They discovered the element from platinum ore samples as well as from the mineral gadolinite. They named it after the Latin word "rhenus", for "Rhine", one of Europe's longest and most important rivers. As for the precious metals gold and silver, both are known to be already in use since ancient times (gold was in use probably as early as before 6000 BC, while silver probably as early as before 5000 BC). It is one of the coinage metals (along with silver and copper). It is used, customarily and legally, as a means of payment or a medium of exchange. Gram and troy weight are the units of measurement used for gold. To indicate the amount of gold present in, say, a piece of jewelry, the term "carat" is used. mol-1 (third) The principal use of rhodium is as a catalytic converter in automotive vehicles, which reduces the toxicity of engine emissions by converting these into less harmful gases. Rhodium is likewise used in jewelry, such as when it is electroplated on platinum, sterling silver, or white gold (called rhodium flashing) to strengthen the metal or give it a reflective surface. A trommel specifically consists of a rotating metal tube that is slightly tilted, with a screen at the discharge end. Attached to the inside part of the metal tube are lifter bars. Ore is fed into the trommel through its elevated end. Pressurized water is supplied to the tube and the screen sections. Canada's official gold bullion coin - The Canadian Gold Maple Leaf - is made of 99.999% gold; and so are these four other gold bullion coins: 1. British Britannia (with a face value of 100 pounds). 2. Chinese Gold Panda (with face values of 500, 200, 100, 50, and 25 Yuan). 3. Swiss Helvetia Head (with face values of 100, 20, and 10 Swiss francs). Trading in GETFs involves payment of commission and storage fee (charged on an annual basis). The expenses incurred in relation to the handling of the fund are charged through the selling of a certain amount of the gold as represented by the certificate. Over time, the amount of gold in the certificate, as may be expected, decreases.