I
According to the most recent analyses, the mean amount of carbonic acid in
the atmosphere is estimated at about 1 part in 1000 by weight. In the various
notices of the gas it has been customary to state that this proportion, although
unexpectedly small, is nevertheless sufficient to supply the entire vegetable
kingdom with the carbon of which their solid tissues is composed. I f my theory
be well founded, this 1 part in 1000 does not represent the quantity originally
present in the atmosphere, but only the residue which remains after supplying the
requii-ements of the ocean and plant-life; in other words, it is the floating
deposit destined to meet current expenditure, the amount being kept up by the
processes already referred to.
According to Vogel, in 10,000 parts by weight of sea-water from the Mediterranean
and the Atlantic there were present I ’l and 2'23 parts, respectively, of
carbonic acid—a quantity extremely small, and yet declared to be sufficient, not
only to retain the whole of the carbonate of lime actually present in sea-water
in solution, but five times as much. According to some valuable experiments
conducted on board the French ship ‘Bonite,’ the fact has been clearly established
that the quantities of atmospheric air, and more particularly of carbonic-acid gas,
increase with the depth. The analyses, as cited by M. Bischoff, are so striking,
and exercise such an important bearing on all questions relating to the deep-sea
deposits, that I am induced to quote them in detail.
Time and place. Depth in
Paris feet.
Gas in 100
Gases. Sum of
oxTcren
volumes of
water. Oxygen. Carbonic
acid. Nitrogen. bonic acid.
1836. South Sea.....................| 0
349
2-09
2-23
0-13
0-23
0-22
0-40
1-74
1-58
0-35
0-63
1837. Bay of Bengal . . . . | 0
997
1-98
3-04
0-11
0-10
0-28
1-77
1-59
1-17
0-39
0-87
1837. Bay of Bengal . . . . j 0
1495
1-91
2-43
0-12
0*14
0-25
0-73
1-54
1-56
0-37
0-87
1837. Indian Ocean . . . . | 0
2243
1-85
2-75
0-18
0-27
0-23
0-96
1-44
1-52
0-41
1-23
1837. Atlantic Ocean. . . . 1994 2-04 0-08 0-59 1-37 0-67
* The specimen of surface-water was lost in this example.
t See ‘ Chemical and Physical Geology,’ by Gustav Bischof. Translated from the German, and
published by the Cavendish Society, vol. 1. p. 114.
In opposition to the views advanced by me with regard to the increase of
atmospheric air in the waters of the ocean with the increase of depth, I would
draw attention to the experiments of M. Biot on the gaseous contents of the
swimming-bladders of fishes*. I t is stated by Sir Henry De la Beche, on the
authority of M. Biot, that whereas the swimming-bladders of fishes caught near
the surface were filled, not with pure atmospheric air, as might have been
expected, but with nearly pure nitrogen, the swimming-bladders of such as
were brought up from a depth of 500 fathoms were filled with oxygen and
nitrogen in the proportion of 9 of the former to I of the latter—the conclusion
arrived at from these facts being that there was a difficulty in obtaining nitrogen
at great depths, whilst it was procurable in abundance near tbe surface, and hence
that atmospheric air was more plentiful in the latter than in the former situation.
I t is worthy of note, however, that these proportions do not tally with the
fact that in a given volume of water, under ordinary pressure, the quantity of
oxygen is rather greater, and that of nitrogen rather less, than is compatible with
the ratios borne by these two gases to each other when in coinbination as atmospheric
air. For, since the normal ratio of oxygen to nitrogen is very nearly as
I to 4, and the relative quantities of these gases absorbed by water are as 3 to
2, and assuming with Sir H. De la Beche that the quantity of atmospheric air
present decreases with the depth, we should expect to find more oxygen present
in the swimming-bladder of the fish taken from the surface than in that taken
from deep water. I t should be borne in mind, moreover, that the swimming-
bladder is in no way connected with respiration, and that it only serves to
regulate the specific gravity of the fish; and hence the secretion, when at
the greater depth, of that gas which is considerably heavier than the other is
precisely what might be looked for when the object to be attained is the maintenance
of equilibrium with the surrounding medium. But it has already been
stated that the normal ratios of the two gases, as they exist in atmospheric air,
are modified to a very considerable extent when they are held in solution by
water, oxygen being taken up in larger quantity, and nitrogen in less, and the
former of these gases constituting fth s of the water itself. Hence assuming, as
is the case, that the gaseous contents, whatever they may be, of the swimming-
bladder are secreted through the circulation, and not imbibed directly into its
* ‘ Eesearches iu Theoretical Geology,’ by Sir H. De la Beche, p. 229.