assaying


assaying
In chemical analysis, the process of determining proportions of metal, particularly precious metal, in ores and metallurgical products.

The most important assaying technique grew largely out of the experiments of the ancient alchemists and goldsmiths. Precious metals tend to occur as scattered particles randomly distributed, so a large sample of ore is required. Such large samples (typically containing gold, silver, and lead) are still most economically assayed by this ancient method, which involves several steps of heating and cooling. More sophisticated recent methods, such as spectrochemical analysis, are not suited to assaying precious metal ores because the samples of the inhomogeneous ore that must be used are larger than the instruments can handle. See also parting.

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▪ chemical process
      in chemical analysis, process of determining proportions of metal, particularly precious metal, in ores and metallurgical products. The most important technique, still used today, grew largely out of the experiments of the ancient alchemists and goldsmiths in seeking to find or create precious metals by subjecting base metals and minerals to heat. More sophisticated methods, such as spectrographic analysis, are not suited to assaying precious metal ores because of the large sample required; precious metals tend to occur as scattered particles randomly distributed, so that a large sample of the ore must be taken. Such large samples—typically containing gold, silver, and lead—can be most economically assayed by the fire method, which usually consists of six steps:

      1. Sampling: a representative proportion is taken.

      2. Fusion: the sample is melted in a crucible with suitable fluxes and other agents so that droplets of lead collect the precious metal and descend through the sample in the crucible. The lead alloy is cooled to produce a metallic “button,” and the slag is discarded.

      3. Cupellation: (cupellation) the button is melted in an oxidizing atmosphere in order to oxidize impurities, including lead and other metals. The silver melts and dissolves the other precious metals, forming a “bead” of silver, gold, and platinum metals sometimes referred to as doré.

      4. Weighing: the bead is weighed to determine the total of gold and silver (the platinum metals are present in too little quantity to affect the measurement).

      5. Parting: (parting) the bead is treated with hot dilute nitric acid to dissolve out the silver. If the gold content of the bead is known to exceed 25 percent, its concentration is first reduced by adding silver in a procedure known as inquartation.

      6. Weighing: the remnant of gold is weighed and subtracted from the gold-silver bead weight to give the weight of silver.

      If platinum, palladium, or rhodium are present, they dissolve in the molten lead and are collected in the gold-silver bead after cupellation. Their concentration in the gold after parting can be determined by arc spectrography. If iridium is present, it forms a black deposit that clings to the doré bead. Osmium and ruthenium, on the other hand, are largely lost during cupellation; if their presence is suspected, chemical methods instead of fire analysis are used.

      Fire-assaying methods are also used to determine easily reducible base metals such as lead, bismuth, tin, antimony, and copper.

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Universalium. 2010.

Look at other dictionaries:

  • Assaying — As*say ing, n. The act or process of testing, esp. of analyzing or examining metals and ores, to determine the proportion of pure metal. [1913 Webster] …   The Collaborative International Dictionary of English

  • Assaying — Assay As*say , v. t. [imp. & p. p. {Assayed}; p. pr. & vb. n. {Assaying}.] [OF. asaier, essaier, F. essayer, fr. essai. See {Assay}, n., {Essay}, v.] 1. To try; to attempt; to apply. [Obs. or Archaic] [1913 Webster] To night let us assay our plot …   The Collaborative International Dictionary of English

  • assaying — prabavimas statusas T sritis Standartizacija ir metrologija apibrėžtis Tauriųjų metalų kiekio nustatymas jų rūdose, lydiniuose, dirbiniuose. atitikmenys: angl. assay; assay analysis; assaying vok. Probierkunst, f rus. пробирный анализ, m;… …   Penkiakalbis aiškinamasis metrologijos terminų žodynas

  • assaying — prabavimas statusas T sritis Standartizacija ir metrologija apibrėžtis Prabos ženklo įspaudimas į tauriųjų metalų lydinius arba jų dirbinius. atitikmenys: angl. assaying rus. пробирование, n …   Penkiakalbis aiškinamasis metrologijos terminų žodynas

  • assaying — prabinė analizė statusas T sritis chemija apibrėžtis Tauriųjų metalų kiekio nustatymas jų rūdose, lydiniuose, dirbiniuose. atitikmenys: angl. assay analysis; assaying rus. пробирный анализ; пробирование ryšiai: sinonimas – prabavimas …   Chemijos terminų aiškinamasis žodynas

  • assaying — noun A trial by assay …   Wiktionary

  • assaying — Смотри пробирный анализ …   Энциклопедический словарь по металлургии

  • assaying — n. testing, analyzing as·say || É™ seɪ n. testing of an ore or alloy to determine the amount of metal contained in it v. test, examine; try; attempt …   English contemporary dictionary

  • assaying — assayˈing noun • • • Main Entry: ↑assay …   Useful english dictionary

  • assaying analysis — kiekybinė analizė statusas T sritis automatika atitikmenys: angl. assaying analysis; quantitative analysis vok. quantitative Analyse, f rus. количественный анализ, m pranc. analyse quantitative, f …   Automatikos terminų žodynas


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