1880.] 



Water supplies of Calcutta. 



117 



minations the second, third, fourth and fifth are the most important 

 from a hygienic point of view. Thus the amounts of organic 

 carbon and nitrogen represent the organic matter existing as such in 

 the water, at the time of analysis. Tlie ammonia may to a certain 

 extent be due to the original ammonia we find in rain water, but more 

 generally it may have been produced by the introduction of sewage 

 matter into the water. The nitrates and nitrites present in water are 

 derived from the oxidation of nitrogenous organic matter ; this oxidation 

 may have taken place either in the water itself, or in the soil on which the 

 rain water fell. These last constituents are to be looked on with suspicion, 

 unless the water is derived from a deep well, when it may contain consi- 

 derable quantities of these substances without giving rise to any alarm. 

 It is not that nitrates in themselves are injurious in any way, but their 

 occurrence in any quantity in river or shallow well waters shows, that the 

 water must have been either contaminated with some nitrogenous organic 

 matter in a state of decomposition, or in some circumstances where decom- 

 posing nitrogenous organic matter had been previously present. It is 

 pointed out that it must be more or less dangerous to drink water that has 

 thus been contaminated with organic matter or with nitrates derived from 

 organicmatter, for it is possible if not probable that in such a water the most 

 noxious of all its constituents would entirely escape oxidation or any kind of 

 change. The reason for this opinion is very clearly expressed in one of 

 Dr. Frankland's papers on potable water. In the Journal of the Chemi- 

 cal Society, March 1868, at page 31 of his Memoir, he says — " There 

 is also another aspect in which the previous sewage contamination of a 

 water {i. e., the presence of large quantities of nitrates etc.) assumes a 

 high degree of importance ; if the shell of an egg were broken, and its 

 contents beaten up with water, and thrown into the Thames at Oxford, the 

 albumen would probably be entirely converted into mineral compounds 

 before it i-eached Teddington, but no such destruction of the nitrogenous 

 organic matter would ensue, if the egg were carried down the stream 

 \inbroken for the same distance ; the egg would even retain its vitality 

 under circumstances which wo;dd break up and destroy dead or unorganised 

 organic matter. Now excrementitious matters certainly, sometimes, if 

 not always, contain the germs or ova of organized beings, and as many of 

 these can doubtless retain tlieir vitality for a long time in water, it follows 

 that they can resist the oxidizing influences which destroy the excremen- 

 titious matters associated with them. Hence great previous sewage con- 

 tamination in a water means great risk of the presence of these germs, 

 which, on account of their sjiarseness and minute size, utterly elude the 

 most delicate determinations of chemical analysis." A considerable number 

 of chemists have put forward the statement, that a river water which has 

 lU 



