1867.] with the supply of water to Calcutta. 125 



August waters, which stood in most cases about five weeks, to allow the 



fine clay to settle. This is a special case and will require further 



remark ; but at present, as I wish to present a view of the whole, they 



will be taken as they are in the construction of the following table. 



Many more determinations of organic matter were made, particularly 



of the waters of the rainy season, but these were made for special 



purposes and with various modifications of the process, so that they 



were not comparable. Only those are given in the table which were 



made by the plan already specified, and so far as this is concerned, 



they are therefore comparable. These variations in plan were chiefly 



tried in September and October, and so unfortunately no results for 



these months can be introduced into the table. But as an illustration 



of these variations, I may instance the case of the water of 6th October, 



which, cleared by Hydrochloric acid, gave 1.05 grains, and cleared by 



sol. potash, gave 3.22 grains organic in 100,000 grains of water. The 



addition of a little of either of these causes the mud to settle, and 



admits of filtering the water clear in course of a few hours. But as 



there is much organic matter adhering to or combined with the clay 



or other earthy matter of the mud, the acid or alkali acts upon this and 



brings it into solution. 



Table V. 



Shewing the amount of Organic matter by weight Ebb. Flood. 



in 100,000 grains of the Hooghly water. Grains. Grains. 



6th July, 1866, Neap, Surface, ... .80 



8th August, Neap, Surface & Deep, . . . .84 



21st August, Neap, Deep, ... .86 



10th November, 1866, Spring, 1.28 



19th Ditto Neap, Deep, ... .94 



,, „ Surface, ... 1.28 



9th January, 1867, Spring, .88 1.50 



30th Ditto, Neap, Deep, ... .58 



„ „ Surface, ... 1.28 



Average, ... .99 1.3 9 



2d May, 1866, Spring, 2.70 



30th Ditto, Spring, 90 2.60 



14th June, Spring, 90 2.20 



Average, 90 2.50 



