ON THE ARTIFICIAL CULTURE OF MARINE PLANKTON ORGANISMS. 433 



side tubulure. This tube is connected, by means of rubber pressure 

 tubing, to another glass tube leading down from the bottom of a small 

 inverted bell-jar, placed some height above (in our case 14 feet, which 

 gives a pressure of ca. 6 lbs. to the square inch inside the jar). 

 A screw pinch -cock on this connection serves as a tap. The carboy 

 containing the treated water stands just above the bell-jar, and is fitted 

 with a tightly fitting rubber bung, through which two tubes pass. One 

 is an ordinary syphon, the other the only air inlet into the carboy. 

 This latter automatically keeps the level of the water in the bell-jar 



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Fig. 1. — Diagram of apparatus for preparing sterile sea-water by filtration, 

 without contact with metal. 



constant, by closing the air-inlet as soon as the water covers the end of 

 the tube. When filtering water, the modus operandi is as follows : — 



The carboy is filled with tank-water, treated, and allowed to settle as 

 before. The Berkefeld candle,*" bung, delivery tube, and connections 

 (see Fig. 1) are sterilized by boiling for half an hour and fitted into 

 place from within. (The delivery tube is shaped so that any drops of 

 water, accidentally running down outside it, do not enter the vessel 

 receiving the filtrate ; and the jar should be large enough to allow the 

 hand to fit the filter into place without much trouble.) The pinch-cock 

 is closed and the syphon from the carboy started, which will automati- 

 cally stop if the bung has been properly fitted. This should be watched 

 to avoid accidents. The pinch -cock is then opened until the water 

 rises in the jar well above the top of the candle, but still leaving some 

 air space. The lid can now be fitted into place and screwed down. 

 The tightness of this joint can be tested by pouring a little water into 



* No. fi. Porcelain •mount ; length 8 ins., diameter 2 ins. 



