V. On the absorption and radiation of heat by gaseous and liquid matter.—Fourth memoir

Abstract

The Royal Society has already done me the honour of publishing in the Philosophical Transactions three memoirs on the relations of radiant heat to the gaseous form of matter. In the first of these memoirs* it was shown that for heat emanating from the blackened surface of a cube filled with boiling water, a class of bodies which had been previously regarded as equally, and indeed, as far as laboratory experiments went, perfectly diathermic, exhibited vast differences both as regards radiation and absorption. At the common tension of one atmosphere the absorptive energy of olefiant gas, for example, was found to be 290 times that of air, while when lower pressures were employed the ratio was still greater. The reciprocity of absorption and radiation on the part of gases was also experimentally established in this first investigation. In the second inquiry† I employed a different and more powerful source of heat, my desire being to bring out with still greater decision the differences which revealed themselves in the first investigation. By carefully purifying the transparent elementary gases, and thus reducing the action upon radiant heat, the difference between them and the more strongly acting compound gases was greatly augmented. In this second inquiry, for example, olefiant gas at a pressure of one atmosphere was shown to possess 970 times the absorptive energy of atmospheric air, while it was shown to be probable that when pressures of 1/30th of an atmosphere were compared, the absorption of olefiant gas was nearly 8000 times that of air. A column of ammoniacal gas, moreover, 3 feet long, was found sensibly impervious to the heat employed in the inquiry, while the vapours of many of the volatile liquids were proved to be still more opaque to radiant heat than even the most powerfully acting permanent gases. In this second investigation, the discovery of dynamic radiation and absorption is also announced and illustrated, and the action of odours and of ozone on radiant heat is made the subject of experiment.