ON STRENGTH AND PROPERTIES OF CAST IRON. 405 
deflections) that we must at some period arrive at a point beyond 
their bearing powers ; or otherwise to that position which indi- 
cates a correct adjustment of the particles in equilibrium with ~ 
the load. Which of the two points we have in this instance at- 
tained is difficult to determine: sufficient data are however ad- 
duced to show that the weights are considerably beyond the 
elastic limit*, and that cast iron will support loads to a much 
greater extent than what has usually been considered safe, or 
beyond that point where a permanent set takes place. But in 
whatever way this may be determined, it is obvious the pre- 
ceding experiments give greater indications of strength than 
has generally been supposed cast iron would do; and should 
the bars continue to support the loads for a few years longer, 
there cannot exist a doubt as to the security of this metal 
under applications hitherto unknown; and the same may be 
said of other materials. 
In the 14th Table we shall find inch square bars loaded on 
the middle, within a few pounds of weights sufficient to break 
them ; we shall also find the bars considerably bent, and the 
resisting powers in full operation to sustain the load. Now the 
question to be determined by this experiment is, the nature of 
this resistance ; and to show in the first instance whether the re- 
sisting power of the extended particles below, and the powers of 
the condensed ones operating above, are sufficient at all times 
ad infinitum to support the load ; or whether those particles, in- 
stead of being united (as we suppose) with a permanent force, 
nicely balanced at all points of resistance, are not absolutely 
giving way; and by slow, though imperceptible degrees, be- 
coming hourly weaker, until the cohesive power is entirely de- 
stroyed and rupture takes place. 
It is not my intention in this place to offer any opinion upon. 
the cohesive properties of matter, but simply to inquire how far 
the bearing powers of cast iron can be depended upon. 
It is evident from these experiments that both sorts of hot and 
cold blast iron possess that power in a high degree ; and we need 
only refer to the experiments for examples to show the patient 
tenacity with which so heavy a load is supported. At first sight 
it would appear, that the heavier loaded bars were progressively 
giving way, as the deflections continue to increase since the 
loads were permanently fixed; this defect is however not more 
conspicuous in the bars supporting 448 lbs., than in those sup- 
* The elastic limit is that point where bodies under strain lose the power to 
restore themselves when the load is removed ; a property which is strongly ex- 
emplified in cast iron. It has been considered by many that materials cannot 
be loaded with safety beyond that point. 
