120 Barrett, I^kown & Hadfield — On the Electrical Conductivity and 



nearly constant, the steel becomes mucli harder magnetically, the permeability 

 falls rapidly, and the coercive force and hysteresis loss each rise to a high figure. 



The above table also affords an interesting comparison of the magnetic effect 

 produced on a chromium steel by adding tungsten instead of nickel. In 1286 A 

 we have a nickel-chromium, and in 1189 B a tungsten-chromium steel of nearly 

 the same relative composition. The last two specimens in Table XIV. show the 

 effect of adding tungsten and then nickel to a manganese steel. The nickel- 

 manganese steel is much worse magnetically than the tungsten-manganese steel. 

 This difference is, however, probably due to the fact that the quantity of 

 manganese is \\ per cent, larger in the former alloy. We have already found 

 that when the quantity of manganese added to steel lies between 3 and 4 per 

 cent., a great change for the worse is produced in the magnetic properties of the 

 alloy, as will be seen by referring to Table IV. and Plate III. 



It is not therefore surprising that high nickel-manganese steels have an 

 enormous electrical as well as magnetic resistance. Out of the group of nickel- 

 manganese steels given in Group 12, p. 89, the following are practically 

 non-magnetic in a field of 45, and, even when annealed, are only feebly magnetic 

 in a field of 300 C. Gr. S. units. Beginning with the least magnetic, we have 

 1109 D, 1414 A, 1414 B, 1339, 1313 C, also the two manganese-tungsten steels, 

 1343 B and 1343 A, given on p. 92, and the copper-manganese-chromium steel, 

 1424 B, given on p. 97. In addition to the foregoing feebly magnetic steels, 

 those manganese steels containing 13 per cent, of manganese and upwards are 

 also nearly non-magnetic. (See Table IV., p. 108.) 



We do not propose, in the present paper, to enter upon a discussion of the 

 interesting facts revealed by the above results, or the relative effect of different 

 elements, when alloyed with iron, in reducing or destroying its magnetic suscepti- 

 bility. We hope to return to this question in another paper. One element, 

 aluminium, may actually increase the susceptibility of iron in comparatively low 

 magnetic fields, and another, silicon, has the same effect still more conspicuously, 

 as will be seen below. 



Added November, 1899. 



The group of steels contained in the next Table shows the most remarkable 

 result we have yet obtained, the effect produced on the magnetic properties of 

 iron by the addition of silicon. Ordinary steel usually contains a small quantity 

 of silicon, and it was noticed early in this investigation that the increase of 

 silicon did not magnetically injure, but rather improve, a carbon steel ; its 

 magnetic effect appeared to resemble that produced by aluminium. 



