ISSO.] 



Writer suppj/es of Calcutta. 



95 



I have previously noticed the three stcaiidards of purity suggested by 

 Prof. Wanklyn, but as in the case of these Calcutta tank and well waters, 

 we shall be dealing with very impure samples, it will be well to adoj^t some 

 standards of greater impurity than before given. I think it will he 

 well witliin the mark to consider, that any sample of water which pro- 

 duces more than 10 parts of total ammonia should be classed as a sewage 

 and not as a water, and that if the amount produced is between 10 and 

 5 parts, the sample may be called a dilute sewage ; from 5 parts to 

 1 part we have a water considerably contaminated witli sewage, and from 

 1 part down to Prof. VVanklyn's limit of O'lO parts of total ammonia, 

 we have tlie class of Dirty Waters, which represent water contaminated 

 more or less with organic or sewage matter. In the same way we may 

 adopt a classification of the amounts of chlorine present, and there is 

 apparently no doubt that a Calcutta tank or well water which contains 

 more than 250 parts of chlorine per million should be classed as a sewage ; 

 that a water containing from 250 to 150 parts of chlorine may be looked 

 on as a dilute sewage; that with from 150 to 100 parts of chlorine present 

 we have a water considerably contaminated with sewage ; and when from 

 100 to 50 parts are present a water may be said to be slightly contaminated, 

 whilst if less than 50 parts of chlorine are present, the water may be 

 considered moderately safe. 



The first of the two following tables contains the results obtained 

 from the analysis of the tank waters, and the second the numbers obtained 

 from the well waters. The tables contain 9 columns, most of which are 

 explained by their headings. Column 1 gives the date on which the water 

 was analysed, 2 and 3 the locality from whicli the sample was drawn and 

 the section of the town in which the tank or well is situated. Column 

 4 gives the reason why my attention was called to the state of the 

 tank or well, and which lead to the water being analysed. Column 5 gives 

 a very brief description of the physical characters of the sample, prin- 

 cipally as to colour, smell, presence or absence of solid matters in 

 suspension, presence of animal life etc., and under this liead it may be 

 mentioned that as most of the waters were extremely dirty and thick, 

 the examination as to colour was made in a glass cylinder only six inches 

 high standing on a white surface. Columns 6 and 7 give the amounts of total 

 ammonia and of chlorine present in every million parts of water. Column 

 8 gives the decision as to whether the water was considered fit for 

 potable purposes or wliether it was condemned for such uses, and tlie last 

 column shews whether the tank or well has been subsequently filled up 

 or dewatered. 



Most of these results have been submitted to the Health Officer to the 

 Municipality in my capacity of Water Analyst, and it is due to the courtesy 

 of Dr. McLcod that 1 am able to give the columns -1, 8 and 9. 



