To measure μT, the gas is pumped continuously at a steady pressure through a heat
exchanger, which brings it to the required temperature, and then through a porous
plug inside a thermally insulated container. The steep pressure drop is measured and
the cooling effect is exactly offset by an electric heater placed immediately after the
plug (Fig. 2.29). The energy provided by the heater is monitored. Because ΔH= qp, the
energy transferred as heat can be identified with the value of ΔH. The pressure change
Δp is known, so we can find μT from the limiting value of ΔH/Δp as Δp→0 and then
convert it to μ. Table 2.10 lists some values obtained in this way.