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
What Are Little Boys Made Of? Iona and Peter Opie, this first appears in a manuscript by the English poet Robert Southey (1774–1843), who added the stanzas other than the two below. Though it is not mentioned elsewhere in his works or papers, it is generally agreed to be by him. The relevant section in the version attributed to Southey was: <poem> What are little boys made of What are little boys made of Snips & snails & puppy dogs tails And such are little boys made of. What are little girls made of Sugar & spice & all things nice</poem> Extracts from the nursery rhyme