18GG.] with the supply of wafer to Calcutta. 211 



A study of the particulars of this table shews that the period 

 during which the water can be obtained with the smallest admixture 

 of sea water is during the last three or four hours of ebb tide and the 

 first one or two of flood. From tables of the analyses of the waters 

 supplied to London which I shall have to refer to more particularly 

 afterwards, it appears that the water of five Thames Companies contains 

 at an average from 26.41 to 26.97 grs. of saline matter per 100,000 ; 

 and that of four other Companies, — two river waters contain about 26 

 grs., and two artesian well waters contain from above 38 to 40 grains. 

 The Hooghly water at Baranagur therefore even during the hot season 

 at ebb tide contains little more solid matter than the Thames water, 

 but probably a larger proportion of this is salt. 



Constituents of River Water proper. 

 We have now to direct our attention to the river water proper, which 

 we may consider that we can get from the Hooghly at different degrees 

 of dilution all the year except three or four months of the hot season. 

 The water of rivers is of course in greater part generally water fallen 

 from the atmosphere. Aided by the carbonic acid of the atmosphere, 

 it acts upon rocks, even silicious rocks, producing a certain amount of 

 decomposition and carrying off their constituents partly in solution, 

 partly in suspension as mud ; it carries off similar constituents from 

 the soil, which consists of decomposed rocks ; and also from this source 

 a quantity of organic matter, the result of the decomposition of vegeta- 

 ble and animal substances, as also the excrementious matters deposited 

 there. Except in special circumstances the water of rivers generally 

 contains a rather small proportion of alkaline salts in the state of 

 silicates, sulphates, chlorides and carbonates, with a larger proportion of 

 carbonates of lime and magnesia kept in solution by excess of carbonic 

 acid gas. They differ from spring or deep well waters and agree with 

 surface waters generally in containing a notable proportion of potash 

 as well as soda, and also more silica, phosphates, earthy carbonates 

 and organic matter, and sometimes ammonia and nitrates, than deep 

 spring waters do. When brought in contact with argillaceous deposits, 

 they part with their potash, ammonia, silica, phosphoric acid and 

 organic matter, while the soda, lime, magnesia, sulphuric acid and 

 chlorine are generally retained, forming the usual constituents of 

 spring waters. This subject is treated of fully in an Essay on the 



