The Principle of Making Well Salt by the Old Method

2015/11/14 bmschem

    Well salt is made by mixing black brine and yellow brine at a certain ratio. Black brine is black with plentiful sulfate ions; yellow brine is brown. Once they mixed, the toxicity can be eliminated and salts are obtained with a good taste and white color. 

    As necessities of life, though salt is not expensive, it makes huge profits for the massive demands. So it is monopolized by government in all ages. Salt monopoly dates back to spring and autumn period and there is a person who specially administers salt industry in ancient times. 

    In ancient times, people who live near the sea boil seawater for salts; people who are near salt lake dry the lake water in the sun for salts; while without convenient transportation and topographical advantages, peoples in the mainland have to dig a well and extract brine with their hands. Then extract and purify the brine to obtain salts. We call the salt prepared in this way well salt. Actually, between 255BC and 251 BC people have already known systematically digging salt well and refining well salt. Well salt is mainly produced in the ancient Bashu area, southwest of China. This area has special geological conditions and buries abundant salt mines. Brine is formed by underground water and finally natural salt spring comes into being. For the color difference between salt spring and common spring, people are easily attracted to be here to exploit resources.

                     

    Well salt production includes shaft sinking, brine extracting, salt making and other steps, among which drilling technique is particularly important. After shaft sinking, use bamboo drain to draw brine which is saline solution with different density. Then transport brine to the place where salts are boiled and decocted. After evaporative crystallization, edible salt is obtained. The brine to refine well salts is divided into black brine and yellow brine. As I mentioned above, black brine is black with plentiful sulfate ions; yellow brine is brown with plentiful barium ions. Sulfate ions do harms to people’s health, while barium ions are poisonous and taste bitter. Whether the salts obtained by this method are edible?

    After constant practice and exploration, ancient wised working people found that they could kill two birds with one stone by mixing the two brines at a certain ratio. In this way the toxicity can be eliminated and salts are obtained with a good taste and white color. In fact, the chemical principle they used is Ba²⁺+SO₄^2-=BaSO₄↓. As we all know, barium sulfate is a precipitate. So they only need to filter out barium sulfate. 

    In the ancient times, in order to shorten the time spent in boiling salts and raise efficiency, people also add salt slag which is crystallized salt into brine. With the development of modern technology, brine extracting by electricity and brine making in a vacuum have already replaced this old well salt production.