380 SEVENTH REPORT—1837. 
In describing the following experiments, I will first give the 
tables and results on the transverse or more usually investigated 
species of strain, where the experiment was made without loss 
of time, and which may be considered a continuation of the 
same class of experiments by Mr. Hodgkinson. We shall then 
proceed to experiments on the Coed-Talon bars, in relation to 
time or indefinite strain. Afterwards we shall exhibit others on 
the effects of temperature ; and finally close with a general sum- 
mary of results. 
Before presenting the experiments in their tabulated forms, 
it may be necessary to supply a brief description of each class, 
in order to show the methods adopted, and how the results 
were obtained.—For this purpose, a number of models were 
prepared, to be 1 inch and 14 inches square; and the metals, 
both hot and cold blast, were run into the form of those mo- 
dels. But as there is generally a slight deviation in the size 
of the casting from that of the model, the dimensions of the 
bars were accurately measured at the place of fracture, and the 
results reduced (when practicable) by calculation. to what they 
would have been if cast to the exact size of the model. This 
was done to ensure more accurate comparisons in the strength 
and other mechanical properties of the bars. The mode of re- 
duction is described in the preceding report. 
In addition to the methods herein adopted to determine the 
strength, tenacity, and value of the different irons made from 
hot and cold blast, I conceived it necessary to institute a series 
of microscopic observations ; to examine with great minuteness 
the appearance of the fracture, and by magnifying the crystals, 
to elucidate such visible indications of the fluidity, strength, 
and ductility of the irons, as would distinguish the qualities of 
the different numbers known in commerce by the name of No. 
1, 2, and 3 iron. 
I also pursued in other respects a close and minute examina- 
tion of the different specimens of hot and cold blast iron, and 
by turning, filing, grinding, &c., endeavoured to discover their 
properties in relation to each other, and their adaptation to the 
arts. 
As the Carron No. 2 irons, hot and cold blast, were among 
the first we obtained, I have, in the description of the fractures 
attached to each table of experiments, made the Carron No. 2 
cold blast iron the basis of comparison. It may therefore be 
proper to give here the following short description of it. 
This iron, when viewed with a microscope, presents a dull 
grey colour, finely granulated, with an appearance of greater 
porosity in the centre than round the extreme edges of the frac- 
ture. It is a free-working iron, easily cut with the turning 
tool, but indicates stiffness under the file. 
