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NOTES ON WATER 449
In common calculation, water may be considered about 800
times heavier than air.
Salt water (sea water) is slightly heavier than fresh water.
Water may exist in three different forms, gaseous, as steam
or as vapor in the atmosphere; liquid, which is the most common
form, or solid in form of frost, ice and snow.
In its natural state, the common temperature of water is
from 55 to 65 degrees Fahr. (12 to 18 degrees centigrade). Or-
dinarily in calculation, the temperature of cold water is consid-
ered as 62 Fahr. (17 C).
Water will freeze to ice at 32 Fahr. (o°C). It will then
expand one-eleventh part of its volume; for instance, 11 cubic
inches of water will become 12 cubic inches of ice. This is the
reason why ice is floating on water.
A cubic foot of ice will weigh about 57^ pounds.
A cubic foot of fresh snow may weigh from 5 to 10 pounds,
but a cubic foot of snow moistened and compacted by rain may
weigh from 15 to 50 pounds.
Water will boil at sea level under atmospheric pressure at
212 Fahr. (ioo°C).
Increasing the pressure will increase the boiling point; for
instance, in a steam boiler at 100 pounds gage pressure per
square inch, the boiling point of the water will be raised to
about 337 Fahr. (170 C.). Decreasing the pressure will de-
crease the boiling point of the water; for instance, under a pres-
sure of a half atmosphere, the boiling point of water will be
only 180 Fahr.
This is the reason why a suction pump cannot draw hot
water the same height as cold water; because when the pump
starts working, the pressure is reduced and the water will com-
mence to boil, and the pump will draw steam instead of water.
If the temperature of the water does not exceed 150 Fahr., the
suction pump may be expected to draw it 5 to 6 feet, but at a
temperature of 180 only a couple feet, and if the water is boiling
hot, the suction pump cannot draw it at all.
We therefore always find that the so-called air pump used
in connection with condensers must be placed lower than the
condenser so that the hot water will flow into the pump by
gravity.
The boiling point of water will decrease at increased alti-
tude. The boiling point of water will decrease about i° Fahr.
for each 550 feet increase or elevation in altitude.
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