298 Mr. Mallet on the Physical Conditions 



Copper, laminated, 84931 



The same, annealed, 8'4525 



„ laminated a second time, . . . . 8 '47 19 



„ hammer-hardened 8-5079 



The volume, thus, is sensibly increased by annealing, presenting in this a 

 remarkable opposition of fact to steel, whose volume is increased by hardening 

 on sudden cooling. 



299. The experiments made by the Franklin Institute, and forming part 

 of its Report on the Strength of IMaterials for Steam-boilers, to the American 

 Government (1831-1837), although, perhaps, the only systematic ones made, 

 present results so discordant as scarcely to admit of confidence. 



It would follow from them, that, in round numbers, wrought-iron, whose 

 strength before being annealed was 53000 lbs. per square inch, becomes 

 46000 lbs. per square inch after annealing. 



They conclude, that the diminution of tenacity is nearly in proportion to the 

 elevation of temperature of annealing, but " were not able to detect any essen- 

 tial change of specific gravity," before and after ; they add, that " in some 

 cases the difference between the strength previous to annealing, and that exhi- 

 bited afterwards was so small, that it was difiicult to refer it to any other cause 

 than the original inequalities of structure. These experiments merely related 

 to the force of ultimate rupture, and as no measurements of extension appear 

 to have been made for hard or annealed bars, or at high temperatures, it is im- 

 possible to compare the " work done" on the rupture of the same bar in the 

 several conditions. This renders these otherwise careful and elaborate expe- 

 riments of very little value. A few comparable results (on wires) are con- 

 tained in a paper by M. Payen (Ann. des Mines, t. vi. 3me ser.) : — "De la 

 puissance mecanique consomme par le tirage a froid des fils," &c. An iron wire 

 having been passed several times through the draw-plate, of one millimetre in 

 diameter, broke with 52 kilogrammes ; having been only once passed through 

 the plate, it broke with 40 kilogrammes ; and having been annealed, it broke 

 with 30 kilogrammes. 



300. The elongation at rupture, in the first case, while quite hard, was only 

 0'"-004 ; after annealing, it was 0"'-200 at rupture. The diameter of the wire 

 increases by annealing 0-055. If we attempt to test this by the " work done" to 



