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1、Todeterminethecontentofboronintheglaze,aweighingofabout0.5gofsampleisfusedinaplatinumcruciblewithsixtimestheweightofanhydroussodiumcarbonate.Thefusionisleachedwithhotwater.Thein-solubleresidueisfilteredoff,dried,andthefilterandresiduearetransferredtothesameplatinumcrucibleandcombust
2、ed,andfusedaga!n.Thefusionisagainleachedwithhotwater,andtheinsolubleresiduefilteredoff.Afterdoublefusing,thewholeoftheboronispracticallypassedintosolution.Thesesquioxidesareprecipi-tatedinthecombinedsolutions;tothesolutionweaddHC1togetanacidreactionwithlitmus,thenfreshlyprrcipitated
3、orchemicallypurecalciumcarbonate(withoutfreeCaO)tocompleteneutralizationofexcessHC1.Thecalciumcarbonateisaddedinsmallportions,sincethereactionofneutralizationisveryvigorousatfirst.EachtimeaftertheadditionofCaCOs,theflaskiscoveredwithawatchglass,allowedtostandforawhile,andthenshaken.
4、TheCaCOsisaddeduntilCO~stopscomingoffanduntilaslightexcessofCaCOsisobtained.Attheendoftheneutralization,thewatchglassiswashedovertheflaskandthecontentsareboiledfor20minwithareversiblecooler;theyarecooledfor5-7min,thecooleriswashedwithwateroverthesameflaskandthecontentsfilteredintoan
5、other(Erlenmeyer)flaskwithacapacityof250ml.Theresidueiswashedbydecantingwithsmallvolumesofwater(3-4times)andthenseveraltimesonafilter.Thefiltratewiththewashwaterisneutralizedinregardtomethylorangewith0.1NHC1,then15-20dropsexcessHC1areadded,afterwhichthesolutionisagainboiledfor20rain
6、withareversiblecoolertoremovetheCOz.ThecooleriswashedovertheflaskwithwaterfreeofCO~,neutralizedwith0.1NNaOHinregardtomethylorangeandthentheHsBO3isdeterminedbythefollowingmanner.Tenmlofinvertsugar,neutraltophenolphthalein,isaddedtotheflask,with5dropsofphenolphthalein.Thesolutionistit
7、ratedwith0.1NNaOHuntilthesteadyappearanceofarosecolor.Afewmoremlofinvertsugarareadded,andifthesolutionbecomescolorless,itisagaintitratedwith0.1NNaOH.Thetitrationiscompleteiftheadditionofinvertsugardoesnotmaketherosecolordisappear;1ml0.1NsolutionofNaOHcorrespondsto0.0035gBzOs.Prepara
8、tionoftheInvert-Sug
