METEORIC AND ARTIFICIAL NICKEL-IRON ALLOYS. 
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§ 11. With respect to the evidence that taenite is a eutectic there is to be noted, 
first, its mode of occurrence and distribution (already indicated), next, its microscopic 
and chemical characteristics, and, in conclusion, as will be seen, the magnetic 
properties of the meteoric iron in which it occurs. 
In connection with the distribution of taenite mention should be made of a very 
striking photograph given by Arnold and McWilliam (‘Nature,’ vol. 71, p. 32, 
1904. Similar photographs have been given by Osmond, ‘ Annales des Mines,’ vol. 17, 
Plate III., 1900—and by others). From this photograph it is evident that a steel 
containing about 0‘4 per cent, of carbon gave, on comparatively rapid cooling after 
casting, a micrographic structure practically identical in form with that of octahedral 
meteorites. The two constituents “ ferrite ” and “ pearlite ” are distributed in the 
same way as the “ kamacite” and “ taenite” in the meteoric iron. 
To indicate the degree of similarity, there are placed side by side in the accom¬ 
panying figure the photograph given in ‘ Nature ’ ( loc. cit.) and a reduced copy of the 
photograph given by Cohen and Brezina (‘ Structur der Meteoreisen,’ Plate X., 
fig. 3) of a specimen of meteoric iron (Tazewell meteorite) containing between 12 and 
15 per cent, of nickel. 
Cast Steel, 
x 22 diameters. 
0 • 4 per cent. Carbon. 
Ferrite (light). 
Pearlite (dark). 
Meteoric Iron, 
x 2 diameters. 
13 per cent, nickel (approx.). 
Kamacite (light). 
Taenite (dark). 
Fig. 25. 
In the one photograph the darker constituent is pearlite (Arnold and McWilliam, 
loc. cit.) and in the other taenite (Cohen and Brezina, Erkliirung der Tafeln, loc. 
cit.). In the one the constituent of lighter colour is ferrite, and in the other 
kamacite. The section is cut parallel to an octahedral face in the meteoric iron, 
but the plane of section is evidently slightly inclined to an octahedral face in 
the steel. 
Now a reference to the equilibrium curves for carbon-iron alloys shows that when 
a 0'4 per cent, carbon steel cools from a temperature above 780° C., ferrite will form 
in gradually increasing amount, in the state a from the state y, until the eutectic 
temperature (690° C.) is reached. At this temperature the remainder of the iron will 
recrystallise as pearlite, a eutectic mixture of ferrite and cementite. 
_ In the same way, by hypothesis, when a nickel-iron alloy, containing, say, 10 per cent. 
VOL, CCVIII.—A, L 
