Sulfur dioxide is a compound formed by the
combination of the elements sulfur and oxygen.
On a weight basis, the proportion of the elements is about I part sulfur to I part oxygen, or
more exactly, 50.05 percent to 49.95 percent,
respectively. At standard conditions of temperature and pressure, sulfur dioxide is a colorless gas with a characteristic pungent odor. It
may be cooled and compressed to a colorless
liquid, which, at one atmosphere pressure, boils
at 14°F (10.0°C) and freezes at -104.6°F (-75.9°C). Sulfur dioxide liquid is heavier than
water, and has a specific gravity of 1.436 at
32°F (0°C). As a gas, it is more than twice as
heavy as air; its relative density is 2.2638 at
atmospheric pressure and 32°F (0°C).
Sulfur dioxide is not flammable or explosive
in either the gaseous or liquid state. It is a relatively stable chemical. Temperatures above
3632°F (2000°C) are required to bring about
detectable decomposition of sulfur dioxide. Dry
sulfur dioxide (less than 100 ppm water) is not
corrosive to ordinary metals. However, in the
presence of even small amounts of water, sulfur
dioxide becomes corrosive to most metals, with
exceptions including lead, Type 316 stainless
steel, and certain alloys. Glass and certain plastics are also resistant to moist sulfur dioxide.
