Salt

Salt is a compound consisting of a positively charged metal ion (cation) bonded with a negatively charged ion (anion), which makes most salts soluble in liquids consisting of polar molecules (the most popular being water).

The best-known salt is sodium chloride (NaCl, common table salt). All salts taste salty, but some, such as arsenic or plutonium salts, are not recommended as table seasonings. Excessive salt consumption can increase the risk of high blood pressure.

Usage of salt
Salt was legendarily used in ancient times (most notably in the case of Carthage) to destroy the usefulness of agricultural land once conquered - the crops would be burned to the ground and the soil "salted" to poison it. Essentially, this would be scorched earth turned up to 11. However, a vast amount of externally-applied salt is required to significantly poison even one acre of land, and even then, soils that are well-drained and/or receive large amounts of rainfall will rapidly flush out the salt (Soil salination as a consequence of irrigation is a different phenomenon in which irrigation concentrates salts initially present in the subsoil into the topsoil). This is a costly proposition because salt was in ancient times far more valuable than it is now. Why a conquering power would render agricultural land worthless to anyone rather than claim it and exploit it for its own interests is not within the scope of this article. However, the legend continues to be told, and as a result, the phrase 'salt the soil' refers to any attempt to extirpate something and prevent its recovery.

Salt is used to melt snow and ice on roads and paths; various salts have reasons making them better for this. This works because water with a salt solution has a lower freezing point; also, the process of dissolving the salt releases some heat. The "ideal" ice melting product would be reasonably cheap, yield a very low freezing point when dissolved in water, have a high exothermic energy release while dissolving, and not be harmful to plants, concrete or road tar, and materials used in vehicles. For instance, potassium or nitrogen salts are less harmful (or even good) to neighboring plants, and calcium chloride is often used because it is a better "melter".

The Strategic Arms Limitation Treaty between the Soviet Union and the United States, signed by President Nixon, was called S.A.L.T.

Table salt
The principal ingredient of table salt is pure sodium chloride (NaCl), consisting of ~97% of the materials of table salt. It is typically mined (or evaporated), ground, purified (most of the time), packaged, and shipped with not much changing. This section is about the food.

Iodine
Sometimes trace iodine is added to salt to allow for easier intake. Iodine deficiency can lead to intellectual or developmental disabilities, so this addition is much like adding fluoride to water or (more accurately) vitamins to milk. If you are not allergic, adding iodine is unlikely to be toxic before succumbing to the high enough sodium levels needed for iodine poisoning.

While iodized salt is widespread in the United States, it's much rarer in the United Kingdom. British people get more of their dietary iodine from milk.

Fluoride
In some European countries (e.g., France, Germany, and Switzerland), fluoride is routinely added to table salt as an alternative to water fluoridation.

Kosher salt
Kosher salt comes in larger grains. That's really about it in terms of difference, apart from minor differences in how to cook with it. Now the salt is not kosher (Judaism is silent on the issue of which salt to use), but larger grains which can be thrown away after covering meat with it are excellent for drawing out any residual liquid/blood, and blood is not kosher. Hence the name. Some chefs prefer it because the coarser grains make it easier to pinch.

Sea salt
Sea salt is produced by evaporating seawater. As a result, it contains more "contaminants" than mined salt, giving it a slightly different flavor. The grinding process is also slightly different, which goes back to differences in how to cook with it. Roughly 30% of all salt sold for human consumption is sea salt.

Low sodium salt
Salt substitutes reduce an individual's salt intake to lower blood pressure. They commonly contain potassium, an essential nutrient, but if taken in excess or by people who cannot excrete potassium normally, it can cause health problems; this is mainly an issue in those with kidney disease, diabetes, or on some medications. Since most salt in the typical western diet comes from prepared, commercially sold food instead of a salt shaker at the table, salt substitutes may not significantly reduce sodium intake.

High blood pressure
The human body needs salt (sodium chloride, NaCl) to survive, and while extremely rare in the developed world, there are areas of the world, such as sub-Saharan West Africa, where salt deficiency is a common and grave public health issue (as a result the salt pans in the Sahara provide one of the few actual uses for the land). That said, the body only needs a teeny tiny bit of it. Ingesting a lot of salt causes a temporary increase in blood pressure.

The American Heart Association recommends that people cut down on salt consumption because of the risk of high blood pressure, "The science behind sodium reduction is clear. Significant evidence links excess sodium intake with high blood pressure, which increases the risk of heart attack, stroke and heart failure." Health authorities who cite research from evidence-based medicine recommend that people eat no more than 6g (about a teaspoon) of salt daily. The majority of sodium in the American diet (more than 70%) is found in processed food.

The Center for Science in the Public Interest advocates a severe, government-imposed restriction on the amount of added salt in processed and restaurant food. But then, they also advocate a tax on sugary drinks and a ban on trans fat, and they hate the entire rainbow of food dyes, so they're pretty big on the whole nanny-state food thing all around.

Various forms of woo
Not content with using it to improve dinner and occasionally ruin your enemies' soil, salt has been hijacked by various woo-meisters and superstitions.

A widespread folk tale is that throwing salt over your shoulder can be good luck or a safeguard against bad luck. In Asian cultures, like in Korea and Japan, salt is used to keep away bad luck and evil spirits, or sometimes as a form of purification. It is often thrown at people or in front of doors or temples. An example of this would be Sumo wrestling. Before every match, salt would be thrown onto the ring for purification.

On the more pseudoscientific side, salt has been touted as a cure-all and the evilest substance one can ingest because of scary words like 'sodium'. Various quack medical treatments involving salt exist, from respiratory problems to the downright barmy to 'special' properties ascribed to pink Himalayan salt (aside from handily coming in block form and, um, being pink).