) 
Physical Properties of an Extensive Series of Alloys of Tron. 123 
PAIRS OW, 
Micro-Srrucrure. 
In the previous Parts of these researches we have shown that a small per- 
centage of the non-magnetic metals silicon and aluminium, alloyed with iron, 
raised the magnetic permeability of the alloy beyond that of the purest commer- 
cial iron; and on the other hand, a metal like manganese, itself feebly magnetic, 
rendered iron practically non-magnetic when alloyed in sufficient quantity with 
iron.* In Part III. we remarked :— 
‘“‘. . . The question remains to be considered, what is the chemical or physical 
change produced in iron by the presence of other metals; so that on the one 
hand the magnetic permeability of the alloy is practically destroved by the added 
element, and on the other increased. From their strong chemical affinities for 
oxygen and the halogens, silicon and aluminium may act both chemically and 
physically. By combining with oxygen or with dissociated gas they may render 
the iron freer from oxide of iron, or give it a closer texture, and prevent fine 
honeycombs being formed. Microscopic examination of sections of all these 
alloys is needed ; such examination cannot fail to throw light on the relation 
between magnetic qualities and the size and nature of the grain, or the crystalline 
structure of the alloys.”+ 
This microscopic examination was most kindly undertaken by Dr. Glazebrook 
at the National Physical Laboratory. Sections of the alloys were made and 
polished, and micro-photographs taken before and after etching. The work, 
which was very laborious, Dr. Glazebrook entrusted to Dr. Carpenter, to whom 
our best thanks are due. Another interesting and anomalous point required 
clearing up. When the very high permeability rod, 1167 H, containing 22 per 
cent. of aluminium alloyed with iron, was carefully turned down to a smaller 
diameter, then subsequently re-annealed, and new B and H curves taken, the 
magnetic permeability was no longer so high, scarcely exceeding that of the best 
iron. The turned-down rod was now drawn down to a still smaller diameter, 
carefully annealed, and again tested magnetically ; its permeability was found to 
be even below that of the purest Swedish charcoal-iron, S.C.I., which had been in 
like manner reduced in diameter and re-annealed. Furthermore, fresh specimens 
of the aluminium-iron alloy, prepared from new castings, were not as good, 
magnetically, as the first specimen. These anomalies, it was hoped, microscopic 
* Sci. Trans. Roy. Dub. Soc., vol. vii., January, 1900, p. 122; vol. viii., September, 1902, p. 6. 
t Lbid., vol. vili., September, 1902, p. 21. 
