234 Mr. Waldie’s investigations connected [No. 3, 
The Salt Water Lake water did not require more oxygen than the 
tank waters.* 
T have little to add in the way of concluding remarks, as my object 
was not to report on any scheme or recommend any plan, but simply 
to communicate to a scientific society the results of numerous experi- 
ments and observations on a subject of practical importance. Some 
of these investigations are defective, but I intend to endeavour to 
remedy these defects by further investigation. And even after these 
are remedied, the results may indicate that there are yet other points 
to examine. There is work for the naturalist in the investigation of 
the animal and vegetable life in such waters, possibly exercising as 
great an influence on their salubrity as their chemical composition, 
Yet even this can only be aided by a full and accurate knowledge of 
their chemical constituents. There are also questions connected with 
the preservation and use of the water, and these too are more likely 
to be correctly answered, the more complete is our knowledge of the 
nature of its composition. 
But I may briefly sum up the conclusions arrived at with reference 
to the application of the Hooghly water to the supply of the wants of 
Calcutta. As regards its inorganic constituents, the Hooghly water 
taken near Calcutta is at least as pure as any of the waters supplied to 
London, or indeed generally more pure for about eight or nine months 
of the year; during the hot season it is mixed with sea water under 
the influence of the tides and thereby rendered brackish. This can 
be avoided by taking the supply of water from further up the river. 
As regards organic matter, again, my results, if correct, indicate that 
the state of the water seems to be worst during the rainy season, and 
that notwithstanding the influence of the tides and the sewerage of 
Calcutta, it is doubtful if even at the hottest part of the hot season in 
June its impurity equals that of the water during the rains; and it is 
* T have already stated that it was with considerable hesitation that I 
left the indications of the permanganate Test in table III. on account of the 
objections raised to their value: similar hesitation was felt as to inserting 
Table IV. and it was the indications given in Table V. which determined me 
to retain them. The same objections indeed apply to the results shewn by it, 
but this does not materially affect the purpose for which it is introduced. It 
will serve sufficiently well for purposes of general comparison, the trials for 
oxidizable matter and ammonia having been made at the same times on both 
river and tank waters, so that generally both kinds were of the same age or 
nearly so, More exact determinations will be made in future, 30th Nov. 1866. 
