_a._ A small flounder was introduced into a vessel filled with solution
of nitrous oxide in water over mercury. He remained at rest for ten
minutes and then began to move about the jar in different directions.
In a half an hour he was apparently dying, lying on his side in the
water. He was now taken out, and introduced into a vessel filled with
water saturated with common air, he very soon recovered.
_b._ Of two large thornbacks,[188] equally brisk and lively. One, A,
was introduced into a jar containing nearly 3 cubic inches of water,
saturated with nitrous oxide, and which previous to its impregnation
had been long boiled; the other, B, was introduced into an equal
quantity of water which had been deprived of air by distillation
through mercury.
[188] I use the popular name. This fish is very common in every part of
England; it is nearly of the same size and color as the minnow, and is
distinguished from it by two small bony excresences at the origin of
the belly. It is extremely susceptible.
A, appeared very quiet for two or three minutes, and then began to move
up and down in the jar, as if agitated. In eight minutes his motions
became very irregular, and he darted obliquely from one side of the
jar to the other. In twelve minutes, he became still, and moved his
gills very slowly. In fifteen minutes he appeared dead. After sixteen
minutes he was taken out, but shewed no signs of life.
B was very quiet for four minutes and half. He then began to move
about the jar. In seven minutes he had fallen on his back, but still
continued to move his gills. In eleven minutes he was motionless; taken
out after thirteen minutes, he did not recover.
_c._ Of two thornbacks, one, C was introduced into about an ounce of
boiled water in contact with hydrogene, standing over mercury. The
other, D, was introduced into well boiled water saturated with nitrous
oxide, and standing in contact with it over mercury. C lived near
thirteen minutes, and died without being previously much agitated. D
was apparently motionless, after having the same affections as A in the
last experiment, in sixteen minutes. At the end of this time he was
taken out and introduced into common water. He soon began to move his
gills, and in less than a quarter of an hour was so far recovered as to
be able to swim.
The last experiment was repeated on two smaller thornbacks; that in the
aqueous solution of nitrous oxide lived near seventeen minutes, that in
the water in contact with hydrogene, about fifteen and half.
The experiments in Res. I. Div. 3, prove the difficulty, and indeed
almost impossibility of driving from water by boiling, the whole of the
atmospheric air held in solution by it; they likewise show that nitrous
oxide by its strong affinity for water, is capable of expelling air
from that fluid after no more can be procured from it by ebullition.
Hence, if water saturated with nitrous oxide had no positive effects
upon fishes; they ought to die in it much sooner than in water deprived
of air by ebullition. From their living in it rather longer;[189] we
may conclude, that they are destroyed not by privation of atmospheric
air, but from some positive change effected in their blood by the gas.
[189] A priori I expected that fishes, like amphibious animals would
have been very quickly destroyed by the action of nitrous oxide.
A long while ago, from observing that the gills of fish became rather
of a lighter red during their death, in the atmosphere; I conjectured
that the disease of which they died, was probably hyperoxygenation
of the blood connected with highly increased animal heat. For not
only is oxygene presented to their blood in much larger quantities in
atmospheric air than in its aqueous solution; but likewise, to use
common language, in a state in which it contains much more _latent
heat_. Without however laying any stress on this supposition, I had the
curiosity to try whether thornbacks would live longest in atmospheric
air or nitrous oxide. In one experiment, they appeared to die in them
nearly in the same time. In another, the fish in nitrous oxide lived
nearly half as long again as that in atmospheric air.