System of measurement The same is true of quarts, gallons, etc. Six US gallons are a little less than five imperial gallons. The Avoirdupois system served as the general system of mass and weight. In addition to this there are the Troy and the Apothecaries' systems. Troy weight was customarily used for precious metals, black powder and gemstones. The troy ounce is the only unit of the system in current use; it is used for precious metals. Although the troy ounce is larger than its Avoirdupois equivalent, the pound is smaller. The obsolete troy pound was divided into 12 ounces, rather than the
Bullion precious metals. Bullion Bullion is gold, silver, or other precious metals in the form of bars or ingots. Typically, bullion is used for trade on a market. The word "bullion" comes from the old French word "bouillon", which meant "boiling", and was the term for the activity of a melting house. The value of bullion is typically determined by the value of its precious metals content, which is defined by its purity and mass. To assess the purity of gold bullion, the centuries-old technique of fire assay is still employed, together with modern spectroscopic instrumentation, to accurately determine its quality