THEORY AND PRACTICE OF CONCRETE-IRON CONSTRUCTIONS. 121 



The new Woolloomooloo baths lately erected, have an 

 enclosure consisting of concrete-iron piles and sheet piles, 

 the main piles are 22 inches x 15 inches and 15 inches x 

 12 inches, and the sheet piles 14 inches x 6 inches, both 

 up to 25 feet 6 inches in length. They were driven with a 

 2J ton monkey, with a drop as much as 7 feet, in places 

 through quarry refuse, without sustaining any damage. A 

 retaining wall has lately been built along the Darling 

 Harbour foreshore, consisting of concrete-iron sheet piles 

 21 feet long and 18 inches wide, ranging from 9 inches to 

 18 inches in thickness, according to the strength required 

 to stand the earth pressure. They were potted in a rock 

 trench, and held back at the top by tie-rods. 



The use of concrete-iron pipes for water supply purposes 

 was first attempted about 14 years ago, and its success has 

 led to its extended adoption in Europe and other places, as 

 it has many points in its favour when compared with cast- 

 iron. Concrete-iron pipes are manufactured to withstand 

 any internal pressures required, and as such are of two 

 distinct types : — 



1. The ordinary pipe, where the imperviousness neces- 



sary depends solely on the concrete. 



2. The pipe which has embedded in the concrete a thin 



metal core to prevent percolation. 



Dealing with the first type, viz., the pipes solely depend- 

 ing on the concrete for its imperviousness ; it has been 

 found that although they may exude or sweat when first 

 put into use under high pressures, they soon " take up." 

 Observations made on a pipe line of 4,920 feet long, on 

 pipes 5 feet 9 inches diameter laid in connection with the 

 Paris Water Supply, designed for a head of water of 44 feet 

 6 inches, showed when tested to be water-tight with a head 

 of 24 feet. Under a pressure of 36 feet 5 inches wet spots 

 appeared, and under a pressure of 44 feet 6 inches a general 



