iv SUMMARIES OF PAPERS I N THIS ISSUE March, 197’9Summaries of Papers in this IssueEnergy- dispersive X-ray Emission AnalysisA ReviewSummary of ContentsIntroductionInstrumentationExcitationX-ray tubesRadioisotopesElectrons and protonsDetectorsElectronicsPre-amplifierAmplifierMulti-channel analyserDead timeData processingSpectral features and interpretationSum peaksEscape peaksDiffraction peaksAnomalous silicon, gold and argon peaksScatter peaksSpectral backgroundComparison of wavelength- and energy-dispersive systemsApplicationsAtmospheric particulatesWatersClinical and biochemicalRocks, ores and cementMetals and alloysCoal and petroleumOn-stream analysisOthersFuture developmentsKeywords : Review ; energy-dispersive X-ray emissiox analysisW.C. CAMPBELLImperial Chemical Industries Limited, Petrochemicals Division, Research andDevelopment Department, P.O. Box 90, Wilton, Middlesbrough, ClevelandT56 6 ; s .Analyst, 1979, 104, 177-195.Analysis of Steroids. Part XXXII. Determination of Allyloestrenolby Titrimetric, Polarographic and Gas-chromatographic MethodsA titrimeLiz method is described for the determination of allyloestrenoibased on methoxymercuration of its double bonds and titration of the aceticacid formed with standard sodium hydroxide solution. The relative standarddeviation of the method is 0.29%. The polarographic reduction of themercury addition compound on the dropping-mercury electrode is used forthe determination of allyloestrenol in a tablet formulation with a relativestandard deviation of 3.1 yo.A gas-chromatographic method with a relati\ estandard deviation of 1.5% is also described. The applicability of the:emethods to the determination of the stability of allyloestrenol and of itsdosage form is discussed.Keywords : Allyloestrenol determination ; titrimetry ; polarography ; gaschromatographySANDOR GORGG, ANNA LAUKO and ZSOFIA SZIKLAYChemical Works Gedeon Richter Ltd., P.O. Box 27, H-1475 Budapest, Hungary.Analyst, 1979, 104, 196-200March, 1.979 SUMMARIES O F PAPERS I N THIS ISSUEDiffusion Assay by an Automated ProcedureEquipment is described that allows cliffusion assays to be performed auto-matically in Petri dishes using the punch-hole technique.With a block ofsix dishes limits of error of approximately 3 2% can be obtained consistently.Various sources of systematic errors and their elimination are discussed.Keywovds : Autowation ; antibiotic assay ; di,ffusion assay ; systematic evvovsJ. W. LIGHTBOWN, R. A. BROADBRIDGE and P. ISAACSONNational Institute for Biological Standards and Control, Holly Hill, Hampstead,London, NW3 6RB.J. E. SHARPEDivision of Engineering, National Institute for Medical Research, Mill Hill, London,NW7 1AA.and A. JONESResearch Division, Keecham Pharmaceuticals, Worthing, West Sussex, BN14 3QH.Analyst, 1979, 104, 201-207.Mechanism of Atom Excitation in Carbon FurnaceAtomic-emission SpectrometryBy consideration of electronic and vibrational excitation temperatures andthe ionisation temperature, it is demonstrated that local thermal equilibrium(LTE) is established under the practical analytical conditions of interruptedgas flow in which commercial carbon furnace atomisers are used as emissionsources. The electron concentration is shown to be derived from thermionicemission from the carbon tube and calculated values of 5.2 x 10lo c r r 3 a t2558 K and 1.3 x 1 0 l 1 ~ m - ~ at 2766 K are reported.The processes thatcontribute to the establishment of LTE are considered in detail, and it issuggested that molecular collisions make the major contribution to atomicexcitation under all conditions, but that radiation absorption may besignificant when a monatomic gas is used as purge gas and when moleculesare present as impurities a t concentrations of only 0.01%.Keywovds ; Atom emission ; carbon furnace atomisation ; excitation mechanism ;electvon concentvation ; local thevmal equilibviumD.LITTLEJOHN and J. M. OTTAWAYDepartment of Pure and Applied Chemistry, University of Strathclyde, CathedralStreet, Glasgow, G1 1XL.Analyst, 1979, 104, 208-223.Determination of Chromium in Natural Waters and SewageEffluents by Atomic-absorption Spectrophotometry Using anAir - Acetylene FlameA simple method for the determination of chromium in natural waters andsewage final effluents by atomic-absorption spectrophotometry using anair - acetylene flame is described. The sample is concentrated by evapora-tion by a factor of five. Interference effects were minimised by the additionof ammonium perchlorate and were further reduced by working with a flameon the verge of luminosity rather than a distinctly luminous flame.Keywords : Chromium detevvnination ; atomic-absorption spectvophotometvy ;air - acetylene jlame ; natuval waters and sewage efluentsK. C. THOMPSON and K. WAGSTAFFSevern-Trent Water Authority, Malvern Regional Laboratory, 141 Church Street,Malvern, Worcestershire, TVR14 2AN.Analyst, 1979, 104, 224-231.