MIL-HDBK-1164
Grade, Hydraulic. In closed circuit under pressure, a line joining the elevations to
which water would rise in pipes freely vented and under atmospheric pressure.
Gram. A metric unit of mass defined as one thousandth of a kilogram. Practically
equal to the weight of a cubic centimeter of water.
Greensand. A common name for glauconite, a natural zeolite, used in water softening.
Gross Alpha Particle Activity. The total radioactivity due to alpha particle emission as
inferred from measurements on a dry sample.
Gross Beta Particle Activity. The total radioactivity due to beta particle emission as
inferred from measurements on a dry sample.
Groundwater. Water occurring in a stratum (aquifer) below the surface of the ground.
The term is not applied to water which is percolating or held in the top layers of the soil,
but to that below the water table.
Groundwater Recharge. Water descending to the zone of saturation under natural
conditions or as added through the activities of man.
Halogen. One of the chemical elements fluorine, chlorine, bromine iodine.
Hardness. A folk term inherited from the past with origins in the household use of
waters for washing. Some waters were hard to use in doing the family laundry. More
soap was needed to produce suds in these waters. Thus, tradition defines hardness in
terms of soap-consuming capacity. However, for practical purposes, hardness is
currently defined as the calcium and magnesium content of water expressed in terms of
calcium carbonate. In addition to increased consumption of soap, hardness minerals
are responsible for deposition of scale in boilers, detrimental effects in some industrial
processes, and sometimes objectionable taste in the water.
Head, Friction. The head lost of water flowing in a stream or conduit as the result of
the disturbances set up by the contact between the moving water and its containing
conduit, and by intermolecular friction. In laminar flow the head lost is approximately
proportional to the first power of the velocity; in turbulent flow it is approximately
proportional to the square of the velocity. While strictly speaking, head losses due to
bends, expansions, obstructions, impact, etc., are not included in this term, the usual
practice is to include all such head losses under this term.
Head, Loss of. The decrease in the head between two points.
Head, Negative. The loss of head in excess of the static head (a partial vacuum)
produced by clogging of rapid sand filters near the end of a filter run.
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