THE AQUARIUM, 



691 



bat the latter is desirable, because it is important that the light re- 

 ceived into the aquarium should be admitted from above, while the 

 dark sides and back give a more natural appearance to the occupants. 

 The framework, if of iron, should be i^lated to prevent its rusting, as 

 that would injure the plants and animals. If the parts are cemented, 

 Portland cement should be used, as it is freer from impurities than 

 other cements • however, even it should be soaked in water for several 

 days previous to using. In the form of an aquarium, superficial area 



Fig. 2. 



Cheap Aquarium. 



is more important than depth, because, the larger the surface in pro- 

 portion to the depth, the greater will be the quantity of oxygen ab- 

 sorbed by the water. For household purposes, the cheapest and most 

 convenient vessel for a small aquarium is the common bell-shaped 

 glass used by confectioners to cover cakes. When this is used, green 

 paper should be pasted upon the outside, except on the front, from 

 the level of the water to the bottom. For marine aquaria the bottom 

 should rise a short distance from the front, and continue in an inclined 

 plane to the surface of the water. The bottom of the aquarium should 



