434 ON THE ARTIFICIAL CULTURE OF MARINE PLANKTON ORGANISMS. 



the crack round the lid, and observing if any bubbles are formed when 

 the pinch-cock is opened. If all is right, no bubbles will be seen, and 

 a good stream of water will flow out from the delivery tube. Our 

 apparatus will filter about twenty litres an hour, and the filtrate 

 is exceptionally bright and clear. The candle should be sterilized 

 every three or four days that the apparatus is in use, to avoid indirect 

 contamination by growths of organisms through the substance of the 

 filter.* The water while passing through this apparatus only comes 

 into contact with glass, earthenware, and rubber, the use of metal 

 liaving been purposely avoided. 



(e) Peroxide of Hydro()cn Water. As it seemed probable that the 

 action of animal charcoal was due to contact oxidation with the oxygen 

 occluded in the charcoal, experiments were made to determine whether 

 a similar effect could be produced by the use of hydrogen peroxide 

 (H2O2). This was used in two ways. In the first method a sufficient 

 quantity of H2O2 was added to the sea-water to ensure complete 

 sterilization (1 cc. of H^Oo of 20 vols, strength per 1000 cc. of tank- 

 water was found to be satisfactory), and the excess of H.3O., was decom- 

 posed by adding manganese dioxide. The water was then filtered 

 through filter cloth, and the filtrate appeared to remain quite sterile. 

 Good cultures of Chactoccras constrictum, Biddidfliia mohiliensis, and 

 SkeUtonema costatum were made in this water, which seemed to be as 

 good as water treated by the animal-charcoal method. 



The second way of using the peroxide of hydrogen was to start with 

 water sterilized by heating to 70° C, and to add to this H^O^, in small 

 quantities at a time, until its presence could just be detected on testing 

 the sea-water with permanganate of potash. In these circumstances, 

 the first amounts of HoOo are decomposed in the oxidation of organic 

 substances in the water, and a very slight excess of H^Oa persists. 

 For tank-water 1 cc. of 1 vol. HoOo per 1000 cc. was found to give the 

 best general effect. Cultures grown in water prepared in this way 

 developed satisfactorily, being practically equal to those made in animal- 

 charcoal water, but they became exhausted rather quickly. 



The treatment of aquarium water with ozone was also tried, as this 

 seems to offer a possibility of treating large quantities of water,f such 

 as the whole bulk of water in an aquarium circulation, without very 

 considerable expense. Experiments on a small scale, which we were 

 able to make, unfortunately only with imperfect apparatus, showed 



* See Bulloch and Craw., Jovr. of Hygiene, VI, No. 3 (1906) ]). 409. 



t The use of ozonized air for the puritication of fresh water for town-water supplies has 

 been adopted in some localities. See Bridge, J. H. Paper read before Franklin Institute, 

 reprinted in Eiujlish Mrchanic (1907), )ip. ^369 and 392, 



