Designation:D2503−92(Reapproved2012)StandardTestMethodforRelativeMolecularMass(MolecularWeight)ofHydrocarbonsbyThermoelectricMeasurementofVaporPressure1ThisstandardisissuedunderthefixeddesignationD2503;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginaladoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscriptepsilon(´)indicatesaneditorialchangesincethelastrevisionorreapproval.ThisstandardhasbeenapprovedforusebyagenciesoftheDepartmentofDefense.1.Scope1.1Thistestmethodcoversthedeterminationoftheaveragerelativemolecularmass(molecularweight)ofhydrocarbonoils.Itcanbeappliedtopetroleumfractionswithmolecularweights(relativemolecularmass)upto3000;however,theprecisionofthistestmethodhasnotbeenestablishedabove800molecularweight(relativemolecularmass).Thistestmethodshouldnotbeappliedtooilshavinginitialboilingpointslowerthan220°C.1.2ThevaluesstatedinSIunitsaretoberegardedasstandard.Nootherunitsofmeasurementareincludedinthisstandard.1.3Thisstandarddoesnotpurporttoaddressallofthesafetyconcerns,ifany,associatedwithitsuse.Itistheresponsibilityoftheuserofthisstandardtoestablishappro-priatesafetyandhealthpracticesanddeterminetheapplica-bilityofregulatorylimitationspriortouse.Forspecifichazardstatements,5.2.1,5.2.3,and5.2.3.2.SummaryofTestMethod2.1Aweighedportionofthesampleisdissolvedinaknownquantityofappropriatesolvent.Adropofthissolutionandadropofsolventaresuspended,sidebyside,onseparatethermistorsinaclosedchambersaturatedwithsolventvapor.Sincethevaporpressureofthesolutionislowerthanthatofthesolvent,solventcondensesonthesampledropandcausesatemperaturedifferencebetweenthetwodrops.Theresultantchangeintemperatureismeasuredandusedtodeterminetherelativemolecularmass(molecularweight)ofthesamplebyreferencetoapreviouslypreparedcalibrationcurve.3.SignificanceandUse3.1Relativemolecularmass(molecularweight)isafunda-mentalphysicalconstantthatcanbeusedinconjunctionwithotherphysicalpropertiestocharacterizepurehyd...
