Feb^2d,y 1876J 



NATURE 



331 



quantitative determination of present or actual organic 

 impurity. 



The past history of a water is made out chiefly through 

 the mineral products of oxidation which the polluting 

 organic matters have yielded, and which are still present 

 in the water. As these products are innocuous, it is 

 obvious that if all kinds of organic matter behaved alike 

 under the influence of oxidising agents, such evidence of 

 previous pollution might be safely disregarded ; but it is 

 almost superfluous to point out that there are wide differ- 

 ences between various kinds of organic matter in regard 

 to the rapidity with which they combine with oxygen ; 

 and of all kinds, that which is organised and living 

 opposes by far the greatest obstacles to oxidation. 

 Now the researches of Chauveau, Burdon Sanderson, 

 Klein, and others, scarcely leave room for doubt that the 

 specific poisens of the so-called zymotic diseases consist 

 of organised and living organic matter, and it is now cer- 

 tain that water is the medium through which some, at 

 least, of these diseases are propagated. It is evident, 

 therefore, that an amount of exposure to oxidising influ- 

 ences which may resolve the dead organic matters present 

 in water into innocuous mineral compounds, may, and 

 probably will, fail to affect those constituents which are 

 endowed with life, and Dr. Frankland adduced, as a 

 striking instance of the persistency of the tjphoid poison 

 when diffused in water, the outbreak of a violent epidemic 

 of typhoid fever in a Swiss village through the use of 

 spring water, which, after contamination with the poison, 

 had filtered through nearly a mile of porous earth, but 

 which had nevertheless lost none of its virulent properties. 

 As the typhoid poison is always liable to be present in 

 sewage, and as there is no_ test for it, except its effects 

 upon man, the discovery of previous sewage contamina- 

 tion in potable water ought to be one of the chief objects 

 of the analyst. 



The actual, or present, as distinguished from the 

 past, polluting organic matter of potable water can 

 only be ascertained from the amount of carbon and 

 nitrogen found as constituents of the organic matter 

 present in the water at the time when the analysis is 

 made. The method of performing this operation, known 

 to chemists as the " combustion " method, was fully de- 

 scribed to the Fellows of the Society by the speaker 

 eight years ago. Improvements since made were men- 

 tioned, and te following proofs of the delicacy and 

 accuracy of the analytical method were adduced : — 



To 100,000 parts of a sample of water, rendered as 

 nearly chemically pure as possible, i'5572 parts of sul- 

 phate of quinine were added. The water was then 

 submitted to the method for determining organic carbon 

 and nitrogen just mentioned. The following data com- 

 pare the quantities of organic carbon and organic nitrogen 

 thus actually added to the water, with those afterwards 

 extracted in each of two analyses : — 



Present. 



Found. 



Present 



Found. 



^ I. II. 



Organic carbon in 100,000 ) o 



parts of water j 0857 part. 0-912 0-904 part 



Organic nitrogen in ditto o-ioo „ 0-0996 0-098 „ 



To 100,000 parts of a similar sample of water 0-7786 

 part of sulphate of quinine was added, and the following 

 results obtained on analysis : — 



Present. Found. . 



^ I. iL Hi. 



Organic carbon in ) 



loo.ooo pirts of / 0-429 part. 0-435 o'442 0-440 part 

 water 



Organic nitrogen in 

 ditto 



r 



0-050 



0-047 0-048 0-048 



To 100,000 parts of a third similar sample of pure 

 water 0-07786 part of sulphate of quinine was added. On 

 analysis this water yielded the following numbers : — 



I. II- III. 



Organic carbon in ] 



100,000 parts of > ox)43 part. 0'047 0-050 0*055 part. 



water ) 



Oi^anic nitrogen in 



ditto 



0-005 >» 0-006 0-005 o-oo6 ,, 



The close approximation of the experimental to the 

 calculated numbers is the more striking when it is remem- 

 bered that the weight of nitrogen actually determimd in 

 the litre of water used for analysis was, in the last series 

 of experiments, only Ts^rrth of a gramme. 



Applied to actual specimens of potable water, the 

 accuracy of the method was tested by the uniformity of 

 results obtained in the following duplicate analyses of the 

 same samples of water : — 



Results of analyses expressed in parts per 100,000 . 

 I. II. 



Thames water as sup- I Organic carbon 0280 0-285 P^wt. 



plied to London ... ( „ nitrogen 0-032 0-035 f» 

 River Lea water as i Organic carbon 0-231 0-239 part. 



supplied to London. ) ,, nitrogen otx\2. 0-042 ,, 

 Kent Company's water j Organic carbon 0054 0056 part, 

 as delivered in London I ,, nitrogen 0016 0-017 »> 



But as practical illustrations of the trustworthiness of 

 the process, the speaker rehed most upon the results of 

 the monthly analyses of the water delivered by the eight 

 metropolitan companies made for the Registrar- General 

 during the last eight years, and embodied in two large 

 diagrams which exhibited, at a glance, the results of 

 nearly 800 separate analyses. One of these diagrams 

 showed, by means of curves, the mean proportions of 

 organic elements (organic carbon and organic nitrogen) 

 in the waters of the Thames and Lea, and compared them 

 with that found in the deep well-water of the Kent Com- 

 pany. It also showed the rate of flow of the Thames 

 nearly opposite Hampton Court Palace, and consequently 

 near the place where the Thames water companies ab- 

 stract their supplies. This diagram showed how sharply 

 the distinction between these three waters is drawn by 

 the method of analysis. In no instance did the cune 

 representing the average organic impurity in the Thames 

 approach near to that indicating the like impurity in the 

 deep-weU water, whilst the curve of organic contamina- 

 tion in the Lea water intersected the Thames curve but 

 thrice, and the deep-well curve only once in eight years ; 

 and even these intersections, when closely studied, were 

 found to be striking illustrations of the delicacy of the 

 analytical method. 



The second diagram might be regarded as a magnified 

 representation of the first. In it the curve representing 

 the average organic impurity in Thames water was de- 

 composed into five constituent curves showing the organic 

 impurity in the water delivered by each of the five 

 metropolitan water companies which abstract their sup- 

 plies from the Thames ; whilst the corresponding curve 

 of impurity in the River Lea was split into two, one 

 representing the impurity in the New River Company's 

 water, and the other that in the beverage delivered by 

 the East London Water Company. As deep-well water 

 is delivered to London by one company only, the curve 

 representing the minute impurity in this water was the 

 same in both diagrams. 



These diagrams demonstrated how faithfully the analy- 

 tical results recorded, firstly, the well-known supe- 

 riority of deep well over river water ; secondly, the 

 superiority of the water of the Lea to that of the Thames ; 

 thirdly, the variations in the three great conditions which 

 govern the intensity of organic contamination in the 

 river waters, viz., heavy floods, small floods when the 

 river is low, and decay of vegetation in autumn ; and 

 lastly, the method has shown itself competent to reveal 

 the finer shades of quality in waters drawn simultaneously 

 from the same source, but treated diflferently by the 

 various companies who manipulate them. 



