149 
The action of Sea-water upon Cast-iron. 
By A. Liversivas, Professor of Geology and Mineralogy in the 
University of Sydney. 
[Read before the Royal Society of N.S. W., 1 September, 1880.] 
THE specimen forming the subject of this note was obtained from 
€ screw of the dredge ‘‘Hunter” employed in Newcastle 
N.S. W. 
Mr. oriarty, the Engineer-in-Chief for Harbours and Rivers, 
tells me that the dredge had not been wrecked as I had previously 
been informed, in fact she is still at work; but that the screw 
me so rotten as to necessitate its removal. He agcounts for 
the rapid decay, and very sufficiently, by the iron having been in 
actual contact with the copper sheathing of the vessel. In the 
Same letter Mr. Moriarty mentions that an old iron cannon was 
taken up from the foul waters at the head of Darling Harbour, 
where it had lain for some twenty years, but the corrosion had 
only eaten its way in to about +; of an inch. 
_Even on the most cursory examination the specimen is seen to 
differ entirely from the original cast-iron, except in form, Been 
Seems j 
of graphite, mixed with brown-coloured oxide of iron and a few 
ice Scattered minute particles of metallic iron; these on 
Tn colour the external part of the i is of a dull 
ithin <4: the specimen 1s Of a grey, 
foll 1s of a rusty brown colour, with darker bands which 
oioW more or less closely the outer contour lines. 
pe friable than the very outside of the specimen ; but even this 
Y contained -04 per cent. of metallic iron; the boss of the 
