260 



U. S. BUREAU OF FISHERIES 



PLACING THE GLASS FRONTS 



The tank fronts of polished plate glass are very heavy, being 1 or 

 1^4 inches thick. The plate is set against a frame of 3-inch angle 

 iron built into the masonry or concrete of the tank. In some aqua- 

 riums the glass is set in a detachable iron frame, which is bolted 

 against the iron frame of the tank from the outside. In the New 

 York Aquarium it is set from the inside, without the use of bolts, 

 being held in position chiefly by the pressure of the water when the 

 tank is filled. When put in place, the plate is secured by a light strip 

 of wood at each end, which is held by brass screws to woodwork 

 firmly set in the concrete of the tank. The lower edge of the plate 

 rests on a strip of wood laid on the angle iron. Between the glass and 

 the iron frame a flat rubber strip 1 inch wide by % inch thick is 

 placed to serve both as a cushion for the glass and an aid in making 

 the edge of the glass water-tight all around. As a further precaution 



Fig. U. 



-Strainers for aquarium tanks. Above, overliow .siiainers ui wire, rattan, 

 and lead ; below, bottom strainers of galvanized iron and lead 



against leakage the border of the plate is packed with flexible aqua- 

 rium cement. Whether set from the inside or bolted on in front, it 

 is absolutely necessary that the glass and its rubber cushion be flat 

 and true against the iron frame ; otherwise cracks will develop under 

 water pressure and the plate be ruined. It is no easy matter, even for 

 experienced aquarium men, to set the glass so " true " that it will be 

 perfectly supported at every part of its border. Polished plate of the 

 thickness required is expensive, at the present time costing $75 for 

 one measuring 4 by 5 feet, ancl $85 for one measuring 4 by 7 feet. 

 While our share of breakage has been reduced to the minimum 

 through long experience, it is a frequent source of annoyance and 

 expense among the new aquariums of the country, judging from the 

 many letters of inquiry received respecting the details of glass 

 setting. Extra thickness of glass does not compensate for uneven 

 pressure against the supporting iron frame. A little crack starting 

 at the edge of the plate will extend clear across it in a few weeks, 



