OTHER PROPERTIES OF CAST IRON 229 
No. 2, and presents greater rigidiy than either 
of the former qualities —From the circumstan- 
ces thus stated, it will be noticed that, in com- 
paring two irons together, it will be necessary 
to observe the quality, and as often as possible to 
compare the No. 1 of one iron with No. | of ano- 
ther iron; and in order to ensure the correct 
value or point of difference, this method should 
also be adopted in the Nos. 2 and Nos. 3. 
In pursuance of these views I have endeavour- 
ed to procure the irons as much alike as possible, 
and to render the comparison still more perfect, 
I have selected the medium, or No. 2 quality, as 
the most suitable for the purpose. In every 
instance, the No. 2 iron could not be obtained, 
but in most cases I have kept as close to it as 
circumstances would admit. We may therefore, 
safely compare similar qualities and numbers 
together, either in reference to their trans- 
verse strength, or power to resist impact. 
The following short summary of results may 
be useful in exhibiting the relative values of the 
No. 2, English Irons, in reference to their 
powers of resisting a transverse strain: their 
powers to resist impact and other properties 
