182 Mr Morren on the Influence of Light on the quality 
cent.), although the weather was fine and the other circumstances favour- 
able. 
What became of the oxygen with which the water of the pond was 
charged, at the moment of its greatest oxygenation? The author placed 
in the pond a reversed globular vessel, open at the lower part, allowing 
the water of the pond to communicate with that contained in the vessel. 
Numerous air-bubbles were disengaged, and this gas, when analysed, 
contained nearly the half of its volume of oxygen. Nevertheless. the 
oxygenation of the water contained in the vessel, and from which this 
air, so rich in oxygen, had been disengaged, had in no degree diminished, 
and was equal to that of the water of the pond at the time when it was 
placed in it. We must conclude from this that the oxygen absorbed by 
the water is not employed to form carbonic acid by combining with the 
organic matters it may contain, but that it is constantly carried off by the 
atmosphere. This source for the production of oxygen must be consider- 
able, for, according to the calculations of the author, made in a favour- 
able day, the pond he examined, and which contained 8000 cubic feet of 
water, disengaged 128 cubic feet of oxygen. 
The running waters of the Maine and Loire, even when the current is 
slow, as in the former, do not present very sensible variations in their 
oxygenation. The author has ascertained that, when the oxygenation of 
the water, either by a sudden swell and overflowing of the neighbouring 
meadows, or by the unexpected destruction of the green matter, descends 
to 18 or 20 per cent. of oxygen in the air it contains, fishes can no longer 
live in it, and they are seen to perish in great numbers as if from asphyxia. 
The author has witnessed the same phenomena, on two occasions, in the 
fishpond ; and on the 8th June 1835, after a sudden swell of the Maine, 
almost all the fishes perished, and their dead bodies diffused a mephitic 
odour. ‘The voracious fishes were the first that suffered, and the author 
is convinced that in all these cases the oxygenation of the air contained 
in the water was very low.* 
It appears that, when the oxygen is found in water in considerable 
proportion, it is merely dissolved in it, and not chemically combined, as 
it is in Mr Thénard’s oxygenated water. In fact, the oxide of silver does 
not disengage the oxygen, as it does in the latter. It is possible, how- 
ever, that this preponderance of oxygen may be the cause of the whiten- 
ing of linen on the bleaching green, the oxygen of the water performing 
the dehydrogenating office of chlore on vegetable colours. 
* Very slight differences in the composition of the water in which fishes live 
are sufficient to cause death. The late Prof. de Candolle has remarked that, when 
the saltness of the salt-pits increased in a warm day one-half per cent., that was 
sufficient to kill all the fishes inhabiting them when this saltness approached the 
extreme limit which these animals can endure. In the morning, the saltness be- 
ing 7°, they were very vigorous, in the evening, the saltness being 73°, they were 
dead. 
