Neither is the variation among the different gases between the ratio of the velocity and pressure, connected with specific gravity, at least I have not been able to observe such a connexion. I have quoted an experiment, or rather the general result of several, on carbonic oxide and olefiant gases, and it is adverse to the supposition; and in others, made on sulphurous acid gas and ammoniacal gas, still further departures from the order of the densities were observed.
If a tube sufficiently fine and long be connected with a portion of gas under high pressure, so that the time occupied in its passage through it be considerable, the effect will be produced, i. e. the times of different gases will vary from each other, but not according to their specific gravities; if the tube, however, be cut off so that the gases pass quickly, then the times will be as the specific gravity. Now, in the long tube, the pressure and velocity will vary throughout its length, the pressure being greatest at the internal or connected end, and least at the other extremity, whilst the velocity is least at the end towards the reservoir, and greatest at the other. But the ratio by which the pressure and velocity decrease and increase, appears different for and peculiar to each gas. At the end of the long tube the olefiant gas issues more rapidly than hydrogen, though the pressure st the reservoir is the same; but shorten the tube, and let that part in which high pressures only exist confine the gases in their passage, and the hydrogen gas will surpass the olefiant gas in velocity as far as 4 or 5 does 2. It would seem, therefore, that in the long tube the pressure or elasticity of the olefiant gas diminishes less rapidly than that of the hydrogen, or that its velocity increases more rapidly.
Perhaps these effects may be accounted for by the supposition of some power of expansion peculiar to each gas, which, if existing, a tube would for many reasons be well calculated to exhibit. The experiment requires numerous repetitions and much time, and I have not yet had sufficient to satisfy myself on the subject. I will therefore refrain from mixing up crude notions with facts, and at some more convenient opportunity endeavour to supply what is wanting in this paper.
