John Dalton had become a secretary of…

John Dalton had become a secretary of the Manchester Literary and Philosophical Society in 1800, and in the following year he had orally presented an important series of papers, entitled "Experimental Essays" on the constitution of mixed gases; on the pressure of steam and other vapors at different temperatures, both in a vacuum and in air; on evaporation; and on the thermal expansion of gases.

These four essays are published in the Memoirs of the Lit & Phil in 1802.

The second of these essays opens with the striking remark, There can scarcely be a doubt entertained respecting the reducibility of all elastic fluids of whatever kind, into liquids; and we ought not to despair of effecting it in low temperatures and by strong pressures exerted upon the unmixed gases further.

After describing experiments to ascertain the pressure of steam at various points between 0 and 100 °C (32 and 212 °F), Dalton concluded from observations on the vapor pressure of six different liquids, that the variation of vapor pressure for all liquids is equivalent, for the same variation of temperature, reckoning from vapor of any given pressure.

In the fourth essay he remarks, I see no sufficient reason why we may not conclude that all elastic fluids under the same pressure expand equally by heat and that for any given expansion of mercury, the corresponding expansion of air is proportionally something less, the higher the temperature.

It seems, therefore, that general laws respecting the absolute quantity and the nature of heat are more likely to be derived from elastic fluids than from other substances.

He has thus enunciated Gay-Lussac's law or J.A.C.

Charles's law, published in 1802 by Joseph Louis Gay-Lussac.

In the two or three years following the reading of these essays, Dalton will publish several papers on similar topics, that on the absorption of gases by water and other liquids (1803), containing his law of partial pressures now known as Dalton's law.