That the relative humidity of the air is not the all-important factor was often proved by the bad scent experienced just before rain and storms, when the hygrometer showed a saturation of considerably over ninety per cent.

The air space above the water in bottle B soon becomes filled by displacement with sulphurous acid gas, which is a little over twice as heavy as air; so in order to expedite the complete saturation of the water, it is convenient to remove the bottle A with its tube from bottle B, and after having closed the latter by its cork or stopper, to agitate it thoroughly by turning the bottle upside down.