<Dl> <Dd> Railroads created virtually every major American industry: coal, oil, gas, steel, lumber, farm equipment, grain, cotton, textile factories, California citrus . </Dd> </Dl> <Dd> Railroads created virtually every major American industry: coal, oil, gas, steel, lumber, farm equipment, grain, cotton, textile factories, California citrus . </Dd> <P> The most important technological innovation in mid 19th century pig iron production was the adoption of hot blast, which was developed and patented in Scotland in 1828 . Hot blast is a method of using heat from the blast furnace exhaust gas to preheat combustion air, saving a considerable amount of fuel . It allowed much higher furnace temperatures and increased the capacity of furnaces . </P> <P> Hot blast allowed blast furnaces to use anthracite or lower grade coal . Anthracite was difficult to light with cold blast . High quality metallurgical coking coal deposits of sufficient size for iron making were only available in Great Britain and western Germany in the 19th century, but with less fuel required per unit of iron, it was possible to use lower grade coal . </P>

What are some periods of nation-building in u.s. history