But of all the novelties connected with the steel manufacture, those by Mr. Bessemer have attracted the most notice within the last few years. He has taken out five or six {patents ou the subject. In his hands the difference between iron and steel is simply one of degree, for it is not easy to say where Bessemer iron ends and Bessemer steel begins. It was at the Cheltenham meeting of the British Association, in 1856, that the process first attracted attention. Mr. Bessemer con ceived that pig-iron might be converted into malleable iron, and then into steel, without any additional consumption of fuel. Pig-iron contains more carbon than the others ; and if oxygen could be made to burn a portion of this away, the object would be accomplished. How, then, to expose molten pig-iron to the action- of oxygen I He decided that a blast would best effect this. He formed a fire-brick furnace of small size, with tuyPre holes near the bottom, and two larger holes half-way up. Molten pig-iron flowed at once from a blast-furnace to this small furnace or cylinder, and a blast was driven into the cylinder. A violent commotion ensued, and an intense heat resulted from the combination of the oxygen in the blast with the carbon in the molten mass. Volumes of flame and a few sparks were produced, and then sort of eruption of slag. flames again appeared ; for 1101110 of the oxygen formed an oxide with eouie of the Iron, and acted as a kind of solvent for sulphur and earthy matters. The pig iron lost about 12 per cent, of its weight during this process. The rich slag thrown out might be afterwards treated with carbon gases, and made to yield more iron. When the flames and sparks had subsided, a plugged hole was opened, and the metal poured into an ingot-mould, without leaving any cinder or oxide. The process took little more than half an hour, and no fuel was used. While in the cylinder, the metal was not a mere pasty mass, it was a boiling fiery fluid. At a certain stage, the iron became crude steel. By continuing the boil, more carbon was driven out, and purer steel resulted. In short, any medium between the softest iron and the hardest steel might bo produced by varying the duration of the process. One kind, called by Mr. Bessemer semt steel, is more elastic, harder, and atrong,er than bar-iron, but not so hard and fine as steel ; it is useful for light and strong purposes; it is more difficult to roll than iron, but is stronger and more durable, and is therefore considered to be cheaper in the end.
In the three years next following this announcement of Mr. Bessemer's invention, the comments took the whole range between the highest praise and the most marked disapproval. The inventor and his friends claimed for the novelty a diminution of labour, time, and cost ; the production of a metal more homogeneous than by the common method; no residue of wasteful slag; and the power of producing ingots of any weight from one to seven or more ewts. Tho Llanelly Tin-Plato Works supplied Mr. Bessemer with some pig-iron such as they used for producing
the best sheet-iron: he converted it into a soft ingot, which was wrought at a white heat into a slab by the force of a steam-hammer, and then rolled into very good sheet-iron for tin-plate. Mr. Adams stated that an amateur might easily make a bit of steel, by melting 4 ozs. of cast iron in a crucible, pouring it into the bowl of a large tobacco-pipe, and using the stem as a blow-pipe. On the other hand, most of the manu facturers found fault with the Bessemer process. Some of them said that, although the process removes the carbon and silicon more com pletely than the ordinary method, and the sulphur about as well, it leaves the phosphorus untouched, which they regarded as a fatal blot. Others made trial of the process, and declared the iron or steel produced to be bad. In 1859, after patenting several modifica tions of his plan, Mr. Bessemer described his process, in a some what altered form, before the Institute of Civil Engineers. He had been endeavouring to get rid more completely of the sulphur and phosphorus. He used Swedish iron instead of English for the best steel, poured the molten metal into cold water instead of into a large mould, re-melted it, and finally poured it into small moulds. Other changes had been made in the apparatus and the process. Some of the ingots exhibited possessed wonderful tensile power. A bar 3 inches square was bent round until the outer curve was lengthened from 12 to 16i inches, and the inner lessened from 12 to 71 inches, cold, and without a flaw. Four iron rods, I inches diameter, were twisted cold into a cable; the rods stretched one foot in four during the process, and thinned out in inverse proportion. A steel bar, 2 inches square, was twisted cold into a spiral at an angle of 45°. A round steel bar was hammered cold into the form of a horse-shoe.
At the present time, the Bessemer process is under probation. Works have been erected at Sheffield to put it in operation ; and similar establishments have been founded in several Continental states. By this means the system will obtain that which alone can determine its value—a fair trial on a large scale. Persona of moderate views believe that the semi-steel will become useful for railway purposes, as being harder than bar-iron, and for marine engine-work, because it is lighter than iron for equal strength. How far fine steel can be profit ably produced, without the converting process, is still a disputed point.
In 1853, Sheffield had 160 steel-converting furnaces, and 1495 east steel " holes "—about 16 holes to a casting-furnace. Of the 20,000 to 40,000 tons of Swedish iron annually imported, nearly all goes to Sheffield to be converted into steeL Including Russian and English iron, it is supposed that about 50,000 tons are annually made into steel, of which 30,000 tona are cast-steel. The value of this quantity is roundly estimated at about 1,500,000/. yearly.