76 OXIGEN IK WATER, 



end J ajid they afterwards assert, that where water is gradu- 

 ally heated, the proportion of oxygen encreases as the heat 

 approaches to ebullition; whence they have concluded, that 

 in the degree ol the heat constituting the temperature of ebul- 

 lition, the oxygen is most easily driven off, and that there is 

 no other power for disengaging it. Bat we find, by experi- 

 ence, that ebullition is not sufficient to divest the water of 

 all the oxygen it contains, whether attached or combined. 

 Ebullition deprives water of much of the oxygen and other 

 gas with which it is impregnated, but it cannot entirely 

 separate them ; for it is proved that water well boiled always 

 retains oxygen. Nothing but congelation, and the respira- 

 tion of fi>hes, can clear water entirely of its oxygen: these 

 two are the only means that complete the separation from 

 water of all osygen it contains interposed between its glo- 

 bules; for it is not till then that we obtain an exact proof of 

 its being divested of it. As to the rest, the detaching and 

 decomposing power of heat, at the degree of ebullition, is 

 not sufficient to overcome the affinity and attractive power 

 of all the oxygen united with the water ; a part of it remains 

 obstinately fixed, in spite of all the heat. 



Fishes, as I have elsewhere observed, are the eudiometers 

 of water, and one of those, shut up in a body of water, is 

 capable of separating, by means of its respiration, in several 

 hours, ail the oxygen from the water, and to exhaust it en- 

 tirely of this principle. It is by this method that boiled water 

 is proved to be not entirely divested of oxygen, but still con- 

 tains it. 



If we take a quantity of water, and boil it for any length 

 of time, and then pour it quite boiling into a bottle, or a glass 

 vessel with a narrow neck, so that it be full up to the top ; if 

 a portion of oil be poured upon it to prevent the air from 

 penetrating, and it be then suffered to cool ; in this .state, 

 let the oil be removed, and a little fish thrown in, and the oil 

 be immediately replaced, the fish will continue to live some 

 time in this water, and will be seen to breathe. 



Ebullition, therefore, has not removed all the oxygen of 

 the water; but a portion of it remains sufficient to serve for 

 the respiration of the fi.sh; for when the water is really 

 deprived of all its oxygen, fishes thrown into it die instantly. 



