Lye is the common name of various alkaline solutions, including soda lye (a solution of sodium hydroxide) and potash lye (a solution of potassium hydroxide).
History
The word derives from the root *
lau, meaning to wash (compare , ) and has
cognates in all the Germanic languages.
Traditionally, lye was made by leaching
in water, creating an alkaline liquor rich in potassium carbonate or potash. The alkalinity could be increased by adding
slaked lime, which would cause the solute to become potassium hydroxide or caustic potash.
Uses
Food
Lyes are used to cure many types of food, including olives (making them less bitter), canned
,
,
,
, candied pumpkins, and
.
Lye is the curing agent and namesake of the traditional Nordic lutefisk, a type of preserved fish. They are also used as a tenderizer in the crust of baked Cantonese Mooncake, in "zongzi" (glutinous rice dumplings wrapped in bamboo leaves), in chewy southern Chinese noodles popular in Hong Kong and southern China, and in Japanese ramen noodles. In the Philippines, lye is used in the making of kutsinta, a type of rice cake, and pitsi-pitsî.
In the United States, food-grade lye must meet the requirements outlined in the Food Chemicals Codex,
Soap
Both sodium hydroxide and potassium hydroxide are used in making
soap. Potassium hydroxide soaps are softer and more easily dissolved in water than sodium hydroxide soaps. Sodium hydroxide and potassium hydroxide are not interchangeable in either the proportions required or the properties produced in making soaps.
"Hot process" soap making also uses lye as the main ingredient. Lye is added to water, cooled for a few minutes and then added to oils and butters. The mixture is then cooked over a period of time (1–2 hours), typically in a slow cooker, and then placed into a mold.
Beauty
Lye, like other
hydroxide-based products, is also used as a hair
relaxer and straightener. Lye relaxers break a third of the chemical bonds in the hair strand and cause the hair to swell. Rinsing and then heating the hair straightens the strands.
Due to their high pH, they often cause scalp irritation.
Though no-lye solutions, which use
guanidine or lithium hydroxide, produce less scalp irritation, they may cause brittleness due to calcium deposits.
People of African descent have used lye to relax or straighten hair since the nineteenth century.
Household
Lyes are also valued for their cleaning effects. Sodium hydroxide is commonly the major constituent in commercial and industrial
Cleaning agent and clogged drain openers, due to its
fat-dissolving abilities. Lyes decompose greases via
Ester hydrolysis, yielding
water-soluble residues that are easily removed by rinsing.
Tissue digestion
Sodium or potassium hydroxide can be used to digest tissues of animal carcasses. Often referred to as alkaline hydrolysis, the process involves placing the animal carcass into a sealed chamber, adding a mixture of lye and water and the application of heat to accelerate the process. After several hours the chamber will contain a liquid with coffee-like appearance,
and the only solids that remain are very fragile bone hulls of mostly calcium phosphate, which can be mechanically crushed to a fine powder with very little force.
Sodium hydroxide is frequently used in the process of decomposing
roadkill dumped in landfills by animal disposal contractors.
Due to its low cost and easy availability, it has also been used to dispose of corpses by criminals.
Italy serial killer Leonarda Cianciulli used this chemical to turn dead bodies into soap.
In Mexico, a man who worked for drug cartels admitted to having disposed of more than 300 bodies with it.
Fungus identification
A 3–10% solution of potassium hydroxide (KOH) gives a color change in some species of mushrooms:
-
In Agaricus, some species such as A. xanthodermus turn yellow with KOH, many have no reaction, and A. subrutilescens turns green.
-
Distinctive change occurs for some species of Cortinarius and boletes
Safety
First aid
When a person has been exposed to lye, sources recommend immediate removal of contaminated clothing/materials, gently brushing/wiping excess off of skin, and then flushing the area of exposure with running water for 15–60 minutes as well as contacting emergency services.
Protection
Personal protective equipment including safety glasses, chemical-resistant gloves, and adequate ventilation are required for the safe handling of lye. When in proximity to lye that is dissolving in an open container of water, the use of a vapor-resistant face mask is recommended. Adding lye too quickly can cause a runaway thermal reaction which can result in the mixture boiling or erupting.
Storage
Lye in its solid state is
deliquescent and has a strong affinity for moisture in the air. As a result, lye will dissolve when exposed to open air, absorbing large amounts of atmospheric moisture. Accordingly, lye is stored in air-tight (and correspondingly moisture tight) containers. Glass is not a good material to be used for storage as severe alkalis are mildly corrosive to it. Similar to the case of other corrosives, the containers should be labeled to indicate the potential danger of the contents and stored away from children, pets, heat, and moisture.
Hazardous reactions
The majority of safety concerns with lye are also common with most corrosives, such as their potentially destructive effects on living tissues; examples are the
skin,
flesh, and the
cornea. Solutions containing lyes can cause
, permanent injuries, scarring and
blindness, immediately upon contact. Lyes may be harmful or even fatal if swallowed; ingestion can cause esophageal stricture. Moreover, the
solvation of dry
solid lye is highly
exothermic and the resulting
heat may cause additional burns or ignite flammables.
The reaction between sodium hydroxide and some metals is also hazardous. Aluminium, magnesium, zinc, tin, chromium, brass and bronze all react with lye to produce hydrogen gas. Since hydrogen is flammable, mixing a large quantity of lye with aluminium could result in an explosion. Both the potassium and sodium forms are able to dissolve copper.
Further reading
External links
