1866.] with the supply of water 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 reack, 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. 
* T 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 the use of the 
water, the point would require to be investigated in connection with the process 
to be employed for the purification of the water. Judgment may be consi- 
dered suspended on them, more particularly on that of the purity of the water 
of 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. 
