ABSTRACT OP PROCEEDINGS. XC1. 



it is a canon in the ethics of water engineering to jealously 

 guard against any form of pollution, and where suspicion 

 rests to purify the water supply. He pointed out that in 

 the inauguration of our country water supplies purification 

 was never contemplated or provided for, and when it is 

 sought to be introduced as an afterthought, the works being 

 completed it is generally either very expensive or imprac- 

 ticable to carry out. The absolutely pure standard of 

 water is not to be found anywhere and not even in a 

 chemical laboratory, but the sanitarian's standard may be 

 defined as follows : — 



1. A clean history 



2. Freedom from pathogenic organisms 



3. The minimum of organic and organised constituents 



4. Reasonably soft, free from odour and colour. 



Bearing this in mind, the impurities to be removed from 

 water, however carefully gathered and stored may consist 

 of living and non-living matter, both groups being sub- 

 divided into the visible and the microscopic. After describ- 

 ing the different modes of filtration he said that with 

 regard to sand filtration a great change has come over the 

 opinion of engineers and chemists as to what happens in a 

 sand filter bed : it was thought at one time to be purely 

 mechanical, but now it is considered to be biological as 

 well, the mechanical action of the films of albuminous 

 matter which entangles all the larger forms of life being 

 only one aspect of the complex action of the filter. 



In reporting on the efficiency of any process of filtration 

 the biological purification is best expressed by giving the 

 comparative number of bacteria per centimeter cube, 

 recording the absence or the presence of pathogenic species, 

 but the general results of the working of a filter is, and 

 will be for some time to come, best expressed in terms of 

 chemical analyses and when these are duly tabulated in 



