Calcium sulfate an unusual property: when mixed with water at normal (ambient) temperatures, it quickly reverts chemically to the preferred dihydrate form, while physically "setting" to form a rigid and relatively strong gypsum crystal lattice: This reaction is exothermic and is responsible for the ease with which gypsum can be cast into various shapes including sheets (for drywall), sticks (for blackboard chalk), and molds (to immobilize broken bones, or for metal casting). Mixed with polymers, it has been used as a bone repair cement. Small amounts of calcined gypsum are added to earth to create strong structures directly from cast earth, an
Blackboard Jungle film was selected for preservation in the United States National Film Registry by the Library of Congress. The film was released on DVD in North America on May 10, 2005 by Warner Home Video. Notes Sources Blackboard Jungle Blackboard Jungle is a 1955 social commentary film about teachers in an interracial inner-city school, based on the novel "The Blackboard Jungle" by Evan Hunter and adapted for the screen and directed by Richard Brooks. It is remembered for its innovative use of rock and roll in its soundtrack and for the unusual breakout role of a black cast member, future Oscar