ON STRENGTH AND PROPERTIES OF CAST IRON. 375 
greater in the hot blast. The cold blast iron is the better, but 
the difference is very small. 
In the iron No. 2, from the Coed-Talon Works in North 
Wales, the tensile strength is greater in the cold blast than 
in the hot ; but the resistance to compression is higher in the 
latter than the former, and that is the case with the specific 
gravity. 
So far as my experiments have proceeded, the irons of No. 
1 have been deteriorated by the hot blast ; those of No. 2 ap- 
pear also to have been slightly injured by it; whilst the irons 
of No. 3 seem to have benefited by its mollifying powers. 
The Carron iron No. 3, hot blast, resists both tension and 
compression with considerably more energy than that made 
with the cold blast; and the No. 3 hot blast iron from the 
Devon Works, in Scotland, is one of the strongest cast-irons 
I have seen, whilst that made with the cold blast is compara- 
tively weak, though its specific gravity is very high, and higher 
than in the hot. The extreme hardness of the cold blast De- 
von iron above prevented many experiments that would other- 
wise have been made upon it, no tools being hard enough to 
form the specimens. The difference of strength in the Devon 
irons is peculiarly striking. 
From the evidence here brought forward, it is rendered ex- 
ceedingly probable that the introduction of a heated blast into 
the manufacture of cast iron has injured the softer irons, whilst 
it has frequently mollified and improved those of a harder 
nature; and considering the small deterioration that the irons 
of the quality No. 2 have sustained, and the apparent henefit 
to those of No. 3, together with the great saving effected by 
the heated blast, there seems good reason for the process be- 
coming as general as it has done. 
Additional evidence will be obtained from the experiments 
in the next paper. 
