lye

lye, name commonly used for a strongly alkaline solution. It originally meant a solution of potassium carbonate (potash) prepared by leaching wood ashes with water, but now the name also means a solution of sodium hydroxide or potassium hydroxide. Lye is also used to refer to the undissolved solute. Common household lye is usually sodium hydroxide. Lye should be used with caution as it is caustic and poisonous.

Alkaline (see alkali) liquid extracted by soaking wood ashes in water, commonly used for washing and in making soap. More generally, lye is any strong alkaline solution or solid, such as sodium hydroxide (caustic soda) or potassium hydroxide (caustic potash).

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Lye is a corrosive alkaline substance, commonly, sodium hydroxide (NaOH). Previously, lye was among the many different alkalis leached from hardwood ashes. In modern day, lye is commercially manufactured using a membrane cell method, which is an improvement from the previous diaphragm cell methods of Castner-Kellner, Gibbs, and Nelson.

Solid dry lye is commonly available as flakes, pellets, microbeads, and coarse powder. It is also available as solution, often dissolved in water. Lye is valued for its use in food preparation, soap making, biodiesel production, and household uses, such as oven cleaner and drain opener.

Food uses

Lye is used to cure many types of food, such as: lutefisk, green olives, hominy, lye rolls, century eggs, pretzels, zongzi (Chinese glutinous rice dumplings), and Chinese noodles. In the United States food-grade lye must meet the requirements outlined in the Food Chemicals Codex (FCC), as prescribed by the US Food and Drug Administration (FDA). Lower grades of lye are commonly used as drain openers and oven cleaners and should not be used for food preparation.

Safety

Both solid dry lye and lye solutions are corrosive and will degrade organic tissue.

Hazardous reactions

Solid sodium hydroxide or solutions containing high concentrations of sodium hydroxide may cause chemical burns, permanent injury or scarring, and blindness. Lye (sodium hydroxide) may be harmful or fatal if swallowed.

Solvation of sodium hydroxide is highly exothermic, and the resulting heat may cause heat burns or ignite flammables.

Avoid all contact with organic tissue (including human skin, eyes, mouth, and animals or pets). Keep away from clothing. Avoid all contact with aluminium.

The combination of aluminium and sodium hydroxide results in a large production of hydrogen gas: 2Al(s) + 6NaOH(aq) → 3H₂(g) + 2Na₃AlO₃(aq). Hydrogen gas is explosive; mixing lye (sodium hydroxide) and aluminium in a closed container is therefore dangerous. In addition to aluminium, lye (sodium hydroxide) may also react with magnesium, zinc (galvanized), tin, chromium, brass, and bronze to produce hydrogen gas and is therefore dangerous. Do not allow lye to contact these metals.

Lye may react with various sugars to generate carbon monoxide, which is a poisonous gas; mixing sodium hydroxide and sugar in a closed container is therefore dangerous. Do not allow lye to contact sugar.

Protection

Personal protection for the safe handling of lye includes safety glasses, chemical-resistant gloves, and adequate ventilation. When in the close proximity of lye dissolving in an open container of water, a vapor-resistant face mask is recommended.

Storage

Lye is a deliquescent salt and has a strong affinity for moisture. Lye will deliquesce (dissolve or melt) when exposed to open air. It will absorb a relatively large amount of water from the atmosphere (air) if exposed to it. Eventually, it will absorb enough water to form a liquid solution because it will dissolve in the water it absorbs. Lye should be stored in an airtight resealable container.

Hygroscopic substances are often used as desiccants to draw moisture away from water-sensitive items. Desiccants should never be placed inside a canister of lye because lye has much stronger hygroscopic properties than activated carbon and silica gel (the most common ingredients in commercial desiccant packets) and will pull and absorb the water from the desiccant packets. Do not place desiccant packets inside containers of lye.

Lye should be stored in air-tight plastic containers. The containers should be labeled to indicate the potential danger of the contents and stored away from children, pets, heat, and moisture.

See also

• Sodium hydroxide, caustic soda
• Potassium hydroxide, caustic potash
• Sodium carbonate, soda ash
• Urine, chamber lye
• Fight Club (film)

Notes

References

1. Federal Food, Drug, and Cosmetic Act. US Food and Drug Administration. .
2. Food Chemicals Codex. United States Pharmacopeia. .
3. Lye Safety Precautions. Certified Lye. .
4. Lye (Sodium Hydroxide). Certified Lye. .
5. Material Safety Data Sheet: Sodium Hydroxide, Solid. Certified Lye. .
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