An Automatic Aerating Apparatus. By J. F. Gemmill. 11 



siphon, as well as the tubes F and G, is of ordinary glass, | in. 

 internal measurement. A good all-round working height is 

 7 or 7h ft. from X to Y. This gives pressure enough to aerate 

 with finely divided air bubbles, but the higher the siphon the 

 better will be the pressure and the finer the streams of bubbles 

 that can be produced. On the other hand, a total height of about 

 2^ ft. is all that is required for the output of ordinary bubbles 

 and for their distribution over different aquaria the depth of which 

 does not exceed a foot or so. (See also commencement of para- 

 graph under G.) 



F. Water valve tube. This is open above at M, and passes 

 into an overflow tube G, the bend being an inch or two above the 

 top of the siphon. The primary purpose of the tube F is to allow 

 the periodic entrance of air into C during the time when the 

 emptying of this chamber by the siphon takes place. Any water 

 which may be in F flows back into C and is followed by air, which 

 bubbles up freely from the lower end of this tube. On the other 

 hand, air is not allowed to escape by F when C is filling up again 

 and the aerating nozzles are working under full pressure. What 

 happens is, that water rises in F, as it does also in the ascending 

 limb of the siphon. The height of the water in the former exceeds 

 that in the latter by exactly the difference of the water levels in 

 B and C. The rise is rapid till overflow from F into G occurs. 

 This does not set up siphon action, because air enters freely at M. 

 But as C fills up, the water level in the siphon creeps higher and 

 higher till its summit is overpassed and siphoning begins. Pressure 

 inside C then becomes negative ; the water in F flows back into 0, 

 and is followed by air entering at M. 



G. Overflow tube, described above. This is hardly required 

 for an apparatus designed only for ordinary bubbles under low 

 pressure. See end of paragraph under E. (Although it is not 

 shown in the sketch, 1 have lately been using the surplus water 

 which overflows by G, in my apparatus at Glasgow University, to 

 provide a supply of air under low pressure. This is done on the 

 principle of the Sprengel pump, with the help of the Naples 

 Station device, viz. a circular bend in the upper part of the tube.) 



H. Aerating nozzles. For ordinary bubbles a bit of glass 

 tubing, slightly turned at the end, will serve. The amount of air 

 which is allowed to escape by such a nozzle has to be regulated, 

 and this can be done with perfect precision by means of a screw 

 clamp on the rubber tubing. Sufficient resistance can thus be 

 applied to insure that the internal pressure will be strong enough 

 to force air also through the kind of nozzles that are required for 

 the production of fine streams of bubbles. For these a dried and 

 partly decayed branch of some suitable wood forms a simple outlet. 

 Attach a rubber tube to a side branch and make some notches 

 along the main one. From each of these notches as well as from 



