An inquiry into the relative efficiency of water filters in the prevention of infective disease / by G. Sims Woodhead and G.E. Cartwright Wood.

  • Woodhead, German Sims, Sir, 1855-1921.
Date:
1898
Catalogue details

Licence: Public Domain Mark

Credit: An inquiry into the relative efficiency of water filters in the prevention of infective disease / by G. Sims Woodhead and G.E. Cartwright Wood. Source: Wellcome Collection.

Provider: This material has been provided by The University of Leeds Library. The original may be consulted at The University of Leeds Library.

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    film from the surface by means of a brush; secondly, by the use of a cleansing solution which they supply. We have not succeeded by the use of the cleansing fluid in obtaining satis- factory results. By the use of the brush, however, in the case of a new candle, the output was usually almost com- pletely restored, but in course of time this method becomes less and less efficacious. This is due no doubt to the pas- sage of the vegetable matter into the pores of the filter, which is not then, of course, removed by the process of brushing the surface. The only efficient means at our ■disposal of restoring the filtering capacity of these candles is, we find, to subject them to a process of baking at a red heat. This is carried out most efficiently in the labora- tory by means of a small muffle furnace, but even where every care is taken to dry the candles previously, a certain amount of breakage takes place; moreover, the process is not one which could conveniently be carried out in practice. In addition it is necessary to retest each candle after it has been subjected to this process, as the heat may have destroyed its filtering efficiency by causing cracks or other defects in the porcelain. This is done by subjecting the candle when submerged in water to an air pressure of 7 lbs., when the -efficiency of the candle is manifested by the pressure being maintained, and by absence of air bells in the fluid. These results bearing on the output of the Chamberland ■candle and on the process of renovation by means of clean- ing, were obtained chiefly with water supplied by the New River Company; in addition a few experiments were carried out with the Lambeth Water Company's water, which gave very similar results. As the London water is supposed to undergo a rather better process of sand filtration than else- where, it is probable that rather better results may be obtained with it than with most other waters. It must be remembered, however, that the slimy coating which in time envelops the candle and restricts the output is usually derived in great part from the growth in the mains and pipes of vegetable organisms which are carried to the filter, and not so much from the par- ticles which have escaped the sand filter. We have also observed that sediment in the pipes derived apparently from repara- tion of the mains or even from the cleaning of cisterns, may lead to a sudden diminution of the output. We are con- vinced, therefore, that what we have described may be taken as a fair sample of what might be expected of these candles under the most favourable conditions. On the other hand, where the filters are used in the army for camp purposes, where turbid water must frequently be supplied to the filters, some experiments carried out with the Thames water taken at Waterloo Bridge (see p. 83 et seq.), indicate that the candle would require to be burned at frequent intervals if anything like their initial output is to be maintained. We must accordingly conclude from our extensive experi-
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