Physical Properties of an Extensive Series of Alloys of Tron. 121 
order of conductivity the same in both series, but equal increments of any given 
element appear to produce a corresponding diminution of conductivity for both 
heat and electricity. The small irregularities in the heat curves are not more 
than might be expected in these preliminary experiments, and where they occur 
in both sets of curves are due to the varying impurities of the alloy. As was 
noticed in our experiments on electrical conductivity of these iron alloys, the first 
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—— Percentage of Added Element 
Fie. 2. 
addition of any given element, especially of carbon or manganese, has the greatest 
effect in reducing the conductivity. 
In a paper by one of us, read before the Royal Society,* it was pointed out that 
the diminution in conductivity of iron, by the addition of a given percentage of 
an element which can be alloyed with it, is closely related to the atomic mass of 
the added element. The greater the atomic mass of the added element, the less 
* Proc, Royal Society, 1902, vol. lxix., p. 480, 
