832 



REPORT — 1901. 



proved that all the ammonia was removed from a sample of sea-water considered 

 to be somewhat highly polluted (0-046 part ammonia per 100,000) by a few 

 days' contact with the sea-weed. Next it was found that the absorption occurred 

 in less than twenty-four hours, while later experiments have shown that the 

 remarkable power of aasimilating ammonia which the sea-Aveed possesses had been 

 altogether underestimated, as well as the rapidity with which the absorption 

 occurs. The method of experiment was that previously employed. A sample of 

 the polluted sea-water was first analysed and placed in a glass dish. Next a frond 

 of the uloa was immersed in it, and finally portions of the sea-water withdrawn 

 and again analysed after suitable intervals. Two diflerent series of experiments 

 were made, the first with a solution of ammonium chloride in pure sea-water, and 

 the second with a mixture of sea-water and the effluent resulting from the 

 treatment of sewage by the so-called 'Bacteria Beds.' All the experiments in the 

 first series were made with the same piece of sea-weed, which had an area of 

 about 200 square inches ; and a similar remark applies to the second series, in 

 which, however, several pieces of sea-weed were used having a total area of about 

 600 square inches. Individual experiments in both series were made to test the 

 absorptive power of the ulva in relation to concentration (of the ammonia), as well 

 as the effects of light and darkness. The following table gives the chief results 

 obtained : — 



The general conclusions to be drawn from the experiments are as follows : — 



(1) The absorption of ammonia by the sea-weed is very rapid, and with the 

 mixtures used practically all the ammonia was absorbed in five hours (with one 

 exception, when 75 per cent, was lost). 



(2) The amount absorbed is greatest during the first hour of contact, and then 

 rapidly falls ofi^ 



(3) Although the concentration of the ammonia exercises some effect on the 

 proportion absorbed, it is by no means so considerable as might have been expected. 



(4) The sea-weed absorbs ammonia both in daylight and in darkness, but tlie 

 proportion in the latter case is rather less than in the former. 



(5) The effects of an increased area of the sea-weed on the proportion of 

 ammonia absorbed are not so great as might have been expected. 



These results may be of practical importance in those districts where a serious 

 nuisance results from the decay of large quantities of the ulva which have been 

 washed ashore, or which have accumulated in shallow water. For it seems probable 

 that hy allowing the effluent from the bacterial treatment of sewage (which 

 treatment gets rid of much of the ammonia originally present) to remain in 

 contact with the growing ulva in specially constructed ponds containing sea-water, 



