Date: Winter 2009-2010
How was lye safely stored before plastic was invented? Why
can you not store lye in a glass container?
Lye - which is usually Caustic Soda or Sodium Hydroxide, is
traditionally stored in glass. It will after long storage discolour and
etch the surface of the glass - but it takes years, and leaves the
bottle looking cloudy and perhaps a bit unsightly.
The material that cannot be stored in glass is is Hydrofluoric Acid - HF
Hydrofluoric acid is used to etch glass - like the ones you used to see
in fancy barber shops. Now it is sold in plastic containers - High
Density Polyethylene. In the past the only safe container was a wax
lined ceramic jar. If you watched the first couple of episodes of
Breaking Bad they try to use HF to dissolve a body - but rather than
find a plastic tub, one of the crooks does the job in the bathtub. Baths
are made of metal and the shiny white coating is enamel glass. Guess
what happened to the bath??
Tennant Creek High School
There are three terms, used in common language: The first, is "lye". This
refers to the chemical compound calcium oxide (CaO). This compound reacts
rapidly with water forming (Ca(OH)2) referred to in the older chemical
literature as "slaked lime". In the presence of air and or some other source
of CO2 forms Ca(CO3), calcium carbonate. You cannot store "lye" in glass
because glass (SiO2) can dissolve in highly alkaline solution. The reaction
is slow, depending upon particle size, and other variables, but it happens.
That is why lye is not stored in glass containers. Before "plastics", which
have various resistance to alkaline substances, high purity "lye" was stored
in platinum or gold containers. At a less demanding container CaO can be
stored in glass if the sample and container are "flame" dried to drive off
the water under vacuum.
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Update: June 2012