
CONDITIONS OF LIGHT, irc: 

animals, taking up the carbon and liberating the purified oxygen. What 
occurs in the air also takes place in the water, though it contains less free 
or suspended oxygen, an average of only 2 to 3 percent, and considerably 
more suspended carbonic acid gas. The animals consume oxygen, give 
off carbonic acid gas, and the plants consume carbonic acid gas and liber- 
ate oxygen. Therefore, unless oxygen is added to the water, either by 
plants or furnished by aeration, animal life must cease. In the properly 
established aquarium the plant life should be in excess, and only as much 
animal life present as will exist comfortably under the conditions. But as 
plants are only active in producing this interchange when growing, and as 
their growth is entirely dependent upon sufficient light, when this is not 
abundantly obtained artificial aeration is necessary or a frequent change of 
water required, surface aeration alone being insufficient. 
There are many methods of furnishing air to the aquarium or larger 
tank. he following have been given thorough trial and have proven 
satisfactory when arranged that the air enters in minute bubbles for ready 
absorption by the water. Good results may be had by either direct ad- 
mission of the air, or by means of a stream of water under the pressure of 
a considerable elevation, through a very finely perforated nozzle fixed 
close to the surface of the water on the opposite side to the overflow 
pipe, so that the force of the water carries with it a large amount of 
minutely divided air. This also permits of warming or cooling the water 
supply by coiling the pipe in a water-tight chamber, if desired, and may 
be installed on a larger or smaller scale to suit the requirements. 
Direct aeration, without the necessity of the overflow pipe, is ar- 
ranged by the use of a pressure tank and bicycle pump, placed at any 
convenient location, and the compressed air admitted into the aquarium by 
a small block tin pipe buried under the pebbles. Several petcocks are 
necessary to hold the pressure and to check the amount of flow, and tiny 
pin holes blocked with pieces of porous wood will best serve to admit the 
air in the required minute bubbles. When properly installed, a pressure 
of 35 pounds in an air chamber 28 inches high and 12 inches in diameter, 
produced in three minutes bya bicycle foot-pump, will furnish a 50 gallon 
aquarium with air for two or three days. This system of aeration is in 
successful use with a number of aquariists in Philadelphia. Care must 
however be taken not to over-oxygenate the water. | 
The simplest fountain device, when the aquarium is placed at a 
window and is as broad as the opening, is the following. A block tin pipe 
may be led under the bottom of the aquarium through the base and 
screened by rockwork. This should have a small stopcock at the end 
and a rubber hose to connect with a water can outside the window or 
178 
