77 



63. It has been already shewn (52.), that fishes 

 cannot live in water deprived of air, nor unless this 

 air be constantly renewed : and Dr Priestley proved, 

 by experiment, that they deteriorate the air which 

 water contains. Several minnows were confined by 

 him in a large phial of water till they died : and the 

 air being afterwards expelled from the water, was 

 examined by the test of nitrous gas, and found to 

 contain less oxygen than that in which a candle goes 

 out. He likewise impregnated water, previously de- 

 prived of its oxygen, with nitrogen and with hydro- 

 gen gases, and found, that in such water, the fishes 

 died in about an hour *. Mr Davy ascertained that 

 fishes die in a few minutes in water containing nitro- 

 gen gas, but live in that which is impregnated with 

 oxygen gas: that the proportion of this latter gas is 

 diminished by them, and carbonic acid is produced ; 

 for, on adding lime-water to that in which the fishes 

 had been confined, a cloudiness was very perceptible, 

 indicating the formation of carbonate of limef- 

 Dr Carradori has observed, that fishes are able to 

 exhaust water entirely of its oxygen, which ebulli- 

 tion is unable to effect : and that they die instant- 

 ly in water wholly deprived of oxygen J. To 

 supply the waste of oxygen gas, occasioned by the 

 respiration of fishes, water, as Scheele first remark- 

 ed, is endued with the power of attracting it in pre- 



* On Air, vol. v. p. 137. et seq. 



f Bcddoes's Contributions to Physical Knowledge, p. 1 3' 



i Nicholson's Journal, vol. xvi, p. 76. 



