58 



SCIENCE. 



[N. S. Vol. XXIII. No. 576. 



vehicle of the germs of disease. Hence the 

 sanitary value of a water analysis depends 

 not on determining the amount of organic 

 matter which a water contains, but on 

 the amount of information it can give in 

 answer to the question, 'Is a given water a 

 normal or a polluted water?' or, stated in 

 other words, 'How far can analysis deter- 

 mine whether or not the organic matter in 

 a water is of vegetable or animal origin?' 



In order to answer this question it is 

 necessary to divide natural waters into 

 three classes: Surface, subsoil or ground, 

 and artesian waters. These waters differ 

 so radically in character from each other 

 that, although the data from which deduc- 

 tions can be drawn as regards pollution are 

 practically the same, yet the correct inter- 

 pretation of these data depends upon the 

 knowledge as to which group the water in 

 question belongs, and a clearer idea of the 

 subject under discussion can be obtained 

 if we first consider surface waters and 

 apply the results of this study to ground 

 and artesian waters. 



It is often claimed that there is no value 

 in a sanitary analysis of a surface watei^, 

 that an inspection of the watershed may 

 give all, and often much more, information 

 than can be obtained from the analysis of 

 the water. If sewage is seen to be entering 

 a pond, an analysis is unnecessary to show 

 that it is polluted. If the watershed is 

 uninhabited, the water can not be polluted. 



There is no question about the value of a 

 survey and that a survey not only aids in 

 drawing the proper deductions from the 

 data of an analysis, but that often it is 

 necessary for a correct explanation of the 

 data. Still, there are many cases where, 

 unless large interests are involved, a care- 

 ful and complete survey is practically im- 

 possible on account of the expense, and 

 where the chief reliance must be placed on 

 the sanitary analysis. Further, a sui'vey 

 alone, though it may show pollution, does 



not tell the amount of pollution, nor show 

 the changes that have taken place in the 

 polluting substances. A survey alone can 

 never give all the desired infonnation, and 

 a sanitary analysis, even of a surface water, 

 must always have a value. It is from this 

 point of view that what I have to say re- 

 garding surface waters must be considered. 



Very early in the study of polluted 

 waters attempts were made to devise meth- 

 ods for detecting certain definite organic 

 compounds which were known to be formed 

 by the decomposition of the nitrogenous 

 products contained in sewage, but without 

 success, and there is very little hope that 

 much knowledge can be gained as to the 

 nature of the organic matter through this 

 line of investigation. The decomposition 

 of the nitrogenous products contained in 

 sewage takes place so rapidly that the isola- 

 tion of any particular compound like crys- 

 tin, or any group of compounds, like the 

 amido group, can only be looked for when 

 the pollution is very recent and in very 

 large amounts. 



Though it is apparently impossible to 

 isolate from a water any particular nitrog- 

 enous organic compound known to occur 

 in sewage, the amount of nitrogen and the 

 amount of carbon contained in these com- 

 pounds can be determined, and among the 

 first, if not the first, to attempt to deter- 

 mine from the amount of nitrogen and 

 carbon in a water whether the organic mat- 

 ter was of animal or vegetable origin was 

 the late Sir Edward Frankland. On ex- 

 amining the residue left on evaporation of 

 water from peat bogs he found the ratio of 

 nitrogen to the carbon was as 1 to 12, while 

 in the residue from fresh sewage it was 

 as 1 to 2.1, and in the residue from pol- 

 luted waters, as water containing leakage 

 from cesspools as 1 to 3.1. From these and 

 similar observations he concluded that in 

 surface waters the ratio of the organic 

 nitrogen to the organic carbon in the residue 



