The Thermal Conductivity of Liquids

This note briefly summarizes new results on the thermal conductivity of liquids which will be described in greater detail in a forthcoming number of the Proceedings of the American Academy of Arts and Sciences. The results are of two kinds: in the first place measurements of the effect of pressure on thermal conductivity, and in the second place a theoretical expression for thermal conductivity. The apparatus used in the measurements was a radial flow apparatus, in which the liquid was contained in the space between two concentric metal cylinders; the axis of the inner cylinder was a source of heat which flowed out radially across the layer of liquid. The temperature difference between the outer and inner surfaces of the layer of liquid was measured, and the thermal conductivity calculated in terms of the dimensions and the temperature difference. The method is particularly adapted to the measurement of substances of low conductivity like liquids, and gave results of much regularity and consistency. It is adapted to give not only the changes of conductivity under pressure, but also the absolute values of conductivity. The accuracy of the results is probably a few tenths of one per cent. Fifteen liquids were measured in all. Many of these were the same as those for which I have previously deterniined the various thermodynamic properties under pressure.1 The pressure range of this work was that usual to all my high pressure measurements, namely 12000 kg./cm.2.; the measurements were also made at two temperatures, 30? and 75?. Not only do the measurements give the pressure coefficient of conductivity, which has never been measured before for liquids, but also the temperature coefficient at atmospheric pressure, for which there are only a few discordant previous measurements, and the temperature coefficient of the pressure coefficient. The new experimental results are contained in table I. The results for each liquid are given in two lines, in the first line are the results for 30? and in the second those for 7 ?. In the first column of figures are the values at atmospheric pressure of the absolute conductivity (in ordinary units, gm. cal. per cm.2 per sec. per degree C. per cm.), in the second column the ratio of the conductivity at 6000 kg. to that at atmospheric pressure, and in the third column the ratio of the conductivity at 12000 kg. to that at atmospheric pressure. The general results may be summarized as follows. At atmospheric pressure the conductivity decreases with rising