104 Expet^iments on two varieties of Iron. 



The fracture of No. 2, presents less of the clear fibrous texture, 

 silky lustre, and uniform compactness, than ought to characterize 

 iron of the first quality. 



A few general remarks seem worthy of attention in connection 

 with the subject of tenacity as presented by the above experiments. 



The first is, that in the annealed state, different kinds of iron- 

 more nearly resemble each other, in respect to strength, than in any 

 other condition. This is verified by the last comparison in which 

 the difference between the two kinds, when annealed is seen to 

 be only eleven per cent; while in the other three conditions, it 

 varies from 15.3 to 21.9 per cent. 



The second remark is, that in the annealed state, the same bar 

 has greater uniformity of strength within itself than in any other 

 case. This is proved by comparing the greatest differences as 

 stated in tables I, and II, in the column of observations. 



The two annealed bars are there seen to give for these differ- 

 ences between their highest and lowest results, 3.2 and 2.3 per 

 cent ; mean =2. 75. 



The two bars hammer-hardened, gave results, 3.5 and 8.2 per 

 cent; mean = 5.S5. 



The two bars ham,m,ered to dull red heat, gave results, 4.15 and 

 4. 9 per cen t ; mean = 4. 425. 



The two bars upset and annealed, gave results 11.2 and 8.4 

 per cent ; mean = 9.8. 



The experiments on the annealed bars were, in both cases, 

 fully as numerous, as those on the same kind of iron in any other 

 state ; and hence, other things being equal, ought to have pre- 

 sented, at least, equal discrepancies ; while in fact, these are 

 scarcely more than one half as great as the least of the others, 

 and are less than one third as great in either kind of iron, as 

 those found in the upset and annealed bars. 



The third observation I would make, is that in upsetting part 

 of a bar, and subsequently annealing the whole of it, the differ- 

 ences in tenacity, between different kinds of iron, and between 

 the several parts of the same bar, are both at a maximum. 



Thus the two varieties of iron, gave a difference of nearly 

 twenty-two per cent, from each other, and their mean diversity 

 for the same bar is 9.8 per cent, of its mean strength. This may 

 be satisfactorily explained only on the supposition, that upset- 

 ting iron increases its direct cohesion, since we know that anneal- 



