CONDITIONS OF LIGHT, ETC. 



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. The 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, SO4 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 by a 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 



