IMODERX METHODS OF WATER PURIFICATION. 347 



few figures, but nothing continued or complete, only patchy, 

 scrappy returns. It may be I was unable to find them; it 

 may be they did not exist, but it is impossible to make decided 

 responsible recommendations without such guiding. 



I think that adequate sedimentation according to require- 

 ments is equal in eiJect to a large increase of filtering area, as 

 the rates of filtering can be increased so much with safety. 

 That view will, I feel convinced, be firmly established by ex- 

 perimental increase of amount of water filtered per acre. 



Stead's method is good, but there may be equal results with 

 easier work and more workable coagulants, but we should 

 not abandon good till we know we have better. If growth 

 of this city of Bloemfontein comes, such as to increase our 

 water demand, such growth will justify further filter expendi- 

 ture and will be welcomed. This increase may come at any 

 time, or may be indefinitely delayed, according to what is 

 going to happen to Bloemfontein under the Union of South 

 Africa, now being formed. 



The question arises, " Why change from the old, simple 

 sedimentation and slow sand-beds?" There are two ways of 

 asking this question that I know and two of answering it. 

 but there may be more. The two ways of answering it are: 

 " Don't abandon good till you get better," as I have advised 

 a few paragraphs above, but when you do find better do it 

 as soon as you can. The other answer is " Don't change 

 anyhow; keep on with the old method, because you know it 

 and have known it." That is not unlike the views of our 

 grandmothers, who preferred the stage-coach to the express 

 train; or, as we could put it to-day, to prefer the crawling" 

 post-cart to the whirling wireless in the sending of a message. 



If you can get as good results for less money, or better 

 results for the same expenditure, in the minds of some that 

 might be time to change; but if you can get better results for 

 a much lower expenditure, that is surely the ideal business 

 proposition that every progressing " live " person or body is 

 looking for. 



The advice given in previous years, by myself and 

 other advisers, to have larger settling pools, pre-filters or 

 roughing filters, and extensive sand-beds worked at the slow" 

 rate laid down long. ago. with, if necessary, double sand 

 filtration, as I proposed years ago, is no longer sound. It 

 belongs to the scrap-heap of worn-out theories now as far 

 as the Modder River water is concerned, and is exploded and 

 effete. Without chemical coagulation we cannot get pure 

 water, and all expenditure on roughing filters or double filtra- 

 tion, or any substitutes for chemical precipitation in the pre- 

 sent state of our knowledge, will be largely useless expendi- 

 ture. Subject to the favourable results of the special investi- 

 gation into our water at the different stages of the purifica- 

 tion process, I am of opinion that our water can be satisfac- 

 torily and safely treated by modern methods of filtration, and 

 here is the important point, granted precipitation, not less 

 safely, but more safely than with the old, slow sand filtration 

 without chemical addition. 



