Polytechnic Association Proceedings. 867 



qiiently discussed, and until lately, it was generally assumed, that 

 a rapid corrosion was inseparable from the use of this metal thus 

 exposed, and when wholly immersed in water. 



Numerous cases were cited to prove these positions, and the 

 every-day experience of constructors seemed to confirm it. Wrought- 

 iron bolts in wooden mill dams, and similar places, were found to 

 rapidly oxydize, and those in sunken vessels, to have become nearly 

 eaten up in a few years. 



Cast-iron cannon and shot, immersed in seawater, from a quarter 

 to one-half a century, were often found, with the structure of the 

 mass of the metal entirely changed from iron into plumbago or gra- 

 phite, and in other cases deeply pitted by oxydation. 



During the earlier discussions of the subject, the inquirer was 

 frequently staggered in his belief of the generally received opinion, 

 by finding both wrought and cast-iron, which had been immersed 

 many years, and was but slightly oxydated, and with no change in 

 the structure of the metal, and that sometimes, as in the cjise of the 

 cannon of the Royal George, which had been submerged for half 

 a century, the metal which had become so soft as to be cut with a 

 knife, hardened rapidly when removed from the water, so much so, 

 as to be able to bear again the same charge in firing. 



Some muskets and cannon sunk in Lakes Erie and Ontario during 

 the war of 1812, were taken up forty years afterwards, almost unin- 

 jured, and only slightly oxydated. An iron steamer, the "Aaron 

 Manly," is cited by Grantham, as having been built in 1822, and 

 kept in constant use, alternately in fresh and salt water for twenty 

 years, and when examined, no signs of corrosion were visible, and 

 the vessel was in use ten years later, having received but small 

 repairs during the whole period. William Fairbairn also cites cases 

 of u'on vessels which had been from six to ten years in saltwater, 

 and showed no corrosion. 



In 1850, when this subject was much discussed in England, the 

 unexpected absence of corrosion of wrought-iron in ships naviga- 

 ting the ocean, was attributed to the constant vibration of the metal, 

 as the same result is noticed in railway bars. It was also remarked 

 that frequently no corrosion took place on the interior surfaces, or 

 the other fixed iron parts of these ships. 



In 1822, Dr. McCullock produced plumbago from cast-iron 

 immersed in acidulated water, and forty years later. Dr. Calvert 

 produced the same result in sea and foul waters. Mr. Mallet, at 

 the request of the Royal Society, made the well-known experiments 



