68 THE SEA SHORE 



is driven downward from a jet just below the surface, and with 

 such force that a multitude of minute bubbles penetrate to a 

 considerable depth before they commence to rise, but in others the 

 air is made to enter at the bottom and must therefore pass right 

 through the water. 



Of course the amateur aquarium-keeper may carry out this 

 method of aeration with every hope of success providing he has 

 some self-acting apparatus for the purpose, or can depend on being 

 able himself to attend to a non-automatic arrangement at fairly 

 regular intervals, always remembering that a single day's neglect, 

 especially in the case of a small tank with a proportionately large 

 amount of animal life, may lead to a loss of valuable specimens. 



We have already mentioned the use of a syringe as a means by 

 which an aquarium may be temporarily restored to a satisfactory 

 condition providing it has not been neglected too long, and some 

 recommend forcing air, or, still better, pure oxygen gas, from an 

 india-rubber bag into the water. We have used, for the same 

 purpose, a stream of oxygen from a steel cylinder of the compressed 

 gas with very satisfactory results ; and since oxygen may be now 

 obtained, ready compressed, at a very low price about twopence 

 a cubic foot there is much to be said in favour of this method as 

 an auxiliary in the hands of the owner of a small tank, though we 

 hardly recommend it as a prime means of aeration to take the 

 place of the fountain. 



In any case, where a stream of air or oxygen is employed, an 

 exceedingly fine jet should be used, in order that the expelled gas 

 may take the form of a stream of minute bubbles ; for, as previously 

 stated, the water can absorb the gas only very slowly, so that there 

 must necessarily be a considerable waste when the gas issues 

 rapidly. Further, the smaller the bubbles passing through the 

 water, the greater is the total surface of gas in contact with the 

 liquid, the volume of the supply being the same, and hence the 

 more effectually will the solution of the gas proceed. Again, 

 another advantage of the fine stream of minute bubbles lies in the 

 fact that the smaller these bubbles are the more slowly they rise to 

 the surface of the water, and thus the longer is the time in which 

 the gas may be absorbed during its ascent. 



A fine jet, well suited to the purpose here defined, may be made 

 very easily by holding the middle of a piece of glass tubing in a 

 gas flame until it is very soft, and then, immediately on removing 

 it, pulling it out rather quickly. A slight cut made with a small 



