a history of science-4-第6章

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ds　prepared　that　had　been　hitherto　unknown。　　His　explanations　of　chemical　phenomena　were　based　on　the　phlogiston　theory；　in　which；　like　Priestley；　he　always；　believed。　　Although　in　error　in　this　respect；　he　was；　nevertheless；　able　to　make　his　discoveries　with　extremely　accurate　interpretations。　A　brief　epitome　of　the　list　of　some　of　his　more　important　discoveries　conveys　some　idea；　of　his　fertility　of　mind　as　well　as　his　industry。　　In　1780　he　discovered　lactic　acid；＇7＇　and　showed　that　it　was　the　substance　that　caused　the　acidity　of　sour　milk；　and　in　the　same　year　he　discovered　mucic　acid。　Next　followed　the　discovery　of　tungstic　acid；　and　in　1783　he　added　to　his　list　of　useful　discoveries　that　of　glycerine。　Then　in　rapid　succession　came　his　announcements　of　the　new　vegetable　products　citric；　malic；　oxalic；　and　gallic　acids。　Scheele　not　only　made　the　discoveries；　but　told　the　world　how　he　had　made　themhow　any　chemist　might　have　made　them　if　he　chosefor　he　never　considered　that　he　had　really　discovered　any　substance　until　he　had　made　it；　decomposed　it；　and　made　it　again。

His　experiments　on　Prussian　blue　are　most　interesting；　not　only　because　of　the　enormous　amount　of　work　involved　and　the　skill　he　displayed　in　his　experiments；　but　because　all　the　time　the　chemist　was　handling；　smelling；　and　even　tasting　a　compound　of　one　of　the　most　deadly　poisons；　ignorant　of　the　fact　that　the　substance　was　a　dangerous　one　to　handle。　His　escape　from　injury　seems　almost　miraculous；　for　his　experiments；　which　were　most　elaborate；　extended　over　a　considerable　period　of　time；　during　which　he　seems　to　have　handled　this　chemical　with　impunity。

While　only　forty　years　of　age　and　just　at　the　zenith　of　his　fame；　Scheele　was　stricken　by　a　fatal　illness；　probably　induced　by　his　ceaseless　labor　and　exposure。　　It　is　gratifying　to　know；　however；　that　during　the　last　eight　or　nine　years　of　his　life　he　had　been　less　bound　down　by　pecuniary　difficulties　than　before；　as　Bergman　had　obtained　for　him　an　annual　grant　from　the　Academy。　　But　it　was　characteristic　of　the　man　that；　while　devoting　one…sixth　of　the　amount　of　this　grant　to　his　personal　wants；　the　remaining　five…sixths　was　devoted　to　the　expense　of　his　experiments。


LAVOISIER　AND　THE　FOUNDATION　OF　MODERN　CHEMISTRY

The　time　was　ripe　for　formulating　the　correct　theory　of　chemical　composition：　it　needed　but　the　master　hand　to　mould　the　materials　into　the　proper　shape。　The　discoveries　in　chemistry　during　the　eighteenth　century　had　been　far…reaching　and　revolutionary　in　character。　　A　brief　review　of　these　discoveries　shows　how　completely　they　had　subverted　the　old　ideas　of　chemical　elements　and　chemical　compounds。　　Of　the　four　substances　earth；　air；　fire；　and　water；　for　many　centuries　believed　to　be　elementary　bodies；　not　one　has　stood　the　test　of　the　eighteenth…century　chemists。　Earth　had　long　since　ceased　to　be　regarded　as　an　element；　and　water　and　air　had　suffered　the　same　fate　in　this　century。　　And　now　at　last　fire　itself；　the　last　of　the　four　〃elements〃　and　the　keystone　to　the　phlogiston　arch；　was　shown　to　be　nothing　more　than　one　of　the　manifestations　of　the　new　element；　oxygen；　and　not　〃phlogiston〃　or　any　other　intangible　substance。

In　this　epoch　of　chemical　discoveries　England　had　produced　such　mental　giants　and　pioneers　in　science　as　Black；　Priestley；　and　Cavendish；　Sweden　had　given　the　world　Scheele　and　Bergman；　whose　work；　added　to　that　of　their　English　confreres；　had　laid　the　broad　base　of　chemistry　as　a　science；　but　it　was　for　France　to　produce　a　man　who　gave　the　final　touches　to　the　broad　but　rough　workmanship　of　its　foundation；　and　establish　it　as　the　science　of　modern　chemistry。　　It　was　for　Antoine　Laurent　Lavoisier　（1743…1794）　to　gather　together；　interpret　correctly；　rename；　and　classify　the　wealth　of　facts　that　his　immediate　predecessors　and　contemporaries　had　given　to　the　world。

The　attitude　of　the　mother…countries　towards　these　illustrious　sons　is　an　interesting　piece　of　history。　　Sweden　honored　and　rewarded　Scheele　and　Bergman　for　their　efforts；　England　received　the　intellectuality　of　Cavendish　with　less　appreciation　than　the　Continent；　and　a　fanatical　mob　drove　Priestley　out　of　the　country；　while　France；　by　sending　Lavoisier　to　the　guillotine；　demonstrated　how　dangerous　it　was；　at　that　time　at　least；　for　an　intelligent　Frenchman　to　serve　his　fellowman　and　his　country　well。

〃The　revolution　brought　about　by　Lavoisier　in　science；〃　says　Hoefer；　〃coincides　by　a　singular　act　of　destiny　with　another　revolution；　much　greater　indeed；　going　on　then　in　the　political　and　social　world。　Both　happened　on　the　same　soil；　at　the　same　epoch；　among　the　same　people；　and　both　marked　the　commencement　of　a　new　era　in　their　respective　spheres。〃＇8＇

Lavoisier　was　born　in　Paris；　and　being　the　son　of　an　opulent　family；　was　educated　under　the　instruction　of　the　best　teachers　of　the　day。　With　Lacaille　he　studied　mathematics　and　astronomy；　with　Jussieu；　botany；　and；　finally；　chemistry　under　Rouelle。　　His　first　work　of　importance　was　a　paper　on　the　practical　illumination　of　the　streets　of　Paris；　for　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　w