Chemical substance made in a laboratory. Other chemical substances commonly encountered in pure form are diamond (carbon), gold, table salt (sodium chloride) and refined sugar (sucrose). However, in practice, no substance is entirely pure, and chemical purity is specified according to the intended use of the chemical. Chemical substances exist as solids, liquids, gases, or plasma, and may change between these phases of matter with changes in temperature or pressure. Chemical substances may be combined or converted to others by means of chemical reactions. Forms of energy, such as light and heat, are not matter, and are thus not "substances" in this
Compound (fortification) Compound (fortification) In military science, a compound is a type of fortification made up of walls or fences surrounding several buildings in the center of a large piece of land. The walls can either serve the purpose of being tall, thick, and impenetrable, in which case they would be made of wood, stone, or some other like substance; or dangerous to attempt to scale, in which case they could be made of barbed wire or electrified. Compounds can be designed to double as living spaces and military structures in the middle of hostile territory or as a military area within