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\ 
ON STRENGTH AND PROPERTIES OF CAST IRON. 361 
Note.—I have been favoured by Mr. Fairbairn with the an- 
nexed examination of the structure of this and the following 
Irons :— 
‘The Carron No. 2, cold blast iron, when viewed with the 
microscope, presents a dull grey colour, finely granulated with 
an appearance of greater porosity in the centre than round the 
extreme edges of the fracture. It is a free working iron, easily 
cut with the turning tool, but indicates stiffness under the file. 
‘Carron No. 2, hot blast. This iron has nearly the same 
character in its working properties as the above; it files with 
rather more freedom, and possesses an appearance of greater 
fluidity than the cold blast. Colour, a greyish blue, accom- 
panied with a greater degree of uniformity in its crystalline 
structure than the cold blast. 
*‘ Buffery No. 1, cold blast, is finer grained than either of the 
Carron irons. It is chiefly composed of minute granules in- 
termixed with small brown specks; it works with less freedom 
than the hot blast, and cuts with difficulty under the tool. In 
this respect it is much akin to the Milton iron (described in 
Mr. Fairbairn’s paper). . 
* Buffery No. 1, hot blast, has a similar appearance to the 
Carron, No. 2, cold blast; it has more lustre than Buffery 
No. 1, cold blast; the crystals are widely separated in the 
centre, but more compact as they approach the outer edge of 
the bar. 
“This appearance is nearly peculiar to the whole of the hot 
blast irons.” 
Remarks upon the Experiments in the preceding Tables.— 
In devising the preceding experiments the writer had several 
_ objects in view, which he will now proceed to state. It has 
been remarked above that the first five experiments on the hot 
blast iron, and the first three on the cold blast, in the tables 
_ above, were made after the others. These will therefore be 
_ passed over for the present, and we shall commence with ex- 
periments 6 and 7, which, like most of the others, are on bars 
from the same model in both tables. The object of these ex- 
periments was to show the influence of form of section in beams 
of cast iron; and it will be seen from the results, that when 
the rib was downwards, the casting broke with 280lbs. in the 
hot blast iron, and 266lbs. in the cold blast. When the rib 
was upwards, the breaking weights were 980lbs. and 1050lbs. 
respectively; the bars bearing nearly four times as much one 
_ way up as the other. These results are contrary to the opi- 
-nions of some leading writers, as Tredgold and others, who, 
_ from their principles, would maintain that the strength should 
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