METEORIC AND ARTIFICIAL NICKEL-IRON ALLOYS. 
97 
This decrease of permeability is of importance, whatever its interpretation may be, 
since it is peculiar to the meteoric iron. No similar phenomenon is shown, to my 
knowledge, in any of the permeability curves of nickel-iron alloys for weak fields 
published hitherto; but there is no doubt of its existence here since, as will be seen 
from the data, it was observed repeatedly. 
Now, just as the data already cited indicate that the taenite contains a nickel-poor 
constituent which disappears or becomes magnetically undetectable under thermal 
treatment, so those just mentioned point to the presence of a nickel-rich constituent 
which behaves in the same way. 
§ 7. By inspection of the curves drawn from Osmond’s data (with which the less . 
complete results published by Hopkinson and by Dumont are in accord) it will be seen 
that an alloy containing more than 30 per cent, of nickel loses during heating, and 
regains during cooling, the greater part of its magnetic proporties at a temperature 
above 15° C., which is higher in proportion as the nickel content (below 70 per cent.) 
is greater. When the magnetic change (now approximately reversible) takes place at 
300° C., the alloy contains about 37 per cent, of nickel (Dumont, ‘ Comptes Rendus,’ 
vol. 126, p. 742, 1898, gives 300° C. as the temperature of disappearance in a particular 
alloy containing 39'4 per cent. Ni). 
Suppose that the taenite is originally a comparatively coarse mixture of alloys 
containing approximately 40 and 6 per cent, of nickel which exist together in 
such proportions that the taenite as a whole contains roughly 27 per cent, of nickel. 
The effect upon such a mixture of repeated heating to a high temperature and cooling 
under ordinary conditions will be to produce eventually the artificial alloy containing 
27 per cent, of nickel in which the structure is comparatively fine (see below, 
Section VIII., § 2, p. 104, and § 11, p. 108). 
During the first heating of the meteorite, after the original crystallisation, the 
permeability of the 6 per cent, alloy in the taenite will rise continuously to 650° C. 
That of the 40 per cent, alloy will rise at first, but will subsequently reach a 
maximum and afterwards practically disappear at about 350° C. (This was not 
observed—the material having been heated to dull redness, as already explained, 
before any observations were taken.) Above 750° C. the taenite will consist of two 
non-magnetic substances containing different percentages of nickel. During the first 
heating to 800° C. and the subsequent cooling there would be appreciable interdiffusion 
of these constituents. 
In subsequent heatings (the material being raised to a high temperature between 
each) there would, on this hypothesis, be 6 per cent, and 40 per cent, alloys and also 
all intermediate artificial alloys in varying proportions. Gradually, however, the 
material as a whole would approach the condition of the artificial alloy of the same 
composition. Comparatively few heatings would be sufficient to convert the more 
intimately mixed portions of the 6 per cent, and 40 per cent, alloys into the artificial 
27 per cent, alloy. 
YOL. CCVIJI.—A. 
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