Tin allowed for the much more complex shapes cast in closed moulds of the Bronze Age. Arsenical bronze objects appear first in the Near East where arsenic is commonly found in association with copper ore, but the health risks were quickly realized and the quest for sources of the much less hazardous tin ores began early in the Bronze Age. This created the demand for rare tin metal and formed a trade network that linked the distant sources of tin to the markets of Bronze Age cultures. Cassiterite (SnO), the tin oxide form of tin, was most likely the original source
Copper in heat exchangers introduced in 1890 for seawater service. By the 1920s, a 70% Cu-30% Ni alloy was developed for naval condensers. Soon afterwards, a 2% manganese and 2% iron copper alloy was introduced for better erosion resistance. A 90% Cu-10% Ni alloy first became available in the 1950s, initially for seawater piping. This alloy is now the most widely used copper-nickel alloy in marine heat exchangers. Today, steam, evaporator, and condenser coils are made from copper and copper alloys. These heat exchangers are used in air conditioning and refrigeration systems, industrial and central heating and cooling systems, radiators, hot water tanks, and