1866.] with the supply ofivater to Calcutta. 235 



questionable if even in the nature or quality of the organic impurities 

 it is worse. Now as it is not likely that during the rains the water 

 is materially different at Barrackpore from what it is at Calcutta, there 

 will be little or nothing gained by taking it from Barrackpore during 

 these months, the chief advantage being therefore that the salt water 

 of the hot season will be avoided. Still even as it is, there seems to 

 be no better source ; for the organic impurities of the tank waters, 

 even the best of them, seem at least equal in amount to those of the 

 river water during flood tide, and greater than the same during ebb tide. 

 And so far as a judgment can be formed from the means of comparison 

 within reach, the water during the rains probably contains less 

 organic impurity than the London waters.* 



Such are the conclusions I have arrived at, some of them unexpected 

 even to myself, and which may be disputed by others. They are of 

 course open to criticism and discussion. They may be suggestive of 

 other things possibly of practical application, but into these I have 

 not yet had time to enter. 



* I have much doubt upon these points, as much of the organic matter of the 

 rainy season is probably adherent to the finely divided mud in suspension in 

 the water, which is so difficult to separate. With a view to t ho use of the 

 water, the point would require to bo investigated in connection with the process 

 to be employed for the purification of the water. Judgment may be consi- 

 dered suspended on them, moro particularly on that of the purity of tho water 

 oi' the best tanks at all seasons of the year, and of the nature and amount of 

 the organic matter of the river water during the rainy season. Further remarks 

 will be made on these subjects in subsequent communications. 30th Nov. 1866. 



