Chemistry (history of Salt)

History of-

"Evidence" shows sodium chloride was** important as long ago as when supposedly, mastodons were on the earth. Sodium chloride was being used before written history began. 2,700 years B.C there was published in China the Peng-Tzao-Kan-Mu, probably the earliest known pharmaceutical guide. (Sodium) A major part of this writing was devoted to a analysis of more than 40 kinds of salt, including descriptions of two methods of extracting sodium chloride and putting it in a usable form that are very much like our processes today.

Egyptian art from as long ago as 1450 B.C. records salt making. A couple of more recent examples are drawings of a 15th century French salt evaporation plant, a 16th century Persian picture of a Kurdish salt merchant and a 17th century Italian print offering instructions in distilling salt.

(N.N.) Salt was of very important economically. A trade in Greece involving exchange of salt for slaves made the expression, "not worth his salt." The Romans were good builders of salt works as well as other vital infrastructure. Special salt rations given early Roman soldiers were known as "salarium argentum," the forerunner of the English word "salary." References to salt abound in languages around the globe, particularly regarding salt used for food. Until the 18th century, there was no distinction made between potassium and sodium. This was because early chemists did not recognize that "vegetable alkali" and "mineral alkali" are distinct from each other. Eventually a distinction was made. (Sodium) Sodium was first isolated in 1807 by Sir Humphrey Davy, who made it by the electrolysis of very dry molten sodium hydroxide, NaOH. Sodium collected at the cathode. Shortly after, Thenard and Gay-Lussac isolated sodium by reducing sodium hydroxide with iron metal at high temperatures. Sometime prior to the autumn of 1803, the Englishman John Dalton was able to explain the results of some of his studies by assuming that matter is composed of atoms and that all samples of any given compound consist of the same combination of these atoms. Dalton also noted that in series of compounds, the ratios of the masses of the second element that combine with a given weight of the first element can be reduced to small whole numbers (the law of multiple proportions). This was further evidence for atoms. Thomas Thomson published Dalton's theory of atoms in the third edition of his System of Chemistry in 1807 and in a paper about strontium oxalates published in the Philosophical Transactions. Dalton published these ideas himself in the following year in the New System of Chemical Philosophy. (N.N.)

Properties

Sodium chloride is readily soluble in water and insoluble or only slightly soluble in most other liquids.(Chang) It forms small, transparent, and colorless white cubic crystals. Sodium chloride is odorless but has a characteristic taste. Because it is made up of equal numbers of* ***positively charged sodium and negatively charged chloride ions, it is an ionic compound,

Physical

Formula weight

58.4 u

Melting point

1074 K (801 oC)

Boiling point

1738 K (1465 oC)

Density

2.2 kg/dmÑ-

Crystal structure

f.c.c.

Solubility

35.9 g/100 cm3 water

Molecular weight

58.44 g/mol

When it is melted or dissolved in water the ions can move about freely, so that dissolved or molten sodium chloride is a conductor of electricity. It can be decomposed into sodium and chlorine by passing an electrical current through it. (McMurry)

Natural Occurrence and Commercial Preparation-

Nearly all chemical compounds that contain either sodium or chlorine are ultimately derived from salt. Salt is widely and abundantly distributed in nature. It makes up nearly 80% of the dissolved material in seawater, and is the greater part of dissolved matter in the Dead Sea, the Great Salt Lake, and in salt wells in various parts of the world. It is also widely distributed in solid form. The mineral halite is pure salt. Rock, or mineral, salt is usually less pure. It is found in large deposits in the United States, notably in Michigan, Ohio, Texas, and Louisiana, and in Great Britain, Russia, China, and India.

The manufacture and use of salt is one of the oldest chemical industries. Salt is mined from deposits or is obtained as brine by introducing water into the deposits to dissolve the salt and then pumping the solution to the surface. Salt is also obtained through the evaporation of seawater, usually in shallow basins warmed by sunlight. Most salt for table use is obtained from seawater. It is usually not pure sodium chloride--it may contain natural impurities that provide dietary minerals, or small amounts of other substances (ex. magnesium carbonate, hydrated calcium silicate, or tri-calcium phosphate) may be