I. Historical reasons

This should start after World War II, when the world was in a hurry and it was urgent to strengthen trade between countries.

However, there was no unified settlement currency at that time. In this context, the American-led Brinton Woods system was established.

According to the regulations, gold and dollars can be exchanged in equal proportions, and an ounce of dollars can be exchanged for 35 dollars. The United States also promised to unconditionally exchange dollars for gold at the ratio of 35: 1.

In this way, the dollar became the main settlement currency at that time, and in order to facilitate the exchange of dollars, many countries simply stored gold in the United States, and they could exchange dollars directly when needed, saving the trouble of transportation.

Second, safety.

Because the United States is said to have the safest vault in the world, there has never been an accident since 1942 was opened.

Third, promote transactions.

Both gold and dollar are the main hedging instruments and reserve currencies in the world. The stronger the dollar, the weaker the demand for gold, so many countries can exchange gold for dollars.

The color of gold is golden yellow, which has a metallic texture and is not easy to decompose. The density is 19.3g/cm3 and the melting point is1064.4℃; Good ductility, can be pressed into thin foil, and has extremely high heat and thermal conductivity. The resistance of pure gold is 2.4P Pure gold has good chemical resistance and is the best electroplating material.

As a precious metal, gold has good physical properties. "Real gold is not afraid of fire" means that gold has high chemical stability and is not easy to react with other substances, so there is no need to worry about oxidation and discoloration. Even in the molten state, it will not be oxidized and discolored, and it will still be golden yellow after cooling. High density and heavy touch. Good toughness and ductility, good electrical conductivity. Pure gold is bright yellow, but the color changes greatly after mixing with other metals, such as gold-copper alloy is dark red, and silver-containing alloy is light yellow or grayish white. Gold is easily ground into powder, which is also the reason why gold is dispersed in nature. Pure gold jewelry is also easy to wear and lose weight.

In Mendeleev's periodic table, the atomic number of gold is 79, that is, the nucleus of gold contains 79 protons, which are positively charged. At the same time, gold has good chemical stability because it conforms to the half-full law. In the metal market, gold and ruthenium, rhodium, palladium, osmium, iridium, platinum and other metals are collectively called precious metals.

Although gold is a very soft metal, it is not as good as lead and tin. Nails can be used to draw marks on pure gold, which makes gold very easy to process. But this is not ideal for the manufacturers of decorations, because it is easy to scratch the decorations, make them lose their luster and even affect their appearance. Therefore, when gold is used to make jewelry, copper and silver are usually added to improve its hardness.

Gold is easy to forge and extend, and can be ground into transparent and green gold foil with a thickness of 0.001mm. 0.5g of gold can be drawn into160m long gold wire.