<P> Puddling produced a structural grade iron at a relatively low cost . Puddling was a means of decarburizing pig iron by slow oxidation as the iron was manually stirred using a long rod . The decarburized iron, having a higher melting point than cast iron, was raked into globs by the puddler . When the glob was large enough the puddler would remove it . Puddling was backbreaking and extremely hot work . Few puddlers lived to be 40 . Puddling was done in a reverberatory furnace, allowing coal or coke to be used as fuel . The puddling process continued to be used until the late 19th century when iron was being displaced by steel . Because puddling required human skill in sensing the iron globs, it was never successfully mechanised . </P> <P> Up to that time, British iron manufacturers had used considerable amounts of imported iron to supplement native supplies . This came principally from Sweden from the mid-17th century and later also from Russia from the end of the 1720s . However, from 1785, imports decreased because of the new iron making technology, and Britain became an exporter of bar iron as well as manufactured wrought iron consumer goods . </P> <P> Hot blast, patented by James Beaumont Neilson in 1828, was the most important development of the 19th century for saving energy in making pig iron . By using waste exhaust heat to preheat combustion air, the amount of fuel to make a unit of pig iron was reduced at first by between one - third using coal or two - thirds using coke; however, the efficiency gains continued as the technology improved . Hot blast also raised the operating temperature of furnaces, increasing their capacity . Using less coal or coke meant introducing fewer impurities into the pig iron . This meant that lower quality coal or anthracite could be used in areas where coking coal was unavailable or too expensive; however, by the end of the 19th century transportation costs fell considerably . </P> <P> Two decades before the Industrial Revolution an improvement was made in the production of steel, which was an expensive commodity and used only where iron would not do, such as for cutting edge tools and for springs . Benjamin Huntsman developed his crucible steel technique in the 1740s . The raw material for this was blister steel, made by the cementation process . </P>

How did cities change in countries affected by the industrial revolution