κ = 10−6 × 0.3849 × 33700 / θ²
= 10−6 × 12970 / θ².
At 15° C. θ = 273 + 15 = 288, and therefore κ = 0.156 × 10-6, nearly the same as the value found by Faraday. At 0° C., κ = 0.174 × 10-6. For air Curie calculated that the susceptibility per unit mass was 106K = 7830/θ; or, taking the mass of 1 c.c. of air at 0° C. and 760 mm. as 0.001291 grm., κ = 10−6 × 2760/θ² for air at standard atmospheric pressure. It is pointed out that this formula may be used as a temperature correction in magnetic determinations carried out in air.
Fleming and Dewar determined the susceptibility of liquid oxygen (Proc. Roy. Soc., 1896, 60, 283; 1898, 63, 311) by two different methods. In the first experiments it was calculated from observations of the mutual induction of two conducting circuits in air and in the liquid; the results for oxygen at −182° C. were
μ = 1.00287, κ = 228 × 10−6.
In the second series, to which greater importance is attached, measurements were made of the force exerted in a divergent field upon small balls of copper, silver and other substances, first when the balls were in air and afterwards when they were immersed in liquid oxygen. If V is the volume of a ball, H the strength of the field at its centre, and κ′ its apparent susceptibility, the force in the direction x is ƒ = κ′VH × dH/dx; and if κ′a and κ′0 are the apparent susceptibilities of the same ball in air and in liquid oxygen, κ′a − κ′0 is equal to the difference between the susceptibilities of the two media. The susceptibility of air being known—practically it was negligible in these experiments—that of liquid oxygen can at once be found. The mean of 36 experiments with 7 balls gave
μ = 1.00407, κ = 324 × 10−6.
A small but decided tendency to a decrease of susceptibility in very strong fields was observed. It appears, therefore, that liquid oxygen is by far the most strongly paramagnetic liquid known, its susceptibility being more than four times greater than that of a saturated solution of ferric chloride. On the other hand, its susceptibility is about fifty times less than that of Hadfield’s 12% manganese steel, which is commonly spoken of as non-magnetizable.
Bismuth.—Bismuth is of special interest, as being the most strongly diamagnetic substance known, the mean value of the best determinations of its susceptibility being about −14 × 10-6 (see G. Meslin, C. R., 1905, 140, 449). The magnetic properties of the metal at different temperatures and in fields up to 1350 units have been studied by P. Curie (loc. cit.), who found that its “specific susceptibility” (K) was independent of the strength of the field, but decreased with rise of temperature up to the melting-point, 273°C. His results appear to show the relation
−Κ × 106 = 1.381 − 0.00155t°.