Properties of Salt

Properties of salt are collected in the U.S. Occupational Safety and Health Administration (OSHA) Chemical Sampling Information database.  More extensive information is available on Material Data Safety Sheets (MSDSs) or can be found on the following table.

Properties of Pure Sodium Chloride

Sodium chloride is sold in several different particle sizes (gradation) and forms, depending on the intended end use. Discrete crystals can be seen in rock salt used for deicing. Fine granules are typical of table salt and even finer popcorn salt. Kosher salt, pickling salt and ice cream salt are slightly coarser. Small compressed pellets are used in water softeners and large salt blocks are used as salt licks for livestock. When viewed under strong magnification, all sodium chloride is crystalline. Very large cubic crystals, of two, three or more inches in size, can be seen in some salt mines. They are transparent and cleave into perfect cubes when struck with a hard object.Purity of rock salt produced in North America varies depending on the type of salt (evaporated, rock, solar) and on the source. Rock salt typically ranges between 95% and 99% NaCl, and mechanically evaporated salt and solar salt normally exceed 99% NaCl. Evaporated salt made with purified brine has the highest purity, in some cases 99.99% NaCl. Voluntary standards, such as those developed by the American Society for Testing and Materials (ASTM), the American Water Works Association (AWWA) assure appropriate quality for the intended use. Mandatory specifications for food grade, drug/medical and analytical use include Food Chemicals Codex, U.S. Pharmacopoeia, and Reagent Grade Chemicals.  Special devices, refract meters are used to measure salinity.
Common salt or sodium chloride is considered by the U.S. Food and Drug Administration as safe for its intended use. This GRAS (generally recognized as safe) classification, and the universal use of sodium chloride since antiquity, affirms its safety. The Merck Index refers to sodium chloride as "(n) to generally considered poisonous." Many substances in everyday use can be toxic in high concentrations, even water. Reports Toxic levels of sodium chloride are reported as:


Oral toxicity (The Registry of Toxic Effects of Chemical Substances, 1986):

Acute aquatic toxicity (U.S. EPA, Ambient Water Quality Criteria for Chloride, 1988):
Rana Breviceps (frog); No observed effect concentration (NOEC): 400 mg/L.
Daphnia pulex 48-hour LC50 or EC50: 1,470 mg/L
Daphnia magna (water flea); 48 hour EC50: 3,310 mg/L
Myriophyllum spicatum (water milfoil); Phytotoxicity (EC50 for growth): 5,962 mg/L
Pimephales promealas (fathead minnow); 69-hour LC50: 7,650 mg/L
Lepomis macrochirus (Bluegill) LC50 or EC50: 7,846 mg/L
Anguilla rostrata (American eel) 48-hour LC50 or EC 50: 13,085 mg/L
EPA says that the chlorides of calcium, magnesium and potassium are generally more toxic to fresh water species than sodium chloride.  Some Antarctic species depend on salt to protect them against the cold.
Sodium and chloride occur naturally in soils and waters, and are added by residential, commercial and industrial activity. Aquatic organisms and vegetation, including crops and roadside grasses, shrubs and trees, tolerate various concentrations of sodium and chloride. The following classification is used by the U.S. Department of Agriculture to indicate the degree of hazard of saline soils to food crops. It is based on conductivity and salinity hazard. (Conductivity can be converted to approximate mg/L dissolved solids).

USDA Salinity hazard ratings:

A number of studies, including a 1992 Transportation Research Board Special Report about deicing salt, confirm that the environmental effects of elevated chloride levels are highly site specific. Other factors that affect the degree of salinity hazard are: soil texture, soil permeability, drainage, and quantity of water applied and the salt tolerance of the vegetation.
For further information contact the Salt Institute, see a cogent summary of uses prepared at the University of Virginia, a popular introduction to salt was published in the Smithsonian Magazine.  MR Bloch Archive "Salt Made the World Go Round," US Geological Survey, USDA Salinity Laboratory, Food and Drug Administration, Codex Alimentarius Commission, American Society for Testing and Materials, Food and Nutrition Board of National Academy of Sciences, United States Pharmacopoeial Convention, American Chemical Society, or the Chamber of Minerals and Energy of Western Australia. 

Read More:
● What is Salt
● Salt Uses
● Chemicals From Salt
● The Economics of Salt