Liquid-in-glass thermometers and fluid selection: considering volumetric expansion with temperature, which of the following liquids has the smallest volumetric expansion over a typical operating range (hence enabling finer scale spacing)?

Introduction / Context:
In liquid-in-glass thermometers, the choice of the working liquid determines readability, linearity, temperature range, and chemical compatibility. A key property is the coefficient of volumetric expansion: lower expansion yields less movement per degree, which affects the scale design and range, while higher expansion permits wider spacing but may limit usable range or linearity.

Given Data / Assumptions:

• Liquids considered: water, mercury, methyl alcohol, carbon tetrachloride, toluene.
• We compare general coefficients over ordinary laboratory ranges (well above the anomalous 0–4 °C region for water).

Concept / Approach:
Mercury exhibits a relatively low and fairly linear volumetric expansion across a wide temperature range compared with many organic liquids. Alcohols (e.g., methyl alcohol) and organic solvents like carbon tetrachloride or toluene have higher expansion coefficients, facilitating low-temperature thermometers but with larger scale changes and different material constraints. Water complicates matters due to its anomaly near 4 °C and is seldom used as a working fluid in sealed thermometers. Hence, among the listed choices, mercury undergoes the smallest volumetric expansion for a given temperature rise in typical practice, which is one reason for its historical dominance in precise laboratory thermometers.

Step-by-Step Solution:
Recall relative expansion: organics > mercury across common lab ranges.Account for water’s anomaly: unsuitable and non-monotonic near 0–4 °C.Select the liquid with the smallest expansion: mercury.

Verification / Alternative check:
Property tables list mercury’s volumetric expansion lower than typical alcohols and many organics; precision thermometers historically favor mercury for this and other reasons (visibility, conductivity, non-wetting glass with proper treatment).

Why Other Options Are Wrong:
Water: Anomalous behavior and not used as a sealed working fluid.Alcohols and CCl4/toluene: Higher expansion coefficients than mercury.

Common Pitfalls:
Confusing “minimum expansion” with “best readability.” High expansion can improve readability but may compromise range and linearity; the question asks strictly for minimum expansion.

Final Answer:
Mercury