[Illustration: FIG. 593.]
_A tank is an artificial receptacle_ for liquids, thus: _a tank
engine_ is one which carries the water and fuel it requires, thereby
dispensing with a tender; _tank-iron_ or steel is common plate used
in building tanks. Steel is cheaper than sheet-iron. _A cistern is
primarily a natural reservoir_—a hollow place containing water; more
commonly an underground reservoir or tank. _Closed pressure tanks_ are
usually cylindrical shells similar to a horizontal steam boiler, having
bumped or rounded heads to save bracing. Closed pressure tanks are
used extensively in connection with hydraulic elevators; the requisite
pressure for these was formerly derived from an open tank installed
upon the roof of the building, but the closed pressure tank, located
in the engine room, now very generally takes the place of the open tank.
_A closed pressure tank_ is shown in Fig. 596 in use with a hydraulic
elevator.
_A reservoir_ is a place where water is collected and kept for use
when wanted, so as to supply a fountain, a canal or a city by means of
aqueducts or to drive a mill-wheel or the like.
[Illustration: FIG. 594.]
_A receiving reservoir_ is a principal reservoir into which an
aqueduct or rising main, delivers water and from which _a distributing
reservoir_ draws its supply.
_A graduated tank_ is one fitted with water gauges and indicating
marks, at different heights, between which, the capacity of the tank is
shown.
_A ship’s ballast tank_ is the compartment for water to be pumped in
and out for the purpose of insuring the proper stability of the vessel,
to avoid capsizing and to secure the greatest effectiveness of the
propelling power.
[Illustration: FIG. 595.]
_A vat_ is a cistern or tub, especially one used for holding liquors
in an immature state, as chemical preparations and tanning liquor for
leather. Fig. 594.
_A tub_ is an open wooden vessel formed with staves, bottom and hoops;
a kind of short cask, half barrel or firkin, usually with but one head.
Fig. 595.
_A gallon_ (U.S.) is equal to 231 cubic inches or 0.13368 cubic feet
and weighs 8-1/3 lbs. nearly, (i.e. 8.3356). This is almost exactly
equivalent to a cylinder 7 inches in diameter and 6 inches in height.
_The imperial gallon of England_ contains 277.274 cubic inches, and is
equivalent to 1.2 U.S. gallons and at 62° Fah. weighs 10 lbs.
_A cubic foot_ contains 7-4805/10000 (7-1/2 nearly) U.S. gallons, and
weighs 62-355/1000 (62-1/3 nearly) lbs.
_A barrel_ = 31-1/2 gallons. 1 hogshead = 2 bbls. = 63 gallons.
_The strength of a tank_ is of the first importance; 235-1/2 gallons of
water weigh as much as a ton of coal, but unlike the latter, it presses
in all directions. Immense losses both of life and property have been
caused by the “bursting” or giving way of tanks; particularly of those
of a considerable size and elevation.
[Illustration: FIG. 596.]
NOTE.—_Tank Valves._ The “Corcoran” valve is made for either side or
bottom outlet and for 1, 1-1/4, 1-1/2, 2 and 2-1/2 inch pipe; its
action is automatic; the pull by which it is operated is controlled
by a ratchet. This valve closes the pipe inside the tank. It thus
becomes easy to empty the pipes in order to prevent freezing. _The
hoops, lugs and lock nut nipples_ are important parts of a well
constructed tank. _The foundations_ upon which tanks are supported
should be carefully considered, as the average weight of a well made
tank, when full of water, is about five tons to 1000 gallons.
The following table gives the capacity of round tanks or cisterns for
each 12 inches in depth, if the tank is 24 inches deep instead of 12
inches, the result would be, twice the number of gallons.