348 Scientific Proceedings, Royal Dublin Society. 
experimental data, showing, amongst other results, that no 
relation exists between the oxygen actually consumed by the 
fermentation of the organic matters in a polluted water, and the 
“oxygen absorbed” from acid permanganate; and that albu- 
minoid ammonia determinations likewise afford no definite 
information as to the character, or quantity, of the organic 
matters in a polluted water. 
ALL THE DISSOLVED GAsES IN A WATER SHOULD BE DETERMINED, 
AND NOY THE DISSOLVED OXYGEN ONLY. 
Some hope has also been entertained that simple determination 
of the dissolved oxygen in the water at the time of collection by 
one of the well established volumetric methods might yield 
important information as to the condition of the water when 
collected, more especially in the examination of river waters for 
pollution. 
It becomes obvious, however, upon reflection that such de- 
terminations, although capable of being made with great accuracy, 
can be of very limited value, since at best they must be liable to 
very serious errors when calculated into percentages of saturation 
in order to reduce them to a standard and comparable form, owing 
to the uncertainty as to the standard quantity of dissolved oxygen 
the water should contain, if unpolluted, when the only datum 
known in connexion with the water at the time of collection is 
that of its temperature. I may here note that this difficulty 
does not arise in the aération method, since the dissolved 
nitrogen is determined in addition to the dissolved oxygen, and 
this gives us the means of calculating the maximum quantity 
of oxygen which should be dissolved in the water at the time of 
collection. 
EXPERIMENTAL Deraits oF THE A#RATION METHOD NoT 
LABORIOUS. 
The failure so far to discover a reliable method of analysis 
without the use of gasometric methods, induces me to again draw 
attention to the aération method, and to illustrate its value by some 
practical applications, more especially as extended experience with 
the method has convinced me that it can be carried out with 
