Physical Properties of an Extensive Series of Alloys of Iron. 125 
Puate X. 
Rod 1167 H. Nos.1 and 2, the same as Nos. 3 and 4, Plate LX., only with 
deep etching. 
‘This reveals the presence of grains of very varying size. Some are about 
2mm. in diameter; others are less than =, mm. in diameter. The white areas 
in relief seen in No. 2 are probably aluminium which has been rendered passive 
by the treatment with nitric acid. The tiny nodules of oxide of aluminium are 
best seen in the high-power photo-micrographs. The fact may be mentioned that 
bar 1167 H was almost unattacked by a 5 per cent. solution of picric acid in 
absolute alcohol—even after prolonged treatment. 
Rod 1167 H turned, and then drawn down. No. 3, deep etching. No. 4, light etching. 
“There is no layer of ferrite running round the edge. No. 3 was taken right 
on the edge. [The outside edge of the rod is seen in the lower flattened edge of 
the dise. | 
Discussion oF Resuurs. 
‘“Tt may be considered that the photo-micrographs throw some light on the 
results recorded in Barrett, Brown, and Hadfield’s paper ; but they cannot be said 
to do more than this. The experimental basis is not sufficiently broad. As an 
illustration of what is meant by this, it is only necessary to point out that, accord- 
ing to analyses recorded in the paper just referred to, the carbon content of 
rod 1167 H is eight times, and that of rod 898 E is seven times, the carbon 
content of rod SCI. The different values for magnetic permeability found for 
these three rods may be connected not only with the presence or absence of 
aluminium or silicon, but also with that of carbon, and the mutual influences 
of these on one another as well as their particular influence on the iron. Accord- 
ingly it seems most desirable to extend the number of alloys already experimented 
with, in such a way that, while, e.g., the aluminium content is kept constant, the 
carbon content is varied, and vice versa. In this way the influence of each con- 
stituent can be found. 
‘‘ But considering the results of the photo-micrographic examination broadly, 
two striking facts are brought to light, which differentiate rod 1167 H from rods 
1167 H drawn down, 898 EK, and SCI, and which may be connected with the 
high magnetic permeability of the first-named rod. (1) A layer of ferrite, 7c. 
pure iron of somewhat varying thickness, probably about one-tenth of a millimetre 
on the average, occurs on the outside of the rod the whole way round. It forms 
TRANS, ROY. DUB. SOC., N.S., VOL. VIII., PART IX. Y 
