Sir Henry Bessemer

Sir Henry Bessemer

British, 1813 - 1898

Sir Henry Bessemer (1813 - 1898)

Son of an expert metalsmith, in 1830 Bessemer took the skills he had learnt in the family workshop to London and for ten years tried to make his fortune with inventions including an embossed stamp to foil fraud, and a complex typesetting machine.

In 1840, he was asked by his sister to paint the title on her portfolio of flower paintings. He was a skilled calligrapher, and he decided to use gold paint for the letters. He knew that the brass used to make the powder cost only sixpence a pound, and was surprised to find that, in powder form, it cost 225 times that. The existing powder was made by hand in Germany, so he set about making it mechanically. After some initial failures, he perfected his machines; the bronze powder made him rich and allowed him the freedom to experiment further.

In 1854 he devised a very accurate, spinning mortar shell. Although the War Office showed no interest, Napoleon was keen, and Bessemer travelled to France to showcase his new design. However, he had to invent a stronger metal - cast steel - as the existing cast guns were too weak and kept cracking. At the time ships, railway lines, pipes and bridges were made from either cast or wrought iron. Wrought iron - made by working red-hot solid iron bars - is almost pure iron, with very little carbon. Consequently it is not brittle, and will bend rather than snap. Cast iron is very versatile, as it can be poured into moulds when molten and cast into complicated shapes, but is very brittle.

What Bessemer wanted was a material that was as malleable as wrought iron, but could be cast in moulds to make strong cannon. Cast steel had been around since the 1750s and was ideal for his purposes, but could only be made in fifty pound batches, insufficient for cannon. It also took a long time in the furnace, making it extremely expensive. Henry started experimenting with a small furnace, melting some steel in a bath of molten pig iron. Blowing air over the surface to raise the temperature to melt the steel, he noticed that a lump or two of pig iron would not melt. He discovered that this was because it was now steel; the air had burnt off the carbon from the surface of the iron.

He realised that if he could expose enough of the molten iron to the air he could convert it all into steel by burning off the carbon, so he made a new furnace with a hole in the top and tried to bubble air through the molten iron. The air blast burned off the excess carbon in the pig iron, and the reaction produced sufficient heat to keep the steel red-hot after the iron has melted, dispelling the need for any further expensive fuel.

Bessemer's process was ten times faster than the previous methods and used no fuel once the charge had been melted. It could make thirty tons at once, rather than fifty pounds. Bessemer was knighted in 1879 and awarded a Fellowship of the Royal Society. His process was used all over the world until the 1970s, when the last blow took place in Workington.