210 [No. 4, 



On the muddy Water of the Httglt DmiNa the bainy sea^soj^ with 



EEFERENCE TO ITS PURIFICATION' AND TO THE CALCUTTA WaTER SUP- 

 PLY. — £t/ D. Waldie, Esq. 



(Received Oct. 29th ; read Nov. 5tli, 1873.) 



Contents. 



I — Introduction, — construction of the Filters at Palta, difficulties in their working — 

 question as to the cause of this, — true cause, according to the author, is the pecu- 

 liar nature of the water. 



II. — Desirableness of explaining the reason of this peculiarity, — considerations which 

 led to its discovery, — its nature, — experimental evidence in proof. 



III. — Corroborative evidence from other sources, direct and indirect. 



IV. — Details of experiments connected with it and results. 



Y. — Further corroborative evidence and additional explanatory remarks. 



I. — The works for the supply of Calcutta with water have been in opera- 

 tion since the early part of 1870. The nature and arrangement cf the 

 filtering materials in the filtering tanks at Palta were decided upon chiefly 

 from the results and conclusions to which I came after a series of experi- 

 ments made during the rainy seasons of 1S68 and 1869, for the purpose of 

 ascertaining what was likely to be most suitable and efficacious for filtering 

 the muddy water of the Hugli during the floods that extend from June 

 to September or October annually. These experiments also included an 

 examination of the value of a particular contrivance called Spencer's Regu- 

 lating Cup, to which great importance was attached by the Engineer who 

 designed the works. The general conclusions to which I came were, that 

 this Ilegulating Cup possessed no special value, for that the retardation of 

 the flow of water which was stated to be its particular function could be 

 attained equall}^ well or better by other means ; and that the better sand of 

 the two kinds submitted to me for comparison was the fine sand from the 

 sand-bank in the river, which, as it could be obtained on the spot, was 

 called Palta sand. The other sand, called Magra sand from the locality at 

 which it was found, was considerably coarser in grain, and was stated to 

 be more like that used for filters in England. Though well enough 

 aware of this, I decidedly preferred the Palta sand for filtering the muddy 

 water of the rains, which was the period of special difficulty. For the 

 remainder of the year, I considered it of little importance which kind of 

 sand should be used. 



In accordance with my recommendation, the filters were fitted up with 

 Palta sand and without the regulating cups. The}^ worked well during the 

 first rainy season ; but afterwards, particularly during last season (1872), there 

 was so much difficulty in getting water filtered through them sufficiently 



