62 



YVES B. PLESSIS 



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H' 



Figure 6. — Intermittent siphon with capillary 

 priming, well made : H and H' represent the 

 range of the "tides." 



ation. Consequently, they are always 

 ready for use. 



On the other hand, the establishment of 

 a siphon for capillary priming is not very 

 easy, and the satisfactory operation of the 

 system is dependent on a certain number 

 of favorable elements : 



1. The curvature of the siphon must be 

 smaller in the downward direction than 

 in the upward direction. The diameter of 

 the tube must be slightly smaller at the 

 highest point so as to facilitate the prim- 

 ing. Any other arrangement will ad- 

 versely affect the satisfactory operation of 

 the system. 



2. The bottom of the siphon must be 

 made in such a way that there will be no 

 hanging drops. A hanging drop would 

 act as a plug and prevent the water from 

 ascending, by capillary action, into the 

 upper part of the system. We have there- 

 fore attached, at the outlet of the siphon, 

 either a flare designed to prevent the 



/////// //A 



Figure 7. — Scheme of a breeding tank for very 

 small animals: B, range of "tides"; A, 'tube 

 into which the little animals are placed. 



hanging drop, or a chamfered "glass drop" 

 at the end of the tube, which serves the 

 same purpose. 



3. The tube must be made of glass that 

 can be whetted, and not of plastic. Some- 

 times it happens that after a prolonged 

 use the tube remains dry for some time. 

 In that case, it is almost always necessary 

 to "wet" it in order to put it back into 

 operation. A washing with a sulpho- 

 chromic mixture is then required to make 

 it as good as new. 



The diameter of the tube, at its narrow- 

 est part, may vary on a wide scale, but it 

 must be sufficiently large to enable a water 

 current to drive the air out of the lower 

 part of the siphon when the siphon is 

 formed by a tube which has an interior 

 diameter of 6 mm. and is tapered in the 

 curvature. When the siphon is formed by 

 a small tube having an interior diameter 

 of 3 mm., the curvature need not be ta- 

 pered, but in this case the lower part of the 

 siphon must be elaborated most carefully 



