1880.] 



Water supplies of Calcutta. 



119 



From these remarks it will be seen tliat in judging of the quality of 

 a potable water by Frankland's process of analysis, we pay tlie greatest 

 amount of attention to the amounts of ammonia and of organic carbon 

 and nitrogen, as representing organic matter actually present, whilst we 

 depend upon the amount of nitrates (and to a considerable extent also 

 on the amount of chlorides as explained in the previous part of this paper) 

 to indicate organic contamination which has become oxidized. The amounts 

 of total solids and of Hardness although important from a manufacturer's 

 point of view, do not seem to have any marked action on the health of 

 persons drinking such water, except when such constituents are present 

 in very large quantities. 



Dr. Frankland has unfortunately not fixed upon any very definite stan- 

 dard as to the amounts of the above substances which may be present in 

 water and yet not render it dangerous, and in fact it is almost impossible 

 to draw any hard and fast rule ; but so far as can be ascertained from bis 

 writings, Dr. Frankland appears to think that a supply which contains 

 O'lO parts of organic carbon and nitrogen in every hundred thousand parts 

 of water is of " great organic purity," whilst one containing 30 parts of 

 the same substances in the same volume should be considered a water of 

 fair organic purity." If the quantity is above this a water would be of 

 doubtful purity, and if in still larger quantities the water would be 

 recognized as impure. 



In order to give an idea of the quantities of these various substances 

 present in the water supplies of m.any of the large towns in England, and to 

 show the average composition of different samples of water from various 

 sources, I append a table giving the results by this method of analysis of the 

 London water supply from the rivers Thames and Lea, and from the deep 

 wells in the chalk, also the results of the Edinburgh, Glasgow, Liverpool, 

 Manchester and Dublin Avater supj^lies, and the average composition 

 derived from the analysis of a large number of samples of rain water, 

 upland surface water, spring water, and sea water. Most of these numbers 

 are taken from the various reports of the lioyal Commissioners who 

 were appointed to investigate the Pollution of liivers in England, but 

 some of the numbers come from the article on Water Analysis given in 

 " Sutton's Volumetric Analj'sis." 



See Table, page 120. 



Having thus settled our standards for comparison, we can now discuss 

 the present water supply of Calcutta, The results obtained by the analysis 

 of the Hydrant water are given in the following table ; the numbers 

 shown for each month are the averages for the past four years, and at the 

 foot of the table, the general average for the whole of the four years is 

 aj^pcnded. 



See Tulle, pdcjG 121. 



