238 The Future Water-su])i)Jij of London. [Apiil, 



collation of tliese results tliat the previous Listory of the water is 

 written. From the amount of uitrogen present, as ammonia and 

 nitrates and nitrites, minus the quantity which may have been 

 derived from aerial sources, Franldaud calculates the "previous 

 sewage- contamination " of the water on the assumption, founded on 

 many analyses, that one part of nitrogen is contained in 10,000 

 parts of average London sewage. Of course, it must not be for- 

 gotten that this estimate includes previous drainage as well as 

 previous sewage-contamination ; for land drainage, especially in 

 times of flood, carries to the rivers much of the soluble portions of 

 the excreta of animals in a more or less complete state of decompo- 

 sition ; and it is obviously impossible to distinguish in a water the 

 nitrogen which comes from sewage from the nitrogen which comes 

 from drainage. But in spite of tliis drawback, the estimate of 

 previous sewage-contamination in the London Companies' waters 

 agrees so well with calculations founded on the number of persons 

 whose sewage pollutes the streams, that it may, I beheve, be 

 accepted as a marvellously close approximation to the truth. 



It is very much to be wished that we were able, by equally 

 direct and accurate processes, to determine the quantity and nature of 

 the " organic matter " which exists in solution in all polluted waters, 

 except those in which natural oxidation has proceeded to its furthest 

 limit. But, unfortunately, the very nature of the subject precludes 

 us, and will perhaps for ever preclude us, from knowing much about 

 the nature of this organic matter. For what is organic matter ? 

 It includes, according to the views of modern chemistry, all except 

 the very simplest of carbon-containing compounds. The phrase is 

 indeed only exceeded in vagueness by the idea for which it stands, 

 and has been long discarded from the realm of pure science, in 

 company with the " extractives " and " earthy matters " which 

 formerly marked unknown regions on the map of science. To find 

 organic matter in water is nothing. Sugar is organic matter, so is 

 strychnine, and so is a worm, or the contents of an e^^. In the 

 complex wanderings which water often pursues in its journey from 

 the clouds back to the sea, it is obviously liable to become con- 

 taminated with " organic matter " from the most various sources. 

 It may pass through peat ; through living plants or dead vegetation ; 

 through a paper-mill, a dye-house, or a soap-boiler's, or through all 

 three ; it may receive the washings of a pig-sty, the drainage of a 

 town, or the garbage from a butcher's shop ; and its composition 

 will differ in every one of these cases. Moreover, if we knew 

 exactly what contaminations the water had received, and their 

 chemical nature, we should still be unable to say in what condition 

 they existed in the water as we found it. For nearly all kinds of 

 organic matter commence a complex series of changes from the 

 moment they enter the water — a series which is only completed by 



