Duringthecourseofmyresearch,Ihadhadoccasiontoexaminenotonlysimplecompounds,saltsandoxides,butalsoagreatnumberofminerals.Certainonesprovedradioactive;thesewerethosecontaininguraniumandthorium;buttheirradioactivityseemedabnormal,foritwasmuchgreaterthantheamountIhadfoundinuraniumandthoriumhadledmetoexpect.
Thisabnormalitygreatlysurprisedus.WhenIhadassuredmyselfthatitwasnotduetoanerrorintheexperiment,itbecamenecessarytofindanexplanation.Ithenmadethehypothesisthattheoresuraniumandthoriumcontaininsmallquantityasubstancemuchmorestronglyradioactivethaneitheruraniumorthorium.Thissubstancecouldnotbeoneoftheknownelements,becausethesehadalreadybeenexamined;itmust,therefore,beanewchemicalelement.
Ihadapassionatedesiretoverifythishypothesisasrapidlyaspossible.AndPierreCurie,keenlyinterestedinthequestion,abandonedhisworkoncrystals(provisionally,hethought)tojoinmeinthesearchforthisunknownsubstance.
Wechose,forourwork,theorepitchblende,auraniumore,whichinitspurestateisaboutfourtimesmoreactivethanoxideofuranium.Sincethecompositionofthisorewasknownthroughverycarefulchemicalanalysis,wecouldexpecttofind,atamaximum,percentofnewsubstance.Theresultofourexperimentprovedthattherewereinrealitynewradioactiveelementsinpitchblende,butthattheirproportiondidnotreachevenamillionthpercent!
Themethodweemployedisanewmethodinchemicalresearchbasedonradioactivity.Itconsistsininducingseparationbytheordinarymeansofchemicalanalysis,andofmeasuring,undersuitableconditions,theradioactivityofalltheseparateproducts.Bythismeansonecannotethechemicalcharacteroftheradioactiveelementsoughtfor,foritwillbecomeconcentratedinthoseproductswhichwillbecomemoreandmoreradioactiveastheseparationprogresses.Wesoonrecognizedthattheradioactivitywasconcentratedprincipallyintwodifferentchemicalfractions,andwebecameabletorecognizeinpitchblendethepresenceofatleasttwonewradioactiveelements:poloniumandradium.WeannouncedtheexistenceofpoloniuminJuly,,andofradiuminDecemberofthesameyear.
Inspiteofthisrelativelyrapidprogress,ourworkwasfarfromfinished.Inouropinion,therecouldbenodoubtoftheexistenceofthesenewelements,buttomakechemistsadmittheirexistence,itwasnecessarytoisolatethem.Now,inourmoststronglyradioactiveproducts(severalhundredtimesmoreactivethanuranium),thepoloniumandradiumwerepresentonlyastraces.Thepoloniumoccurredassociatedwithbismuthextractedfrompitchblende,andradiumaccompaniedthebariumextractedfromthesamemineral.Wealreadyknewbywhatmethodswemighthopetoseparatepoloniumfrombismuthandradiumfrombarium;buttoaccomplishsuchaseparationwehadtohaveatourdispositionmuchlargerquantitiesoftheprimaryorethanwehad.Itwasduringthisperiodofourresearchthatwewereextremelyhandicappedbyinadequateconditions,bythelackofaproperplacetoworkin,bythelackofmoneyandofpersonnel.
Pitchblendewasanexpensivemineral,andwecouldnotaffordtobuyasufficientquantity.AtthattimetheprincipalsourceofthismineralwasatSt.Joachimsthal(Bohemia)wheretherewasaminewhichtheAustriangovernmentworkedfortheextractionofuranium.Webelievedthatwewouldfindalltheradiumandapartofthepoloniumintheresiduesofthismine,residueswhichhadsofarnotbeenusedatall.ThankstotheinfluenceoftheAcademyofSciencesofVienna,wesecuredseveraltonsoftheseresiduesatanadvantageousprice,andweuseditasourprimarymaterial.Inthebeginningwehadtodrawonourprivateresourcestopaythecostsofourexperiment;laterweweregivenafewsubventionsandsomehelpfromoutsidesources.
Thequestionofquarterswasparticularlyserious;wedidnotknowwherewecouldconductourchemicaltreatments.Wehadbeenobligedtostarttheminanabandonedstoreroomacrossacourtfromtheworkroomwherewehadourelectrometricinstallation.Thiswasawoodenshedwithabituminousfloorandaglassroofwhichdidnotkeeptherainout,andwithoutanyinteriorarrangements.Theonlyobjectsitcontainedweresomewornpinetables,acast-ironstove,whichworkedbadly,andtheblackboardwhichPierreCurielovedtouse.Therewerenohoodstocarryawaythepoisonousgasesthrownoffinourchemicaltreatments,sothatitwasnecessarytocarrythemonoutsideinthecourt,butwhentheweatherwasunfavorablewewentonwiththeminside,leavingthewindowsopen.Aviewoftheextractionofradiumintheoldshedwherethefirstradiumwasobtained