378 K. .r. ALLEN AND E. W. NELSON. 



through this apparatus only comes into contact with glass, 

 earthenware, and rubber, the use of metal having been pur- 

 posely avoided. 



(e) Peroxide of Hydrogen Water. — As it seemed 

 probable that the action of animal charcoal was due to contact 

 oxidation with the oxygen occluded in the charcoal, experi- 

 ments were made to determine whether a similar effect could 

 be produced by the use of hydrogen peroxide (HjOo). This 

 was used in two ways. In the first method a sufficient quantity 

 of HoO;3 was added to the sea-water to ensure complete 

 sterilisation (1 c.c. of H^Oo of twenty vols, strength per 1000 

 c.c. of tank-water was found to be satisfactory), and the 

 excess of HnOo was decomposed by adding manganese dioxide. 

 Tiie water was then filtered through filter-cloth, and the 

 filtrate appeared to remain quite sterile. Good cultures of 

 Chaetoceras constrictum, Biddulphia mobiliensis, 

 and Skeletonema costatum were made iu tiiis 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 sterilised by heating to 70° C. and to add to 

 this HoOo, in small quantities at a time, until its presence 

 could just be detected on testing the sea-water with perman- 

 ganate of potash. In these circumstances, the first amounts 

 of HnO^ are decomposed iu the oxidation of organic substances 

 in the water, and a very slight excess of H^Oo persists. For 

 tank-water 1 c.c. of one vol. HoOg per 1000 c.c. was found to 

 give the best general effect. Cultures grown in water 

 prepared in this way developed satisfactorily, being practi- 

 cally 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 Avater,^ such as the whole bulk of water in an aquarium 



' The use of ozonised air for the purification of fresh water for town 

 water supplies has been adopted in some localities. (See Bridge. J. H.. 

 paper read before Franklin Institute, reprinted in ' English Mechanic,' 

 1907, pp. 369 and 392.) 



