Chemical Analysis of Potable Waters. 



20? 



1. Chlorine. — This occurs chiefly in combination with sodium. In 

 waters not naturally brackish the determination of its amount is 

 regarded as decidedly important. Chlorides occur in all human 

 excreta and slop waters, and, therefore, in all sewage, and their pres- 

 ence in considerable quantity is a sign of probable contamination. 

 The estimation is generally made volumetrically with a nitrate of sil- 

 ver solution. Over five parts in 100,000 were regarded by the Rivers 

 Pollution Commission of Great Britain as in most cases due to sewage 



2. Phosphoric acid.— "Much nonsense " says Wanklyn "has been 

 talked about phosphates." This talk has had to do with the presence 

 of phosphates in sewage and the evidence afforded by them of such 

 contamination. The fact, however, is that in presence of carbonate 

 of lime phosphates can only exist in exceedingly small traces in a 

 clear water, but a qualitative test for their presence is usually made. 



3. Nitrites and nitrates. — These compounds are believed to result 

 mainly from the oxidation of nitrogeneous organic matter, chiefly 

 animal, and are considered by some chemists as indicating quite 

 accurately the amount of such defilement. In themselves, of 

 course, they are harmless, but if they aid us in determining the 

 amount of pollution their quantity becomes a matter of importance. 

 It is now pretty generally conceded that the conversion of nitro- 

 geneous organic matteriuto these forms takes place under the in- 

 fluence of micro-organisms and is a process of fermentation, the 

 rapidity of which depends upon degree of dilution, temperature and 

 other conditions. Kecent experiments, as for instance, those of War- 

 rington at the Eothamsted laboratory reported in Nature, for October 

 30, 1884, seem to prove quite conclusively that such is the case, and if 

 so, the old view that nitrification is a mere oxidation must be aban- 

 doned and our ideas concerning the value of natural aeration, long 

 considered by many chemists so important, must be greatly modified. 

 Warrington asserts that nitrification will not take place in an acid solu- 

 tion. Some base must be present with which the nitric acid formed 

 may combine, and when this is exhausted the oxidation ceases. If this 

 is true then a study of the amount of certain mineral constituents 

 present in a water which may furnish bases to the nitric acid pro- 

 duced, becomes indirectly important in determining the rapidity and 

 completeness with which sewage matter may be oxidized, and a study 

 of this subject, yet practically undeveloped, bids fair to yield valuable 

 results. 



At the same time it is to be borne in mind, as Wanklyn and others 

 have pointed out, that certain mineral strata yield nitrates to water 

 containing no organic matter, and that processes of vegetation in rivers 



