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POPULAR SCIENCE MONTHLY 



thermopile, the galvanometer shows a slowly falling temperature till 

 we reach 1380° C, when solidification takes place. The changes which 

 now go on take place in solid metal. After a time the temperature 

 again falls until we reach 680°, when there is an evolution of heat; had 

 the steel been free from carbon there would have been evolution of 

 heat at 895° and again at 766°. JSTow throughout the cooling molecular 

 changes are going on in the steel. By quenching the steel suddenly 

 at any given temperature we can check the change and examine micro- 

 scopically the structure of the steel at the temperature at which it was 

 checked. 



In the figure, with the exception of specimen Xo. 6, the metal has 

 not been heated above 1050°, over 300° below its melting point. 





Section of Good Rail. 



Section of Bad Rail, show- 

 ing Surface to which 

 Fracture was Due. 



Section of Rail after 

 Rolling. 



At temperatures between about 900° and 1100° the carbon exists 

 in the form of carbide of iron dissolved in the iron, at a temperature 

 of 890° tJie iron which can exist in different forms as an allotropic 

 substance passes from the y form to the ^9 form, and in this form 

 cannot dissolve more than .9 per cent, of carbon as carbide. Thus at 

 this temperature a large proportion of the carbon passes out of the 

 solution. At 680° the remainder of the carbide falls out of the solution 

 as lamina. 



Thus the following temperatures must be noted: 1380°, melting 

 point; 1050°, highest point reached by specimen; 890°, .6 per cent, of 

 carbon deposited; 680°, rest of carbide deposited. 



To turn now to the dstails of the photo, the center piece is the 

 cemented steel as it comes from the furnace after the usual treatment. 



These slides are sufficient to call attention to the changes which 

 occur in solid iron, changes whose importance is now beginning to be 

 realized. On viewing them it is a natural question to ask how all the 

 other properties of iron related to its structure ; can we by special treat- 

 ment produce a steel more suited to the shipbuilder, the railway engi- 

 neer or the dynamo maker than any he now possesses ? 



These marked effects are connected with variations in the condition 

 of the carbon in the iron ; can equally or possibly more marked changes 

 be produced by the introduction of some other elements ? Guillaume's 



