TROPICAL AQUARIUM FISHES 111 
plished by a very simple, and at the same time, clever device. The water 
is discharged with some force from a small pipe into the open end of 
another pipe just enough larger that the water discharge pipe will fit 
loosely in it. The second pipe is the liberator, and is carried to the bottom 
of the aquarium, where it is bent to a right-angle so as to shoot the air 
somewhat horizontally across the aquarium. If the aquarium is very deep 
(3 to 5 feet), the liberator pipe should extend about 8 inches above the 
surface of the aquarium. Otherwise the air in the column of water in 
the liberator pipe would make it so light that it would back up instead 
of discharging in the bottom of the aquarium. In shallower aquaria the 
liberator pipe will not need to stand so high above water-level. By this 
method the air bubbles are mostly very minute, producing the effect, 
from a little distance, of smoke. The heavy specific gravity of marine 
water enables us to break up the air finer than in fresh water. 
Marine Aquaria. While it may not always be possible to entirely 
avoid having metal come into contact with the water of the marine 
aquarium, this risk should be reduced to a minimum. Copper, brass and 
zinc are particularly dangerous. The metal now coming into use, Monel 
metal, is not entirely free from copper, but, on the whole, is very satis- 
factory, and has the advantage of great strength as well as a pleasing 
light color. Marine bronze is also good and not so expensive as Monel. 
Iron pipes and valves lined with lead are now made, especially for resisting 
chemicals. These are very fine for carrying marine water to and from 
the aquarium. Something less expensive, but quite satisfactory for large 
work, is wooden pipe. Quantities of this piping are used in the marine 
division at the Philadelphia Public Aquarium, with perfectly satisfactory 
results. For the aquarian, working on a comparatively small scale, lead 
pipe is best. 
With the all-glass aquarium we have no metal problem to contend 
with. Aquaria of the smaller sizes are satisfactory for marine purposes 
if not overstocked. In the executive offices of the Battery Park Aqua- 
rium in New York City, they have in successful operation a number of 
bell-jar aquaria, one of them having continued without interruption, except 
for change of animals, since 1900. This should give reassurance to those 
who hesitate to establish marine aquaria. 
In using metal-framed aquaria a narrow strip of glass should be 
placed over the cement in the corners. A recent improvement is a glass 
rod of suitable diameter, say about one-quarter inch. This can be pressed 
in all the way to the glass and the surplus cement wiped away, making a 
substantial, quick and neat result. The disadvantage of glass strips is 
that no thin glass is straight, the bend always making an unsatisfactory 
job. 
