MATERIALS. 



141 



One point of great value, which Mr. Andrews has established, 

 and which is deserving of careful attention, is the desirability of 

 reducing, as far as possible, the internal causes of disintegration 

 in iron or steel structures in sea-water, by avoiding the use of 

 dissimilar metals, and endeavouring to have all plates, bars, clips, 

 rivets, bolts, etc., as nearly as practicable, not only of similar 

 material, but also of the same temper and composition as regards 

 the percentages of combined carbon, manganese, etc., which they 

 contain. 



In the year 1871, the iron screw steamship Gambia was 

 stranded in Algoa Bay, and became a total wreck. She was 

 built in the year 1860 by Messrs. Leslie & Co., of Newcastle-on- 

 Tyne, and was therefore a comparatively new ship. 



In the year 1881, or ten years after the wreck occurred, 

 I carefully measured several of the plates, angles, etc., which 

 lay between high and low water mark, and, for purposes of 

 comparison, I obtained from the builders the original thickness 

 of these. 



The following list shows the results of these measurements, 

 and the loss resulting from the ten years of exposure : 



On detaching masses of sea-growth from the skin plates 

 near low-water mark, I found red paint still adhering to the 

 plates in some places. 



In the letter giving the original thicknesses of plates, etc., 

 which Messrs. Leslie & Co. were kind enough to furnish, they 

 said 



" We may mention that we have now in dock here for repairs, 

 two vessels built by us about the same time as the Gambia, and we 

 find that where the iron has been protected with cement and paint 

 there has not been the slightest deterioration, and the plates of the 

 bottom are now of the fall original thickness." 



