not live in water deprived of those elastic
fluids.

100 cubic inches of the New River water, with which part of this
metropolis is supplied, contains 2,25 of carbonic acid, and 1,25 of
common air. The water of the river Thames contains rather a larger
quantity of common air, and a smaller portion of carbonic acid.

If water not fully saturated with common air be agitated with this
elastic fluid, a portion of the air is absorbed; but the two chief
constituent gases of the atmosphere, the oxygen and nitrogen, are not
equally affected, the former being absorbed in preference to the latter.

According to Mr. Dalton, in agitating water with atmospheric air,
consisting of 79 of nitrogen, and 21 of oxygen, the water absorbs 1/64
of 79/100 nitrogen gas = 1,234, and 1/27 of 21/100 oxygen gas = 778,
amounting in all to 2,012.

Water is freed from foreign matter by distillation: and for any chemical
process in which accuracy is requisite, distilled water must be used.

Hard waters may, in general, be cured in part, by dropping into them a
solution of sub-carbonate of potash; or, if the hardness be owing only
to the presence of super-carbonate of lime, mere boiling will greatly
remedy the defect; part of the carbonic acid flies off, and a neutral
carbonate of lime falls down to the bottom; it may then be used for
washing, scarcely curdling soap. But if the hardness be owing in part to
sulphate of lime, boiling does not soften it at all.

When spring water is used for washing, it is advantageous to leave it
for some time exposed to the open air in a reservoir with a large
surface. Part of the carbonic acid becomes thus dissipated, and part of
the carbonate of lime falls to the bottom. Mr. Dalton[11] has observed
that the more any spring is drawn from, the softer the water becomes.

CHEMICAL CONSTITUTION OF THE WATERS USED IN DOMESTIC ECONOMY AND THE
ARTS.

_Rain Water_,

Collected with every precaution as it descends from the clouds, and at a
distance from large towns, or any other object capable of impregnating
the atmosphere with foreign matters, approaches more nearly to a state
of purity than perhaps any other natural water. Even collected under
these circumstances, however, it invariably contains a portion of common
air and carbonic acid gas. The specific gravity of rain water scarcely
differs from that of distilled water; and from the minute portions of
the foreign ingredients which it generally contains, it is