These investigations of the expansion of gases led me naturally to examine the expansion of vapors; but since I expected from the preceding results that they would expand like gases I decided to make my experiments only with one vapor, and I chose by preference the vapor of sulphuric ether as being the easiest to manage.
To determine the expansion of the vapor of ether I used the two tubes of which I have already spoken, taking atmospheric air for comparison. I then introduced ether vapor into one of the tubes and atmospheric air into the other, in such a way that each of them corresponded to the same division. I then raised the temperature of the vessel from 60° to 100°, and I had the satisfaction of seeing that, whether rising or falling, the ether vapor and the atmospheric air always corresponded at the same time to the same divisions. This experiment, which was shown to Citizen Berthollet, was repeated several times, and I never was able to observe any difference in the expansion of the ether compared with that of atmospheric air. I may however remark that when the temperature of the ether is only a little above its boiling point, its condensation is a little more rapid than that of atmospheric air. This fact is related to a phenomenon which is exhibited by a great many bodies when passing from the liquid to the solid state, but which is no longer sensible at temperatures a few degrees above that at which the transition occurs.
I have reported from Saussure and my experiments confirm him, that very dry air and air carrying more or less water in solution are equally expansible; I am therefore authorized to draw from all that I have said the following conclusions
This experiment, by showing that ether vapor and the gases expand equally, shows that this property depends in no way on the particular nature of gases and vapors, but only on their elastic state, and leads us in consequence to the conclusion that all gases and all vapors expand equally between the same degrees of heat.
Since all gases are equally expansible by heat and equally compressible, and since these two properties depend on each other, as I shall show in another place, the vapors which are equally expansible with the gases should also be equally compressible; but I may mention that this last conclusion cannot be true except so long as the compressed vapors remain entirely in the elastic state; and this requires that their temperature shall be sufficiently elevated to enable them to resist the pressure which tends to make them assume the liquid state.
All gases, whatever may be their density and the quantity of water which they hold in solution, and all vapors expand equally between the same degrees of heat
2. For the permanent gases the increase of volume received by each of them between the temperature of melting ice and that of boiling water is equal to of the original volume for the thermometer divided into 80 parts, or to of the same volume for the centigrade thermometer.
To complete this work I must determine the law of the expansion of gases and vapors, so as to establish the true progress of a thermometer. I shall occupy myself with these new investigations; and when they are finished I shall have the honor of presenting them to the Institute. A literal translation of the whole title includes a reminder that this work was done during the first French republic: “On the expansion of gases and vapors, read at the National Institute on 11 pluviose, year 10, by citizen Gay-Lussac” (Pluviose was one of the nature-descriptive names of months used in the republican calendar. It is the “rainy” month corresponding to late January and early February.) –CJG