1869.] The Future Water-sui)]jhj of London. 239 



entire oxidation. These changes, no doubt, vary greatly with the 

 nature of the organic matter, the amount of free oxygen which it 

 meets with, the conditions of rest or agitation, the temperature, and 

 so on. They belong to that most complex department of chemistry 

 which deals with the processes of putrefaction, fermentation, and 

 decay, and as such they are connected in some direct, but ill- 

 understood manner, with the vital changes of low forms of organic 

 hfe in the water. It is not wonderful that in such a chaos we 

 should have to pick our way carefully, and should be compelled 

 to decide rather by inference than direct proof, on the nature and 

 significance of the organic contaminations in our river and well 

 waters. The methods upon which rehance is placed vary from 

 time to time as sounder views and wider knowledge are acquired, 

 and they are still very imperfect, but enough has been done to 

 justify great hopes in the futm-e. It is unnecessary in this place 

 to enter into the details of the recent improvements in analytical 

 method, but some of their leading features must not pass unnoticed. 



The old incineration process, in which organic matter is esti- 

 mated by igniting the dried residue and noting the loss of weight, 

 appears now to be pretty generally discredited. Its indications 

 cannot, of course, furnish the least clue to the nature of the volatile 

 matter, and do not even correctly record its amount ; for even when 

 aU precautions are taken, some of the mineral substances, such 

 as ammonia and nitrates, are sure to be volatilized, wholly or in 

 part; and Frankland and Armstrong have, on the other hand, 

 shown that urea, a very significant and imjsortant impurity, is not 

 entirely volatihzed during the process. To show the utter untrust- 

 worthiness of the method, it will be sufficient to mention that a 

 water residue sometimes weighs more after ignition and treatment 

 with carbonic acid than it did before. In such a case the analysis 

 would, of course, indicate rather less than no organic matter ! 



The permanganate of potash process, suggested in the year 

 1850 by Forchhammer, has in the last few years been very largely 

 employed, and has received many modifications of form. The per- 

 manganate, when applied in solution to the acidified water, loses a 

 definite portion of its oxygen to the organic matter present ; and 

 the amount of oxygen so employed can be ascertained by the amount 

 of the beautiful violet solution of the salt wliich is decolourized. 

 Most chemists are content to record the amount of oxygen so indi- 

 cated, or, at any rate, the amount of permanganate employed ; but 

 Dr. Letheby calculates the organic matter from the oxygen by 

 multiplying its weight by eight. This would give a perfectly 

 correct result, if all organic matter were equivalent to oxalic acid 

 in its action on the permanganate. But this is so far from being 

 the case, that it appears, from the careful experiments of Frankland 

 and Armstrong, that of nine different kinds of organic matter 



