Chem 120 / Dr. Rusay

Water: Ions, Solutions
and Table Salt
Web references and links:

Exercise: Ions & Solutions; Salt Farming
San Francisco Bay & Cuzco, Peru

 
From Wikipedia, the free encyclopedia:

Salt's ability to preserve food was a foundation of civilization. It eliminated the dependence on the seasonal availability of food and it allowed travel over long distances. It was also a desirable food seasoning. However, salt was difficult to obtain, and so it was a highly valued trade item. Until the 1900s, salt was one of the prime movers of national economies and wars. Salt was taxed from as far back as the 20th century BC in China.

Aside from being a contributing factor in the development of civilization, salt was also used in the military practice of salting the earth by various peoples, beginning with the Assyrians.

It is believed that Roman soldiers were at certain times paid with salt, and this is still evident in the English language as the word "salary" derives from the Latin word salarium that means payment in salt (Latin sal). The Roman Republic and Empire controlled the price of salt, increasing it to raise money for wars, or lowering it to be sure that the poorest citizens could easily afford this important part of the diet.

It was also of high value to the Hebrews, Greeks and other peoples of antiquity.

During the late Roman Empire and throughout the Middle Ages salt was a precious commodity carried along the salt roads into the heartland of the Germanic tribes. Caravans consisting of as many as forty thousand camels traversed four hundred miles of the Sahara bearing salt, sometimes trading it for slaves.

It is possible to use solar evaporation of sea water to produce salt. Brine is evaporated in a linked set of ponds until the solution is sufficiently concentrated by the final pond that the salt crystalises on the pond's floor. Salt evaporation ponds are shallow man-made ponds designed to produce salt from sea water. The seawater is fed into large ponds and water is drawn out through natural evaporation which allows the salt to be subsequently harvested. The ponds also provide a productive resting and feeding ground for more than 70 species of waterbirds, including several endangered species. The ponds are commonly separated by levees.

Notable salt ponds include the San Francisco Bay salt ponds in the United States, and the Dead Sea salt ponds in Israel and Jordan. Abandoned salt pans are a major feature of the southwest coast of Taiwan.
 

San Francisco Bay Salt Ponds:

Due to variable algal concentrations, vivid colors, from pale green to bright red, are created in the evaporation ponds. The color indicates the salinity of the ponds. Micro-organisms change their hues as the salinity of the pond increases. In low to mid-salinity ponds, green algae are predominant. In middle to high salinity ponds, an algae called Dunaliella salina shifts the color to red. Millions of tiny brine shrimp create an orange cast in mid-salinity ponds. Other bacteria such as Stichococcus also contribute tints. These colors are especially interesting to airplane passengers or astronauts passing above due to their somewhat artistic formations of shape and color.


Images below: Coffee colored river high in Peru's Andes with white colored salt covering its banks; Salt Terraces;  50 kilogram bags of finished salt for market: worth about US $0.50 per bag.
 (To view better quality images click on the image.)

 

Photos: Diane Goldsmith, SquareMoon Productions 
© Copyright 1998 Diane Goldsmith, SquareMoon Productions