616 Adeney — Dissolved Gases and Fermentative Changes. 



PART III. 



Bearing of tlie foregoing Experiments on the Analysis of Potable and 



Polluted Waters. 



Up to the present time the bacteriological methods which have been proposed 

 for the examination of waters have not resulted in bringing any very great 

 practical assistance to bear on the subject of the technical examination of pure 

 and polluted waters. I except, of course, those most important ones which can 

 be employed for demonstrating the presence or absence of pathogenic organisms in 

 a water. The suggestion that the number of microbes present in a given volume of 

 water would give a useful indication or otherwise of its purity, from which so 

 much was at first expected, has been shown, more especially in this country by 

 the researches of Dr. P. F. Frankland,* to be of little practical value, except when 

 applied for the examination of the efficiency of filtration, since many bacteria are 

 capable of enormous and extraordinarily rapid multiplication even in waters of 

 very high organic purity. "j" 



Bacteriological research has been instrumental rather, as I observed, in the 

 introduction to this Paper, in demonstrating the true agencies at work in setting 

 up processes of oxidation in waters, and in thereby indicating new lines of research 

 for completing our knowledge of the chemistry of natural and polluted waters. 



The experiments which have been described in this Paper, may, I ventm-e to 

 hope, prove a step onward in this direction, since they clear up, on the one 

 hand, certain points in reference to the analysis of potable waters which have 

 hitherto been more or less obscure ; and, on the other hand, they indicate a 

 satisfactory method for the examination and analysis of polluted waters. 



First, as regards the examination of potable waters, these experiments show 

 conclusively that (1) the absence of easily fermentable matters of all kinds, and 

 (2) the indication that the water has been subjected to efficient artificial or natural 

 filtration, are two conditions, positive evidence of which it is of the first impor- 

 tance to seek for in all waters to be used for dietetic purposes. 



Broadly speaking the first condition will have been established if the water 

 contains no free ammonia, or only small traces of this substance, since of the 

 easily fermentable substances found in waters it is the last to be fermented. 



The second condition will, no doubt, have been established, if, in addition to 

 the absence of free ammonia, traces only of organic matter (fermented) are 

 found in the water. 



* "Pioc. Roy. Soc," 1886, p. 526. 



f Article by Dr. P. F. Frankland, on "Water," already referred to, p. 990; see, also, work on 

 " Micro-organisms in Water," by Dr. and Mrs. P. F. Frankland. 



