where the pressure is comparatively small; but the Tuscan laguna offers the only instance in which the action of these fires extends, or has extended, to the surface at which the water collected in the mountains finds its way to the sea, so as to enable it to dissolve caustic calcareous matter.
On the Escape of Gases through Capillary Tubes[1].
As the mobility of a body, or the ease with which its particles move among themselves, depends entirely upon its physical properties, little delay would arise in the mind, on a consideration of the probable comparative mobilities of the different gases. These bodies being nearly similar in all the physical properties, except specific gravity, which can interfere with internal motions generated in them, would be supposed to have those motions retarded in proportion as this latter character increased; but as this supposition has not been distinctly verified, the following experiments, though possessed of no peculiar claim to attention, may deserve to be recorded.
The apparatus was a copper vessel of the capacity of 100 cubic inches nearly, to which a condensing gauge was attached. Four atmospheres of the gas to be tried were thrown into it, and then a fine thermometer tube, 20 inches in length, was fixed on by adjusting pieces: the gas was suffered to escape until reduced to an atmosphere and a quarter, and the time noticed by a seconds' pendulum. In this way,—
| Carbonic acid gas | required | 156·5 | minutes | to escape. |
| Olefiant gas | „ | 135·5 | „ | „ |
| Carbonic oxide | „ | 133 | „ | „ |
| Common air | „ | 128 | „ | „ |
| Coal-gas | „ | 100 | „ | „ |
| Hydrogen | „ | 57 | „ | „ |
These experiments tend to show, that the mobility of the gases tried decreases as their specific gravity increases, and they are corroborated by others made with vanes. A wheel, having small planes attached to it, as radii perpendicular to the plane of motion, was made to rotate by a constant force in atmospheres of different gases, and the times which the motion
- ↑ Quarterly Journal of Science, iii. 354.
