DISCUSSION. STATISTICAL AND EXPERIMENTAL DAT A ON FILTRATION AND THE SHEFFIELD WATER SUPPLY AND STATISTICS RELATING THERETO
Minutes of the Proceedings of the Institution of Civil Engineers
observed that he had been designing, making, and working filters for nearly 30 years, and the subject of the second Paper was one of great fascination to him on account of its wonderful complexity. Very many conditions governing the working of sand filters had to ha taken into consideration, e.g., the amount and incidence of the previous rainfall, the temperature, the amount of bright sunshine, and many other factors. He thought some writers on the subject had been inclined to dogmatize a
... o dogmatize a little too much from their own experience, forgetting that the conditions which obtained with one water did not obtain with water taken from other sources. It was possible to go even farther and to say that water stored for 14 days would behave quite differently on a filter from the same water after it had been stored for 3 months. The effect of storage before filtration bore very much on the actual process of filtration itself. I n some respects, so f a r as the economical working of the filters was concerned, it might be beneficial ; in other respects, it might be the reverse. One great safeguard when dealing with river-water was the elimination of bacterial life by prolonged storage. In London, storage was needed primarily for the regulation of the flow of the river which provided the larger quantity of the water, and it was a happy circumstance that incidentally the effect of that storage was to improve the water immensely and to furnish safeguards which otherwise would not be present. The researches of Dr. Houston were already almost classical, and it was hardly necessary to mention the results he had obtained, first in a series of experiments, extending over 12 months, in which he tried in vain to isolate the Bacillus typhosus in river-water, and in further experiments in which he srtificially inoculated river-water with that bacillus, and watched the progress of the organism and its gradual elimination from the water. Briefly, 98 per cent. of the artificially added contamination was eliminated within 4 weeks and the whole of it within 8 weeks. From the point. of view of filtration, however, another result of prolonged storage had to be considered-a result that had not been observed until the last few years, owing to the fact that it was only within that time that ordina.ry river-water, as distinguished from moorland water, had been stored for any prolonged period : the growth of algE in water so stored had to be seriousIy considered and combated. Downloaded by  on [11/09/16].