1874.] Engineering. 269 
The chimneys are constructed with the lower parts. of brick and the upper 
parts of wrought-iron, and are sufficiently light to be placed on the benches, 
so that no floor space is occupied by them: they are 71 feet 6 inches high, 
3 feet square at the bottom, and 3 feet in diameter at the top, the least sec- 
tional area giving 1 square inch for each lineal foot of retort—a proportion 
which has proved satisfactory. There are twenty-four benches of retorts, each 
bench having eight long retorts, there being two mouth-pieces to a retort, or 
384 mouth-pieces in all. The retorts are cylinders, 16 inches in diameter and 
20 feet long, and each retort will carbonise r ton of coal per day. Allowing 
one-sixth as the number for reserve, the remainder will produce 1,500,000 cubic 
feet of gas every twenty-four hours, or 300 millions per annum. The engine- 
house contains four exhausters, each exhauster being driven diredtly by an 
independent engine. The entire cost of the works has been about £72,000; 
and when a proposed second retort-house and coal-store are erected upon the 
site allotted for them, the total expenditure will amount to £100,000. The 
works will then be capable of producing 600 millions cubic feet of gas per 
annum, at a cost of £166 per million on the capital expended. 
Concrete Blocks.—The use of concrete blocks, of large size, in the construc- 
tion of marine works, has, within recent years, come to be greatly extended. 
An interesting paper, ‘‘ On the Construction of Harbour and Marine Works 
with Artificial Blocks of Large Size,” by Mr. B. B. Stoney, formed one of the 
subjects under discussion at the Institution of Civil Engineers last February. 
The author described a new method of submarine construction with blocks of 
masonry, or concrete, far exceeding in bulk anything hitherto attempted. 
The blocks are built in the open air, on a quay or wharf, and, after from two 
to three months’ consolidation, they are lifted by a powerful pair of shear- 
legs, erected on an iron barge or pontoon. When afloat, they are conveyed 
to their destination in the foundations of a quay wall, breakwater, or similar 
Structure, where each biock occupies several feet of the permanent work, and 
reaches from the bottom to a little above low-water level. The superstructure 
is afterwards built on the top of the blocks, in the usual manner. By this 
method the expenses of coffer-dams, pumping, staging, and similar temporary 
works are avoided, and economy and rapidity of execution are gained, as well 
as massiveness of construction, so essential for works exposed to the violence 
of the sea. There is now being built in this manner an extension, nearly 
43 feet in height, of the North Wall Quay, in the port of Dublin. Each of 
the blocks composing the lower part of the wall is 27 feet high, 21 feet 4 inches 
wide at the base, 12 feet long in the direction of the wall, and weighs 350 tons. 
The foundations for the blocks are excavated and levelled by means of a 
divine-bell. The hull of the floating shears is rectangular in cross section, 
48 feet wide, and 130 feet long. The aft end forms a tank, into which water 
is pumped to balance the weight of the block suspended from the shears at 
the bow of the vessel. 
Dublin Water Supply.—*‘ The Water Supply of the City of Dublin” formed 
the subje&@ of a paper, by Mr. Parke Neville, at the Institution of Civil 
Engineers, on the 24th of February. The water supply of the City of Dublin 
was for several centuries derived from the River Dodder. In 1775 this source 
was found to be insufficient, and the Corporation entered into contracts with 
the then Grand Canal Company for a supplemental supply, which were 
extended in 1808. The water from this source was hard and subjeé to pollu- 
tion, and from 1850 to 1857 the question of obtaining a better supply was 
constantly under consideration. This ultimately led to the appointment of a 
Royal Commission, and Sir John Hawkshaw was appointed by the Govern- 
ment as Commissioner. . The result of his enquiries was the recommendation 
of the River Vartry as the best source, and works for that object were com- 
menced in November, 1862, and finished in 18608. The Vartry rises at the 
base of the Sugar-Loaf Mountain, in the county of Wicklow, and the place 
selected for the storage reservoir is near the village of Roundwood, about 
7% miles below the source of the river. The embankment across the valley, 
at its deepest point, is 66 feet high, and its total length is 1640 feet. The 
VOL. IV. (N. S.) 2M 
