Moisture is always present in the air, even when it is driest. To prove
this, press a piece of sheet copper into the form of a cup; place on
it a piece of phosphorus, thoroughly dried between blotting-paper; put
the cup on a dry plate, and beside it a small piece of quick-lime; turn
over it a glass tumbler, and leave it for ten minutes, that the lime
may remove all moisture from the included air; take off the tumbler,
touch the phosphorus with a hot wire, and instantly replace the glass;
when a dry solid will be formed, resembling snow. As soon as the flame
is extinct, examine the plate; when the solid will, in a very short
time, attract so much water from the air, that it will pass into small
drops of liquid.