956 



SCIENCE 



[N. S. Vol. XXXI. No. 807 



leeting in the bottle. To work properly it 

 should have the form shown in the sketch. 

 (In the siphon it is essential to have the part 

 at m of just the form shown in the cut. If m 

 is lower than shown in the sketch, the part r 

 to m will act as a small independent siphon, 

 and the stream of bubbles into the aquarium 



will in consequence be frequently interrupted.) 

 The aquarium is represented by F and the 

 surface of the water by /. In the bottle E, n 

 represents the level of the water while run- 

 ning. The bottle E is fitted with an air- 

 tight rubber stopper with three holes through 

 which the tubes A, B and C pass. 



The mere description of the apparatus may 



not be sufficient to give a clear understanding 

 of its action. Its mode of working may be 

 briefly described as follows : Suppose the appa- 

 ratus, as described, is connected up properly, 

 as shown in the sketch, and the bottle is empty 

 of water. Now on opening the tap, a little of 

 the water comes down A and B and runs into 

 E, carrying with it a certain quantity of air. 

 Water and air collect in E until there is 

 enough pressure to force the water into D so 

 that it begins to flow out at m. The water 

 will have reached a point a little below before 

 the siphon begins to work. At first the siphon 

 takes out the water faster than it is delivered 

 into E, but finally there is reached a stage 

 where the siphon draws out in a steady stream 

 just as much water as is brought in by B, and 

 in the same interval of time. This point is at 

 n, and this is the permanent level of the 

 water in the bottle as long as the apparatus is 

 run. At the moment the level of the water 

 reaches n, the tube G delivers air into the 

 aquarium through fc in a constant stream. 



There must be more water in B below d 

 than there is in C from j to h; otherwise the 

 air could not be forced out at h. For this 

 reason the greater the distance d to e, the 

 more air will be carried into the bottle. (The 

 ratio is not constant, however. Various fac- 

 tors seem to operate, as shown by experiment.) 

 The distance / to h should be at least twice 

 the vertical distance / to Tc, to prevent possible 

 flooding of F. The siphon should be of a bore 

 at least twice as great as that of B to guard 

 perfectly against flooding. 



It will be obvious that the vertical distance 

 i to Ti can never be greater than the vertical 

 distance I to m. Also that vertical distance 

 / to fc equals approximately vertical distance 

 n to m. 



The cut is a sketch of the writer's most 

 efficient aerator. The cut is not drawn to 

 scale. A number of different designs of 

 siphons and mixers were tried, but those 

 sketched gave the best results. One centi- 

 meter of water carries into the bottle (and 

 therefore into the aquarium) from four to 

 seven times the quantity of air (the quantity 

 depending on the length of the tube B and 



