Page:Proceedings of the Royal Society of London Vol 69.djvu/504

484 atomic weight produce the least increase in electric resistivity and vice versd. For the sake of such a comparison, the molecular weights of these elements, if we knew them, rather than the atomic weights, should be taken. This is especially true in the case of carbon, the molecular weight of which, if this analogy holds good, would appear to be four times its atomic weight. If, instead of the atomic weights, we take the specific heats of these elements, so far as they are known, we ure likely to arrive at a better knowledge of their relative atomic or molecular masses, and a comparison of the order of specific heats with the order of increase of electric resistivity is very striking. This is shown in the next table.*

Dividing the increase in electric resistivity by the percentage of the added metal, we obtain the increase in the specific resistance of iron produced by 1 per cent, of the added element. This is shown for a 2 per cent, alloy (except in the case of carbon) in the second column of Table II, along with the specific heats and atomic weights of the elements named in the first column.

Table II.

Alloy of iron. Increase of resistivity for 1 per cent.

Specific heat.

Atomic weight.

2-0

0-035

184

Cobalt

3-0

0-107

59

Nickel

3-5

0-109

59

5-0

o-i (?)

52

5-0

-160t

12

8-0

0-122

55

13-0

0-183

28

14-0

0-212

27

I venture to think that the correspondence shown in columns 2 and 3 of the foregoing table is something more than a chance coincidence. It is, however, desirable to have exact determinations of the resistivity of a larger number of alloys of iron before any definite conclusions can be reached.

A series of experiments are in progress for the measurement of the relative thermal conductivity of the foregoing alloys. About forty determinations have been made, and so far the order of thermal

work on Physical Constants. The specific heat determinations are chiefly by Reguault, between 9 and 97 C.
 * The values for the specific heats are taken from Landolt and Bernstein's great

t For a 1 per cent, alloy.

J As graphite; as diamond the specific heat of carbon is O'llS, according to H. F. Weber.