296 ]Mr. Mallet on the Physical Conditions 



We shall elicit these properties most fully, when the wrought-iron applied 

 has been slowly cooled — in other words, has been annealed; and this neces- 

 sarily happens, when the shrunk-on rings are permitted to cool slowly, while, 

 (with many classes of hard "steely iron," like the Swedish, if suddenly cooled, 

 an approach, more or less complete, is made) to the brittle and dangerous con- 

 dition of hardened and untempered steel. 



34. — Of the Relations between Annealing and Tenacity. 



296. It will be desirable, therefore, to make some remarks on the subject 

 of annealing wrought-iron, — one upon which our experimental information is 

 deplorably deficient. 



That the condensation, produced by "hammer-hardening," and, still more, 

 the longitudinal arrangement of crystal induced by lamination, rolling, and wire- 

 drawing, considerably increase the longitudinal tenacity of iron, copper, and 

 several of the alloys of the latter, is certain. The evidence of it is most remark- 

 able in the case of fine brass wire, which, when hard from the draw-plate, closely 

 approaches wrought-iron in tenacity, resisting, according to Baudrimont, to 

 87,000 lbs. per square inch. On the other hand, that " annealing" is attended 

 with a greater or less loss of tenacity, appears to admit of little doubt ; but 

 to what extent this loss reaches, in proportion to the temperature, &c., still re- 

 quires additional experimental investigation ; for the experiments hitherto made, 

 appear only to have had regard to the absolute final force required for rupture, 

 and to have taken no note of the increased range of extension, induced by the 

 annealing. Yet, upon both of these, the " work done" in producing rupture 

 depends, and it may not improbably be ultimately found, that the coefficient 

 Tr, is not altered at all by annealing, but is, for the same iron or other metal, 

 a constant, only changeable in the ratio of the factors whose product it is. 



297. Even the temperature at which that change of molecular condition 

 which constitutes perfect annealing, takes place, remains yet to be determined, 

 for every metal. There seems to be, at least, a fixed and rather narrow range 

 of temperature, for every metal, without the limits of which annealing does 

 not take place, and the mean temperature within this range appears to be more 

 elevated in proportion as the metal itself has a higher fusing temperature. 

 Thus platina, after lamination or wire-drawing, is not annealed, under an 



