226 Scientific Proceedings, Royal Dublin Society. 
The results are given in the following Table in grains per 
gallon :— 
Date—November, 7 8 9 | 10 | 11 | 12 | 18 | 14 | 15 | 16 | 17 | 18 
Ammonia, 6 . ]0.0020]0.0008]2.0014/0.0008]/0.0007|0.0010|0.0018]0.0018}0.0008/0.0003}0.0022/0.0018 
Albuminoid Ammonia, |0.0045]0.0063/0.0045|0.0055|0.0072/0.0054/0.0042|0.0067|0.0063}0.0055|0.0075|0.0049 
Chlorine, 5 . [0.94 0.92 Jo.92 |o.9r |o0.92 — |o.9g2 |0.92 |0.94 |0.04 — — 
Solids, . 5 - [3-78 [4.62 |4.20 |3.64 |4.20 |4.48 |3.08 [3.08 13.78 13.36 |3.64 |4.06 
Oxygen absorbed, . |0.053 |0.069 |0.088 |0.094 |0.089 |0.094 |0.078 |0.072 |0.079 |0.086 |0.089 |0.096 
The chlorine was very constant, but the other constituents, and 
the oxygen absorbed, showed wide variations from day to day. 
It will be noticed that an increase in the solids was usually, 
though not always, accompanied by an increase in ammonia. The 
largest quantities of ‘albuminoid ammonia’ occur at intervals 
of three days; with one exception, these maximum quantities show 
a progressive increase. 
It is generally considered that pure upland surface-water 
should not absorb more than 0:07 grains of oxygen per gallon. 
My results show that, on every day after November 8th, that 
quantity was exceeded. The limit commonly assigned to 
‘albuminoid ammonia’ in really good drinking water is 0:0056 
grains per gallon; that limit was exceeded on the 8th, 11th, 14th, 
and 17th. 
There are no means of ascertaining the source of the impurity 
which these figures reveal, or the cause of the daily variations. The 
unfiltered water from the Dargle river which was admitted to the 
mains during this period may have contributed to produce some 
of the results observed. It is possible, too, that, under the severe 
strain to which the filter-beds at Roundwood were submitted, 
filtration was not always efficient. Another possible explanation 
is to be found in the intermittent character of the supply. That 
the contents of the mains are affected by the daily turning off of 
the water is proved by the superaerated condition of the water 
during this period. When quickly drawn from the service-pipe 
the water was generally found to present a milky appearance, 
owing to the abundant separation of gas in minute bubbles. I 
