Magnetic Properties of Pure Iron. 361 



equation (1) is extended to metallic alloys is worthy of brief 

 consideration here. Such alloys as consist entirely of a 

 single solid solution should obey the rule equally with pure 

 metals. It was found, however, in the course of an investi- 

 gation on the effect of annealing on the electrical resistance 

 of the copper-zinc-nickel alloys which belong to this class, 

 that in many cases with a high nickel content the size of a 

 crystal exercised no appreciable influence on the resistance. 

 The values for an alloy containing 61' 2 per cent, of copper, 

 9*81 per cent, zinc, and 28*6 per cent, nickel (a) with the 

 very fine structure obtained immediately that re-crystalli- 

 zation had been induced, and (b) after subsequent prolonged 

 annealing at 696° O.to coarsen the size of the crystals, were 

 found to be 41*2 and 41*0 michroms per c.c. respectively. 

 An explanation of this lack of dependence of the conductivity 

 on the crystal size in these alloys, however, is not difficult, 

 and the validity of the relationship (1) is not called : in question. 

 There is now little doubt that in solid solutions such as this 

 alloy an internal strain of considerable magnitude must be 

 assumed, which will re-act on the electrical conductivity, 

 lowering it until, in certain cases, the conductivity of the 

 crystalline and of the amorphous parts is practically the 

 same. 



Returning to the values of the specific resistance of iron, 

 that obtained for the sample as received from the rolls 

 (7* 56) is in excellent agreement with the value (7*6) arrived 

 at by Benedicks * by extrapolation of his results on the 

 specific resistance of steels in the same condition. It is 

 evident, however, that his equation for the specific resistance 

 of steels 



p = 7-6 + 26*82C, 



where SO is the sum of the carbon and the equivalents in 

 carbon of the other elements present in solution, can only be 

 be an approximation to the truth, since heat-treatment, 

 e. g. annealing which varies the grain-size of the material 

 without any chemical change, would result in a change of 

 specific resistance. 



An observation made during the present work on pure 

 iron would seem to throw light on the conductivity of carbon 

 steels. The drastically annealed sample of iron showed the 

 curious irregularity already referred to. About nine-tenths 

 of the mass consisted of crystals so coarse as to be readily 



* Benedicks, ' Thesis for Doctorate,' Upsala, 1904. 



