352 SEVENTH REPORT—1837. 
Ratio of Tensile to compressive forces in Cast Iron. 
Having obtained the forces per square inch necessary to 
tear asunder and to crush masses of cast iron of the kinds 
previously enumerated, we will seek for the ratio of these 
forces, taking the breaking weights from the preceding table 
and that on tension. 
Compressive force | Tensile force 
Description of metal. per square inch. | per sq. inch. Ratio. 
Devon Iron, No.3. Hot blast 145,435 21,907 6-638 : 1 
Buffery Iron, No.1. Hot Blast. 86,397 13,434 6-431: 1 
do. No.1, Cold Blast. 93,385 17,466 5°346: 1 
Coed-Talon Iron, No.2. Hot Blast. 82,734 16,676 4-961 :1 
do. » Cold Blast, 81,770 18,855 4-337 : 1 
Carron Iron, No,2. Hot Blast. 108,540 13,505 8-037 : 1 
do. » Cold Blast. 106,375 16,683 6376 :1 
Carron Iron, No.3. Hot Blast. 133,440 17,755 7515: 1 
do. ss Cold Blast. 115,442 14,200 8-129: 1 
Before quitting the subject of compression, I may mention 
that, in experiments upon various bodies besides cast iron, a 
tendency to form cones or pyramids in the fracture was ob- 
servable, showing that the same laws were in operation in these 
as have been developed in the experiments upon cast iron. For 
instance, in the crushing of short cylinders of bone obtained 
from the thigh of an ox, fracture always took place by cones 
or wedges, In marble the same result was frequently obser- 
vable, though less obvious than in iron, through a disposition 
to split in the direction of the strata. 
On the power of timber of various kinds to resist a crushing 
force, I have, through the liberal views of Mr. Fairbairn, made 
a considerable number of experiments, with an apparatus si- 
milar to that employed in the crushing of cast iron, but much 
larger. In this material, though fibrous, fracture always 
took place by wedges sliding off, or by cones or wedges 
splitting the prism in the manner of cast iron, though at a 
much less angle with the horizon than in that metal. In the 
crushing of malleable iron likewise, short specimens always 
bulge out in the middle through the operation of the opposing 
cones or pyramids formed at their bases. 
As this principle is found to obtain in the crushing of short — 
bodies so widely different as bones, marble*, timber of all kinds, 
* Rondelet (Traité de l Art de bdtir) crushed stones of various kinds, and © 
has given the forms of pyramids obtained from crushing prisms with square 
bases. 
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