1906.] on the Internal Architecture of Metals. 255 



formation of pearlite into hardenite, in the most perfect manner 

 yet recorded. The two constituents, pearlite and hardenite, might 

 humanly be described as the most important in nature, since upon 

 unhardened and hardened steel depended the remarkable triumphs of 

 the civil, the mechanical, and the electrical engineer. 



The quartz-hard transformation product of pearlite discovered by 

 the versatile genius of Dr. Sorby, itself presented what might be 

 termed effective and futile phases, dependent upon the temperature 

 of quenching. In properly quenched steel, the accidental section 

 before referred to showed that at a moderate temperature, the trans- 

 formation proceeded not suddenly, but from a series of converging 

 centres until the whole mass consisted of the obsidian-like substance, 

 structureless hardenite. At too high a temperature, this steely 

 obsidian developed decisive cubic crystallisation, recorded in the 

 micro-structure by equilateral etching figures indicative of ruined 

 steel. In supersaturated steel in the unhardened condition, the cells 

 of pearlite were environed by brilliant walls of cementite FcgC, 

 which in hardened steel, enveloped similar cells of hardenite, corre- 

 sponding to the empirical formula Fe24C. 



Of the three broad types of steel described, by far the most 

 important was unsaturated steel, a synonymous term for which was 

 structural steel, embracing boiler-plates, ship-plates, bridge-plates, 

 rails, and the gigantic engine parts which formed the backbone of our 

 battleships and cruisers. 



To show the enormous importance of the scientific study of this 

 class of steel, it was well to indicate not only its failure, but after 

 brilliant service, also that of the microscope scientifically applied. 



The figure thrown upon the screen was that of a boiler, which 

 might be described as several sorts of boiler. It was a marine boiler, 

 a cruiser's boiler, and possibly a mad boiler — it was at any rate, 

 cracked. Fortunately this rupture occurred before the cruiser was put 

 into commission, and a defect in the steel which might have resulted 

 in a catastrophe, was detected by an extra inspection after the boiler 

 had been impressed with the Government pass mark. The chronology 

 of the testing operations, was recorded in the following table : 



The mechanical tests of the boiler-plate steel, which had thus 

 failed, left little to be desired, and the same remark applies to static 

 mechanical tests taken along the line of fracture. Micrographic tests 

 indicated that the steel presented marked features of inferiority when 

 compared with undoubtedly good boiler-plate steel. Superficially the 

 matter was thus solved, but, under alternating or dynamic stress tests, 



