1867. J with the supply of water to Calcutta. 137 



makes this point of chief importance is this, that though the town 

 contamination may be avoided by going up the river, this cannot. 



That flood waters (that is, floods produced by rain fall) are most 

 impure, as regards organic matter, is now a recognised fact in England. 

 It is by no means a new observation. In the Report on the Metropo- 

 litan Water Supply by Messrs. Graham, Miller and Hofmann, presented 

 to the Secretary for the Home Department in June 1851, this 

 point is repeatedly noticed and the remedy for it discussed, though 

 from the nature of their remarks it is evident that the amount of 

 finely suspended mud, and the degree of its putridity, have probably 

 been much smaller than those of the Hooghly water in the rains. 

 It must be remembered that while in England' there are numerous 

 small floods, here we have but one large flood in the year, washing 

 down the accumulated refuse of seven or eight months. It is true 

 that the large quantity of rain dilutes the muddy mixture, and, so 

 far as matter in actual solution is concerned, improves the water. 

 Still we have it loaded with mud, part of that in a very fine state 

 of suspension, very slow in settling, and which cannot be separated 

 by any ordinary filtration. And as the finely suspended clay 

 contains organic matter, putrid or putrefiable, the water must be 

 deprived of it to be rendered fit for use. 



The subject has engaged the attention of the Engineer to the 

 Justices, and in his Report on the works for the supply of water 

 to Calcutta, he details the plan for meeting the difficulty alluded to. 

 He admits the difficulty, for the says, para. 28, " The muddy character 

 of the water to be dealt with is an unusual feature in works of this 

 description and necessitates peculiar aud- special arrangements being 

 provided." Let us see what these are. 



It is to be settled in large tanks 6 or 7 feet deep for 36 hours ; 

 then the upper portion, to the depth of 4 feet, is to be drawn carefully 

 off to the filter, after passing through which it is conveyed to covered 

 reservoirs for storage, whence it is to be distributed as required. 

 The filter is composed of sand and gravel, and also, according to 

 Mr. Clark's original proposal, a layer of- " Spencer's magnetic carbide." 

 The object of this is to purify the water from organic matter, and 

 it is also said that it removes the suspended matter. 



But so far as lean gather from the Report, Mr. Clark seems t© 



18 



