CHAMBERS'S INFORMATION FOR THE PEOPLE". 



and presently a red stream of molten spiegeleisen 

 is run into its mouth, till it amounts to from 5 to 

 10 per cent of the whole charge. The spiegel- 

 eisen restores the proper amount of carbon to 

 produce steel ; and after it is added, the blast is 



Fig. 6. Bessemer Converting Vessel : 

 a, a, a, tuyeres ', b, air-space : c, melted metal. 



again turned on for a few minutes to secure its 

 thorough incorporation. A man standing on a 

 small platform can by means of the hydraulic 

 machinery empty the contents of the huge con- 

 verters into the ladle, raise or lower the ladle 

 itself, and turn it round from point to point, so as 

 to fill the moulds by means of a plug in its 

 bottom. Steel made in this way is not sufficiently 

 dense, and accordingly the moulds are lifted off 

 the ingots by means of a hydraulic crane, and the 

 latter removed while still hot, and condensed 

 under heavy steam-hammers. After this, they 

 are rolled into rails, tires, plates, and various 

 other heavy objects, for which this steel has been 

 found to be suitable. 



Until very lately, Bessemer steel has only been 

 made from a high-priced pig-iron such as that 

 obtained from haematite; but in the year 1879, 

 Messrs Thomas & Gilchrist, by adopting a basic 

 instead of an acid (siliceous) lining to the 

 Bessemer converter, succeeded in making good 

 steel from Cleveland and other cheap pig-irons. 

 Previously the difficulty had been to get rid of 

 the phosphorus so commonly present to an 

 injurious extent in these, since it destroyed the 

 usual siliceous lining. When, however, a lining 

 of magnesian limestone made into bricks, and 

 fired at a high temperature, is used, it provides, 

 with the help of some lime and oxide of iron, a 

 base for the phosphoric acid to combine with, 

 and thus this deleterious body is eliminated from 

 the steel. Indeed it seems to be the case that 

 sulphur, another common impurity, is removed 

 during the process as well. This method of 

 converting impure pig-iron into steel has already 

 become a most important one. 



Since the year 1868 what are called the 

 Siemens and the Siemens-Martin processes of 



410 



making steel have become rapidly developed. 

 In both the hearth portion of the furnace used 

 resembles that shewn in fig. 5, but Siemens' 

 gas-producers and regenerators are employed. 

 Dr Siemens' direct process consists in melting 5 

 tons of pig-iron on the bed of the furnace, adding 

 to this 2 to 2i tons of any rich and pure iron ore, 

 and finally some spiegeleisen a small quantity 

 of limestone being from time to time thrown in 

 during the operation. In the Siemens-Martin 

 process, pig-iron is also first melted down, but 

 either iron or steel scrap is then added to the 

 extent of from 3 to 10 times the weight of pig; 

 and finally, as in the direct process, a certain 

 quantity of spiegeleisen or ferro-manganese, each 

 of which contains a known percentage of carbon 

 and manganese, is thrown into the molten metal, 

 which is then cast into ingots. It is well to bear 

 in mind that the steel so produced cannot be 

 tempered like crucible steel. 



Like wrought-iron, steel is malleable, ductile, 

 forgeable, and weldable ; but it differs from 

 wrought-iron in being fusible and highly elastic, 

 as well as more tenacious. It also takes a 

 higher polish, and rusts less easily ; but the most 

 characteristic and useful property of steel is that 

 by which it can be tempered to any degree of 

 hardness. Thus it is made exceedingly hard and 

 brittle if plunged while red-hot into cold water, 

 but its original softness may be restored by re- 

 heating and then slowly cooling it. When it is 

 first hardened in the manner just stated, the 

 various degrees of hardness are given by reheat- 

 ing and suddenly cooling it at different tempera- 

 tures. The 'temper' or hardness is shewn by 

 the colour the steel assumes during the process of 

 reheating, as the following table, taken from 

 Parkes' Chemical Essays, will explain : 



Until within the last fifteen years, steel received 

 its chief application in the manufacture of cutting- 

 tools and instruments used in different trades, 

 small-arms, domestic cutlery, wire of various 

 kinds, springs, needles, steel pens, and other 

 objects of limited size. For these purposes a 

 fine quality of steel is required ; but, at the 

 present time, the cheaper kinds made by the 

 Bessemer and Siemens-Martin processes are 

 replacing malleable iron with great advantage 

 for many objects of large size. Among these 

 are rails and plates, ships, toothed wheels, 

 shafts, cranks, bells, and heavy guns. Steel 

 rails are now very largely used ; and owing 

 to the new processes, steel rails lately costing 

 .45. a ton, could, in 1885, be bought for $. 

 In .the construction of large tools, steel is 



