S AND PNEUMATICS.

(_Cabinet Cyclopaedia_, vol. xvii.)

_Easier to swim in the Sea than in a River_.

Sea water has a greater buoyancy than fresh water, being relatively
heavier; and hence it is commonly said to be much easier to swim in
the sea than in a river: this effect, however, appears to be greatly
exaggerated. A cubic foot of freshwater weighs about 1,000 ounces; and
the same bulk of sea water weighs 1,028 ounces; the weight, therefore,
of the latter exceeds the former by only 28 parts in 1,000. The force
exerted by sea water to support the body exceeds that exerted by fresh
water by about one thirty-sixth part of the whole force of the
latter.--_By Dr. Lardner._

_Ice lighter than Water_.

It is known that in the process of congelation, water undergoes a
considerable increase of bulk; thus a quantity of water, which at
the temperature of 40 deg. measures a cubic inch, will have a greater
magnitude when it assumes the form of ice at the temperature of 32 deg.
Consequently ice is, bulk for bulk, lighter than water. Hence it is
that ice is always observed to collect and float at the surface.--A
remarkable effect produced by the buoyancy of ice in water is observable
in some of the great rivers in America. Ice collects round stones at the
bottom of the river, and it is sometimes formed in such a quantity that
the upward pressure by its buoyancy exceeds the weight of the stone
round which it is collected--consequently it raises the stone to the
surface. Large masses of stone are thus observed floating down the river
at considerable distances from the places of their formation.--_Ibid_.

_Domestic Use of the Hydrometer_.

The adulteration of milk by water may always be detected by the
hydrometer, and in this respect it may be a useful appendage to
household utensils. Pure milk has a greater specific gravity than
water, being 103, that of water being 100. A very small proportion of
water mixed with milk will produce a liquid specifically lighter than
water.--Although the hydrometer is seldom applied to domestic uses,
yet it might be used for many ordinary purposes which could scarcely
be attained by any other means. The slightest adulteration of spirits,
or any other liquid of known quality, may be instantly detected by it;
and it is recommended by its cheapness, the great facility of its
manipulation, and the simplicity of its results.--_Ibid._

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THE GAT