80 Papers connected with the construction No. 81] 



ttratch of the file caused them to disappear, 3d that the interior wires of 

 the cables were perfectly untouched." Eight years is a short space of 

 time, but if we consider that the effects of oxidation probably continues to 

 decrease, we may conclude that they are not so very rapid, and that the 

 fears entertained, upon this point, are greatly exaggerated. 



In the Select Committee upon Steam Navigation, June 1834 McGre- 

 gor Laird Esq. being interrogated. Can you state any thing as to the 

 durability ? The Alburkah, when I left her had been in water about 

 three years, and I could see no symptoms of decay in her. 



Was there no corrosion ? 1 There was not any that was visible.' It appears 

 to me generally that, after the first scale comes off the iron, very little effect 

 is produced by the corrosion. Whenever the iron is in contact with 

 wood, it is sure to go, the acid of the wood destroys it. Iron vessels 

 have worked on canals for 35 years, without repair ; the two iron boats 

 built for the Seine in 1822, as yet shew no symptoms of decay. (It must 

 be observed, that iron vessels are built with plates a few lines in thick- 

 ness.) 



The suspension Pier at Trinity near Edinburgh, was built in 1821, and 

 is still in a very good state of preservation. 



The erection of this Pier, of a similar one at Brighton, the great exten- 

 sion given to iron ship-building, are as many proofs of the advantages 

 there are to substitute iron for timber, for these kinds of structure, and 

 that the builders are no longer stopped by the fears of a too rapid corro- 

 sion. M. Mallet estimates the progress of oxidation to £ ff of an inch in 

 a century, and still his experiments have'been made upon irons, for the 

 preservation of which no means had been employed. Those that are em- 

 ployed now, consist in the application of minium of coaltar on the iron 

 while it is hot, of a compound of tallow, bright varnish, arsenic, and 

 brimstone, and at last, in the process called zincing. 



On these the following remarks are found, in the Civil Engineer and 

 Architect's Journal. 



In speaking of the iron, Queen Steamer, it is said there is no appear- 

 ance of corrosion, the red lead being fresh on the plates, and neither 

 shells, barnacles nor any foulness was on her bottom. This desirable 

 result is caused by the single application of a compound of tallow, bright 

 varnish, arsenic and brimstone. 



On the process called zincing. 



