Water Supply of Belfast. 6i 



As will occur to those present, sand is not the only medium 

 used for filtration purposes. This is quite true, and I regret 

 that I cannot say something about the many filtering mediums 

 now available for domestic use. Thus we have animal char- 

 coal in grains and in block. We have also spongy iron and 

 polarite ; also the well-known and efficient Filtre Rapide; all 

 of which for household purposes seem to leave nothing more to 

 be desired. But all household filters require to be paid for, and 

 to the general bulk of our population this is a strong bar to 

 their use. Further, they require to be cleaned and renewed 

 from time to time, and this is a further obstacle to their general 

 employment. In fact, in many cases the domestic filter even- 

 tually becomes a valuable pantry ornament, and at this stage I 

 must leave it. 



By means of a well-constructed and well-managed system of 

 sand filtration, the authorities in many towns have shown that 

 it is possible to deliver to their consumers a water, bright, 

 pleasant-tasted, and showing a fair analysis, which, if unfiltered, 

 would be often turbid and unsatisfactory to the consumers. 

 Take the case, for instance, of London, which mainly draws its 

 supply from the Thames above Hampton Court. Here is a 

 sample of unfiltered Thames water, taken in the month of July, 

 which Professor Wanklyn shows, according to the well-known 

 ammonia process, to contain as follows : — Free ammonia, 4*5 

 parts per 100 million ; albuminoid ammonia, 28. After filtra- 

 tion through sand by one of the companies, the resultant water 

 gave the following : — Free ammonia, i part per 100 million ; 

 albuminoid ammonia, 6. Before passing from this I may 

 mention that on an average the Thames water after filtration 

 gives an analysis as follows: — Free ammonia, 2 parts per 100 

 million ; albuminoid, 8. But I shall now be asked what I 

 mean by so many parts of ammonia, and in reply I say that 

 many chemists accept this method of measuring and indicating 

 the quantity of organic matter in a given sample of water. We 

 all know the pungent odour often felt in the presence of decay- 

 ing organic matter. This is due to the ammonia which results 



