Magnetic Properties of Iron and Nickel. 21 



Nickel. 



f 200° C. Specific heat of electricity changes sign. 

 .. ■< 200°. For low magnetizing forces the magnetic sus- 

 (, ceptibility begins to rapidly increase. 



Magnetic susceptibility begins to very rapidly 

 B. •{ decrease. 



Specific heat of electricity again changes sign. 



f300°. 



\. 1 dec 



(320°. 



Iron. 



i 550° C. Specific heat of electricity changes sign. 

 .. < 550°. Internal friction of iron begins to rapidly in- 

 (^ crease. 



680°. Specific heat of electricity again changes sign. 

 o ) 680°. Magnetic susceptibility begins to very rapidly 

 decrease. 

 660°-720°. Heat becomes latent. 



1000°. Very rapid increase of internal friction. 

 1000°-1050°. Heat becomes latent. 

 About 1000° *. Remarkably sudden permanent yielding 

 p J when under stress, and equally remarkable temporary 

 ' changes when under stress or strain. Also at this 

 temperature hot iron, which at any temperature is 

 thermoelectrically negative to cold iron, becomes 

 suddenly much more negative. 



In the above table the author has not included certain 

 remarkable changes which take place in the electrical con- 

 ductivity of nickel and iron f, because these do not appear to 

 be sufficiently near any of the above critical points. Thus 

 Smith and MacGregor make the electrical conductivity of 

 pure nickel foil to change suddenly at 149° C, a temperature 

 considerably below 200° C. 



Xeither has the author included certain remarkable changes 

 which have been observed to occur in the thermal expansion 

 of steel at high temperatures if, because in the first place there 

 are no such remarkable changes in iron§, and in the second 

 the critical temperature in the thermal expansion of steel 

 varies very considerably with different specimens ; thus in 

 three specimens we have abrupt changes at the temperatures 



* At least as judged by the colour. 



t Macfarlane, Proc. R. S. E. 1875 ; C. M. Smith and J. G. MacGregor, 

 Proc. R. S. E. 1675, 1876. 



X Xouel, Genie civil, April 1887. 



§ In the curve showing the relation between the thermal expansion of 

 iron and the temperature there is a very slight inflection at 400° C. 



