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 Inc. Blackboard Inc. Blackboard Inc. is an educational technology company with corporate headquarters in Washington, D.C.. It is known for Blackboard Learn, a learning management system. The company's CEO is William L. Ballhaus, formerly president and CEO of SRA International, who was also named chairman and president on January 4, 2016, following the resignation of Jay Bhatt, who had led Blackboard since October 2012. The firm provides education, mobile, communication, and commerce software and related services to clients including education providers, corporations and government organizations. The software consists of seven platforms called Learn, Transact, Engage, Connect, Mobile, Collaborate and Analytics that