1880.] 



Water supplies of Calcutta. 



127 



but I do think that they may indicate that certain samples are less pure than 

 others, and so on. For the purpose of a simple comparison, these results 

 will be almost as useful as absolute statements, for we may work on the 

 basis, that the good quality of our Hydrant water has been satisfactorily 

 demonstrated. 



In passing I may mention that Mr. Waldie disj^utes the correctness 

 of Dr. Macnamara's results as to amount of organic matter present in the 

 water, but it would be quite as easy for me, with a knowledge of the 

 progress of the last ten years, to dispute the correctness of Mr. Waldie's 

 results, so that in both cases, the results of the old analyses as to organic 

 matter ai-e to be accepted as comparative statements, rather than actual 

 truths. It must be clearly understood, however, that I have no wish to 

 under-rate the value of the work done by Dr, Macnamara and by Mr. 

 "VValdie ; far from it, I believe that the results criticized are as accurate 

 and reliable as could be obtained by the processes then known, and in 

 those portions of the work, where the methods of analysis have not been 

 changed, I think we may rely, with certainty, on the accuracy of the 

 results given. 



In the face of the above facts, I may be pardoned, if in considering 

 these old analyses I draw more particular attention to the determination 

 of the inorganic substances present, where the methods of analysis have 

 scarcely changed, and refer less to the determinations of the organic 

 substances present in the water. 



In tidal water, that is water of which a part at least has been derived 

 from the sea, sodium chloride, or common salt, is a prominent ingredient. 

 In the table given on p. 120, it will be seen that sea water contains no less 

 than 1975*6 parts of chlorine per hundred thousand of water ; this substance, 

 on the other hand, is present in very minute quantities in the true river 

 water, and hence we have a crucial test to apply, in order to determine the 

 presence or absence of tidal water in the samples in question. It may here 

 also be well to remark that the process of analysis for the determination 

 of chlorine in waters has not changed since the period when the analyses 

 by Dr. Macnamara and Mr. Waldie were made, and therefore we may 

 entirely rely on the accuracy of the results given as to the amounts of this 

 constituent present in the samples of water analysed. 



In the following table I quote four sets of analyses made by Dr. 

 Macnamara of water collected, at low loater in each case, from three 

 different points in the river, namely, at Chinsurah, Pultah and off Cossi- 

 pore, (one mile above Baug Bazar Bridge). For the sake of comparison I 

 have added to the table some of the numbers obtained in the regular analysis 

 of water for the year 1878. 



