MARINE AQUARIUM PROCEDURES AND TECHNIQUES 



57 



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Figure 1. — General scheme of an exhausting 

 device. Air arrives through tube D and 

 ascends through tube BA ; in doing so, it pulls 

 water along with it. 



starts moving, the water pulled along by 

 the air bubbles joins it. The entire mass 

 of water then exercises a downward pres- 

 sure. The air which continues to reach 

 C will be driven back toward B, and its 

 pressure will increase until it reaches a 

 maximum that is equal to the pressure 

 exercised by a water column of the height 

 OB. The device can function only when 

 the pressure exercised in that way exceeds 

 the thrust of the water mass contained in 

 the part CA. In practice, an apparatus of 

 this type is not used if it functions only 

 with such intermissions as are due to the 

 variations of the pressure at C. Tlie 

 height OA does not exceed two thirds of 

 OC, and CB is very small. 



It is advantageous to study the border- 

 line cases; they have only a very weak out- 

 put but are sometimes useful to know. A 

 well-regulated apparatus, which works 

 under the best conditions, has an output 

 of more than 6 liters per hour. The nee 

 essary air pressure is a function of the 

 height of the water OB. The pressure 

 utilized under the most favorable condi- 

 tions is theoretically slightly higher than 

 the pressure of a water column of the 

 height OC. 



We have stressed the theoretical aspect 

 of the problem of the exhausting device, 

 since in practice the apparatus is suscep- 

 tible of many variations in form, and since 

 the conditions under which it is used and 

 its perfection before use prevent a great 

 many failures. 



We have built most of our exhausting- 

 devices with glass tubing. A straight 

 glass pipe 6 to 8 mm. in diameter ends at 

 its lower part in a vinyl tube which is 10 

 to 15 cm. long and has an inside diameter 

 large enough for the glass pipe to be 

 inserted (fig. 2). Its bottom forms a 

 strainer and is chamfered ; it is perforated 

 by small openings so as to prevent the 

 deposition of sediments that may occur at 

 any time. As near the glass pipe as pos- 

 sible, a hole has been made in the vinyl 

 for the insertion of the end of the com- 

 pressed-air pipe. This is a vinyl tube of 

 small diameter. Plastic rings make it pos- 

 sible to keep it joined to the glass pipe for 

 part of its length. 



The upper end of the exhausting device 

 is curved ; it can be made in one piece ex- 

 tended and joined by a plastic ring. 



BREEDING TANKS 



In each one of our installations, the 

 breeding tanks are made of molded glass. 

 We have used several models the sizes of 

 which correspond to the various popula- 

 tions. 



