tructure far exceeds that of similar tanks in the
United States. The stand-pipe at Attleboro, 50 ft. in diameter and 100
ft. high, cost about $25,000. Several years ago the writer proposed to
build an elevated tank, 60 ft. in diameter and 40 ft. deep, the bottom
of which was to be 50 ft. above the ground, for $21,000.

Among other elevated tanks known to the writer is one having a capacity
of 100,000 gal., the bottom being 60 ft. above the ground.[C] The total
quantities of material required for this tank are given as 4,480 cu. ft.
of concrete, 23,200 lb. of reinforcing steel, and 27,600 ft., b. m., of
form lumber and staging. Calculating at the abnormally high unit prices
of 40 cents per cu. ft. for concrete, 4 cents per lb. for steel, and $50
per 1,000 ft., b. m., for lumber, the cost of the concrete would be
$1,792, the steel, $928, and the form lumber and staging, $1,380. Adding
to this the cost of a spiral staircase, at the high figure of $7 per
linear foot in height, the total cost of this structure would be $4,598.
The factor of safety used in this structure was four, but some engineers
who are not familiar with concrete construction may require a higher
factor. By doubling the quantities of concrete and steel, which would
mean a tensile stress in the steel of only 8,000 lb. per sq. in., and a
compressive stress in the concrete of only 225 lb. per sq. in., the cost
of the tank would be only $7,318, as compared with the $16,578 mentioned
in the paper. This enormous discrepancy between a good design and an
amateur design, and between day-labor work and contract work should be a
lesson which consulting engineers and managers of large corporations,
who prefer their own designs and day-labor work, should take to heart.

A. H. MARKWART, ASSOC. M. AM. SOC. C. E. (by letter).--It is the
writer's opinion that the steel tank enclosed within the concrete of the
upper cylinder, to take up the hoop tension and presumably to provide a
water-tight tower, will not fulfill this latter requirement. If a
plastered surface on the dome-shaped bottom provided the necessary
imperviousness, it would seem that plastered walls would have proved
satisfactory.

Apparently, the sheet-metal tank is intended to exclude the possibility
of exterior leakage, but it occurs to the writer that it will fail to be
efficient in this particular, because, under pressure, the water will
force itself under the steel tank and the dome thrust rings and ou