060 Scientific Proceedings, Royal Dublin Society. 
After the references I have made to the two preceding tables 
it will be unnecessary to make any detailed reference to these 
further tables. I need only remark that the application of the . 
aération method to sea water is attended with results quite as 
definite and as valuable as those obtainable when applied to the 
examination of fresh waters. 
The “ outfall’ referred to in the tables is, I should explain, 
situated a few yards to the north of the South Wall, and about 
half a mile below the Pigeon House Harbour. 
These analyses, besides illustrating the value of the aération 
method when applied to the analysis of sea-waters, will be 
found, on careful examination, to afford some valuable evidence 
upon the question of the disposal of sewage matters from which 
the heavy solid matters have been previously separated by dis- 
charging them into tidal waters. It will be seen from the analyses 
that the effect of the liquid and the lighter solid sewage matters 
discharged from so populous a city as Dublin and its neighbour- 
ing districts is confined in calm weather to the surface waters 
of the estuary, the bottom waters being but slightly affected even 
at low tides. ‘Thus in samples 9 and 10, Table IV., the percentage 
of oxygen found in a sample of the surface water, collected at low 
spring tide opposite the Pigeon House Harbour, and in calm 
weather, was 9°9, after it had been kept for five days out of con- 
tact with air, while the percentage of oxygen found in the sample 
collected at the same spot, but 14 feet below the surface, was 
86°37. 
ERRORS ARISING WHEN THE OxYGEN ONLY OF THE DiIssoLVED 
GaAszEs Is DETERMINED. 
One further point which these analyses illustrate, and which 
must be here emphasized, is the nature and extent of the error 
to which I referred in the earlier part of this paper as more or 
less seriously affecting the results obtained by volumetric methods 
for dissolved oxygen. 
The practice hitherto amongst analysts for the estimation of 
the dissolved oxygen in a water when such has been necessary, 
has been to adopt one of the volumetric methods, and to employ, 
for the purpose of calculating the quantities of oxygen found into 
percentages of saturation, tables giving the maximum quantities 
of oxygen which distilled water holds in solution when saturated, 
at different temperatures. 
