Well, we cannot vouch for different kinds of glasses. Some break more
easily than others, and some are less brittle. If a piece of glass
already has a crack in it, the crack will grow over time and weaken the
glass. Water only makes this worse -- water molecules can get inside a
crack in glass and speed the growth of the crack. A good rule of thumb
is that it's best to make the glass too thick than too thin. Better
safe than sorry, we always say!
What we can help you with is how much pressure there is at the
bottom of your tank. The pressure of water in the tank will be rho*g*h
at a depth h from the top. Add to that one atmosphere of air pressure,
and subtract it again because there's one atmosphere of air pressure on
the other side of the glass. rho is the density of water, 1000 kg per
cubic meter, and g is the acceleration of gravity, 9.81
meters/second**2. h is measured in meters, and the pressure will then
be in Pascals.
One suggestion for making a strong tank that is very large is to
use acrylic plastic instead of glass. Lucite, for example, is very
strong, very transparent, and resists cracking. Many of the very large
aquariums use acrylic plastic windows instead of glass.
(republished on 08/02/06)