Tuscan order A plain astragal or taenia ringed the column beneath its plain cap. Palladio agreed in essence with Serlio: "The Tuscan, being rough, is rarely used above ground except in one-storey buildings like villa barns or in huge structures like Amphitheatres and the like which, having many orders, can take this one in place of the Doric, under the Ionic." Unlike the other authors Palladio found Roman precedents, of which he named the arena of Verona and the Pula Arena, both of which, James Ackerman points out, are arcuated buildings that did not present columns and entablatures. A striking feature is
Ionic compound usually in a crystalline structure. Ionic compounds containing hydrogen ions (H) are classified as acids, and those containing basic ions hydroxide (OH) or oxide (O) are classified as bases. Ionic compounds without these ions are also known as salts and can be formed by acid–base reactions. Ionic compounds can also be produced from their constituent ions by evaporation of their solvent, precipitation, freezing, a solid-state reaction, or the electron transfer reaction of reactive metals with reactive non-metals, such as halogen gases. Ionic compounds typically have high melting and boiling points, and are hard and brittle. As solids they are almost