= Andrews's carbon dioxide experiment
{c}
The 1869 <The Bakerian Lecture: On the Continuity of the Gaseous and Liquid States of Matter by Thomas Andrews> describes dried <carbon dioxide> trapped above <mercury (element)> in a sealed <capillary tube>. A steel screw pressurized <water> in a strong <copper> tube; movable <mercury (element)> transmitted the load. A second <capillary tube> held air as a <pressure> gauge. Flowing <water> around the visible <capillary tubes> controlled <temperature>; a <thermometer> read the bath. A <cathetometer> read column positions, converted to <volume (thermodynamics)> readings using weighed-<mercury (element)> calibration.<The Bakerian Lecture: On the Continuity of the Gaseous and Liquid States of Matter by Thomas Andrews>[Andrews, pp. 576–578 and Plate LXIII, figures 3 and 5–7: sample preparation, screw, coupled capillaries, water jackets and optical readout]{ref}
Below the critical <temperature>, compression produced a visible <liquid>–<gas> boundary; above it, large density changes occurred without that boundary. Three trials gave $30.92\,{}^\circ\mathrm C$ as his critical <temperature>. Purity checks detected residual air; <mercury (element)> height corrections accounted for unequal <hydrostatic pressures>. He explicitly left air nonideality and pressure-induced tube-capacity corrections unresolved, so his air-gauge <pressures> were approximate. These readouts support a <liquid-gas critical point>; they do not measure a homogeneous unstable loop or establish universal quantitative accuracy of the later <Van der Waals equation>.<The Bakerian Lecture: On the Continuity of the Gaseous and Liquid States of Matter by Thomas Andrews>[Andrews, pp. 576, 578–580 and 583: residual air, approximate air-gauge pressure, hydrostatic corrections and three critical-temperature trials]{ref}
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