process　of　calcination；　whereby　the　phlogiston　of　the　metal　was　supposed　to　have　been　drawn　off。　But　far　from　finding　that　phlogiston　or　any　other　substance　had　been　driven　off；　he　found　that　something　had　been　taken　on：　that　the　metal　〃absorbed　air；〃　and　that　the　increased　weight　of　the　metal　corresponded　to　the　amount　of　air　〃absorbed。〃　Meanwhile　he　was　within　grasp　of　two　great　discoveries；　that　of　oxygen　and　of　the　composition　of　the　air；　which　Priestley　made　some　two　years　later。

The　next　important　inquiry　of　this　great　Frenchman　was　as　to　the　composition　of　diamonds。　　With　the　great　lens　of　Tschirnhausen　belonging　to　the　Academy　he　succeeded　in　burning　up　several　diamonds；　regardless　of　expense；　which；　thanks　to　his　inheritance；　he　could　ignore。　In　this　process　he　found　that　a　gas　was　given　off　which　precipitated　lime　from　water；　and　proved　to　be　carbonic　acid。　　Observing　this；　and　experimenting　with　other　substances　known　to　give　off　carbonic　acid　in　the　same　manner；　he　was　evidently　impressed　with　the　now　well…known　fact　that　diamond　and　charcoal　are　chemically　the　same。　But　if　he　did　really　believe　it；　he　was　cautious　in　expressing　his　belief　fully。　　〃We　should　never　have　expected；〃　he　says；　〃to　find　any　relation　between　charcoal　and　diamond；　and　it　would　be　unreasonable　to　push　this　analogy　too　far；　it　only　exists　because　both　substances　seem　to　be　properly　ranged　in　the　class　of　combustible　bodies；　and　because　they　are　of　all　these　bodies　the　most　fixed　when　kept　from　contact　with　air。〃

As　we　have　seen；　Priestley；　in　1774；　had　discovered　oxygen；　or　〃dephlogisticated　air。〃　　Four　years　later　Lavoisier　first　advanced　his　theory　that　this　element　discovered　by　Priestley　was　the　universal　acidifying　or　oxygenating　principle；　which；　when　combined　with　charcoal　or　carbon；　formed　carbonic　acid；　when　combined　with　sulphur；　formed　sulphuric　（or　vitriolic）　acid；　with　nitrogen；　formed　nitric　acid；　etc。；　and　when　combined　with　the　metals　formed　oxides；　or　calcides。　Furthermore；　he　postulated　the　theory　that　combustion　was　not　due　to　any　such　illusive　thing　as　〃phlogiston；〃　since　this　did　not　exist；　and　it　seemed　to　him　that　the　phenomena　of　combustion　heretofore　attributed　to　phlogiston　could　be　explained　by　the　action　of　the　new　element　oxygen　and　heat。　This　was　the　final　blow　to　the　phlogiston　theory；　which；　although　it　had　been　tottering　for　some　time；　had　not　been　completely　overthrown。

In　1787　Lavoisier；　in　conjunction　with　Guyon　de　Morveau；　Berthollet；　and　Fourcroy；　introduced　the　reform　in　chemical　nomenclature　which　until　then　had　remained　practically　unchanged　since　alchemical　days。　Such　expressions　as　〃dephlogisticated〃　and　〃phlogisticated〃　would　obviously　have　little　meaning　to　a　generation　who　were　no　longer　to　believe　in　the　existence　of　phlogiston。　　It　was　appropriate　that　a　revolution　in　chemical　thought　should　be　accompanied　by　a　corresponding　revolution　in　chemical　names；　and　to　Lavoisier　belongs　chiefly　the　credit　of　bringing　about　this　revolution。　In　his　Elements　of　Chemistry　he　made　use　of　this　new　nomenclature；　and　it　seemed　so　clearly　an　improvement　over　the　old　that　the　scientific　world　hastened　to　adopt　it。　　In　this　connection　Lavoisier　says：　〃We　have；　therefore；　laid　aside　the　expression　metallic　calx　altogether；　and　have　substituted　in　its　place　the　word　oxide。　　By　this　it　may　be　seen　that　the　language　we　have　adopted　is　both　copious　and　expressive。　The　first　or　lowest　degree　of　oxygenation　in　bodies　converts　them　into　oxides；　a　second　degree　of　additional　oxygenation　constitutes　the　class　of　acids　of　which　the　specific　names　drawn　from　their　particular　bases　terminate　in　ous；　as　in　the　nitrous　and　the　sulphurous　acids。　The　third　degree　of　oxygenation　changes　these　into　the　species　of　acids　distinguished　by　the　termination　in　ic；　as　the　nitric　and　sulphuric　acids；　and；　lastly；　we　can　express　a　fourth　or　higher　degree　of　oxygenation　by　adding　the　word　oxygenated　to　the　name　of　the　acid；　as　has　already　been　done　with　oxygenated　muriatic　acid。〃＇9＇

This　new　work　when　given　to　the　world　was　not　merely　an　epoch…making　book；　it　was　revolutionary。　　It　not　only　discarded　phlogiston　altogether；　but　set　forth　that　metals　are　simple　elements；　not　compounds　of　〃earth〃　and　〃phlogiston。〃　　It　upheld　Cavendish's　demonstration　that　water　itself；　like　air；　is　a　compound　of　oxygen　with　another　element。　　In　short；　it　was　scientific　chemistry；　in　the　modern　acceptance　of　the　term。

Lavoisier's　observations　on　combustion　are　at　once　important　and　interesting：　〃Combustion；〃　he　says；　〃。　。　。　is　the　decomposition　of　oxygen　produced　by　a　combustible　body。　　The　oxygen　which　forms　the　base　of　this　gas　is　absorbed　by　and　enters　into　combination　with　the　burning　body；　while　the　caloric　and　light　are　set　free。　　Every　combustion　necessarily　supposes　oxygenation；　whereas；　on　the　contrary；　every　oxygenation　does　not　necessarily　imply　concomitant　combustion；　because　combustion　properly　so　called　cannot　take　place　without　disengagement　of　caloric　and　light。　Before　combustion　can　take　place；　it　is　necessary　that　the　base　of　oxygen　gas　should　have　greater　affinity　to　the　combustible　body　than　it　has　to　caloric；　and　this　elective　attraction；　to　use　Bergman's　expression；　can　only　take　place　at　a　certain　degree　of　temperature　which　is　different　for　each　combustible　substance；　hence　the　necessity　of　giving　the　first　motion　or　beginning　to　every　combustion　by　the　approach　of　a　heated　body。　This　necessity　of　heating　any　body　we　mean　to　burn　depends　upon　certain　considerations　which　have　not　hitherto　been　attended　to　by　any　natural　philosopher；　for　which　reason　I　shall　enlarge　a　little　upon　the　subject　in　this　place：

〃Nature　is　at　present　in　a　state　of　equilibrium；　which　cannot　have　been　attained　until　all　the　spontaneous　combustions　or　oxygenations　possible　in　an　ordinary　degree　of　temperature　had　taken　place。。。。　To　illustrate　this　abstract　view　of　the　matter　by　example：　Let　us　suppose　the　usual　temperature　of　the　earth　a　little　changed；　and　it　is　raised　only　to　the　degree　of　boiling　water；　it　is　evident　that　in　this　case　phosphorus；　which　is　combustible　in　a　considerably　lower　degree　of　temperature；　would　no　longer　exist　in　nature　in　its　pure　and　simple　state；　but　would　always　be　procured　in　its　acid　or　oxygenated　state；　and　its　radical　would　become　one　of　the　substances　unknown　to　chemistry。　By　gradually　increasing　the　temperature　of　the　earth；　the　same　circumstance　would　successively　happen　to　all　the　bodies　capable　of　combustion；　and；　at　the　last；　every　possible　combustion　having　taken　place；　there　would　no　longer　exist　any　combustible　body　whatever；　and　every　substance　susceptible　of　the　operation　would　be　oxygenated　and　consequently　incombustible。

〃There　cannot；　therefore；　exist；　as　far　as　relates　to　us；　any　combustible　body　but　such　as　are　non…combustible　at　the　ordinary　temperature　of　the　earth；　or；　what　is　the　same　thing　in　other　words；　that　it　is　essential　to　the　nature　of　every　combustible　body　not　to　possess　the　property　of　combustion　unless　heated；　or　raised　to　a　degree　of　temperature　at　which　its　combustion　naturally　takes　place。　When　this　degree　is　once　produced；　combustion　commences；　and　the　caloric　which　is　disengaged　by　the　decomposition　of　the　oxygen　gas　keeps　up　the　temperature　which　is　necessary　for　continuing　combustion。　When　this　is　not　the　casethat　is；　when　the　dis