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Mr. W. N. Hartley on Attraction and [Apr. 12, 



The repulsion of bubbles by heat, water being the only liquid present. 



With regard to this second point, the repulsion of bubbles by heat. 

 It occurs quite as frequently, if, indeed, not more so, in the specimens 

 which I have examined, than attraction, and it is seen to occur in cavities 

 containing water and liquid carbonic acid. (See fig. 4.) 



I have noticed some cavities of a remarkable nature, inasmuch as they 

 were apparent under similar conditions to those which I have already 

 described, though they behaved in an exactly opposite manner. They 

 were water-cavities which adjoined others containing both liquid car- 

 bonic acid and water. A blast of warm air, insufficient to vaporize 

 the carbonic acid, is sufficient to propel the gas -bubble to the other end of 

 the cavity. I next ascertained that five puffs of warm air only just warmed 

 the carbonic acid to the critical point, that is to say, from 16° to 31° C. I 

 then took a thin bar of copper, and warmed it two degrees above the tem- 

 perature of the room ; this repelled the bubble easily ; and other trials 

 showed that a rise of temperature of less than §° C. was quite sufficient. 

 It was curious to see that when the gas-bubble touched the walls of the 

 cavity at only one point it moved with extraordinary ease and slowly, 

 but otherwise it was more difficult to stir, and it went with rather a 

 sudden jerk. This subject will be treated more fully later on. 



The largest specimen of a bubble readily movable by heat was in a 

 water-cavity in a green crystal of fluor-spar kindly lent me by Mr. James 

 Bryson, of Edinburgh. The cavity measured T ^ x -fa of an inch, the 

 bubble being fa of an inch in diameter. To my surprise, I found it to 

 be easily repelled by a jet of warm air. 



The sinking of gas-bubbles by rise of temperature in cavities containing 

 water as the only liquid. 



In a paper which I have lately communicated to the Chemical Society, 

 I have given details of experiments on certain bubbles in water-cavities, 

 which prove that by rise of temperature the bubbles become denser than 

 the water and sink (Journal of the Chem. Soc. vol. i. 1877, p. 245). 



When exposed to a uniformly diffused rise of temperature on the micro- 

 scope-stage the very slow sinking motion of the bubble was remarkable ; as 

 the specimen cooled it returned in the same manner. In some cases a tem- 

 perature of 40° C. was apparently sufficient ; but several experiments on 

 an exceedingly good cavity, which measures x of an inch, and 

 the bubble in which is of an inch in diameter, fixed the temperature 

 for this specimen at 150° C. The cause of this sinking appears to 

 be that the bubble consists of a gas so highly compressed that it is 

 nearly of the same density as water. On heating the water expands, 

 and the gas is contracted until the relative densities of the two sub- 

 stances are reversed. Professor Andrews has shown that a mixture 

 of 3 vols, of carbonic acid with 4 vols, of nitrogen at 7°'6 C. con- 

 tracts -^-J-g- of its original bulk by a pressure of 284 atmospheres. This 



