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    • Rights: Measurement Standards Laboratory of New Zealand
    Published 15 August 2019 Referencing Hub media
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    Dr Peter Saunders notes that, from 1879–2019, the kilogram1 and the metre2 were defined by physical objects known as international prototypes.

    Discussion point: Over time, the IPK3 has changed and is a tiny bit different from the replicas that were distributed in 1875 – but only by 50 micrograms. Does this matter4?

    Transcript

    PETER SAUNDERS

    Shortly after the Metric Treaty was signed in 1875, they decided to make some new artefact5 masses and length standards. Instead of being based on platinum6, these are based on platinum-iridium – so it was an alloy7 – and the iridium8 makes the metal9 a lot more stable and less porous10. So they made 30 of the length bars and 40 of the standard masses, and they picked one of each at random to become the international prototype11 kilogram and the international prototype metre, and those were deposited into a vault in the basement of the BIPM12 – in fact, they’re still there today. So the remaining standards that they made, so the other 30 and the other 40 were distributed amongst the member states of the Metric Treaty.

    Acknowledgements

    This video clip is from a recording of a presentation by the Measurement Standards Laboratory of New Zealand (MSL13) in celebration of the redefinition of the International System of Units (SI14), which happened on 20 May 2019. The presentation by Peter Saunders and Farzana Masouleh of MSL was filmed at Unleash Space, Faculty of Engineering, Auckland University.

    Filming and editing by Jonathon Potton of Chillbox Creative. MSL produced these videos to share the story of metrology15 development.

    1. kilogram: The base unit of mass in the International System of Units (SI).
    2. metre: The base unit of length in the International System of Units (SI).
    3. IPK: Acronym for the international prototype kilogram. The IPK is made of a platinum/iridium alloy and is cylindrical in shape with the height and diameter having the same dimensions – 39.17 mm. The IPK is kept at the International Bureau of Weights and Measures in Sèvres on the outskirts of Paris.
    4. matter: The basic structural component of all things that have mass and volume.
    5. artefact: 1. A product of human art and workmanship. 2. An object remaining from a particular period. 3. In the context of the international prototype kilogram (IPK), a 1 kilogram cylinder of platinum-iridium alloy was manufactured in France in the 1880s to serve as the mass standard. 4. Something observed during a scientific investigation that is not naturally present but has been introduced as a result of the experimental procedure. Artefacts are commonly introduced during preparation of specimens for microscopy.
    6. platinum: A transition metal in Group 10 of the periodic table – symbol Pt, atomic number 78.
    7. alloy: A mixture of a metal with one or more other elements to modify its metallic properties, for example, brass is an alloy of copper and zinc.
    8. iridium: A transition metal in Group 9 of the periodic table – symbol Ir, atomic number 77.
    9. metal: Any of a category of elements that usually have a shiny surface, are generally good conductors of heat and electricity and can be melted or fused, hammered into thin sheets or drawn into wires (for example, copper).
    10. porous: Containing pores, holes or cavities which may be connected (high porosity) or not well connected (low porosity).
    11. prototype: A trial working model or preliminary version of something. Sometimes a prototype might be smaller than the final version of an engineered object, so that the engineers can check if the design works before committing themselves to large-scale commercial production.
    12. BIPM: The acronym for the International Bureau of Weights and Measures (Bureau International des Poids et Mesures).
    13. MSL: The acronym for the Measurement Standards Laboratory.
    14. SI: A measurement system used worldwide in the scientific community. SI stands for Système International d’Unités.
    15. metrology: The science of weights and measures.

    Appears in

    INTERACTIVE

    The SI – past and present

    The International System of Units – the SI – was created to meet the needs of growing globalisation.

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      kilogram

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      2. The base unit of mass in the International System of Units (SI).

      matter

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      3. The basic structural component of all things that have mass and volume.

      alloy

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      4. A mixture of a metal with one or more other elements to modify its metallic properties, for example, brass is an alloy of copper and zinc.

      porous

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      5. Containing pores, holes or cavities which may be connected (high porosity) or not well connected (low porosity).

      MSL

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      6. The acronym for the Measurement Standards Laboratory.

      metre

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      7. The base unit of length in the International System of Units (SI).

      artefact

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      8. 1. A product of human art and workmanship.

      2. An object remaining from a particular period.

      3. In the context of the international prototype kilogram (IPK), a 1 kilogram cylinder of platinum-iridium alloy was manufactured in France in the 1880s to serve as the mass standard.

      4. Something observed during a scientific investigation that is not naturally present but has been introduced as a result of the experimental procedure. Artefacts are commonly introduced during preparation of specimens for microscopy.

      iridium

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      9. A transition metal in Group 9 of the periodic table – symbol Ir, atomic number 77.

      prototype

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      10. A trial working model or preliminary version of something. Sometimes a prototype might be smaller than the final version of an engineered object, so that the engineers can check if the design works before committing themselves to large-scale commercial production.

      SI

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      11. A measurement system used worldwide in the scientific community. SI stands for Système International d’Unités.

      IPK

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      12. Acronym for the international prototype kilogram. The IPK is made of a platinum/iridium alloy and is cylindrical in shape with the height and diameter having the same dimensions – 39.17 mm. The IPK is kept at the International Bureau of Weights and Measures in Sèvres on the outskirts of Paris.

      platinum

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      13. A transition metal in Group 10 of the periodic table – symbol Pt, atomic number 78.

      metal

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      14. Any of a category of elements that usually have a shiny surface, are generally good conductors of heat and electricity and can be melted or fused, hammered into thin sheets or drawn into wires (for example, copper).

      BIPM

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      15. The acronym for the International Bureau of Weights and Measures (Bureau International des Poids et Mesures).

      metrology

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      16. The science of weights and measures.

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