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Glossary of Terms - N

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nanometer - Abbreviated "nm", a unit of length equal to one thousandth of a micrometer. Often used to express the wavelength of ultraviolet light and the colors of visible light in colorimetric analytical procedures.

negative charge - The electrical potential of an atom which gains one or more electrons, therefore leaving it with more electrons than protons. Anions carry a negative charge. See electron, anion.

negative head - A condition of negative pressure or of partial vacuum.

negative pressure - A pressure below that of existing atmospheric pressure taken as a zero reference.

nephelometric turbidity unit (NTU) - An arbitrary unit of measuring the turbidity in water by the light scattering effect of fine suspended particles in a light beam.

neutral - (Electrical systems) - The term used to indicate neither an excess nor a lack of electrons; a condition of balance between positive and negative charges. (Chemistry) - The term used to indicate a balance between acids and bases; the neutral point on the pH scale is 7.0, indicating the presence of equal numbers of free hydrogen (acidic) and hydroxide (basic) ions.

Neutralite - A trade name for a calcite mineral product (crushed southern limestone) which is used in loose media bed filters to modify the pH of low pH water sources.

neutralization - The addition of either an acid or a base to a solution as required to produce a neutral solution. The use of alkaline or basic materials to neutralize the acidity of some waters is a common practice in water conditioning.

neutralizer - A common designation for alkaline materials such as calcite (calcium carbonate) or magnesia (magnesium oxide) used in the neutralization of acid waters.

nitrate (NO₃^-) - A natural nitrogen compound sometimes found in well or surface waters. In high concentrations, nitrates can be harmful to young infants or young livestock.

non-carbonate hardness - Hardness caused by calcium or magnesium existing in compound form with chloride, sulfate, and nitrate anions rather than with the more common carbonate or bicarbonate anions. Non-carbonate hardness will not be precipitated by boiling. Non-carbonate hardness is the excess of total hardness over total alkalinity. High concentration (e.g. as caused by evaporation) of non-carbonate hardness anions can make the water more corrosive. The term non-carbonate hardness has largely replaced the term permanent hardness, which has the same meaning.

normal solution - A solution containing a gram equivalent weight of a substance in one liter of solution. (See equivalent weight.)

NTU - Nephelometric Turbidity Unit