Meteorological observations and essays / By John Dalton.

  • John Dalton
Date:
1834
Catalogue details

Licence: Public Domain Mark

Credit: Meteorological observations and essays / By John Dalton. Source: Wellcome Collection.

    215/280 (page 189)
    been exhausted, is precipitated upon the admission of perfectly dry air. Hence, then, we ought to conclude, till the contrary can be proved, that the condensation of vapour exposed to the common air, does not in any manner depend upon the pressure of the aor. All the facts, however, conspire to prove that the ¢emperature of the air bears a relation to the condensation of vapour; thus, the utmost force which vapour of 212° can exert, is equivalent to the weight of 30 inches of mercury ; and any greater force than this, acting upon vapour alone of that temperature, will condense the whole into water ; and, if the temperature be less, then the utmost force or spring of vapour is less, as is indi- cated by the table in page 127; and no doubt, as the utmost force decreases, the utmost density will decrease also, though probably not in the same ratio. Hence, then, atmospheric air, saturated with vapour, is such wherein the vapour, con- sidered abstractedly from the air in which it is diffused, is at its utmost density for the tempera- ture; in such case, if a quantity of atmospheric air and vapour be taken, and mechanically con- densed, a portion of the vapour will be condensed into water, and give off heat ; on the contrary, if it be expanded, or, which amounts to the same thing, if a quantity be taken out of a receiver, the remain- der will have its capacity for vapour increased, as has been already observed. Though the pressure of the air does not promote