96 
a 561b., intending to add small weights when suspended, 
raised so imperceptibly by the screw, that the only way 
of ascertaining that it was suspended was by looking under 
the scale to see that it was clear of the rest. As soon as 
it was half-an-inch clear it snapped, thus breaking at once 
with one pound less than it resisted for nearly two minutes. 
Sis experiments were carefully conducted at 60° Fah. 
the parts of the bars being selected so as to give to each 
set of experiments similar portions of both bars : the 
results arc marked on the pieces. My assistant now 
prepared a refrigerating mixture which stood at zero 
and the bars were immersed for some time in this, and 
we prepared for the breaking trials to be made as 
quickly as could be, consistently with accuracy, and to 
secure the low temperature each bar on being placed in the 
machine had its surface at top covered with the freezing 
mixture. The bars at zero broke with more regularity than 
at 60°, but instead of the results confirming the general 
impression as to cold rendering iron more brittle they are 
calculated to substantiate an exactly opposite idea, namely, 
that reduction of temperature ccvteris paribus increases the 
strength of cast iron. The only doubtful experiment of the 
whole twelve is the first, and as it stands much the highest, 
the probability is that it should be lower ; yet, even taking 
it as it stands, the average of the six experiments at 60° Fah. 
gives 4cwt. Mbs. as the breaking weight of the bar at that 
temperature, while the average of the six experiments at 
zero gives 4cwt. 201bs. as the breaking weight of the bar at 
zero, being an increase of strength from the reduction o^ 
temperature equal to 3 -5 per cent. 
Mr. Wm. Radford, C.E., asked if Mr. Brockbank had con- 
sidered what the effect must be upon iron used in Russia, 
Sweden, Norway, and Denmark, for if the theory which wa s 
sought to be established were true, the tires of railway 
wheels in those countries must fly to pieces in winter; as far 
as his experience went in Denmark such had not been the 
case on the Copenhagen Railway. 
