Report on the purification of the Hoogley water for the supply of Calcutta / by Thomas Spencer.

  • Spencer, Thomas.
Date:
1866
Catalogue details

Licence: Public Domain Mark

Credit: Report on the purification of the Hoogley water for the supply of Calcutta / by Thomas Spencer. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    the lighter particles of suspended matters, on the surface of the fine sand at the top. To understand the, as yet, unwritten philosophy of filtra- tion, it is necessary to bear in mind that what I term the re- tarding layers are placed in the beds for the sole purpose of acting in opposition to, or partially overcoming the downward gravitation of the water, in order that the lateral or capillary attraction, between the water and the media itself, may be allowed to operate. Consequently, any arrangements that shall bend or retard the flow of the water in its downward passage, necessarily promotes the attraction of the suspended matters to the sand at the surface, and thus prevents them from being carried down along with the water. In short, it is to the sand's attraction of the lighter matters in suspension, that mechanical filtration is due. Hence the necessity for the masses of filtering media which are placed in filter beds of the ordinary construction. SUBSIDENCE. However great the advantages of the new system are in themselves, they will be considerably lessened, if, previously to filtration, the water is not made to undergo a thorough system of subsidence. Indeed it is not too much to say that the suc- cess of the purifying process will greatly depend on the care with which the arrangements are made for this department. I find that the amount of suspended matter in a cubic foot of the Hoogly water, is variously estimated by diflFerent experimentalists, which no doubt arises from the different states of weather prevailing at the time the experiments were made, though under any circumstances the amount is large. As in all questions of general engineering, it is deemed best to estimate strength by the weakest parts, so in the present case, the quantity of mud to be dealt with in the subsiding reservoirs, ought to be estimated by very nearly the maximum