Denatured alcohol

Denatured alcohol is ethanol which has been rendered toxic or otherwise undrinkable, and in some cases dyed. It is used for purposes such as fuel for spirit burners and camping stoves, and as a solvent. Traditionally, the main additive was 10% methanol, which gave rise to methylated spirits. There are diverse industrial uses for ethanol, and therefore literally hundreds of recipes for denaturing ethanol. Typical additives are methanol, isopropanol, methyl ethyl ketone, methyl isobutyl ketone, denatonium, and even (uncommonly) aviation gasoline.

In the phrase denatured alcohol, denatured means "a specific property of ethanol, its usefulness as a beverage, is removed". The ethanol molecule is not denatured in the sense that its chemical structure is altered.

There is no duty on denatured alcohol in most countries, making it considerably cheaper than pure ethanol. Consequently, its composition is tightly defined by government regulations which vary between countries. Different additives are used to make it both unpalatable and poisonous in such a way that is hard to rectify through distillation or other simple processes. Methanol is commonly used for this in part because it has a boiling point close to that of ethanol, and separating it by distillation is difficult, but not impossible as methanol and ethanol form a zeotropic mixture (the opposite of an azeotropic mixture). In many countries, it is also required to be dyed blue or purple with an aniline dye.

The tax-exempt status for denatured alcohol dates from the mid-19th century. For instance the United Kingdom introduced legislation in 1855 to permit ethanol containing 10% wood-naphtha to be exempt.

Formulations
There are several grades of denatured alcohol, but the denaturants used are generally similar. The formulation for completely denatured alcohol, according to British regulations is typical:

"Completely denatured alcohol must be made in accordance with the following formulation: with every 90 parts by volume of alcohol mix 9.5 parts by volume of wood naphtha or a substitute for wood naphtha and 0.5 parts by volume of crude pyridine, and to the resulting mixture add mineral naphtha (petroleum oil) in the proportion of 3.75 litres to every 1000 litres of the mixture and synthetic organic dyestuff (methyl violet) in the proportion of 1.5 grammes to every 1000 litres of the mixture."

Uses
A common use is as a fuel for marine and ultra-light camping (backpacking) stoves. Its main advantages are its low cost, its ability to be extinguished by water, the fact that it is not explosive, and its ability to be transported without special containers. However, safety concerns do arise from the near-colourless flame with which alcohol burns. In brightly-lit areas, an alcohol flame can be essentially invisible, creating a potential hazard wherein persons can be burned by contacting flames they cannot see.

One notable use is as a sanding aid, as the alcohol helps to more easily remove the excess sawdust that results from sanding wood, because it does not open the wood grain the way that water would. Methylated spirits may also be used to kill mealybugs.

Denatured alcohol is often also used for its solvent properties, for example to remove ink stains from upholstery or clothes. It is also well known to burn cold relative to paraffin when thrown upon a naked flame.

Antiseptic mouthwash such as Listerine is denatured to avoid being taxed as an alcoholic beverage.

Consumption and toxicity
Despite its poisonous nature, denatured alcohol is sometimes consumed by the desperate or ignorant, which can result in blindness or death. To help prevent this, denatonium is often added to give the substance an extremely bitter flavor. Substances such as pyridine help to give the mixture an unpleasant odor, and emetic (vomiting) agents such as syrup of ipecac may also be included.

Methanol itself is not toxic; rather, the toxicity is due to the accumulation of its metabolites &mdash; formaldehyde and formic acid. Because the metabolic pathways for ethanol and methanol share a common enzyme, alcohol dehydrogenase, ethanol can be used to treat methanol poisoning by blocking the enzyme until the body can excrete enough methanol through the lungs and skin. In a documented case, a ship worker poisoned while cleaning out a methanol tank was successfully treated with administration of a good portion of the liquor in the ship's "medicine chest."

It has also appeared to be a problem in some parts of South Africa, homeless people drink denatured alcohol, using pieces of bread as a filter for the bad taste. The use of the bread is nullified, as after using it as a filter, the bread is sometimes eaten. The amount of homeless drinking denatured alcohol in South Africa has led to a change in the concoction, removing methanol to make it less toxic.