Troy weight them Holland troy, Paris troy, etc. Their values varied from one another by up to several percentage points. Troy weights were first used in England in the 15th century, and were made official for gold and silver in 1527. The British Imperial system of weights and measures (also known as Imperial units) was established in 1824, prior to which the troy weight system was a subset of pre-Imperial English units. The troy ounce in use today is essentially the same as the British Imperial troy ounce (1824–1971), adopted as an official weight standard for United States coinage by Act of
Refractory metals to other refractory metals, where it adds ductility and tensile strength. Rhenium alloys are being used in electronic components, gyroscopes and nuclear reactors. Rhenium finds its most important use as a catalyst. It is used as a catalyst in reactions such as alkylation, dealkylation, hydrogenation and oxidation. However its rarity makes it the most expensive of the refractory metals. Refractory metals and alloys attract the attention of investigators because of their remarkable properties and promising practical usefulness. Physical properties of refractory metals, such as molybdenum, tantalum and tungsten, their strength, and high-temperature stability make them suitable material for hot metalworking