Zolotnik Zolotnik A zolotnik (in Russian: золотни́к; abbr.: zol.) was a small Russian unit of weight, equal to 0.1505 avoirdupois ounces, or 4.2658 grams (about 65.83 grains). Used from the 10th to 20th centuries, its name is derived from the Russian word "zoloto", meaning gold. As a unit, the zolotnik was the standard for silver manufacture, much as the troy ounce is currently used for gold and other precious metals. This unit was originally based on a coin of the same name. The zolotnik circulated in the Kievan Rus until the 11th century; it was equal in weight to the Byzantine
Refractory metals Refractory metals Refractory metals are a class of metals that are extraordinarily resistant to heat and wear. The expression is mostly used in the context of materials science, metallurgy and engineering. The definition of which elements belong to this group differs. The most common definition includes five elements: two of the fifth period (niobium and molybdenum) and three of the sixth period (tantalum, tungsten, and rhenium). They all share some properties, including a melting point above 2000 °C and high hardness at room temperature. They are chemically inert and have a relatively high density. Their high melting points make powder