Despite our doctors' warnings, we put it on almost all of our food. We add it to both savory foods (like ketchup or bacon) as well as sweet ones (cookies? bread? you bet!), and something as boring as butter doesn't taste at all the same without salt. After all, salt is one of the several basic tastes that the human tongue is capable of discerning.
When we're dehydrated, we go to the hospital for intravenous saline solution, which (not coincidentally) has the exact same concentration of saline as the saline solution we use for our contact lenses and which we would use to flush out a wound. How is it so important to have the right amount of Sodium in our bodies? My doctor tells me to avoid Sodium!
We know you can't water living beings with salty water, although just what is in those sports drinks that "replace electrolytes?" We admire tropical fish in salt water aquariums, and we notice it's easier to swim in salt water than in chlorinated pool water. We try not to let fertilizer salts build up in our plants and we pour rock salt in the road to melt ice. Are you confused yet? I was.
A few definitions
in chemistry a salt is a metal plus a non-metal. Table salt is a metal (sodium) plus a non-metal (chlorine). Salt can refer to any combination of a metal plus a non-metal; sodium or calcium or potassium plus chloride or fluoride or something more complex.
words that refer to SALT: salt (the word) comes from the Latin sal which is also the root of the words salary and salad (a salted vegetable dish). Salt once was worth a lot of money. Salt water is also called saline or saline solution, or brine.
Any word with a preix of halo- is talking about salt too--like halophtye for a plant which can live in high salt concentrations and halophile for a plant which requires a high salt concentration. Halle is ancient Celtic for salt, and Salz is German for salt: the great Austrian city of Salzburg was built around salt deposits. Of course, when you actually see the word salt such as The Great Salt Lake in Utah, it refers to just what you'd think: SALT.
fertilizer salts: when fertilizer is dissolved in water, it is present as a salt. As such, it will build up in the soil, especially of plants in containers. These need to be flushed periodically.
rock salt: a form of salt that is used to keep icy roads from freezing. Usually Sodium Chloride is used. Halite is another term for naturally occuring NaCl, which may have a grey appearance due to impurities. Pure NaCl is white, clear, pale pink or pale gray.
Iodized salt: Since 1920, the US has added microscopic amounts of iodine to salt to combat goiter and mental retardation, both caused by iodine deficiency. Iodine is not stored by the body and must be ingested. Iodized salt may react differently in recipes than non-iodized salt. The amounts of iodine added have an infinitestimal actual cost.
brine: a salt solution usually used for cooking or pickling.
Kosher salt is used for butchering, especially Kosher butchering. The salt isn't what's Kosher, it's the meat you drain with it that ultimately becomes Kosher. Kosher salt dissolves more easily on the tongue and so is perceived as saltier. It may contain additives.
pickling salt is also coarser and irregular, and also is perceived as saltier than table salt. Hopefully, it contains NO additives.
sea salt is generally salt that is produced by evaporating sea water (as opposed to mined or gathered from salt flats).
artisinal salts there are salt deposits and high salinity areas all over the world. People evaporate their local water to get salt that is from The Bonneville Salt Flats, The Dead Sea, Ethiopia or the Antartic.
don't be confused by chlorophyll and chloroblasts which do not contain chloride (although they have the same sickly yellow-green color as chlorine gas) or soda water which contains no sodium! It got its name from the sodium salts that were added a century ago to mimic the flavor of naturally occuring mineral carbonated water. Salt water taffy has no salt water! Another misleading term is Epsom Salts, which is MgSO4 (Magnesium sulfate, with Magnesium, Sulfur and Oxygen) and you'll notice it also contains neither Sodium nor Chloride. It is named after the salty town of Epsom, England, which was an ancient source of salt, but gardeners use it for its available Magnesium content.
Mixing bicarbonate of soda (NaCO4 baking soda) with water releases carbon dioxide naturally into the atmosphere and has a sour salty taste. This fizzy water became known as soda water (or even seltzer, after the German town of Selters with a naturally occuring carbonated spring).
In the rest of this article, I will focus on NaCl (sodium chloride or table salt).
Sodium: at room temperature, sodium is a soft, white metal which is not terribly stable--it would like to form a reaction with something, anything. Substances with a lot of SODIUM in them tend to be named "SODA," such as Baking Soda (Bicarbonate of Soda, or NaCO2), Washing Soda (Sodium Carbonate, Na2CO3).
Na = the element sodium. In Latin it's natrium, which is why its chemical symbol is Na.,
Chloride: Cl is the chemical symbol for chlorine, which combines so happily with other elements it is never ever found alone. Think of chlorine bleach, hydrochloric acid or chloroform. Chlorine's chemical symbol is Cl, and now that we know what it is (chlorine gas was first isolated in 1774) and how it works, we produce it and store it for industrial and disinfectant purposes. It is not a safe thing to have around. Even chlorine bleach (which is extremely .... fragrant) is only about 5% chlorine.
Sodium and Chlorine together are more stable and way cheaper than either of them is alone. Sodium chloride contains an ionic bond: the slight positive charge that Sodium has and the slight negative charge of Chlorine mean that together, they form Sodium Chloride, or table salt. The Na+ and the Cl- do some hanky-panky with electricty to from that ionic bond. An ionic bond can conduct electricity very well in water, which is one of the reasons you should never use your lawn mower at the beach.
Water, a Hydrogen and two Oxygens, is composed of two quite flammable gases (oxygen, O, and hydrogen, H,) so its bonds are also tight, but different from NaCl. Water arranges itself into a slippery arrangement (a liquid) with the H-O-H all lined up and sliding across each other. When the crystal NaCl comes along with its snug ionic bonds, the bonds loosen as the H20 sneaks in between or the salt dissolves in water. NaCl + H2O.
When salt is dissolved in water it becomes something different than either salt or water by themselves: it changes its basic properties. Where H2O usually has a freezing temperature of 0° C (or 32° F), salt water has a freezing point of -21.1° C which is about 6° F. Quite a lot lower than 32° F, especially if it's a frosty day and you're trying to avoid slipping and breaking yourself.
Anything dissolved in water will similarly lower the water's freezing point. If you're trying to avoid salt in your garden, you might try sugar or molasses to lower the freezing point of water on your steps. Please note that if it is much colder, lower than 6° F or -21.1° C, you will just have frozen salt water or molasses water or whichever.
Less intuitive perhaps is the relationship between salt and blood pressure. If you ingest high amounts of Sodium, your body will add water to dilute the salt in your blood. Increased blood volume leads to trying to squeeze more liquid blood in the same size blood vessels can lead to high blood pressure.
And it may now be self-explanatory but if you get takeout Chinese or pizza, or popcorn at the movie theater, its saltiness will make you thirsty, in a chemical way! When you wake up thirsty the next day, you are trying to dilute the excess Sodium in your blood with water or soda pop or anything.
We take advantage of these different properties of salt water every day. It's instinctive that salty water is colder than sweet water. That's why old-fashioned ice cream churners used rock salt to keep the ice colder. Anyone who lives in where the temperature loiters below freezing knows that if you put salt down before the road freezes, it will sustain colder temperatures before freezing.
Let's say you're making making dill pickles. Before you actually do the cooking part with the jars and the boiling, you usually salt the sliced cucumbers and let them rest that way for a while. Why this step? The salt (NaCl) draws the water (H20) out of the cucumbers. I've read that this also works with vegetables which can be watery like tomatoes, eggplant, zucchini, or cabbage. You only need a little salt, as table salt is so much saltier than the inside of a vegetable's cell walls. Drain off the salty water before using your recipe.
So now you know a little about why salt works the way it does: it attracts plain water to equalize the concentration gradiant.
Salt has been used as a preservative for eons. Think of salty meats like bacon or corned beef. Today, the salt is part of the flavor for us, but traditionally, these meats became salty because they were preserved with salt. It is hard for dangerous bacteria to start a family in a highly salty environment. Salt causes their cell walls to malfunction as well.
Or, imagine the salt pulling all the water out of cell walls in your vegetables. Then imagine the same salt in your garden soil! it will pull all the water out of the cell walls of your plants! Certainly not what you want.
People have written entire books about salt--this is just a brief introduction. Here is some more information about salts, and here and here. Real Simple has its own take on salts so does about.com. Here is a link where you can buy all these different kinds of salt. And finally, the reason you read this article, here, here and here are lists of salt-tolerant plants. And read what Organic Gardening has to say about plants exposed to rock salt.
pictures are all available through Creative Commons.
picture of salt shakers avvailable from crayonbeam through Flickr.