A Treatise On The Principles And Practice Of Dock Engineering

142 DOCK ENGINEERING. wrought iron is affected very quickly, so that thick flakes may be detached from it with ease. The following instances are cited : — “ Cast-iron cannons from a vessel which had been sunk in the fresh-water of the Delaware river for more than 40 years, were perfectly free from rust.” The cast-iron work of the “ Royal George” and the “ Edgar/ ’ sunk in the sea for 62 years and 133 years respectively, when examined by Gen. Pasley had become quite soft and resembled plumbago. The wrought iron was not so much injured, except when in contact with copper, or brass gun-metal. Two other experimentalists—Rennie and Mallet—adopt antithetical opinions as to the relative corrosion of cast and wrought iron in salt-water. The former maintains a higher rate for cast iron; the latter, for wrought iron. The following table extracted from a paper on the corrosion of iron and steel, by Mr. David Phillips,* relates to a series of experiments made by him with five sets of iron and steel plates, 4 inches square by | inch thick, exposed to various corrosive agencies. “To avoid even a suspicion that galvanic action had any influence in these cases, all the plates were suspended on glass rods, and each plate was separated from its neighbour by glass ferrules.” It is important to note that Mr. Phillips attributed the generally greater corrosion during the first period of trial to the fact that the weather in the summer of 1879 was much more changeable than that in 1880. TABLE X.—Corrosion of Iron and Steel. Metal. Water. Loss of Weight. First 12Months. Second 12Months. Total. Average per Sq. Ft. of Surface. j N Bessemer steel, . Grs. Grs. Grs. Grs. Rain-water, . 186-7 141-4 328-1 1,246-9 I Y Siemens steel, 174-1 147-0 321-1 1,220-3 jB B Staffordshire iron, 165-3 119-0 284-3 1,080-5 DD Yorkshire iron, . N Bessemer steel, . Sea-water, 185-1 136-2 321-3 1,221-1 42-4 36-9 79-3 301-4 Y Siemens steel, 33-5 34-7 68-2 259-2 B B Staffordshire iron, 35 4 35-6 71-0 269-8 DD Yorkshire iron, . 1 Exposed to weather ; j and dipped in sea-> (water daily, .) 36-9 31-6 68*5 260-3 N Bessemer steel, . B B Staffordshire iron, 1,044-7 417-9 501-6 259-1 1,545-6 677-0 5,874-0 2,572-9 Y Siemens steel, (Exposed to thel 234'4 135-9 370-3 1.407-3 D 1) Yorkshire iron, . I weather only, ./ 147-6 52-7 200-0 761-2 In the discussion which followed the reading of the paper, much emphasis was laid by Dr. Siemens, Mr. Barnaby, Mr. Farquharson, and others, on the importance of removing the magnetic oxide scale from the * Phillips on “The Comparative Endurance of Iron and Steel when Exposed to Corrosive Influences,” Min. Proc. Inst. C.E., vol. Ixv.