AQUARIUM

A tank or ve el made of gla , containing either salt or fresh water, and in which either marine or fresh-water plants and animals are kept in a living state. In principle, the aquarium depends upon the interdependence of animal and vegetable life. The carbonic acid evolved by the animals is decomposed under the influence of solar light by the plants, and the oxygen nece ary for the maintenance of the life of the animals is thus eliminated, whilst the carbonic acid e ential to the existence of the plants is supplied by the animals. The aquarium, therefore, must be stocked both with plants and animals, and for the welfare of both, something like a proper proportion should exist between them. But even under these conditions the water should be frequently aërated, whether the aquarium contains fresh or salt-water. This may be done by simply blowing through a gla tube which reaches to near the bottom, or, still better, in the following manner:—Take a gla syringe which can be easily worked. Having filled it with water, hold it with the nozzle about two inches from the surface of the water in the aquarium, into which the contents are to be discharged quickly and with a sort of jerk. By this means a multitude of small bubbles are forced down into the fluid. This operation should be several times repeated. A simpler method is to take out a portion of the water from the aquarium and to pour it back again from a height. When, as not infrequently happens, the aquarium is provided with a fountain, this of course ensures a continual change of water; but even where this is the case the joint presence both of plants and animals is advantageous to the health of both. When sea-water cannot be procured for the marine aquarium a substitute for it may be made as follows:—Mix with 970,000 grains of rain-water 27,000 grains of chloride of sodium, 3600 of chloride of magnesium, 750 of chloride of pota ium, 29 of bromide of magnesium, 2300 of sulphate of magnesia, 1400 of sulphate of lime, 35 of carbonate of lime, and 5 of iodide of sodium. These all being finely powdered and mixed first, are to be stirred into the water, from which a stream of air may be caused to pa from the bottom until the whole is di olved. On no account is the water to be boiled, or even to be heated. Into this water, when clear, the rocks and seaweed may be introduced. As soon as the latter are in a flourishing state the animals may follow. Care must be taken not to have too many of these, and to remove immediately any dead ones. The lo that takes place from evaporation is to be made up by adding clear rain-water. The presence of a number of molluscous animals, such as the common periwinkle, is nece ary for the consumption of the vegetable matter continually given off by the growing plants, and of the multitudinous spores, particularly of the confervæ, which would otherwise soon fill the water, rendering it greenish or brownish, and turbid. In a fresh-water aquarium the bottom should be covered with a layer of fine sand and shingle, and in this the weeds should be planted. The best for this purpose are valesneria spiral is , anacharis , and chara vulgar is . A few water-snails should also be put in; the best are plan orb is , paludina , and amphibia glutinosa . One plant and two or three snails should be used for each gallon of water put into the aquarium.