AvENnEY—Studies in Chemical Analysis of Fresh & Salt Waters. 353 
fall after a somewhat lengthened period of fine dry weather, and 
at a time when rain had commenced to affect the water in the 
upper reaches of the river. 
Sample 7 was collected on the following day, after heavy rain 
had been falling for some hours previously. I mention these 
points to draw attention to the marked influence of the rain upon 
the quantity of carbon dioxide in the water at the commencement 
of the autumn season. 
APPLICATION TO THE Stupy oF A PorasLE WATER-SUPPLY. 
The next subject of examination which I wish to notice is 
that of the Rathmines water-supply, and I notice it in order to 
illustrate the value of a knowledge of the composition of the 
dissolved gases in certain cases of doubt in connexion with 
potable waters. 
The Rathmines water-supply is an upland surface-water of 
excellent quality, the catchment area being most carefully guarded 
against contamination of sewage matter of any kind. 
In June and the early parts of July of last year, serious 
complaints were made by the residents of the Rathmines district, 
that the water as supplied to them was turbid and decidedly 
coloured, and often emitted unpleasant fish-oil odours, and even at 
times developed oily scums on its surface when drawn in large 
quantities for bath purposes, &ec. 
On investigation, the bad appearance and odour complained of 
were found to be due to unusually luxuriant growths of microscopic 
organisms of various kinds, but chiefly of Algw and Diatoms. 
The water at the time was unfiltered, and consequently the 
consumers experienced to the full the effect of these luxurious 
growths immediately they began to die down and decay. The 
Waterworks comprise two reservoirs: the upper reservoir situated 
at Glan-na-Smol, Co. Dublin, and forming the storage tank, is 
50 feet deep in the deepest part, and possesses a storage capacity 
of 850,000,000 gallons; and the lower or service reservoir, situated 
nearer Dublin, at Ballyboden, which has a storage capacity of 
11,000,000 gallons. 
The microscopic growths were particularly luxuriant in this 
latter reservoir, so much so, indeed, that the stones all round it, 
from the surface to a depth of 18 inches, were completely covered 
with a most luxuriant growth of filamentous Algze. 
Oe 
