{
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  "id": "matter-in-disguise",
  "title": "Matter in Disguise",
  "language": "en-GB",
  "description": "Five elements explored through identity, weight, scale and changes of state; twenty independent passages from CC0 facts.",
  "playbackPolicy": {
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    "axes": [
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      "passage-within-topic"
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    "rangeDegrees": [
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      360
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    "circular": true,
    "allocation": "random-with-spacing-on-edition-load",
    "stableFor": "loaded-edition-session",
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    "receptionGaps": "required-between-stations-on-both-axes",
    "maxAudiblePassages": 1
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  "topics": [
    {
      "id": "hydrogen",
      "title": "The Lightest Beginning",
      "sourceIds": [
        "wikidata-q556"
      ],
      "passages": [
        {
          "id": "hydrogen-identity",
          "title": "One",
          "text": "Hydrogen carries atomic number one and the symbol H. Imagine a catalogue of matter beginning with a single entry. Before the familiar metals and the complicated names, there is this smallest number: a starting point for the periodic table."
        },
        {
          "id": "hydrogen-room",
          "title": "A roomful of almost nothing",
          "text": "A cubic metre of hydrogen gas weighs about ninety grams at zero degrees Celsius and ordinary atmospheric pressure. Imagine that invisible cube beside a small weight in your hand. A large occupied space need not contain much matter by mass."
        },
        {
          "id": "hydrogen-cold",
          "title": "A different state",
          "text": "At a pressure close to one atmosphere, hydrogen boils at roughly minus two hundred and fifty-three degrees Celsius. A substance familiar as a gas can belong to another state entirely. Its boiling point marks a boundary far below everyday temperatures."
        },
        {
          "id": "hydrogen-mass",
          "title": "The decimal",
          "text": "Hydrogen's standard atomic weight is about one point zero zero eight. Its atomic number, meanwhile, is exactly one. The two entries describe different quantities. Even the first element invites a useful pause: a number identifying something need not be a measurement of its weight."
        }
      ]
    },
    {
      "id": "helium",
      "title": "A Quiet Element",
      "sourceIds": [
        "wikidata-q560"
      ],
      "passages": [
        {
          "id": "helium-identity",
          "title": "Two letters",
          "text": "Helium has atomic number two, but its symbol uses two letters: a capital H and a small e. Those letters form one chemical symbol. A tiny written distinction keeps one element separate from another, giving a short notation a very precise meaning."
        },
        {
          "id": "helium-family",
          "title": "A name for a family",
          "text": "Helium belongs to the noble gases. That family name sounds like a social rank, yet here it identifies a chemical grouping. Imagine a cabinet arranged by relationships instead of appearance: an invisible gas has a place beside its chemical relatives."
        },
        {
          "id": "helium-cold",
          "title": "Near the lower end",
          "text": "At one atmosphere, helium boils at about minus two hundred and sixty-nine degrees Celsius. A room-temperature description cannot tell the whole story of a material. Change the conditions enough, and even the word gas becomes a description of a situation rather than a permanent identity."
        },
        {
          "id": "helium-weight",
          "title": "Two and four",
          "text": "Helium's atomic number is two, while its standard atomic weight is approximately four. The table gives the same element two different numerical descriptions. Doubling a number in your imagination does not establish a general chemical rule; this is one particular element's pair of values."
        }
      ]
    },
    {
      "id": "carbon",
      "title": "One Element, Different Forms",
      "sourceIds": [
        "wikidata-q623"
      ],
      "passages": [
        {
          "id": "carbon-identity",
          "title": "A single letter",
          "text": "Carbon is element six, represented by the letter C. Such a small mark can stand for an entire category of matter. Imagine removing the names from a chemical catalogue and keeping only its symbols: a single letter would still identify carbon."
        },
        {
          "id": "carbon-density",
          "title": "Two forms",
          "text": "The carbon entry records different densities for graphite and diamond: about two point three and three point five grams per cubic centimetre. One element appears in two material forms. Sharing an elemental identity does not require those forms to pack equal mass into equal space."
        },
        {
          "id": "carbon-cubes",
          "title": "Equal spaces",
          "text": "Imagine two tiny cubes, one of graphite and one of diamond, each one cubic centimetre in volume. Using their listed densities, the diamond cube would weigh roughly one and a quarter grams more. The cubes occupy equal space, yet the scale would distinguish them."
        },
        {
          "id": "carbon-weight",
          "title": "Six and twelve",
          "text": "Carbon has atomic number six and a standard atomic weight close to twelve. These are separate entries, not interchangeable labels. A table that looks like a collection of simple numbers is quietly asking which property each number describes before comparisons begin."
        }
      ]
    },
    {
      "id": "oxygen",
      "title": "A Familiar Name, Unfamiliar Numbers",
      "sourceIds": [
        "wikidata-q629"
      ],
      "passages": [
        {
          "id": "oxygen-identity",
          "title": "The round symbol",
          "text": "Oxygen is represented by O and has atomic number eight. The round letter and the number are two ways of locating the same element in a catalogue. Neither is a picture of an atom; scientific notation can identify something without resembling it."
        },
        {
          "id": "oxygen-weight",
          "title": "Almost sixteen",
          "text": "Oxygen's standard atomic weight is approximately sixteen, while its atomic number is eight. The decimal entry in a data table may look less memorable than a whole number. Rounding helps us carry a value in our heads, provided we remember it is an approximation."
        },
        {
          "id": "oxygen-boiling",
          "title": "Ninety kelvin",
          "text": "Oxygen's listed boiling point is about ninety kelvin under standard pressure conditions, roughly minus one hundred and eighty-three degrees Celsius. Those two temperatures name the same physical boundary. Changing the scale can make a measurement sound entirely different without changing the event it describes."
        },
        {
          "id": "oxygen-melting",
          "title": "Two boundaries",
          "text": "Oxygen's listed melting point is about fifty-five kelvin, and its boiling point about ninety kelvin. Between those values lies a liquid range under the corresponding ordinary pressure conditions. A short interval in a table becomes a region of possibilities when imagined as changing temperature."
        }
      ]
    },
    {
      "id": "iron",
      "title": "Weight and Change",
      "sourceIds": [
        "wikidata-q677"
      ],
      "passages": [
        {
          "id": "iron-identity",
          "title": "An unexpected symbol",
          "text": "Iron is element twenty-six, but its chemical symbol is Fe. The symbol does not begin like the English name. Reading a scientific table therefore involves a small act of translation: a familiar substance can have an identity that is not obvious from its everyday spelling."
        },
        {
          "id": "iron-density",
          "title": "A small heavy cube",
          "text": "At twenty degrees Celsius, a cubic centimetre of solid iron has a mass of about seven point nine grams. Imagine that small cube resting on a scale. Density connects a visible amount of space to the less visible quantity of matter contained within it."
        },
        {
          "id": "iron-larger-cube",
          "title": "Ten times wider",
          "text": "Imagine an iron cube one centimetre wide, then another ten centimetres wide. The larger cube holds a thousand times the volume, giving it a mass of roughly seven point nine kilograms at room temperature. A modest change in length becomes a much larger change in weight."
        },
        {
          "id": "iron-melting",
          "title": "Solid is conditional",
          "text": "Iron melts at about fifteen hundred and thirty-eight degrees Celsius under ordinary pressure conditions. The solidity we associate with it belongs to a range of temperatures. Imagine the material's identity continuing through that boundary: the name stays iron even when its shape can no longer stay fixed."
        }
      ]
    }
  ],
  "provenance": {
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    "rightsLimitations": "CC0 applies to the cited structured data, not to images, recordings, linked websites or discussion pages. None of those assets are included. The source designation does not relicense REVOUAR software or branding.",
    "endorsement": "An independent REVOUAR presentation; no affiliation or endorsement by Wikidata or the Wikimedia Foundation is implied.",
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