Salt, despite being an essential component of our cooking and even a necessity to our diet, is not used primarily for human consumption. All of the salt manufactured for food processing only accounts for 4 percent of the total production in the United States. A much larger usage of salt is for the deicing of roads, sidewalks, and walkways with rock salt, which, in recent years, has accounted for 43 percent of the total production of salt in the country. ASTM D632-12(2020)e1- Standard Specification for Sodium Chloride covers guidelines that determine the suitability of a sample of sodium chloride for use as road salt to melt ice and snow.
Throughout history, salt has maintained a status somewhat different than today. The idea of pouring salt on the ground would seem horrendous to the average ancient Roman, since to them sodium chloride was a rare necessity acquired through trade routes from faraway lands. It was so important to people and their well-being that the original Latin word for salt (sal) used by the Romans was derived from the Roman goddess of health, Salus. In fact, the crystalline powder was so essential to a soldier’s wages (it is even rumored that a fraction of the soldier’s pay was just salt) that their payment became known as solarium argentum. This term was adapted centuries later into the word salary. The original meaning of the word salary literally translates to “soldier’s compensation for the purchase of salt”.
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| Rock Salt |
Centuries later, once the Dark Ages took over following the collapse of the Roman Empire, salt remained a strong commodity, even taking the place of money. During this time, Moorish merchants traded salt ounce-for-ounce with gold, and in modern-day Ethiopia, blocks of rock salt, called amolés, became an official currency. This value of salt all throughout society did not soon diminish, and the amolé remained the official currency of the area until the Nineteenth Century. In other parts of the world, taxes on salt were considered unjustifiable, and might have even helped inspire the poor to revolt and commence the French Revolution.
Because of industrialization in the past century, salt does not equal its weight in gold, but is a commodity that most people can easily acquire. Salt, found naturally in the oceans, can be extracted through several different processes, and it is one of the most abundant minerals on Earth. The primary method for creating salt used for consumption is the solar evaporation process, in which salt water ponds are managed in warm climates so that all of the water will evaporate, leaving behind only the salt.
In addition, resulting from climatic shift throughout the geologic history of the Earth, there is a lot of salt in underground caverns that used to occupy oceans that have long dried up. These areas serve as the locations of rock salt, which is extracted through either traditional deep shaft mining or solution mining, in which water is injected to dissolve the salt, which is pumped out and heated to evaporate the water.
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| Sidewalk being salted with rock salt |
ASTM D632-12(2020)e1 specifies the chemical and physical requirements for rock salt used for deicing roads and other purposes. Today, salt isn’t exactly what it used to be, but its use on pavement and other surfaces gives it a practical use to keep cities and towns running that the Romans would have never utilized.
