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. developer, increased Blackboard's client base to nearly 6,000 educational institutions, companies and government agencies. The company has also made acquisitions in order to expand its product base with other education-related services and software. Such acquisitions include: NTI Group in 2008, which became the basis for Blackboard Connect; providers of online and mobile collaboration tools, Wimba, Inc. and Elluminate, Inc. in 2010, to form Blackboard Collaborate; iStrategy in December 2010, which led to the creation of Blackboard Analytics; Presidium Inc. in 2011, which developed into Blackboard Student Services. Following the company's merger with Edline in 2011, Edline was later renamed Blackboard