470 



Scientific Proceedings, Royal Dublin Society. 



treated in a similar way to the ingots, being magnetized in a suitable 

 helix in a field of 700 c. g. s. units, the current being maintained 

 for half a minute, and then immediately each bar was tested with 

 the mirror magnetometer. The fracture of the test bars was in all 

 cases granular. Their relative hardness was tested by a file in the 

 same way as the ingots, and found to be precisely in the order of 

 the per-centages of manganese contained. To the composition per 

 cent, of each specimen, kindly supplied to me by Mr. Hadfield, I 

 have added the breaking strain of each test bar taken from Mr. 

 Hadfield's admirable paper on manganese steel, 1 and also how each 

 b>ar was treated after forging. 



It will be seen that, as with the ingots, additional per-centages 

 of manganese do not produce a corresponding decrease of magnetic 

 moment. In fact the moment appears to rise pretty regularly with 

 increasing per-centages of manganese up to 13 - 7 per cent., and then 

 to decrease again from this point. 



Table VI. 

 Magnetic Moment of forged test bars of Manganese Steel, 



The presence of foreign substances in the alloy, such as silicon, 

 or the variable amounts of carbon, have doubtless a considerable 

 influence on the magnetic character of the different specimens ; 

 but these do not account for the wide divergence in the magnetic 

 moment. Thus Nos. 547 and 552 have almost an identical com- 



1 See Proceedings of the Institute of Civil Engineers, February, 1888. 



