TROPICAL AQUARIA 75 



system and aquarium water proper. This system also gives a higher 

 percentage of heating efficiency than the outside form. 



For the highest efficiency and greatest all-round satisfaction, note 

 should be taken of Fig. No. 59. This is a 4-inch agate pan set in the 

 cement base described on page 216. When making the aquarium it is little 

 extra labor to set this in. For aquaria already constructed it is somewhat 

 of an undertaking to cut a sufficiently large hole, but it can be done and 

 the pan cemented on top. Fig. 58 shows a simple and fairly effective 

 expedient. After hole is cut in slate, pour in lead or tin. When the 

 metal is poured, use a form made of putty so that the surface of metal 

 will come as high as the sand. The object in using the inverted pan is to 

 have the heating surface come just above the sand. Then the heat is the 

 most efficient as well as fairly diffused and does not interfere with the 

 roots of plants. The objections to this type are that the aquarium has to 

 be raised and that there is an occasional drip of condensed water caused 

 by combustion. The best flame to use is a small gas Bunsen burner. 

 They may be had of some scientific apparatus concerns or dealers in 

 German aquarium supplies. These dealers also handle a rather good all- 

 glass aquarium for heating by lamp, and which does not need to be raised. 

 There is, however, the eternal liability of cracking. All-glass aquaria at 

 best are liable to crack, and particularly when unevenly heated. In the 

 German catalogs and aquarium publications will be found numberless 

 heating devices, but after trying many of them and conducting numerous 

 experiments himself, the author finds those described here the most 

 practical. Smells are caused by chilling the flame before combustion is 

 complete. No more than the tip of flame should be allowed to touch the 

 heating surface. Even this is not necessary in system shown in Fig. 59. 



Heat Control. In a room where there are wide changes of tem- 

 perature, particularly when these dip to the cold side, it -is desirable to 

 have some means of heat control. To start in the simplest way first, an 

 aquarium may be kept noticeably warmer over night by covering with a 

 thick blanket, quilt or any warm fabric. If near a window the curtain 

 should be pulled completely down. Another help for any aquarium near 

 a window is to have a sheet of glass standing nearly vertical on the base 

 and leaning against the top of the aquarium. This sheds much of the 

 cold air which constantly falls from a window in cold weather. 



Tropical aquaria, if not too small, may be kept at a satisfactory 

 temperature standing on a board on the radiator of a hot-water sys- 

 tem, the heating result not being so extreme as might be expected. 



The most satisfactory means of controlling temperature is to heat by 

 gas and use a thermostat to control gas flow. See I''ig. 60. This is 

 placed either in the water or tightly against the outside of the aquarium 



