Moss—WNotes on the Vartry Water in November, 1893. 227 
found it easy to collect this gas in quantity. The gas escaped 
from the water issuing from the tap in the proportion of 1 volume 
of gas to 77 volumes of water at a temperature of 4° C. The 
composition of the gas, collected on two occasions at an interval of 
three days, was found to be as follows :— 
A. B. 
Nitrogen, ; : . 82°86 84°30 
Oxygen, ; : S690 15°58 
Carbon dioxide, : 5 00217 00:17 
100:00  100°00 
A. given volume of the gas, exploded with detonating gas, 
underwent no alteration in volume, and no carbon dioxide was 
produced; marsh gas and other hydrocarbons were therefore 
absent. The gas is, in fact, atmospheric air deprived of some of 
its oxygen, and with an increased quantity of carbon dioxide. 
Owing to the coefficient of absorption of oxygen by water being 
greater than that of nitrogen, such a mixture of oxygen and 
nitrogen would result from the action of water upon air. There 
ean be no doubt as to the source of this air. Assuming the water, 
when it enters the mains from the reservoir, to be saturated with 
air, it would, at the same temperature, absorb still more air at the 
lower level at which it was drawn from the mains, owing to the 
greater atmospheric pressure at this level. But, instead of being 
capable of absorbing more air, the water is found to be super- 
saturated; it must accordingly have been aerated after it left the 
reservoir. The obvious explanation is that it is aerated in the 
mains, the air being drawn into the mains by the suction result- 
ing from the outflow of water from the mains when the supply 
from the reservoir is cut off each day. It is a question for 
consideration whether the excess of dissolved oxygen does not 
largely promote the oxidation of the iron mains and the lead 
service-pipes and cisterns; this, however, is a matter of minor 
importance. The serious consideration is that the air sucked into 
the mains is certain in many cases to be derived from tainted 
sources; and it is highly probable that the defective fittings 
which admit the air admit liquid impurities also. This result of 
an intermittent water supply might be attended with disastrous 
consequences. 
