70 Brown—The Densities and Specific Heats of some Alloys of Iron. 
0-5, 2°25, and 4:5 per cent. of aluminium, respectively ; and in fig. 4 the 
observed values of the specific volumes, as well as the specific volumes 
corrected for carbon, silicon, and chromium, ure plotted against the percentage 
of aluminium present. 
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Percentage of Aluminium. 
Fic. 4.—ALuUMINIUM STEELS. 
By drawing a mean line through the corrected points, we see that the 
addition of one per cent. of aluminium to iron duereases the specific volume of 
the alloy at the rate of 0:0025 ¢.c. for every 1 per cent. of aluminium added, 
or specific volume = 0:1269 + 0:0025 Al, where Al represents the percentage 
amount of aluminium present. 
If no change were to take place in the specific volumes of the constituents 
when one per cent. of aluminium is added to 99 per cent. of iron, the specific 
volume of the resultant alloy would be 0:00258 c.c. greater than the specific 
volume of pure iron; and since the observed change is 0:0025¢.c., there is 
practically neither contraction nor expansion. 
