1867.] 



Waters under the influence of Vegetation ^c. 



193 



in a gaseous state and is lost. During the winter season, however, when 

 the active functions of vegetation are to a great extent dormant, from the 

 diminished quantity and intensity of the sun's hght, the amount of car- 

 bonic acid produced by the respiration of the fish is greater than the plants 

 are capable of consuming, and the excess must necessarily accumulate in the 

 water. Were the production of carbonic acid confined to a short period, 

 the water would doubtless right itself after a time, the poisonous gas passing 

 away and fresh atmospheric air being absorbed. As, however, the production 

 of carbonic acid is constant, this ameliorating action can have little effect ; 

 the water must remain always highly charged with carbonic acid. Here, then, 

 its solvent action on the carbonate of lime, present in the rockwork and gra- 

 vel, comes into play, and the hardness of the water is gradually increased in 

 proportion as the light diminishes. Now, supposing for an instant that no car- 

 bonate of lime had been present in the arrangement, the question arises, what 

 must then have ensued? The fish would have continued to respire, and would 

 produce carbonic acid as before, which, remaining in a free state dissolved in 

 the water, would unquestionably have had a most detrimental effect upon 

 their health. Every one must have noticed the manner in which the golden 

 carp confined in a globe of water, in which there is no growing vegetation 

 to decompose the carbonic acid generated, or no limestone to combine with it, 

 rise to the surface and continually gulp in the air required for their vital 

 functions. Nothing whatever of this kind has ever been noticed in the 

 aquarium under consideration, although the quantity of carbonic acid dis- 

 solved in the water has been at times very large. 



From the experiments of Bischof *, we glean that the carbonic acid con- 

 tained in a saturated aqueous solution is entirely displaced by a current of 

 atmospheric air passed through it for five minutes ; and also f 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 mi- 

 nutes, leaving the water with bicarbonate of lime in solution. It is in this 

 form of combination that MM. Peligot J and Poggiale § consider the car- 

 bonate 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 

 6^ 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 



Bischof s ' Elements of Cliemical Greology,' Cavendish Society's edition, vol. iii, p. 5. 

 t Op. cit. vol. iii. p. 7. 



X Comptes Rendus, vol. xl. p. 1121, and Bischof's 'Elements,' vol, iii. p. 117. 

 § Journal de Pharmacie, vol. xxviii. p. 321, and oj). cit. vol. iii. p. 118. 

 II Comptes Eendus, vol. xli. p. 511, and op. cit. vol. iii. p. 118. 



