1867.] with the supply of water to Calcutta. 129 



It is unnecessary at present to say more respecting the quantity of 

 organic matter in the Hooghly water near Calcutta. It does not 

 appear to exceed two grains per gallon even in the most unfavourable 

 circumstances of season and tide, and during ebb tide is only about 

 half that or less. Dr. Parkes says that it should not exceed one and 

 a half grain per gallon in drinking waters, and the London authorities 

 seem to be endeavouring to reduce it almost to nothing. In view of 

 the difficulty of judging of its nature, it is desirable to have as little 

 of it as possible. 



In the original paper I have discussed the nature of the organic 

 matter, and have not now much to add. The season of the year since 

 that communication is the least favourable to the examination of the 

 impurities in the water, as during these months — October to February 

 — all the waters are at their purest. I formerly expressed an opinion 

 on the amount of ammonia being probably a good indication of the 

 impurity of a water, and gave reasons for it. The following are the 

 results of some examinations of the river water, during these months, 

 for ammonia. 



Table VII. 

 Showing proportion of Ammonia in 100,000 fl. grs. of water. 



grains. 



18th September, 1866, River Water, 0620 



10th November, 1866, Flood tide, 0065 



9th January, 1867, Ebb, , 0160 



Flood, „ 0145 



22nd January, 1867, Shore, 0260 



30th January, 1867, Ebb, Deep, 0090 



Surface, 0160 



20th February, 1867, Circular canal at mouth, 0170 



at 3rd bridge, 0190 



18th February, 1867, Salt Water Lake Marsh, , .0250 



The quantities are small, yet consistent enough with the previous 

 observations. Reference may be made to them in remarks that 

 follow. 



But the Ammonia is not the only thing to look to in connection with 

 organic matter. As formerly observed, there are the products of 

 oxidation of nitrogenised matter, including that of ammonia itself 



17 



