Sodium bicarbonate

• 1. Introduction

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  Sodium bicarbonate, the white powder better known as baking soda, was once offered to the United States Senate as a cure for the Spanish flu. On the 26th of January 1919, Senator Lee Overman interrupted a debate to announce the news. He said a judge in the mountain country of North Carolina had told him about a remedy. In Overman's words, "They say that common baking soda will cure the disease." He reported that the people using it had suffered no deaths at all. The announcement carried an implied criticism of modern science and a tribute to the simple wisdom of simple people. Today the same powder sits in kitchen cupboards, hospital supply rooms and laboratory shelves. What exactly is it, and why does one plain white solid keep turning up in so many unexpected jobs?

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• 2. Many Names

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  Salaratus, bread soda, cooking soda, brewing soda: sodium bicarbonate has gathered a long list of everyday names. Americans say baking soda, while people in Australia, the United Kingdom and New Zealand prefer bicarbonate of soda. Shortened forms such as bicarb, bicarb soda and sodium bicarb are widely used. Shoppers can often find a box near the baking powder in stores.

  The formula NaHCO3 describes a salt built from a sodium cation and a bicarbonate anion. Its formal IUPAC name is sodium hydrogen carbonate. As a solid it is white and crystalline, though it usually looks like a fine powder. The taste is slightly salty and alkaline, much like washing soda, which is sodium carbonate.

  The prefix bi- in the name is a fossil from an older naming system that predates any knowledge of molecules. Chemists had noticed that sodium bicarbonate holds twice as much carbonate per sodium as sodium carbonate does. The name bi-carbonate of potash was coined before anyone knew the precise compositions that modern formulas now spell out.

  The word sodium itself travelled a long road. It came through Arabic naṭrūn from the Greek nítron, a word recorded by Herodotus and traced further back to ancient Egyptian ntr. The Arabic term is linked to Wadi El Natrun in Lower Egypt, where a mixture of sodium carbonate and sodium hydrogen carbonate was used to dry out mummies. The Greek word also passed into Latin as sal nitrum and into German as Salniter, the root of nitrogen and nitrate.

  Nineteenth-century cooks knew the powder by another name, saleratus, from the Latin sal æratus, meaning aerated salt. The word covered both sodium and potassium bicarbonate.

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• 3. Rising Dough

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  Soda bread, cakes and quick breads all depend on tiny bubbles of carbon dioxide. Baking soda makes that gas when it meets an acid or when it is heated. The expanding gas lifts the batter and gives baked and fried foods their characteristic texture and grain. Acidic partners include cream of tartar, citric acid, lactic acid, vinegar and hydrogen phosphates.

  Heat alone can do the job too, because sodium bicarbonate breaks down above 80 degrees Celsius. Without an acid, however, only half of the available carbon dioxide escapes. The leftover sodium carbonate is strongly alkaline. It gives the finished bake a bitter, soapy taste and a yellow color.

  Baking powder was designed around that problem. It contains around 30 percent bicarbonate, plus acidic ingredients that wake up when water is added. Common partners are calcium acid phosphate, sodium aluminium phosphate and cream of tartar. The acid also heads off the metallic taste that sodium carbonate would otherwise leave behind.

  In the European Union the compound carries the E number E500. It is often used alongside other additives in bottled water to add taste. The same heat-triggered release of carbon dioxide has a far more dramatic use when something is burning.

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• 4. Fire And Fireworks

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  BC dry chemical fire extinguishers use sodium bicarbonate as a less corrosive alternative to the monoammonium phosphate found in ABC extinguishers. Its alkaline nature also made it, besides Purple-K, the only dry chemical agent used in large suppression systems installed in commercial kitchens.

  Several mechanisms work at the same moment. Heating breaks the powder into water and carbon dioxide, an endothermic reaction that draws heat away from the fire. It also forms intermediates that scavenge the free radicals responsible for keeping a fire going. On grease fires, a mild saponification effect produces a soapy foam that helps smother the flames. Heat absorption and radical scavenging matter more than the gas itself.

  People can throw the powder over small grease or electrical fires. A deep fryer is the exception. The sudden release of gas may make the grease splatter.

  The common black snake firework shows the same chemistry in a playful setting. Its two main components are sodium bicarbonate and sucrose. Heat decomposes the powder, and the carbon dioxide it releases pushes out a long, snake-like column of ash left by the burning sugar. The powder also slows combustion, because the carbon dioxide and water it gives off act as flame retardants.

  Acid indigestion and heartburn are a very different kind of burning, and the powder is used there too.

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• 5. Hospital And Bathroom

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  Stirred into water, sodium bicarbonate works as an antacid for indigestion and heartburn. It reacts with stomach acid to make salt, water and carbon dioxide.

  In hospitals, an intravenous solution treats acidosis and cases where the blood lacks enough sodium or bicarbonate ions. In respiratory acidosis, the infused bicarbonate shifts the buffer system of the plasma and raises its pH. That is why the compound appears in medically supervised cardiopulmonary resuscitation. Infusion is indicated only when blood pH falls markedly low, below roughly 7.1 to 7.0.

  Bicarbonate also drives potassium back into cells, which helps with hyperkalemia during acidosis. Because it can cause alkalosis, it is sometimes used for aspirin overdoses. Aspirin needs an acidic environment to be absorbed, and a basic one reduces absorption. It has also been used in the treatment of tricyclic antidepressant overdose.

  A mixture of sodium bicarbonate and polyethylene glycol in water makes an effective laxative and gastrointestinal lavage preparation. People take it before gastrointestinal surgery or gastroscopy. The compound can also be added to local anaesthetics to speed their onset and make the injection less painful. It is a component of Moffett's solution, used in nasal surgery.

  Effervescent tablets rely on the same fizz. The powder is paired with a mild acid such as tartaric acid. Dropped in a glass of water, the tablet releases gas and falls apart. The medication is left suspended or dissolved in the water along with the resulting sodium tartrate.

  Protesters have used antacid solutions, baking soda among them, to ease the effects of tear gas. A paste of three parts baking soda to one part water can relieve some insect bites and stings and the swelling that follows. Athletes take it as a supplement to improve muscular endurance. Studies, conducted mostly in males, found the biggest benefit in short-term, high-intensity activity.

  In the bathroom, some mouthwashes include it for its anticaries and abrasive properties. It works as a mechanical cleanser on teeth and gums, neutralizes acid production in the mouth and acts as an antiseptic. Combined with other ingredients, it can make a dry or wet deodorant. Mixed with table salt, it buffers a nasal irrigation solution. It also has weak disinfectant properties and may be an effective fungicide against some organisms.

  Not every claim holds up. Tullio Simoncini promoted baking soda as a cancer cure, and the American Cancer Society warned against it because its effectiveness is unproven and its use potentially dangerous. Edzard Ernst called the promotion "one of the more sickening alternative cancer scams I have seen for a long time". The idea that acidic diets weaken bones fares no better. One systematic meta-analysis found no such effect. Another found no evidence that alkaline diets improve bone health, though it suggested that there "may be some value" to them for other reasons.

  For blepharitis, eye hygiene advice calls for a teaspoon of the powder in cool water that was recently boiled. Gentle scrubbing of the eyelash base follows, using a cotton swab dipped in the solution.

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• 6. Scrubbing And Science

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  In the early 1940s, the Manhattan Project to develop the nuclear bomb ran into the chemical toxicity of uranium. Uranium oxides stuck firmly to cotton cloth and would not wash out with soap or laundry detergent. A 2 percent solution of sodium bicarbonate did remove them.

  Sodablasting uses the powder as a blasting medium to strip away paint and corrosion. It suits softer, less resilient surfaces such as aluminium, copper or timber, which silica sand abrasive could damage.

  One manufacturer recommends a paste of baking soda with minimal water as a gentle scouring powder. Rust forms a water-soluble compound in a concentrated alkaline solution, so the paste can help with surface rust. Cold water is advised, because hot solutions can corrode steel. Aluminium is a poor candidate for cleaning, since the powder attacks its thin protective oxide layer. Yet a warm solution removes tarnish from silver that touches a piece of aluminium foil.

  Chemistry laboratories use the powder to neutralize unwanted acid solutions and acid spills. It reacts spontaneously with acids and releases carbon dioxide. It can serve as a milder, safer alternative to strong bases like sodium hydroxide. The compound is amphoteric, meaning it reacts with both acids and bases, yet it is not appropriate for neutralizing a base. Raising the temperature to 200 degrees Celsius speeds its breakdown, and above 850 degrees the resulting sodium carbonate converts to the oxide.

  On farms, a spray on leaves can stop fungi from growing, although it does not kill them. A two percent solution can discolour fruit, and a one percent solution can cause chlorosis. Sheep may receive it as a free choice dietary supplement to help prevent bloat. Cattle feed uses it as a buffering agent for the rumen.

  Classrooms know the powder best from the Baking Soda and Vinegar Volcano. The acid in vinegar produces carbon dioxide so fast that the liquid foams up and overflows its container. Dish soap and food coloring can sharpen the visual effect. Sealed inside a bottle with no escape for the gas, the same mixture can explode if the pressure climbs high enough.

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• 7. Ground To Factory

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  The biggest trona deposits lie in the Green River basin in Wyoming. In nature, sodium bicarbonate occurs almost exclusively as the mineral nahcolite or as part of trona. Trona is more common, because nahcolite dissolves more easily in water and the chemical equilibrium between the two favors trona. Significant nahcolite deposits sit in the United States, Botswana, Kenya, Uganda, Turkey and Mexico. It is sometimes found as a component of oil shale.

  Miners recover nahcolite by solution mining. Heated water is pumped through the nahcolite beds, and the dissolved mineral is then crystallized by cooling. Because the mineral is sometimes found in shale, it can come out as a co-product of shale oil extraction.

  Factories make the compound from sodium carbonate, carbon dioxide and water. Commercial baking soda is produced in a similar way. Soda ash, mined as the ore trona, is dissolved in water and treated with carbon dioxide. Sodium bicarbonate then precipitates out of the solution as a solid. Production ran at about 100,000 tonnes per year as of 2001, against a worldwide capacity of 2.4 million tonnes per year as of 2002.

  A box kept cool and dry, ideally in an airtight container that keeps out moist air, lasts at least two or three years without significant decomposition.

  The French chemist Nicolas Leblanc produced sodium carbonate, also called soda ash, in 1791. In 1801 in Berlin, the pharmacist Valentin Rose the Younger is credited with discovering sodium bicarbonate. In 1846 two American bakers, John Dwight and Austin Church, established the first factory in the United States to make baking soda from sodium carbonate and carbon dioxide.

  Rudyard Kipling's novel Captains Courageous mentions saleratus being used extensively in the 1800s in commercial fishing. Its job was to keep freshly caught fish from spoiling.

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• 8. Fridge And Film

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  In 1972, Arm & Hammer, the leading American brand of baking soda, began an advertising campaign built on an odd idea. Keep an open box in the refrigerator, the ads urged, and it will absorb odors. The campaign is considered a classic of marketing. Within a year, more than half of American refrigerators held a box of baking soda. There is little evidence that it works in that role, though it may be effective against musty smells in books.

  Groucho Marx turned "bicarbonate of soda" into a recurring punch line in Marx Brothers movies. In Duck Soup, he plays the leader of a nation at war. When a message arrives that his general is reporting a gas attack, Groucho tells his aide: "Tell him to take a teaspoonful of bicarbonate of soda and a half a glass of water."

  In A Night at the Opera, Groucho addresses the opening night crowd at an opera. Of the lead tenor he says: "Signor Lassparri comes from a very famous family. His mother was a well-known bass singer. His father was the first man to stuff spaghetti with bicarbonate of soda, thus causing and curing indigestion at the same time."

  The classic film All About Eve gives the powder a quieter scene. Gregory Ratoff plays Max Fabian, who has heartburn and asks for bicarbonate of soda. He drinks it in front of Margo Channing, played by Bette Davis, and lets out a prominent burp. Channing promises to always keep a box of bicarb with Max's name on it.

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