METALS AND SOME OF THEIR COMPOUNDS 263 



removal. The mould being placed round the rail end receives 

 the melted metal, and after solidification the excess of iron can 

 be cut or ground away to the level of the rail. The temperature 

 produced in the mixture is said to be about 3500 C. ; it is 

 sufficiently high to melt every known metal. 



The reaction in thermit being once started cannot be stopped, 

 and this material has been found in many of the incendiary 

 bombs used in the war. 



STEEL 



Man has been described as a tool-using animal, but the 

 materials accessible in prehistoric times were very different from 

 those which are available now. The use of stone and bone cer- 

 tainly preceded that of any metal, and naturally the metals 

 which were obtainable either in the native state, like gold and 

 copper, or by very simple operations, would come into use 

 before those which were more difficult to procure. The Stone 

 Age therefore preceded the Bronze Age, and this came before 

 the Iron Age, though doubtless these periods overlapped. 



Modern metallurgy is the result of constant experiment and 

 research. It has given the world modern steel, which means 

 greater security on railway and steamship, greater capacity in 

 foundry and forge, and consequently the monster ocean-going 

 passenger ships as well as ships of war and big guns. 



One of the difficulties which surround any attempt to give an 

 account of some of these developments in a small space is to 

 find a definition of steel. Everyone knows that it is a sort of 

 iron but with qualities of its own. Pure elemental iron is a pro- 

 duct which is extraordinarily difficult to obtain and is not found 

 among commercial metals. The nearest approach to it is the 

 finest malleable iron of which wire is made. This is distinguished 

 by its fibrous texture, toughness, and capability of welding. 

 Wrought-iron is fusible only at a white heat, but at any tempera- 

 ture above redness & is soft and can be hammered or drawn into 

 any desired shape, and if at this temperature two pieces are 

 hammered together they become completely united. This is, 

 of course, the basis of the blacksmith's art. 



The cast-iron from which wrought-iron is made is the product 

 of the blast furnace. Iron ore, coal or coke, and limestone being 

 heated together, the materials melt and settle to the bottom of 

 the furnace in two liquid layers. The upper is slag, the lower is 



