138 HARBOUR CONSTRUCTION. 



it contains an essential pungent oil, which renders it equally as 

 good as greenheart in resisting the ravages of sea- worms. 



I have, nevertheless, on one or two occasions, found Teredo 

 navalis in the very heart of it. 



Unfortunately, sneezewood trees do not attain a large size, 

 and it is very rare indeed to find a straight one. Hence scarfing 

 becomes necessary if piles of even moderate length and scantling 

 are required, and the structure in which they are used presents 

 an unsightly appearance. 



The timber is, nevertheless, a valuable one, and its culti- 

 vation well deserves the attention of the Colonial Forestry 

 Departments. 



It seems probable that, if the trees were grown in dense 

 forests, and received proper attention when young, they might 

 grow straight and attain a larger size than they do at present. 



In exceptional cases, where the sea-worms are very active, 

 it is well, as far as possible, to substitute iron for timber in 

 pile-work, and also for under- water bracings, etc., timber fenders 

 or rubbing-pieces being so arranged that they may be renewed 

 without difficulty. 



SECTION VI. IKON AND STEEL. 



Durability in sea-water Kecords differ widely Results of experiments Effect of 

 galvanic action Structural and chemical differences affect rate of corrosion- 

 Simple corrosion Kate of corrosion of plates, etc., of s.s. Gambia Effect of 

 exposure on castings at Bell Rock lighthouse, on wrought-iron rails at Port 

 Elizabeth, on ironwork of piers at Ramsey and Port Elizabeth, and on ironwork 

 of beacon at Wolf Rock Beardmore on decay of iron Wrought iron more 

 durable than cast iron in sea- water Mallet on preservation of iron Redman 

 on decay of iron Pier at Milton-on-Thames Gravesend town pier. 



Iron and Steel have not hitherto entered very largely into 

 the designs of breakwaters, but their use in the construction of 

 landing-piers and kindred sea-works is very general. 



To describe the numerous varieties of iron and steel, their 

 production, distinctive qualities, uses, strength, and so forth, 

 would occupy too much space in the present work, and would, 

 moreover, be out of place. The subject has been very fully 

 treated in works by Fairbairn, Bloxam, Percy, Matheson, and 

 others, and also in Part III. of " Building Construction " (Long- 

 mans & Co.), where, in about eighty pages which are devoted 



