SECTION III.
OF WATER.
As water is perpetually an object of our senses, and made use of for
most of the purposes of life, it might be imagined the nature of this
element was perfectly understood: but they who have enquired into
it with the greatest care, find it very difficult to form a just idea of it.
One reason of this difficulty is, water is not easily separated from
other bodies, or other bodies from water. Hartshorn, after having
been long dried, resists a file more than iron; yet, on distillation,
yields much water. I have already observed, that air is intimately
mixed with, and possibly never entirely separated from it, but in a
vacuum; how is it possible then ever to obtain water perfectly pure?
In its most perfect state, we understand it to be a liquor very fluid,
inodorous, insipid, pellucid, and colourless, which, in a certain
degree of cold, freezes into a brittle, hard, glassy ice.
Lightness is reckoned a perfection in water, that which weighs less
being in general the purest. Hence the great difficulty of determining
the standard weight it should have. Fountain, river, or well waters,
by their admixture with saline, earthy, sulphureous, and vitriolic
substances, are rendered much heavier than in their natural state;
on the other hand, an increase of heat, or an addition of air, by
varying the expansion, diminishes the weight of water. A pint of rain-
water, supposed to be the purest, is said to weigh 15 ounces, 1
drachm, and 50 grains, but, for the reasons just now mentioned, this
must differ in proportion as the seasons of the year do from each
other.
Another property of water, which it has in common with other
liquors, is its fluidity, which is so great, that a very small degree of
heat, above the freezing point, makes it evaporate. Experiments to
ascertain the proportion steamed away of the quantity of water used
in brewing, is an object worthy of the artist’s curiosity; but the purer