Magnetic Permeability of various Alloys of Iron. 91 
contains 43 per cent. more nickel than 1109 D, and 1414 B has 6 per cent. more 
nickel than 1414 A. Taking the sp. resistances of these in the form of wire 
(being in similar condition), and comparing the increase in resistance for each 
1 per cent. of nickel added to the alloy, we find a very similar result to that given 
previously from the measurements in Group 3. On p. 80 we found that, in 
alloys of iron containing from 1 to 11 per cent. of nickel, the average increase 
of resistance for each 1 per cent. of added nickel was 1:6 microhms. From 
Group 12 we see that in composite steels, containing from 19 to 25 per cent. 
of nickel, the imcrease of resistance for each 1 per cent. of added nickel is 
1:2 microhms, between these limits the same rate will be found on referring to 
Group 3, p. 78. From Groups 3 and 12 we get the following :— 
DarcanticectoteNicleeleinvallon Average increase of specific resistance for each 
=e) ate 1 per cent. of added nickel. 
From 1 to 4 per cent. 2°2 microhms. 
be) 1 >i) 11 ”? 1°6 +) 
nC) op OF ay 1-2 
te) 
This indicates a continuous reduction in conductivity produced by nickel, 
when added to alloys of iron, even up to very large percentages, though, as 
already stated, the effect of small quantities of nickel in steel is not nearly 
so great as that of manganese, silicon, or aluminium. 
Having examined the conductivity of the nickel-manganese, or manganese- 
nickel steels, we will now take a series of specimens where other elements 
besides nickel are added to manganese steels. Here is a group of manganese 
chromium steels. 
Group 13.—Maneanese-Curomium STEELS. 
Marks. Percentage Composition. Conductivity Copper = 100. | Sor eee 
Mn Cr | C Unann. | Ann. Unann. Ann. 
1274 A 3°00 5°00 1:15 2°50 3°6 68°3 47°8 
1430 3°09 8°92 1:30 3°40 4:7 50°6 36°6 
12338.A | 2-60 9-22 1:36 RH | ORF 69:4 63°7 
620 17:50 3°50 | 0°88 2°20 2°5 TDS 68°8 
the same result; the substance has been submitted to prolonged and repeated heating and cooling for 
upwards of three years, in most cases no sensible deterioration of the material has been noticed. For 
some time past all the resistance coils in the electric installation of the Royal College of Science have 
been replaced by reostene with a great saving of space and economy of material. Some specimens of 
thin reostene wire haye, however, undergone a molecular change and become brittle and useless.—W.F.B. 
TRANS. KOY. DUB, SOC., N.S. VOL. VII., PART Iv. IP 
