444 Mr. C. Tomlinson on some Phenomena 



of its volume of nitrogen and one twenty-fifth of its volume of 

 oxygen j and these small quantities must be reduced to an almost 

 inappreciable amount in hot or boiling water. But M. Gernez 

 assumes that in raising water to the boiling-point very little of 

 the dissolved air is expelled by the heat, that so much of it re- 

 mains as to convert the liquid into a supersaturated solution of 

 oxygen and nitrogen ; that is, the water contains more of these 

 gases at any .given high temperature up to boiling or superheating 

 than it could absorb at such temperatures; and he justifies his 

 assertion by the statement that, however long the water be 

 allowed to boil, a speck of air can always be detected in it, as 

 already noticed. And he quotes an experiment by M. F. Marco, 

 the description of which is entitled " Demonstration de la cause 

 mecanique de Febullition." He says, " I take a thermometer- 

 tube with a spherical bulb at its extremity and break the bulb 

 so that there remains a tube with a sort of funnel with irregular 

 edges. I plunge this tube into water contained in a matrass, so 

 that the funnel rests on the bottom of the matrass. I have thus 

 a small mass of air imprisoned by the funnel and by the water. 

 I afterwards heat the water to boiling by means of the flame of 

 a spirit-lamp. Then, by a suitable arrangement of the flame, 

 bubbles of vapour may be seen to escape continually from the 

 funnel." M. Gernez, who claims the priority in this experiment, 

 remarks that it shows in an interesting manner the part played 

 by air in the ebullition of liquids. At the same time I may 

 remark that, supposing such to be the case, it does not exclude 

 other modes of liberating vapour, although, according to M. 

 Gernez, access of air is the only mode. 



I have repeated this experiment with a small thermometer- 

 tube and a thin cylindrical bulb, the end of which had been 

 broken off. Now, what is the action of this small bell-glass, 

 lowered, full of air, to the bottom of a tube 8 inches in length, 

 1^ inch in diameter, containing a depth of 6 inches of water ? 

 The first effect is to compress the air and to admit a portion of 

 water into the bell. When heat is applied the air expands, ex- 

 pels the water, and a portion of the air escapes in the form of a 

 bubble. A larger quantity of water now enters the bell ; and as 

 the heat slowly increases, the remaining volume of air again 

 expands, forces out the water, and another bubble escapes; 

 more water enters ; but the water is now charged with vapour 

 which rises into the bell and mingles with the small amount of 

 air that remains in it. Expansion goes on as before; another 

 bubble of mixed air and vapour escapes ; water charged with 

 vapour again ascends, but is forced back by another bubble of 

 vapour and a still smaller proportion of air; and in this way a 

 sort of oscillatory motion is kept up, until most of the air is got 



