346 



H. M. Vernon 



Part 1. The Puriflcation of Water l>y Tegetable Life. 



The Effects of Algie on the Purification of Water. 



a. The Effects of Ulva latissima. 



As the observers above mentioned foimd that equilibrium conld 

 be obtained in marine aquaria by the introduction of vegetable life 

 in the form of growing algie, it was natural that the pnrifying effects 

 of plant life upon sea-water should first be studied. A series of 

 experiments was therefore made upon the influence of Ulva latissima^ 

 which has been found so favourable by other iuvestigators. In order 

 to determine the effects of the alga upon the ammonia present in 

 the water, a piece of the Ulva^ attached to a stone, was placed in 

 a covered jar holding about 3Y2 litres of sea-water, and this was 

 exposed to diffuse daylight at a temperature of about 21" C. The 

 Ulva was present in the proportion of about 12 Square centiuietres 

 per litre of water, and when any water was removed from the jar 

 for analysis, a corresponding quantity of the weed was removed at 

 the same tinie. Analyses of the water from time to time gave the 

 following results. 



From this table it will be seen that the free ammonia present is 

 very rapidly diminished, it being decreased by 62^ after two days. 

 The organic ammonia on the other band slowly increases in amount. 

 When the proportionate amount of Ulva present is very considerable, 

 even the free ammonia may be increased. Thus in the last Obser- 

 vation cited in the above table, a volume of only 300 cc. of the water 

 was left in contact with 24 sq. cm. of Ulva for twelve days. 



In a parallel experiment to the above, in which some of the 

 same sea-water was exposed to the action of sunlight, instead of 

 diffuse light, but to which only half the quantity of Ulva was added, 

 the following result was obtained. 



