Physical Properties of an Extensive Series of Alloys of Tron. 119 
absolute conductivity, and 4’, 7’, K’ the same for the second rod. Putting in 
these values we have 
lee _ lose Ji = 1) 
KBr ~ \og (n+ /n®— 1) 
“The surfaces of the two bars had the same treatment, so that # may be 
assumed to be equal to £”; and we get 
= le@tfG@ =1) pve? 
JK’ = ae ae 
log (nm + /n? — 1) ys Vie 
‘Taking for our standard copper rod the values A = 100 and 7 = 0:25 ems., 
this becomes 
Sk log (n + fn? =, 5 
* log (n’ + /n? = 1) Jr 
‘rom this formula the conductivities of the rods were found relative to the 
copper standard, where n for each rod was obtained from the temperatures at 
points distant 5 ems., 7-5 cms., and 10 cms. from the source of heat, these being 
taken from the temperature gradient curve previously drawn for each rod.” 
The first experiment made was with the specimen of very pure Swedish 
charcoal iron (S8.C.I.), referred to in our previous memoirs. The total impurities 
in this iron amounted to only 0:15 per cent. Its thermal conductivity was found 
to be 23, calling the standard copper 100. 
It has already been stated that the specimens jad all been carefully annealed ; 
the difference in conductivity caused by annealing is very marked, especially 
in the nickel steels. ‘his was shown in our previous papers, where in the 
case of one composite iron containing 14 per cent. of nickel, 5 per cent. of 
manganese, and 2 per cent. of aluminium, alloyed with 78:5 per cent. of iron, 
the annealed specimen had an electric resistivity of 48 microhms per c.c., 
whilst the same specimen when hardened had the enormous resistivity of 
89 microhms, an increase of 85 per cent. produced by hardening. In_ like 
- manner, thermal conductivity is increased by annealing. The nickel steel 
1287 K, containing 19°6 per cent. of nickel, was found to have a relative 
thermal conductivity of 11:1 in the annealed state, and of 7:1 in the hardened 
state, copper being 100: that is, an increase of over 54 per cent. in conductivity 
produced by annealing. 
The results obtained by Mr. Edmonds with 20 of the iron alloys are shown 
grouped together in the following table, the thermal and electrical conductivities 
of the sume rod being each compared with the same copper rod taken as 100. 
X 2 
