Reading ComprehensionDifficulty: Medium

PT143 S2 P4 Q22 Explanation

The Myth of Liquid Glass

A free, expert breakdown of this official LSAT Reading Comprehension question.

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Passage

To glass researchers it seems somewhat strange that many people throughout the world share the persistent belief that window glass flows slowly downward like a very viscous liquid. Repeated in reference books, in science classes, and elsewhere, the idea has often been invoked to explain ripply windows in old houses. The origins glass retains an amorphous atomic structure, but it takes on the physical properties of a solid.

However, a new study debunks the persistent belief that stained glass windows in medieval cathedrals are noticeably thicker at the bottom because the glass flows downward. Under the force of gravity, certain solid materials including glass can, in fact, flow slightly. But Brazilian researcher Edgar Dutra Zanotto has calculated the time needed cathedral glass would require a period well beyond the age of the universe.

The chemical composition of the glass determines the rate of flow. Even germanium oxide glass, which flows more easily than other types, would take many trillions of years to sag noticeably, Zanotto calculates. Medieval stained glass contains impurities that could lower the viscosity and speed the flow to some degree, but even negligible ability to flow, it would have to be heated to at least 350 degrees Celsius.

The difference in thickness sometimes observed in antique windows probably results instead from glass manufacturing methods. Until the nineteenth century, the only way to make window glass was to blow molten glass into a large globe and then flatten it into a disk. Whirling the disk introduced ripples and thickened the edges. is made by floating liquid glass on molten tin. This process makes the surface extremely flat.

What this question is testing

Five Questions

Your task

Pin down exactly what the question asks about the passage — a detail, the author's view, the structure, or the main point — before looking at the choices.

Common trap

Answers that restate a true detail from the passage but don't answer the specific question being asked.

Winning move

Anticipate the answer in your own words from the passage, then find the choice that matches that prediction.

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The question
22.

The passage most helps to answer which one of the

Answer choices

  1. Out of Scope: 17th century6% picked this

    What is one way in which seventeenth-century windowpane manufacturing techniques differ from those commonly used

    If we do a quick search/scan for 17th century, we'll see it's never mentioned in the passage. The change in windowpane manufacturing techniques that is discussed in the last paragraph is a difference between medieval windows and 19th century windows.

  2. Correct80% picked this

    What is one way in which nineteenth-century windowpane manufacturing techniques differ from those

    Why this is right

    The last paragraph explains this (and it's pretty connected to the main point). The author is dispelling the misconception that glass bulges at the bottom because of glass's downward flow and telling us that it's really just because those old medieval windows were made differently. They blew molten glass into a globe and then flattened it into a disk. But once we hit the 19th century, glass was drawn into sheets by pulling it from the melt on a rod.

    Skill tested: Five Questions · how this choice captures the passage's function is the move to repeat next time.

  3. Inverse Bait: prior to medieval2% picked this

    Was glass ever used in windows prior to

    The passage talks about glass in medieval cathedrals, but it never talks about glass in any era prior to medieval times. So we have no way of knowing from the passage whether glass was first used in medieval times or whether it predated medieval times.

  4. Word Salad4% picked this

    Are unevenly thick stained-glass windowpanes ever made of germanium

    We can find "germanium oxide" mentioned once, in the 3rd paragraph, and nothing in that sentence or the surrounding context reveals whether or not any unevenly thick stained-glass windowpanes are made of that type of glass.

  5. Unsupported Causal Relationship: how8% picked this

    How did there come to be impurities in medieval

    "Impurities" are discussed in the sentence following the one about germanium oxide (3rd paragraph). We're just told that medieval glass contained impurities. We don't know the backstory of how those impurities got there.

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