Magnetic PermeahiUty of various Allot/s of Iron. 



107 



for the specimen B are rej^eatecl in each table for convenience of comparison.* It 

 will be noticed from Table II. that the maximum induction for the highest field 

 we employed (viz. H = 45) decreases as the percentage of carbon increases, and the 

 coercive force increases in a similar manner. When the carbon reaches 1 per 

 cent, the addition of | per cent., as in the specimens marked 613 and 614, has 

 practically no efiect on the maximum induction and coercive force, but as will be 

 seen from the next table, the permeability for low magnetising forces is consider- 

 ably higher in 613 than in 614. The fuller chemical analysis, of these and the 

 other steels given in Part I., that was subsequently made, reveals the same fact, 

 noticed in electrical conductivity, that small quantities of impurities seriously 

 affect the magnetic property of these alloys. 



We have mentioned two other magnetic properties of considerable practical 

 importance which can be deduced from the B and H curves, viz. (1) the permeability 

 (ju, = B/H) of each specimen for any given value of H, up to the highest magnetic 

 field we employed ; and (2) the hysteresis loss per complete cycle, i.e., the energy 

 dissipated in each alloy in passing through a com2ilete magnetic cycle. The 

 work, W, thus done in ergs per cubic centimetre can be found by measuring the 

 area of the cycle curve.f 



The next table gives the permeability for a magnetising force of 8 C.G.S. 

 units, and the hysteresis loss of a few of the carbon steels ; the maximum magne- 

 tising force of the cycle being in all cases 45 C.G.S. Here, and in all subsequent 

 tables, the permeability is that given by the initial ascending curve shown by 

 a thin line on the curves in the plates. 



Table III. — Carlon 



The work done in magnetising these steels, as might be expected, increases as 

 the percentage of carbon increases, the permeability diminishing at the same time. 

 We now pass to alloys of iron and manganese, of which the specimens marked 

 (p) in Table IV. are given in Plate III. ; another specimen of steel with 1 per cent, 

 of manganese, 1420, is given in the annealed and unannealed states on Plate V. 



* The specimen B is called " Iron " in all the tables, except the carbon steels. 



tFor W- — 'H.d'B, see " Ewing's Magnetic Induction in Iron and other Metals," chap. iv. 

 4?rJ 



TKANS. Tier. DUB. SUC., N.S. TOL. VII., TAET TV. K 



