468 Scientific Proceedings, Royal Dublin Society. 



after casting. In forging the material becomes throughout of 

 uniform texture, and hence we must turn to the subsequent ex- 

 periments on the test bars for further information on this point. 



It would be extremely interesting to ascertain the magnetic 

 permeability of this specimen, that is, the ratio of the induction 

 produced to the magnetizing force producing it. But for this 

 purpose it would be necessary to have rings forged, and this was 

 out of the question, in fact many of the ingots would not forge. 

 What the Table shows is the general magnetic character of the 

 specimens, or if the moment be divided by the volume, the perma- 

 nent intensity of magnetization that can be conferred on the ingots. 

 This power of retaining magnetism when the inducing force ceases 

 is attributed to the so-called " coercive force," the harder the steel 

 the higher being the coercive force. But manganese steel is in- 

 tensely hard, and, as might be expected, has a very high coercive 

 force, no loss of magnetism being observed in those specimens 

 again tested, without re-magnetizing some weeks later. 



Some of the specimens were harder than others,, and accord- 

 ingly experiments were made to determine their relative hardness. 

 The scale of hardness used by mineralogists is judged by one 

 material scratching another. Thus the softest in the scale No. 1 

 is mica ; No. 2 is gypsum ; No. 3, calcspar ; No. 4, fluorspar ; 

 No. 5, apatite ; No. 6, orthofelspar ; No. 7, quartz ; No. 8, topaz ; 

 No. 9, sapphire; No. 10, diamond. At best this is an unsatisfac- 

 tory means of estimation, and when we find the different varieties 

 of steel lying between No. 5 and No. 6, it will be seen how 

 extremely imperfect such a scale is. Ferromanganese containing 

 82 % of manganese is nearly as hard as quartz, but the ingots 

 were softer lying near to No. 6 on the scale. The best mode of 

 testing their relative hardness was to use a new glass-hard file, and 

 judge by the touch in filing. In this way two of my assistants, 

 both of whom were expert in the use of the file, arranged the 

 ingots, according to hardness, independently of each other ; neither 

 of them at the time knowing the composition of the blocks. They 

 found the order as follows: — No. 29 the hardest; Nos. 6, 14, 8, 

 and 13, next ; No. 40, next ; and Nos. 46, 44, and 43, next, being 

 the softest. It will be seen by reference to Table V. that this 

 order is practically the order of the quantities of manganese in 

 each ingot, No. 29 containing 16^ per cent., and the Nos. 46-43 



