The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica (SiO2) plus sodium oxide (Na2O) from soda ash, lime (CaO), and several minor additives. Often, the term glass is used in a restricted sense to refer to this specific use.
In science, however, the term glass is usually defined in a much wider sense, including every solid that possesses a non-crystalline (i.e. amorphous) structure and that exhibits a glass transition when heated towards the liquid state. In this wider sense, glasses can be made of quite different classes of materials: metallic alloys, ionic melts, aqueous solutions, molecular liquids, and polymers. For many applications (bottles, eyewear) polymer glasses (acrylic glass, polycarbonate, polyethylene terephthalate) are a lighter alternative to traditional silica glasses.
Paris (English /ˈpærɪs/, i/ˈpɛrɪs/; French: [paʁi] ( listen)) is the capital and largest city of France. It is situated on the river Seine, in the north of the country, at the heart of the Île-de-Franceregion. Within its administrative limits (the 20 arrondissements), Paris has a population of about 2,230,000, and its metropolitan area is one of the largest population centres in Europe, with more than 12 million inhabitants.