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
Devil sticks Devil sticks The manipulation of the devil stick (also devil-sticks, devilsticks, flower sticks, gravity sticks, or juggling sticks) is a form of gyroscopic juggling or equilibristics, consisting of manipulating one stick ("baton", 'center stick') between one or two other sticks held one in each hand. The baton is lifted, struck, or stroked by the two control sticks ('handsticks', 'sidesticks', or 'handles'), stabilizing the baton through gyroscopic motion. Devil sticks are believed to have originated in China in the distant past, in the form of simple wooden juggling sticks. Manipulating devil sticks is one of the circus arts and is sometimes