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, in 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. 



Table III. 



River water taken from the Hooghly two to three miles: above the north 



end of the toivn, except when otherwise specified. 



For 100,000 fl. gs. water. 



6th July, 1866 Ebb, from surface, 



10th ditto, from shore, 



8th August, Ebb tide, 



21st ditto ditto, 



31st August, 1865, Ebb tide ; had stood in stopper- 

 ed bottles ten months, and much vegetable 

 growth had been removed, 74 .0225 



Organic 



matter dried, at 



212° to 220° 



Fah. 



Grains. 



.80 



Oxycren re- 

 quired. 

 Grains. 



.0375 



# 



.0338 



.60 



.0450 



.86 



.0345 



