How was pig iron used in material change?

The first example of the use of pig iron in construction was the iron bridge over the SevernRiver, built at Colebrookdale, England, from 1775 to 1779. It spanned the river with a width of 30 meters. Within a few years, pig iron was widely used for roofs, columns and frames.The Theatre de France, built in Paris in 1786, had an iron constructed roof.The seven-storey production halls of the Salford South Cotton Spinning Mills, built in Manchester, England, in 1801, had a mixed structure of pig iron beams, columns and load-bearing walls, intended to facilitate fireproofing of the mills, in conjunction with the use of hollow clay bricks.At the beginning of the 19th century, this system developed into a complete internal beam-column skeleton. The skeleton originated as a basic method for primitive buildings, and its original role is reproduced here, as in the case of the Indian Royal Villa in Brighton, England, where the designers used thin iron columns to support the large dome roof, which weighed about 50 tons. Because, in addition to its small size, pig iron was superior in strength and economy to masonry materials, such buildings were fashionable at the time. in 1839, the stone vaults of Chatteris Cathedral were replaced with a new cast-iron roof; a few years later, iron roofs were used on the New Palace at Westminster. Later a new breakthrough in light was made by combining iron and glass. 1829~1831 saw the pioneering use of this combination of iron members and glass on the roof of the Orleans Gallery in the old Palais Royal in Paris. the Botanical Gardens of the Conservatory of Paris, constructed in 1833, is said to be the first large-scale building to be constructed entirely of iron frames and glass. This construction clearly influenced the later Crystal Palace in London.The use of pig iron declined for a time after the 1850s, largely due to architects' preference for other materials. However, iron remained a common material for most ordinary buildings with traditional functions, such as bridges, railway stations, greenhouses, vegetable farms, stores and office buildings. The United States, in particular, referred to the period between 1850 and 1880 as the "Pig Iron Era," and in 1854 the Harper & Brothers Building, a five-story printing press, was constructed in New York City.

London's Crystal Palace