150 Royal Society. 
acid contained in a saturated aqueous solution is entirely displaced 
by a current of atmospheric air passed through it for five minutes ; 
and also * that, by the same means, a solution of carbonate of lime, 
in water previously saturated with carbonic acid, will have all the 
excess of gas displaced in fifteen minutes, leaving the water with 
bicarbonate of lime in solution. It is in this form of combination 
that MM. Peligot | and Poggiale ¢ consider the carbonate of lime 
to exist in the water of the Seine, and M. Bineau § in that of the 
Rhone, in which rivers they_state there is no free carbonic acid. In 
the present investigation we shall therefore assume it to be in the 
same state of combination. We have, in the series of experiments 
detailed above, an increase in the quantity of carbonate of lime held 
in solution, amounting to 14:2 grains in the imperial gallon, which 
would require nearly 63 grains of carbonic-acid gas to dissolve it. 
Besides this there is also the quantity already present in the water 
at its minimum, which amounts to nearly four grains more, or in 
all to about ten grains, equal to nearly 215 cubic inches of that 
gas in the ten gallons of water, or more than ;);th its volume. The 
exact numbers will be seen in the following Table :— 
CaO, CO, in the gallon. CO,,. 
1861 { Maximum 23:0 grs., requiring 10°120 grs. to form CaO,2CO,,. 
Minimum 9°3 ” 99 4°092 99 ry) » 
1862 Maximum 21'8 ,, 9 9°592 5, 9» 9 
Minimum 88 ,, “ 3°872 ,, ee. 
Car. acid required todissolve the increase 6°248 grs. = 13-269 cub. in. 
if 5S minimum 3°872_ ,, 8°228". 5. 
10°120 | 45° 21-407. @ 
Yet, although the quantity of poisonous gas had been thus in- 
creased, we find no deleterious action on the health of the fish, no 
disturbance in the ordinary respiration, no gulping at the surface 
of the water for fresh air. It is quite evident, therefore, that the 
carbonic acid, by entering into combination with carbonate of lime, 
however weak that combination may be, is thereby rendered per- 
fectly innocuous, and a wonderful provision is thus afforded for 
preventing this poisonous agent from becoming fatal to animal life. 
We turn now to the next member of our arrangement. 
3. The Vegetation. 
It will be seen from the foregoing numerical results that the 
maximum quantity of dissolved carbonate of lime, and consequently 
of carbonic acid, is found just before the period of the reviving 
energies of the plant’s growth, namely, the spring time of the year, 
when the days are lengthening and the sun’s light is continually 
increasing in strength ; the minimum quantity when this growth 
* Op. cit. vol. iii. p. 7. 
+ Comptes Rendus, vol. xl. p. 1121, and Bischof’s ‘Elements,’ vol, iii. p. 117. 
t Journal de Pharmacie, vol. xxviii. p. 321, and op. ct. vol. iii. p. 118. 
§ Comptes Rendus, vol. xli. p. 511, and op. cé¢. vol. iii, p. 118. 
