COMPARATIVE VALUE OP VABIOUS KINDS OF STONE. 43 

 Limestone. 



!b«. peraqnar* 

 inch. 



No. 11. — 3in. cube Anglesea limestone, weighing 



2 lbs. 10 ozs., set between boards. Crushed 



with 26 tons 1 1 cwt. 3 qrs. 9 lbs = 6618. 



This stone formed numerous cracks and splinters 



all round, and was considered crushed ; but on 



removing the weight about two-thirds of its 



area were found uninjured. 

 No. 12. — 3in. limestone, weighing 2 lbs. 9 ozs., set 



between deal boards. Crushed with 32 tons 



6 cwt. qr. I lb = 8039. 



This stone also began to splinter externally with 



25 tons (or 6220 lbs. per square inch), but 



ultimately bore as above. 

 No. 13 3in. limestone, weighing 2 lbs. 9 ozs., set 



in deal boards. Crushed with 30 tons 18 cwt. 



3 qrs. 24 lbs = 7702.6 



No. 14. — Three separate lin. cubes limestone, 



weighing 2 lbs. 9 ozs., set in deal boards. 



Crushed with 9 tons 7 cwt. 1 qr. 14 lbs = 6995.3 



All crushed simultaneously. 



Mean 7579. 



All the limestones formed perpendicular cracks and splin- 

 ters a long time before they crushed. 



Weight of the material from above =165 lbs. 5 ozs. per 

 cubic foot, or 13 J feet per ton. 



The weight required to crush this limestone is 471.15 tons 

 per square foot, equal to a column 6433 feet high of such 

 material." 



Previously to the experiments just recorded, it was deemed 

 advisable not to trust to the resisting powers of the material 

 of which the towers of either bridge were composed ; and, to 

 make security doubly sure, it was ultimately arranged to rest 



