1866. ] with the supply of water to Calcutta. 219 
It thus removes the matters which are actually in a state of putrefac- 
tion, and I believe preserves the water from further putrefaction for 
at least a considerable time, For this purpose it is advantageously 
employed for the purpose of purifying water for domestic use. In such 
application it is used alone, no sulphuric acid being used: a very 
small quantity being added to the water, just sufficient to give it a 
very slight pink tinge, which will remain for above 15 minutes; the 
water is allowed to stand till next day, and is then decanted off and 
filtered and is fit for use. The minute quantity of potash salt 
produced can do no harm. 
Provided it be properly understood what the use of this re-agent 
indicates, and it be not credited with more than it does effect, the 
permanganate test is a valuable addition to our means of examining 
the quality of drinking water. The results of my examination of 
the Hooghly water by means of it, and the amount of organic matter 
by weight, are given together in one table. 
The quantity of oxygen required is very small. The results are 
given as obtained, but cannot be counted on too minutely, as there is a 
certain amount of error unavoidable, in not getting the colour exactly 
of one degree of intensity, im slight difference of quantity required 
dependent on rapidity of adding the liquid, and probably on other causes 
not very well ascertained. The purity of the waters as respects such 
offensive constituents is in proportion to the oxygen required to oxidize 
them : the purer the water the less oxygen is necessary. 
Taste III. 
River water taken from the Hooghly two to three miles above the north 
end of the town, except when otherwise specified. 
For 100,000 f. gs. water. 
Organic 
matter dried. at 
212° to 220° Oxygen re- 
Fa 
Grains. pee : 
6th July, 1866 Ebb, from surface, Meh ao .80 0375 
10th ditto, from shore, eae ane SOON abo 0338 
8th August, Ebb tide, ... . ue a .60 0450 
21st ditto ditto, 505 ; 86 0345 
dist August, 1865, Ebb tide ; Tie sean in Oe 
ed bottles ten months, aa much vegetable 
growth had been removed, aie pe aa ea 14 0225 
