Magnetic Permeability of various Alloys of Iron. 123 
A correction is of course necessary for the demagnetising effect of the ends in all 
these highly permeable specimens; see Note A at end. Experiments arein progress 
with more slender and carefully turned rods and rings of silicon iron, and the best 
iron (S. C. I.), in order to compare more accurately their magnetic properties; as 
far as they have gone, these confirm the general results above stated. The com- 
paratively small susceptibility of iron to feeble magnetic forces has been long 
known, but we believe that hitherto no other substance has been found better 
than iron in this respect. 
The coercive force of the silicon steel is about one half that of the best iron, 
S.C. 1., its retentivity is also much less, and the hysteresis loss per complete 
magnetic cycle is therefore much smaller. The B and H curves of S.C. I., and 
the 54 per cent. silicon steel, were carefully plotted, their areas measured, and 
the ergs dissipated per complete cycle, with a maximum magnetising force of 
45 C. G. S. units, were found, with the following results :— 
Taste XVIII. 
Marks. | Percentage. | eee per 
C | Si 
Iron (B) 0:08 — 11090 ergs. 
oy (So Ce IL) 0:028 — 10100 _,, 
Silicon Steel (898 H) 0:26 5:5 6500 ,, 
It is hardly necessary to point out the great importance of the above results 
from a theoretical as well as practical point of view. We may add that these 
silicon-iron alloys, as well as some of the manganese steels, manganese-nickel 
steels, and tungsten steeis are patented products. 
Some low silicon steels were tested by Mdme. Sklodowska Curie in her inves- 
tigation on the magnetic properties of tempered steels. Mdme. Curie states that 
‘‘ the presence of small quantities of silicon does not appear sensibly to alter the 
magnetic properties of steel.” * But in the table of results, given by this able 
experimenter, it will be seen that a tempered steel, containing 1:28 per cent. of 
silicon, has its coercive force reduced about 32 per cent. when compared with 
steel containing the same percentage of carbon, but without silicon. 
The specimens employed by Mdme. Curie were those used by M. le Chatelier, 
to which we have referred on p. 99, and consisted of short bars, whose length 
was only twenty times their diameter; the magnetic reaction of the ends was 
* See Bulletin de la Société d’ encouragement pour l’industrie nationale, Janvier 1898, p. 58. 
TRANS. ROY. DUB. SOC., N.S. VOL. VII., PART IY. I 
