Period 6 element form, as an X-ray radiocontrast agent for imaging the human gastrointestinal tract. Soluble barium compounds are poisonous due to release of the soluble barium ion, and have been used as rodenticides. New uses for barium continue to be sought. It is a component of some "high temperature" YBCOsuperconductors, and electroceramics. The lanthanide or lanthanoid (IUPAC nomenclature) series comprises the fifteen metallic chemical elements with atomic numbers 57 through 71, from lanthanum through lutetium. These fifteen elements, along with the chemically similar elements scandium and yttrium, are often collectively known as the rare earth elements. The informal chemical symbol Ln is
Nickel silver (Shadow model); these are far rarer than traditional lacquered brass saxophones. Student-level flutes and piccolos are also made of silver-plated nickel silver, although upper-level models are likely to use sterling silver. Nickel silver produes a bright and powerful sound quality; an additional benefit is that the metal is harder and has more corrosion resistance than brass. Because of its hardness, it is the most commonly used material for woodwind keys. Most clarinets, flutes, oboes and similar wind instruments have nickel silver keys, normally silver-plated. It is used to produce the tubes (called staples) onto which oboe reeds are tied. Many