ON STRENGTH AND PROPERTIES OF CAST IRON. 369 
__ The last experiment in both the preceding tables was upon a 
___ beam of the best form of section, according to the writer’s expe- 
_ riments, (Manchester Memoirs, vol. 5.) the top and bottom 
rib being nearly in the ratio of the tensile to the compressive 
forces of the metal, as mentioned above. ‘The intention was 
to compare the strength of the beam with that of a rectangular 
one of the same weight, length, and depth. For this purpose 
the beams were cast uniform throughout, and in comparing the 
strength of that in the hot blast iron with the mean from the 
strengths of the two preceding rectangular beams, reduced as 
above, we find that the breaking weight of these is 19,108 lbs., 
and the beam of best form was broke with 25,817 Ibs. In the 
cold blast Devon iron the difference in strength is much greater. 
The rectangular beam, from the mean of the two experiments 
on the beams 3 inches and 5 inches deep, when reduced as 
above, gives 11,183 lbs. for the breaking weight, whilst the 
beam of the best form required 22,227 lbs. to break it. 
VOL. VI. 1837. 2B 
