Magnetic Permeability of various Alloys of Tron. 83 
Group 5.—AtLuMINIuM STHELS. 
| 
Marks, Percentage Composition. Conductivity Copper = 100. Specific resistance (calculated). 
Al C | Si Unann. | Ann. | Unann. Ann. 
1167D | 0:75 017 | 0-10 6-9 78 | 94:8 29:0) 
1167 H 2°25 0:24 | 0:18 a7 | 4-4 46°3 39:0 
11671 | 5:50 0:22 | 0-20 2:2 2°5 78:1 70:0 
It will be seen, upon referring to Plate II., that the curve is a very smooth 
one: the samples being fairly uniform in their composition, except as regards 
the percentage of aluminium. The curve shows us that the reduction of con- 
ductivity by adding comparatively small percentages of aluminium to iron is 
most startling, being greater than that of any other metal so far examined. 
Between 0°75 and 5:5 per cent. of added aluminium, the specific resistance 
increases 48:0 microhms, equivalent to an increase of 10:1 microhms for every 
1 per cent. of aluminium added to the iron; between 2°25 and 5:5 per cent. of 
aluminium, nearly the same increase occurs, viz. 9°5 microhms. (See also p. 94.) 
The alloy No. 1167 I with 5§ per cent. of aluminium was soft and ductile: a 
sample was rolled into strip, and drawn into wire No. 20 B.W.G., and the specific 
resistance and temperature coefficient of both carefully determined. The mean 
specific resistance of the annealed wire was found to be 74:69 microhms per c.c. 
at 15° C.; the resistance of the strip was slightly lower. The specific resistance 
of the annealed rod of the same alloy, calculated from the conductivity given in 
Group 5, was somewhat lower. The percentage variation of resistance for increase 
of temperature was found to be 0:063 per 1°C. between 0° and 150°C. This 
is remarkably good, being exactly ten times less than iron, and nearly as low 
as German silver, which has a temperature coefficient of 0-044. As the resistance 
of this aluminium steel is three and a half times greater than German silver, 
it promises to be a valuable and cheap alloy for use in resistance coils, though we 
cannot yet speak of its behaviour after repeated heating and cooling. 
We now come to the alloys of silicon and iron :— 
Group 6.—SILICON STEELS. 
Marks. Percentage Composition. Conductivity Copper = 100. | Specific resistance (calculated). 
] ] | 
Si | C Unann. | Ann. | Unann. | Ann. 
| | | 
898 E 2°5 | 0:20 3°65 | 4:09 | 47-1 42-1 
5) al 5:5 0:26 2°50 | 2°64 | 68°8 | 65:2 
TRANS. ROY. DUB. SOC., N.S. VOL VII., PART Iv. O 
