The diffusion of hydrogen through commercial and very pure anode nickel has been studied in a precision manner throughout the temperature interval 1100deg; to 150deg; Centigrade. It was found that the diffusion rates vary in a perfectly regular manner throughout this region, except for a discontinuity at the Curie point, namely near 360deg;C.A very exact agreement with the formulaR = ATzpytimes;exp (mdash;b/T) was found in all cases. After long heat treatment with hydrogen the value ofyin the above equation for anode nickel becomes +0.50plusmn;0.01 with the possible exception of a region within 3deg; of the Curie point. All the nickel used had isotherms whose slope at the start of observations was a maximum in the Curie region and markedly greater than 0.5, but which approached 0.5 as the heat treatment, ordinarily considered as having a decarburizing effect, progressed.The magnetic transition as shown by diffusion is abrupt, the isobars below the Curie region being quite as straight as above. There is always a sudden drop in the value ofbas calculated from the simple equationR = Aexp (mdash;b/T) at the Curie point, the value changing in the purest nickel from 6600 to 5800 with rising temperature. No systematic breaks appear in the isobars at high temperatures, such as found in pure iron, but nevertheless the value ofzindicates that the diffusing hydrogen possesses appreciable energy within the lattice.The Curie region shows marked hysteresis, and is similar to the Curie region of pure iron in this respect.Existing theories of ferromagnetism seem to require modification, inasmuch as the Curie transition in nickel appears to take place about as abruptly as the bodyhyphen;centeredhyphen;facehyphen;centered transition in iron. The loss of magnetism at the Curie transition is essentially an atomic phenomenon and should not be associated primarily with conditions in aggregates of atoms or atomic domains. During the transformation for a finite time, there appears to be an additional electron in the valence shell of some nickel lattice points.A possible description of the process of the change from the ferromagnetic to the paramagnetic condition in the transition elements is that an electron is moved from the 3dshell to one of the 4 levels, followed more or less quickly by a drop of another 4hyphen;level electron back to such a 3dlevel as to result in the pairing of electron spins in the 3dshell.
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