Smelting is the process in which an ore is melted to separate the useful metal form other elements. This process is usually carried out in a blast furnace, which is a tall, cylindrical furnace lined with refractory bricks. The ore, along with a flux (such as limestone) and a fuel (such as coke), is charged into the furnace at the top. The fuel is burned at the bottom of the furnace, which creates a hot, reducing atmosphere. This atmosphere causes the ore to melt and the metal to be reduced to its elemental form. The molten metal then flows to the bottom of the furnace, where it is tapped off. The slag, which is a mixture of the flux and the impurities from the ore, floats on top of the molten metal and is also tapped off.