Brown—The Densities and Specific Heats of some Alloys of Iron. 81 
In the first specimen the carbon—as in the case of the chromium steels— 
seems to dominate the action of the cobalt as well as that of the manganese 
and silicon, since the result for this specimen also lies on the carbon curve in 
fig. 5. 
In the second specimen the increase in the specific heat that would be 
expected from the increased amount of carbon present seems to be counteracted 
by the extra 5:2 per cent. of cobalt. ‘These specimens, however, are not pure 
enough to enable one to draw from their results any definite conclusion; but it 
would appear that cobalt added to iron diminishes the specific heat. The 
thermal capacity per unit bulk is also fairly constant in these specimens. 
TABLE XIX. 
ALUMINIUM STEELS. 
| Percentage Composition | Sorelle 
at Heat 
Mark C Si | Cr | Al o px o 
| | 
808 0°67 2°25 | 0°50 0°1158 0°8798 
LIG? Jel 0:24 | 0-18 _ Des 0°1165 0°8753 | 
1178 E | 0-29 1 | AA O1195 | 0:8554 | 
| } 
In Table XIX. are given the results for three aluminium steels containing from 
0:5 to 4°5 per cent. of aluminium. They also contain fairly large proportions of 
other elements, and are not pure enough to warrant any definite conclusions being 
drawn from their results. Taking, however, the purest specimen, marked 1167 H, 
and comparing it with the pure iron 8.C.I. in Table XI., and assuming that the 
increase in the specific heat due to adding 1 per cent. of carbon to iron is 0:0088, 
and that the increase for the addition of 1 per cent. of silicon to iron is 0:0029, 
then on correcting the specific heat of the specimen 1167 H for carbon and silicon 
it becomes 0°1139, which is practically that of pure iron, so that the addition of 
2°25 per cent. of aluminium to iron does not appear to alter practically its specific 
heat. 
The last column in Table XIX. shows that the thermal capacity per unit volume 
is decreased nearly 3 per cent. by the addition of 4 per cent. of aluminium. 
