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. the CourseInfo brand was dropped in 2000. As an extension of CourseInfo's original two weeks for free courses, the company provided a hosted version "CourseSites" for teachers to try out for free. After having raised its seed round, the new company made a profit in its first year, and its sales in 1998 approached US$1 million. Other early products included Blackboard Classroom and Blackboard Campus both derivatives of the original platform. In 2000, Blackboard acquired iCollege/College Enterprises Inc.'s campus card, introducing commerce capability to Blackboard's portfolio. By 2006, the firm's learning platform software was used in more than 40% of