Long-term exposure to these compounds, on the other hand, may cause skin and respiratory allergies. Palladium: Palladium in bulk metallic form is completely inert. The same can't be said though of the metal in finely divided form, which can readily ignite in air. Silver: Silver compounds (example, colloidal silver), when absorbed into the body, may cause argyria, a condition characterized by the bluish-gray pigmentation of the skin, mucous tissues, and the eyes. Opening a silver account: An investor may open a silver account with one of the major banks in Switzerland. Here, silver can be bought or sold over the counter just like any foreign currency. However, the bank client does not own the actual silver metal. Instead, he/she has a claim against the bank for a specified quantity of the metal. It is the third element (after tungsten and carbon) with the highest melting point and the fourth densest (after platinum, iridium, and osmium). Commercially, rhenium is traded in powder form. Its principal application is in the making of certain parts of jet engines. Here, the metal is added to high-temperature nickel-based superalloys. Compared to gold, platinum is more precious, although its price is considered more volatile. One of the reasons for this is that its demand is driven by industrial uses or applications. For example, its price tends to be double that of gold's when world economy is stable, but significantly goes down in times of economic uncertainty. In the pH diagram, the pH symbol is labeled on the horizontal axis to signify the -log function of the concentration of H+ ion. The lines, which represent equilibrium for the concentration, are drawn for ions at unit activity. Other concentrations may be represented by additional lines. The voltage potential is represented by a vertical axis, which is labeled Eh, where "h" stands for hydrogen. They are offered in four varieties: 1. 1/10 ounce (oz.) coin - With a face value of USD10, 3.112 grams (g) in weight, 0.95 millimeters (mm) thick, and 16.5 mm in diameter. 2. 1/4 oz. coin - With a face value of USD25, 7.78 g in weight, 1.32 mm thick, and 22 mm in diameter. 3. 1/2 oz. coin - With a face value of USD50, 15.56 g in weight, 1.75 mm thick, and 27 mm in diameter.