Re: Is water the only substance that can exist as solid, gas, and liquid?

The short answer is: Yes, most substances can exist as a solid, liquid, and 
gas. However, at common temperatures and atmospheric pressure, only a few 
substances exist in all three phases.

Some examples:
	mp is melting point in degrees C
	bp is boiling point in degrees C
	All data are from the Merck Index, a reference work found in 
most libraries

Acetic acid (vinegar is a dilute solution of acetic acid)
	mp 16.7, bp 118
	Pure acetic acid is frequently called "glacial acetic acid" because its 
melting point of about 62 degrees F allowed it to freeze in the laboratory 
in winter.

Benzene
	mp 5.5, bp 80

Chloroform
	mp –63, bp 61
	It would have to be very cold to freeze chloroform, but this is not as 
cold as dry ice.

Mercury
	mp –38.8, bp 357
	While mercury has a high boiling point, it has a relatively high vapor 
pressure at room temperature, and requires careful handling.

Ammonia
	mp -78, bp –33
	It would have to be very cold to freeze ammonia, but this is comparable 
to the temperature of dry ice.

I am sure a more thorough investigation would turn up quite a few more 
substances.