ApENEY—Studies in Chemical Analysis of Fresh & Salt Waters. 355 
The effect of the débris from the luxuriant vegetation is shown 
by the analyses recorded in Table II. Samples 2 and 8 were 
drawn from the lower service reservoir. The other samples 
represent the condition of the upper storage reservoir. On 
comparing the analyses recorded in the table, it is at once seen 
that the water from the upper reservoir, during its passage 
through the lower reservoir, received a marked addition of 
polluting matters; but I am more concerned at the present to draw 
attention to the value of a knowledge of the composition of the 
dissolved gases in the samples 5, 6, and 7 from the upper reservoir. 
. These were all collected on the same day, namely July 24th, and 
represent the condition of the water in the reservoir at two 
different levels below its surface—sample 5 at about 5 feet below 
the surface, and samples 6 and 7 at about 20 feet below the 
surface. Sample 5 may be fairly taken to represent the average 
condition of the water as it entered the reservoir through the 
ceatch-water channels. Its analysis shows it to be slightly different 
in quality from the samples 6 and 7 from the 20-foot level. The 
analyses of the two latter samples indicate the existence of 
slight quantities of polluting matter at the lower depths of the 
reservoir; but with a knowledge of the composition of the 
dissolved gases in addition to the ordinary analytical data, 
we find that an active state of both carbon and nitrogen 
fermentation was taking place in the lower levels of the reservoir, 
and that the carbon fermentation was practically wholly due to 
vegetable débris. 
The dissolved gases determinations also afford the necessary 
data for distinguishing the proportion of the dissolved oxygen 
consumed by the carbon fermentation from that consumed by the 
nitrogen fermentation in the manner I have described above. 
APPLICATION TO THE STUDY OF THE WATERS oF A TIDAL 
River. 
The third subject of study which I have to notice is the tidal 
portion of the river Liffey, or rather its estuary. Analyses 
of samples collected from both the surface and bottom waters 
of the estuary are recorded in Tables III. and IV. in the 
following pages. 
