第22章

THE"PNEUMATIC"CHEMISTS

ModernchemistrymaybesaidtohaveitsbeginningwiththeworkofStephenHales(1677-1761)，whoearlyintheeighteenthcenturybeganhisimportantstudyoftheelasticityofair。Departingfromthepointofviewofmostofthescientistsofthetime，beconsideredairtobe"afineelasticfluid，withparticlesofverydifferentnaturefloatinginit"；andheshowedthatthese"particles"couldbeseparated。Hepointedout，also，thatvariousgases，or"airs，"ashecalledthem，werecontainedinmanysolidsubstances。Theimportanceofhiswork，however，liesinthefactthathisgeneralstudieswerealonglinesleadingawayfromtheaccepteddoctrinesofthetime，andthattheygavetheimpetustotheinvestigationofthepropertiesofgasesbysuchchemistsasBlack，Priestley，Cavendish，andLavoisier，whosespecificdiscoveriesarethefoundation-stonesofmodernchemistry。

JOSEPHBLACK

ThecarefulstudiesofHaleswerecontinuedbyhisyoungerconfrere，Dr。JosephBlack(1728-1799)，whoseexperimentsintheweightsofgasesandotherchemicalswerefirststepsinquantitativechemistry。Butevenmoreimportantthanhisdiscoveriesofchemicalpropertiesingeneralwashisdiscoveryofthepropertiesofcarbonic-acidgas。

BlackhadbeeneducatedforthemedicalprofessionintheUniversityofGlasgow，beingafriendandpupilofthefamousDr。

WilliamCullen。Buthislikingwasforthechemicallaboratoryratherthanforthepracticeofmedicine。Withinthreeyearsaftercompletinghismedicalcourse，andwhenonlytwenty-threeyearsofage，hemadethediscoveryofthepropertiesofcarbonicacid，whichhecalledbythenameof"fixedair。"Afterdiscoveringthisgas，Blackmadealongseriesofexperiments，bywhichhewasabletoshowhowwidelyitwasdistributedthroughoutnature。Thus，in1757，bediscoveredthatthebubblesgivenoffintheprocessofbrewing，wheretherewasvegetablefermentation，werecomposedofit。Toprovethis，hecollectedthecontentsofthesebubblesinabottlecontaininglime-water。

Whenthisbottlewasshakenviolently，sothatthelime-waterandthecarbonicacidbecamethoroughlymixed，aninsolublewhitepowderwasprecipitatedfromthesolution，thecarbonicacidhavingcombinedchemicallywiththelimetoformtheinsolublecalciumcarbonate，orchalk。Thisexperimentsuggestedanother。

Fixingapieceofburningcharcoalintheendofabellows，hearrangedatubesothatthegascomingfromthecharcoalwouldpassthroughthelime-water，and，asinthecaseofthebubblesfromthebrewer’svat，hefoundthatthewhiteprecipitatewasthrowndown；inshort，thatcarbonicacidwasgivenoffincombustion。Shortlyafter，Blackdiscoveredthatbyblowingthroughaglasstubeinsertedintolime-water，chalkwasprecipitated，thusprovingthatcarbonicacidwasbeingconstantlythrownoffinrespiration。

TheeffectofBlack’sdiscoverieswasrevolutionary，andtheattitudeofmindofthechemiststowardsgases，or"airs，"waschangedfromthattimeforward。Mostofthechemists，however，attemptedtoharmonizethenewfactswiththeoldertheories——toexplainallthephenomenaonthebasisofthephlogistontheory，whichwasstilldominant。ButwhilemanyofBlack’sdiscoveriescouldnotbemadetoharmonizewiththattheory，theydidnotdirectlyoverthrowit。ItrequiredtheadditionaldiscoveriesofsomeofBlack’sfellow-scientiststocompleteitsdownfall，asweshallsee。

HENRYCAVENDISH

ThisworkofBlack’swasfollowedbytheequallyimportantworkofhisformerpupil，HenryCavendish(1731-1810)，whosediscoveryofthecompositionofmanysubstances，notablyofnitricacidandofwater，wasofgreatimportance，addinganotherlinktotheimportantchainofevidenceagainstthephlogistontheory。

Cavendishisoneofthemosteccentricfiguresinthehistoryofscience，beingwidelyknowninhisowntimeforhisimmensewealthandbrilliantintellect，andalsoforhispeculiaritiesandhismorbidsensibility，whichmadehimdreadsociety，andprobablydidmuchindetermininghiscareer。Fortunatelyforhim，andincidentallyforthecauseofscience，hewasabletopursuelaboratoryinvestigationswithoutbeingobligedtominglewithhisdreadedfellow-mortals，hiseverywantbeingprovidedforbytheimmensefortuneinheritedfromhisfatherandanuncle。

Whenayoungman，asapupilofDr。Black，hehadbecomeimbuedwiththeenthusiasmofhisteacher，continuingBlack’sinvestigationsastothepropertiesofcarbonic-acidgaswhenfreeandincombination。Oneofhisfirstinvestigationswasreportedin1766，whenhecommunicatedtotheRoyalSocietyhisexperimentsforascertainingthepropertiesofcarbonic-acidandhydrogengas，inwhichhefirstshowedthepossibilityofweighingpermanentlyelasticfluids，althoughTorricellihadbeforethisshowntherelativeweightsofacolumnofairandacolumnofmercury。OtherimportantexperimentswerecontinuedbyCavendish，andin1784heannouncedhisdiscoveryofthecompositionofwater，thusrobbingitofitstime-honoredpositionasan"element。"Buthisclaimtopriorityinthisdiscoverywasatoncedisputedbyhisfellow-countrymanJamesWattandbytheFrenchmanLavoisier。Lavoisier’sclaimwassoondisallowedevenbyhisowncountrymen，butformanyyearsabittercontroversywascarriedonbythepartisansofWattandCavendish。Thetwoprincipals，however，seem。nevertohaveenteredintothiscontroversywithanythinglikethesameardorassomeoftheirsuccessors，astheyremainedonthebestofterms。[1]Itiscertain，atanyrate，thatCavendishannouncedhisdiscoveryofficiallybeforeWattclaimedthattheannouncementhadbeenpreviouslymadebyhim，"and，whetherrightorwrong，thehonorofscientificdiscoveriesseemstobeaccordednaturallytothemanwhofirstpublishesademonstrationofhisdiscovery。"EnglishmenverygenerallyadmitthejustnessofCavendish’sclaim，althoughtheFrenchscientistArago，afterreviewingtheevidencecarefullyin1833，decidedinfavorofWatt。

ItappearsthatsomethinglikeayearbeforeCavendishmadeknownhiscompletedemonstrationofthecompositionofwater，WattcommunicatedtotheRoyalSocietyasuggestionthatwaterwascomposedof"dephlogisticatedair(oxygen)andphlogiston(hydrogen)deprivedofpartofitslatentheat。"Cavendishknewofthesuggestion，butinhisexperimentsrefutedtheideathatthehydrogenlostanyofitslatentheat。Furthermore，Wattmerelysuggestedthepossiblecompositionwithoutprovingit，althoughhisideawaspracticallycorrect，ifwecanrightlyinterpretthevagariesofthenomenclaturetheninuse。ButhadWatttakenthestepstodemonstratehistheory，thegreat"WaterControversy"wouldhavebeenavoided。Cavendish’sreportofhisdiscoverytotheRoyalSocietycoverssomethinglikefortypagesofprintedmatter。Inthisheshowshow，bypassinganelectricsparkthroughaclosedjarcontainingamixtureofhydrogengasandoxygen，waterisinvariablyformed，apparentlybytheunionofthetwogases。Theexperimentwasfirsttriedwithhydrogenandcommonair，theoxygenoftheairunitingwiththehydrogentoformwater，leavingthenitrogenoftheairstilltobeaccountedfor。Withpureoxygenandhydrogen，however，Cavendishfoundthatpurewaterwasformed，leavingslighttracesofanyother，substancewhichmightnotbeinterpretedasbeingChemicalimpurities。Therewasonlyonepossibleexplanationofthisphenomenon——thathydrogenandoxygen，whencombined，formwater。

"Byexperimentswiththeglobeitappeared，"wroteCavendish，"thatwheninflammableandcommonairareexplodedinaproperproportion，almostalltheinflammableair，andnearone-fifththecommonair，losetheirelasticityandarecondensedintodew。

Andbythisexperimentitappearsthatthisdewisplainwater，andconsequentlythatalmostalltheinflammableairisturnedintopurewater。

"Inordertoexaminethenatureofthemattercondensedonfiringamixtureofdephlogisticatedandinflammableair，Itookaglassglobe，holding8800grainmeasures，furnishedwithabrasscockandanapparatusforfiringbyelectricity。Thisglobewaswellexhaustedbyanair-pump，andthenfilledwithamixtureofinflammableanddephlogisticatedairbyshuttingthecock，fasteningthebentglasstubeintoitsmouth，andlettinguptheendofitintoaglassjarinvertedintowaterandcontainingamixtureof19，500grainmeasuresofdephlogisticatedair，and37，000ofinflammableair；sothat，uponopeningthecock，someofthismixedairrushedthroughthebenttubeandfilledtheglobe。Thecockwasthenshutandtheincludedairfiredbyelectricity，bymeansofwhichalmostallofitlostitselasticity(wascondensedintowatervapors)。Thecockwasthenagainopenedsoastoletinmoreofthesameairtosupplytheplaceofthatdestroyedbytheexplosion，whichwasagainfired，andtheoperationcontinuedtillalmostthewholeofthemixturewasletintotheglobeandexploded。Bythismeans，thoughtheglobeheldnotmorethanasixthpartofthemixture，almostthewholeofitwasexplodedthereinwithoutanyfreshexhaustionoftheglobe。"

Atfirstthiscondensedmatterwas"acidtothetasteandcontainedtwograinsofnitre，"butCavendish，suspectingthatthiswasduetoimpurities，triedanotherexperimentthatprovedconclusivelythathisopinionswerecorrect。"Ithereforemadeanotherexperiment，"hesays，"withsomemoreofthesameairfromplantsinwhichtheproportionofinflammableairwasgreater，sothattheburntairwasalmostcompletelyphlogisticated，itsstandardbeingone-tenth。Thecondensedliquorwasthennotatallacid，butseemedpurewater。"

Fromtheseexperimentsheconcludes"thatwhenamixtureofinflammableanddephlogisticatedairisexploded，insuchproportionsthattheburntairisnotmuchphlogisticated，thecondensedliquorcontainsalittleacidwhichisalwaysofthenitrouskind，whateversubstancethedephlogisticatedairisprocuredfrom；butiftheproportionbesuchthattheburntairisalmostentirelyphlogisticated，thecondensedliquorisnotatallacid，butseemspurewater，withoutanyadditionwhatever。"[2]

Thesesameexperiments，whichwereundertakentodiscoverthecompositionofwater，ledhimtodiscoveralsothecompositionofnitricacid。Hehadobservedthat，inthecombustionofhydrogengaswithcommonair，thewaterwasslightlytingedwithacid，butthatthiswasnotthecasewhenpureoxygengaswasused。Actinguponthisobservation，hedevisedanexperimenttodeterminethenatureofthisacid。Heconstructedanapparatuswherebyanelectricsparkwaspassedthroughavesselcontainingcommonair。

Afterthisprocesshadbeencarriedonforseveralweeksasmallamountofliquidwasformed。Thisliquidcombinedwithasolutionofpotashtoformcommonnitre，which"detonatedwithcharcoal，sparkledwhenpaperimpregnatedwithitwasburned，andgaveoutnitrousfumeswhensulphuricacidwaspouredonit。"Inotherwords，theliquidwasshowntobenitricacid。Now，sincenothingbutpureairhadbeenusedintheinitialexperiment，andsinceairiscomposedofnitrogenandoxygen，thereseemednoroomtodoubtthatnitricacidisacombinationofnitrogenandoxygen。

ThisdiscoveryofthenatureofnitricacidseemstohavebeenaboutthelastworkofimportancethatCavendishdidinthefieldofchemistry，althoughalmosttothehourofhisdeathhewasconstantlyoccupiedwithscientificobservations。Eveninthelastmomentsofhislifethishabitasserteditself，accordingtoLordBrougham。"HediedonMarch10，1810，afterashortillness，probablythefirst，aswellasthelast，whichheeversuffered。Hishabitofcuriousobservationcontinuedtotheend。

Hewasdesirousofmarkingtheprogressofthediseaseandthegradualextinctionofthevitalpowers。Withtheseendsinview，thathemightnotbedisturbed，hedesiredtobeleftalone。Hisservant，returningsoonerthanhehadwished，wasorderedagaintoleavethechamberofdeath，andwhenbecamebackasecondtimehefoundhismasterhadexpired。[3]

JOSEPHPRIESTLEY

WhiletheopulentbutdiffidentCavendishwasmakinghisimportantdiscoveries，anotherEnglishman，apoorcountrypreachernamedJosephPriestley(1733-1804)wasnotonlyrivallinghim，but，ifanything，outstrippinghiminthepursuitofchemicaldiscoveries。In1761thisyoungministerwasgivenapositionastutorinanonconformistacademyatWarrington，andhere，forsixyears，hewasabletopursuehisstudiesinchemistryandelectricity。In1766，whileonavisittoLondon，hemetBenjaminFranklin，atwhosesuggestionhepublishedhisHistoryofElectricity。Fromthistimeonhemadesteadyprogressinscientificinvestigations，keepinguphisecclesiasticaldutiesatthesametime。In1780heremovedtoBirmingham，havingthereforassociatessuchscientistsasJamesWatt，Boulton，andErasmusDarwin。

Elevenyearslater，ontheanniversaryofthefalloftheBastileinParis，afanaticalmob，knowingPriestley’ssympathieswiththeFrenchrevolutionists，attackedhishouseandchapel，burningbothanddestroyingagreatnumberofvaluablepapersandscientificinstruments。Priestleyandhisfamilyescapedviolencebyflight，buthismostcherishedpossessionsweredestroyed；andthreeyearslaterhequittedEnglandforever，removingtotheUnitedStates，whosestruggleforlibertyhehadchampioned。ThelasttenyearsofhislifewerespentatNorthumberland，Pennsylvania，wherehecontinuedhisscientificresearches。

EarlyinhisscientificcareerPriestleybeganinvestigationsuponthe"fixedair"ofDr。Black，and，oddlyenough，hewasstimulatedtothisbythesamethingthathadinfluencedBlack——thatis，hisresidenceintheimmediateneighborhoodofabrewery。Itwasduringthecourseofaseriesofexperimentsonthisandothergasesthathemadehisgreatestdiscovery，thatofoxygen，or"dephlogisticatedair，"ashecalledit。ThestoryofthisimportantdiscoveryisprobablybesttoldinPriestley’sownwords:

"Thereare，Ibelieve，veryfewmaximsinphilosophythathavelaidfirmerholduponthemindthanthatair，meaningatmosphericair，isasimpleelementarysubstance，indestructibleandunalterable，atleastasmuchsoaswaterissupposedtobe。InthecourseofmyinquiriesIwas，however，soonsatisfiedthatatmosphericairisnotanunalterablething；forthat，accordingtomyfirsthypothesis，thephlogistonwithwhichitbecomesloadedfrombodiesburninginit，andtheanimalsbreathingit，andvariousotherchemicalprocesses，sofaraltersanddepravesitastorenderitaltogetherunfitforinflammation，respiration，andotherpurposestowhichitissubservient；andI

haddiscoveredthatagitationinthewater，theprocessofvegetation，andprobablyothernaturalprocesses，restoreittoitsoriginalpurity……

"Havingprocuredalensoftwelveinchesdiameterandtwentyincheslocaldistance，Iproceededwiththegreatestalacrity，bythehelpofit，todiscoverwhatkindofairagreatvarietyofsubstanceswouldyield，puttingthemintothevessel，whichI

filledwithquicksilver，andkeptinvertedinabasinofthesame……Withthisapparatus，afteravarietyofexperiments……onthe1stofAugust，1774，Iendeavoredtoextractairfrommercuriuscalcinatusperse；andIpresentlyfoundthat，bymeansofthislens，airwasexpelledfromitveryreadily。Havinggotaboutthreeorfourtimesasmuchasthebulkofmymaterials，I

admittedwatertoit，andfoundthatitwasnotimbibedbyit。

ButwhatsurprisedmemorethanIcanexpresswasthatacandleburnedinthisairwitharemarkablyvigorousflame，verymuchlikethatenlargedflamewithwhichacandleburnsinnitrousoxide，exposedtoironorliverofsulphur；butasIhadgotnothinglikethisremarkableappearancefromanykindofairbesidesthisparticularmodificationofvitrousair，andIknewnovitrousacidwasusedinthepreparationofmercuriuscalcinatus，Iwasutterlyatalosstoaccountforit。"[4]

The"newair"was，ofcourse，oxygen。Priestleyatonceproceededtoexamineitbyalongseriesofcarefulexperiments，inwhich，aswillbeseen，hediscoveredmostoftheremarkablequalitiesofthisgas。Continuinghisdescriptionoftheseexperiments，hesays:

"Theflameofthecandle，besidesbeinglarger，burnedwithmoresplendorandheatthaninthatspeciesofnitrousair；andapieceofred-hotwoodsparkledinit，exactlylikepaperdippedinasolutionofnitre，anditconsumedveryfast；anexperimentthatIhadneverthoughtoftryingwithdephlogisticatednitrousair。

"……Ihadsolittlesuspicionoftheairfromthemercuriuscalcinatus，etc。，beingwholesome，thatIhadnoteventhoughtofapplyingittothetestofnitrousair；butthinking(asmyreadermustimagineIfrequentlymusthavedone)onthecandleburninginitafterlongagitationinwater，itoccurredtomeatlasttomaketheexperiment；and，puttingonemeasureofnitrousairtotwomeasuresofthisair，Ifoundnotonlythatitwasdiminished，butthatitwasdiminishedquiteasmuchascommonair，andthattherednessofthemixturewaslikewiseequaltoasimilarmixtureofnitrousandcommonair……ThenextdayIwasmoresurprisedthaneverIhadbeenbeforewithfindingthat，aftertheabove-mentionedmixtureofnitrousairandtheairfrommercuriuscalcinatushadstoodallnight，……acandleburnedinit，evenbetterthanincommonair。"

AlittlelaterPriestleydiscoveredthat"dephlogisticatedair……isaprincipalelementinthecompositionofacids，andmaybeextractedbymeansofheatfrommanysubstanceswhichcontainthem……Itislikewiseproducedbytheactionoflightupongreenvegetables；andthisseemstobethechiefmeansemployedtopreservethepurityoftheatmosphere。"

ThisrecognitionoftheimportantpartplayedbyoxygenintheatmosphereledPriestleytomakesomeexperimentsuponmiceandinsects，andfinallyuponhimself，byinhalationsofthepuregas。"Thefeelinginmylungs，"hesaid，"wasnotsensiblydifferentfromthatofcommonair，butIfanciedthatmybreathingfeltpeculiarlylightandeasyforsometimeafterwards。Whocantellbutthatintimethispureairmaybecomeafashionablearticleinluxury？……Perhapswemayfromtheseexperimentsseethatthoughpuredephlogisticatedairmightbeusefulasamedicine，itmightnotbesoproperforusintheusualhealthystateofthebody。"

Thissuggestionastothepossibleusefulnessofoxygenasamedicinewasprophetic。Acenturylatertheuseofoxygenhadbecomeamatterofroutinepracticewithmanyphysicians。EveninPriestley’sowntimesuchmenasDr。JohnHunterexpressedtheirbeliefinitsefficacyincertainconditions，asweshallsee，butitsvalueinmedicinewasnotfullyappreciateduntilseveralgenerationslater。

SeveralyearsafterdiscoveringoxygenPriestleythussummarizeditsproperties:"Itisthisingredientintheatmosphericairthatenablesittosupportcombustionandanimallife。Bymeansofitmostintenseheatmaybeproduced，andinthepurestofitanimalswilllivenearlyfivetimesaslongasinanequalquantityofatmosphericair。Inrespiration，partofthisair，passingthemembranesofthelungs，uniteswiththebloodandimpartstoititsfloridcolor，whiletheremainder，unitingwithphlogistonexhaledfromvenousblood，formsmixedair。Itisdephlogisticatedaircombinedwithwaterthatenablesfishestoliveinit。"[5]

KARLWILHELMSCHEELE

Thediscoveryofoxygenwasthelastbutmostimportantblowtothetotteringphlogistontheory，thoughPriestleyhimselfwouldnotadmitit。ButbeforeconsideringthefinalstepsintheoverthrowofStahl’sfamoustheoryandtheestablishmentofmodernchemistry，wemustreviewtheworkofanothergreatchemist，KarlWilhelmScheele(1742-1786)，ofSweden，whodiscoveredoxygenquiteindependently，althoughlaterthanPriestley。InthematterofbrilliantdiscoveriesinabriefspaceoftimeScheeleprobablyeclipsedallhisgreatcontemporaries。Hehadaveritablegeniusforinterpretingchemicalreactionsanddiscoveringnewsubstances，inthisrespectrivallingPriestleyhimself。UnlikePriestley，however，heplannedallhisexperimentsalongthelinesofdefinitetheoriesfromthebeginning，theresultsobtainedbeingthelogicaloutcomeofapredeterminedplan。

ScheelewasthesonofamerchantofStralsund，Pomerania，whichthenbelongedtoSweden。Asaboyinschoolheshowedsolittleaptitudeforthestudyoflanguagesthathewasapprenticedtoanapothecaryattheageoffourteen。Inthisworkhebecameatoncegreatlyinterested，and，whennotattendingtohisdutiesinthedispensary，hewasbusydayandnightmakingexperimentsorstudyingbooksonchemistry。In1775，stillemployedasanapothecary，hemovedtoStockholm，andsoonafterhesenttoBergman，theleadingchemistofSweden，hisfirstdiscovery——thatoftartaricacid，whichhehadisolatedfromcreamoftartar。

Thiswasthebeginningofhiscareerofdiscovery，andfromthattimeonuntilhisdeathhesentforthaccountsofnewdiscoveriesalmostuninterruptedly。Meanwhilehewasperformingthedutiesofanordinaryapothecary，andstrugglingagainstpoverty。HistreatiseuponAirandFireappearedin1777。Inthisremarkablebookhetellsofhisdiscoveryofoxygen——"empyreal"or"fire-air，"ashecallsit——whichheseemstohavemadeindependentlyandwithouteverhavingheardofthepreviousdiscoverybyPriestley。Inthisbook，also，heshowsthatairiscomposedchieflyofoxygenandnitrogengas。

EarlyinhisexperimentalcareerScheeleundertookthesolutionofthecompositionofblackoxideofmanganese，asubstancethathadlongpuzzledthechemists。Henotonlysucceededinthis，butincidentallyinthecourseofthisseriesofexperimentshediscoveredoxygen，baryta，andchlorine，thelastoffargreaterimportance，atleastcommercially，thantherealobjectofhissearch。Inspeakingoftheexperimentinwhichthediscoverywasmadehesays:

"Whenmarine(hydrochloric)acidstoodovermanganeseinthecolditacquiredadarkreddish-browncolor。Asmanganesedoesnotgiveanycolorlesssolutionwithoutunitingwithphlogiston[probablymeaninghydrogen]，itfollowsthatmarineacidcandissolveitwithoutthisprinciple。Butsuchasolutionhasablueorredcolor。Thecolorisheremorebrownthanred，thereasonbeingthattheveryfinestportionsofthemanganese，whichdonotsinksoeasily，swimintheredsolution；forwithoutthesefineparticlesthesolutionisred，andredmixedwithblackisbrown。Themanganesehashereattacheditselfsolooselytoacidumsalisthatthewatercanprecipitateit，andthisprecipitatebehaveslikeordinarymanganese。When，now，themixtureofmanganeseandspiritussaliswassettodigest，therearoseaneffervescenceandsmellofaquaregis。"[6]

The"effervescence"hereferstowaschlorine，whichheproceededtoconfineinasuitablevesselandexaminemorefully。Hedescribeditashavinga"quitecharacteristicallysuffocatingsmell，"whichwasveryoffensive。Heverysoonnotedthedecolorizingorbleachingeffectsofthisnowproduct，findingthatitdecolorizedflowers，vegetables，andmanyothersubstances。

Commerciallythisdiscoveryofchlorinewasofenormousimportance，andthepracticalapplicationofthisnewchemicalinbleachingclothsoonsupplantedthe，oldprocessofcrofting——thatis，bleachingbyspreadingtheclothuponthegrass。ButalthoughScheelefirstpointedoutthebleachingqualityofhisnewlydiscoveredgas，itwastheFrenchsavant，Berthollet，who，actinguponScheele’sdiscoverythatthenewgaswoulddecolorizevegetablesandflowers，wasledtosuspectthatthispropertymightbeturnedtoaccountindestroyingthecolorofcloth。In1785hereadapaperbeforetheAcademyofSciencesofParis，inwhichheshowedthatbleachingbychlorinewasentirelysatisfactory，thecolorbutnotthesubstanceoftheclothbeingaffected。Hehadexperimentedpreviouslyandfoundthatthechlorinegaswassolubleinwaterandcouldthusbemadepracticallyavailableforbleachingpurposes。In1786JamesWattexaminedspecimensofthebleachedclothmadebyBerthollet，anduponhisreturntoEnglandfirstinstitutedtheprocessofpracticalbleaching。His