WHARF CONSTRUCTION, SYDNEY HARBOUR. XXXIX. 
whereby chemically pure copper is produced may have 
something to do with the rapid corrosion. 
Advices from Hngland recommended the trial of Navy 
brass, a sheathing made by the Muntz firm, and which 
consists of Muntz metal with 1% of tin added to harden it. 
This alloy being hard does not exfoliate on the surface like 
Muntz metal, and therefore fouls much more rapidly in 
sea-water. This however, is not an objection for pile 
sheathing. Navy brass is a little more costly than ordinary 
yellow metal. Jam unable to afford any reliable informa- 
tion as to its durability, as it has only been recently placed 
on the market. I have heard however that it has shown 
but little superiority over the older brands. Coating the 
inside surface of the metal (that which goes next the pile) 
with coal tar has been found to protect the metal from 
corrosion set up by the juices from the wood. 
Scantling.— Without doubt ironbark is the strongest and 
most durahle of Australian timber suitable for caps and _ 
girders. Grey Gum and Brush Box are also excellent. 
Turpentine is a good timber and only a little less durable 
than ironbark, and also possesses the advantage of being 
less open to attack by white ant, but it has not the strength. 
The wharf at the eastern side of Cockatoo Island was built 
with turpentine piles, girders, and headstocks over 24 years 
ago. The headstocks and most of the girders are in good 
condition where the water has not found its way into the 
interior of the beams. The cause of rottenness in wharf 
girders—which always decay before the caps—arises from 
the opening of the grain by the deck spikes. <A row of 3 
inch or 3 inch spikes driven into a beam cause it to split 
in long cracks, especially when the work is done on green 
timber. Rain washes humus matter into these cracks and 
a rot issetup. To overcome this difficulty, Ihave adopted 
the use of malthoid damp course laid over each girder, 
