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Magnetic Permeability of various Alloys of Iron. 85 
Notwithstanding that copper is at least six times the conductivity of iron, 
alloying iron with a small percentage of copper does not appear to increase its 
conductivity materially, if at all. This indefinite conclusion is due to the fact 
that the specimens tested contained a large percentage of carbon or manganese 
(and 1149 A contained aluminium), so that the true conductivity of a pure alloy 
of copper and iron is not shown in these results. ‘The only comparison possible 
is between 1264 A and B, where an increase of 0:9 per cent. of copper diminishes 
the resistance half a microhm, equivalent to 0°6 microhm for one per cent. of 
added copper; but even here this small decrease may be due to the rather lower 
carbon and manganese present in 1264 B. 
These copper steels were drawn into wire (about No. 20 B. W.G.) and 
annealed, the specific resistance at 15°C. ; and the temperature-coefficient between 
10° C. and 120° C. of each specimen was then determined with the following 
results. The percentage composition is given in the preceding table, and the 
results are here arranged in the order of increasing resistance. 
Specrric Rustsrance or Copper Sreets (Tested in Form of Wire). 
| Marks. Specific resistance In microhms. | [Pemoemoe wade © GH HeSSaNe 
1264 B 13°55 0°457 
5) AN 13:92 0:418 
1263 C 16°15 0°366 
1149 A 20:77 0°280 
It will be noticed that the specific resistance of these annealed wires, as 
directly determined, agrees fairly well with the resistance as deduced from the 
conductivity of the same alloy in the form of a rod, given in the last column of 
the table in Group 8; the somewhat lower resistance in the former case is 
doubtless due to slight differences in the annealing of the two series of speci- 
mens. 
For the convenience of those who prefer results given in terms of resistance 
rather than conductivity, the curves shown in fig. 6 have been drawn. Here the 
ordinates are sp. resistances in microhms per c¢.c. (at about 16°C.), and the 
abscissee the various percentages of the elements named which were added to the 
iron. These curves are, of course, merely the reciprocals of those shown in 
Plate II., the results having been deduced from the conductivity in the manner 
already described (p. 72). As the determinations of the conductivity of the 
specimens in the annealed state were not finished when the figure was engraved, the 
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