64 MODERN SCIENCE READER 



Moreover, a rail low in phosphorus or sulphur, which 

 contains no traces of a pipe or segregation, may prove 

 defective. The composition of the rail is normal. What 

 then is the matter? On polishing and etching and exam- 

 ining it under the microscope the structure seen in Fig. 7 

 is brought to light. To the inexperienced it looks all right, 

 but to the steel man it shows that the rolling of the rail was 

 finished at too high a temperature, that the grains of the 

 steel are too large, and long experience has shown that 

 these large grains produce brittleness, and when the great- 

 est toughness combined with strength is required, the finest 

 possible grains should be sought for. This may be accom- 

 plished by continuing the rolling down to a certain "criti- 

 cal temperature," below which no crystallization takes 

 place when the rails cool after rolling. Such a structure 

 is seen in Fig. 1 and such a rail will be strong, yet tough, 

 and will resist sudden shocks. 



I do not intend to convey the meaning that the microscope 

 is the telescope by which all the ills prevalent in metals 

 can be viewed face to face; but as used by the scientific 

 man, together with his indispensable etching compounds, 

 the microscope is able in many cases to give a clear clue 

 to the sins of our metals and their makers. 



