1866.] Proceedings of the Asiatic Society. 199 



in the Journal. He remarked on the great difference between the 

 quantity of salt brought up by neap tides and by spring tides, the 

 former bringing only about one-fourth of the salt the latter did : also 

 on the difference depending on the time of tide, that being also great. 

 The smallest quantity of salt was found at about the last two hours 

 of ebb, and the first one or one and half of flood tide. Excluding the 

 period of three or four months when the influence of the tides pre- 

 vailed, the river water was on the whole purer, or contained less 

 saline matter than that of any of the water companies supplying 

 London as represented by the latest reports. 



Attention was then directed towards the organic constituents of the 

 water, which, with reference to sanitary considerations, were the most 

 important impurities. Some remarks were made on the very incor- 

 rect processes which had been frequently employed by chemists for 

 ascertaining the quantity of these, and the very unsatisfactory nature 

 of the results. The process, however, had been improved of late, and 

 with the aid of a fine balance, patience and care gave very fair results. 

 By such means the author had determined the amount of organic 

 matter in the river water at various seasons, but the results obtained 

 were very different from those given in Dr. Macnamara's report, being 

 very much smaller, more particularly in the case of the water in the 

 hot season. On account of the difficulties attending the correct deter- 

 mination of organic matter by weight, a new process had of late come 

 into favour, which was much simpler and easier of execution. This 

 depended on the oxidising properties of the permanganate of potash. 

 A weak solution of this, of known strength, was added with certain 

 precautions to a measured quantity of water, until a slight shade of 

 pink colour remained for a certain time. The purer the water, the 

 less of the permanganate solution is required; the greater the quan- 

 tity of this solution required, the more impure is the water ; so that by 

 delivering the solution from a graduated tube, the quantity required 

 can be ascertained, and consequently the amount of impurity estimat- 

 ed, or rather the quantity of oxygen required to destroy it. This test 

 does not indicate all the organic matter, only some kinds of it ; but it 

 acts on those kinds of organic impurities which have an offensive 

 smell and destroys them. The results of the estimation by weight of 

 the organic matter and of the amount of oxygen required by this test 



