14 



CIVIC BIOLOGY 



Tinsmith's snips and square-nosed pincers, for cutting and bending 

 the angle tin. 



A soldering outfit, soldering iron and fluid or resin, and some safe 

 and convenient means of heating the iron. 



If the tools are not at hand, the frames may be made at the tinsmith's ; 

 or often a handy janitor can make them in his shop, or a good-natured 

 one may let the boys use his tools, if they are very careful to leave every 

 tool in its place and the shop in better order than they find it. 



Dimensions for the frames are given in the table below. " Three- 

 cross " tin is heavy enough for all smaller sizes, and " four-cross " for 



FIG. 7. Showing relations of frames, cement, and glass in aquaria, 

 of different sizes 



a, for the larger sizes; b, for smaller sizes; c, arrangement at top and cover. 

 Black lines, metal ; flashed areas, glass ; dotted surface, cement 



aquaria between 15 and 24 inches in length. The more slender the 

 frame the trimmer and better the aquarium appears. For aquaria-dimen- 

 sions in inches : 



5 x 7 x 4 to 8 x 10 x 5 : use f-inch angle tin. 

 10 x 12 x 6 to 8 x 10 x 5 : use 1-inch angle tin. 

 15 x 12 x 8 to 18 x 15 x 9 : use |-inch angle tin. 

 20 x 12 x 9 to 24 x 18 x 12 : use 1-inch angle tin (around base, 



and if the work is carefully done, f-inch, or even -|-inch, is 



strong enough for the rest). 



Fig. 7 gives the relation of cement to the angle tin and the glass for 

 large and small sizes. In the larger sizes the strip of glass, with the 



